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We performed a pilot study that examined the clinical and pharmacokinetic interactions between zidovudine (ZDV) and a pyridinone derivative, L-697-661. The results indicate that the drugs were well tolerated, with no important pharmacokinetic interactions, when administered concomitantly for as long as 8 weeks. Although the number of study participants was small, we noted rapid emergence of resistance to L-697,661 among ZDV-naive study subjects who were administered L-697,661 as monotherapy but did not observe isolates of human immunodeficiency virus type 1 (HIV-1) resistant to L-697,661 among those who were administered concomitant ZDV. These results suggest a potential interaction between development of resistance to L-697,661 and ZDV. Although the clinical development of L-697,661 has been halted, our results support the need for further studies to test whether specific interactions among antiretroviral agents administered in combination and the molecular target can delay the emergence of isolates that exhibit resistance to all drugs in the regimen.

For population pharmacokinetic analysis of multiple oral doses one of the key issues is knowing as precisely as possible the dose inputs in order to fit a model to the input-output (dose-concentration) relationship. Recently developed electronic monitoring devices, placed on pill containers, permit precise records to be obtained over months, of the time/date opening of the container. Such records are reported to be the most reliable measurement of drug taking behavior for ambulatory patients. To investigate strategies for using and summarizing this new abundant information, a Markov chain process model was developed, that simulates compliance data from real data from electronically monitored patients, and data simulations and analyses were conducted. Results indicate that traditional population pharmacokinetic analysis methods that ignore actual dosing information tend to estimate biased clearance and volume and markedly overestimate random interindividual variability. The best dosing information summarization strategies consist of initially estimating population pharmacokinetic parameters, using no covariates and only a limited number of dose records, the latter chosen based on an a priori estimate of the half-life of the drug in the compartment of interest; then resummarizing the dose records using either population or individual posterior Bayes parameter estimates from the first population fit; and finally reestimating the population parameters using the newly summarized dose records. Such summarization strategies yield the same parameter estimates as using full dosing information records while reducing by at least 75% the CPU time needed for a population pharmacokinetic analysis.

Medical students were introduced to issues relating to medication noncompliance in a simulated clinical setting. Compliance with either a twice-a-day or a three-times-a-day regimen was monitored with use of electronic monitoring devices for a 2-week interval. Compliance with the twice-a-day regimen was higher than compliance with the three-times-a-day regimen, although the difference was not significantly different. Overall, 71% of the prescribed doses were taken by the medical student participants; however, only 46.5% of the doses were taken at the prescribed dosing frequency and 28.5% were taken at the prescribed intervals. The majority of students linked dose taking with routine daily activities and reported that their hectic lifestyles adversely influenced compliance. Similar factors might be expected to influence compliance in patient populations. The goal of this exercise was to demonstrate to future physicians the difficulties that patients have with compliance to prescribed medications.

Rifabutin is structurally similar to rifampin, but there are important pharmacokinetic differences between the two drugs. Rifabutin is more lipid soluble than is rifampin, resulting in more-extensive tissue uptake, a larger volume of distribution, lower maximum plasma concentrations, lower trough concentrations, a longer terminal half-life, and higher tissue-to-plasma drug concentration ratios. The oral bioavailability of rifabutin is low. Like rifampin, rifabutin induces its own metabolism during multiple dosing. Rifabutin is extensively metabolized. The two major metabolites of rifabutin contribute to its antimicrobial activity. Rifabutin induces hepatic metabolism but is not as potent an inducer as is rifampin. Rifabutin does not affect the pharmacokinetics of antiretroviral drugs that are excreted in the urine. Although rifabutin decreases plasma concentrations of zidovudine, this finding does not appear to be clinically relevant. When administered during rifabutin prophylaxis, fluconazole decreases the incidence of Mycobacterium avium complex bacteremia. The coadministration of clarithromycin and rifabutin results in increased plasma concentrations of rifabutin and decreased plasma concentrations of clarithromycin; however, the plasma concentration of clarithromycin's active metabolite is increased.

Background This trial studied the feasibility and efficacy of a new preparatory regimen for autologous bone marrow transplantation for patients with advanced lymphoid malignancies. Methods Twenty-one patients with Hodgkin's disease (n = 12) and non-Hodgkin's lymphoma (n = 9) were treated in this study. Lomustine was substituted for carmustine) in a dose-escalation study with an initial dose of 6 mg/kg and increasing by 3 mg/kg in groups of four patients. The preparatory regimen consisted of lomustine (6-15 mg/kg) orally on Day -6, etoposide (60 mg/kg) intravenously (i.v.) on Day -4, and cyclophosphamide (100 mg/kg) i.v. on Day -2. Peripheral blood progenitor cells and/or bone marrow were infused on Day 0. Results Lomustine was well tolerated in all patients with no significant toxicity specific to this drug. Engraftment was prompt: the time to achieving greater than or equal to 500 granulocytes/microliters was 12 days (range, 9-16 days) and the time to achieving greater than or equal to 25,000 platelets/microliters without transfusion support was 16 days (range, 9-22 days). Five patients experienced interstitial pneumonitis, three of whom had active or recent interstitial pneumonitis before bone marrow transplantation, and one who just completed mantle irradiation. Three patients died from this preparatory regimen, one of progressive interstitial pneumonitis, one of Legionella pneumonia, and one of multiorgan failure. Three patients with non-Hodgkin's lymphoma relapsed. Fourteen patients are currently alive and disease free to date. The actuarial are currently alive and disease free to date. The actuarial disease free survival was 57%, with a median follow-up of 23 months (range, 1-48 months). Conclusion The preparatory regimen consisting of lomustine/etoposide/cyclophosphamide is active in treating patients with lymphomas. Further trials with high doses of lomustine are warranted.

beta-Adrenergic responses have been shown to decline with aging, particularly in the cardiovascular system. We infused terbutaline, a selective beta 2-adrenoceptor agonist, into the brachial artery of 10 young (mean age 25 yr, range 22–31 yr) and 9 elderly (mean age 73 yr, range 68–81 yr) healthy subjects to examine its effects on nutrient flux. Forearm K+, PO4, free fatty acid (FFA), and glycerol uptake were determined by measurement of forearm blood flow (using dye dilution) and brachial arterial and deep venous plasma substrate concentrations. Elderly subjects were less sensitive to terbutaline-mediated increases in forearm blood flow, net fluxes of K+, and glycerol but not net fluxes of FFA or PO4. The mean fitted slopes of each parameter vs. the log of the terbutaline concentration, a measure of forearm beta-adrenergic sensitivity, for young and elderly groups were 4.9 +/- 1.7 (SD) vs. 2.4 +/- 2.3 for forearm blood flow (P

Low energy dynamics of magnetic monopoles and anti-monopoles in the U(2)c gauge theory is studied in the Higgs (non-Abelian superconducting) phase. The monopoles in this phase are slender ellipsoids, pierced by a vortex string. We investigate scattering of monopole with anti-monopole and find that they do not always decay into radiation, contrary to our naive intuition. They can repel, make bound states (magnetic mesons) or resonances. We point out that some part of solutions in 1 + 3 dimensions can be mapped exactly onto the sine-Gordon system in 1 + 1 dimensions in the first non-trivial order of rigid-body approximation and we provide analytic formulas for such solutions there.

Epoxyeicosatrienoic acids (EETs) produced by cytochrome P450 (CYP)-dependent epoxidation of arachidonic acid (AA) inhibit thrombocyte adhesion to the vascular wall. Upon dietary omega-3 fatty acid supplementation, EETs are partially replaced by eicosapentaenoic acid (EPA)-derived epoxyeicosatetraenoic acids (EEQs) and docosahexaenoic acid (DHA)-derived epoxydocosapentaenoic acids (EDPs). We hypothesized that the omega-3 epoxy-metabolites may exhibit superior anti-thrombogenic properties compared to their AA-derived counterparts. To test this hypothesis, we analyzed the effects of 11,12-EET, 17,18-EEQ and 19,20-EDP on Ristocetin-induced thrombocyte aggregation (RITA), a process that mimics thrombocyte adhesion to the vascular wall. The eicosanoids were added for 5, 30, or 60 minutes to thrombocyte-rich plasma freshly prepared immediately after blood collection from stringently selected apparently healthy subjects. Thrombocyte aggregation was then induced by Ristocetin (0.75 mg/mL) and assessed by turbidimetric measurements. After 60 minutes of preincubation, all three epoxy-metabolites significantly decreased the rate of RITA. 17,18-EEQ and 19,20-EDP were effective already at 1 μM, whereas 5-fold higher concentrations were required with 11,12-EET. Addition of AUDA, an inhibitor of the soluble epoxide hydrolase, potentiated the effect of 17,18-EEQ resulting in a significant further decrease of the velocity as well as amplitude of the aggregation process. In contrast to their profound effects on RITA, none of the epoxy-metabolites was effective in reducing collagen- or ADP-induced thrombocyte aggregation. These results indicate a highly specific role of CYP-eicosanoids in preventing thromboembolic events and suggest that the formation of 17,18-EEQ and 19,20-EDP may contribute to the anti-thrombotic effects of omega-3 fatty acids.

Es werden Versuche zur Ermittlung des Zugtragverhaltens an Betonkorpern mit unterschiedlichen Abmessungen unter mittiger und ausmittiger Zugbeanspruchung beschrieben.

The enzyme nitric oxide synthase mediates synthesis of nitric oxide (NO) from 1-arginine in endothelial cells. NO, also known as endothelium-dependent relaxing factor (EDRF), diffuses to smooth muscle cells where it leads to cGMP production and dilation. We characterized the potency, efficacy and time course of NG-monomethyl-l-arginine (l-NMMA) as an inhibitor of bradykinin-mediated, endothelium-dependent dilation using the human hand-vein compliance technique. We also compared the efficacy of l-NMMA with methylene blue, an inhibitor of guanylate cyclase, in blocking bradykinin-mediated vasodilation. l-NMMA potently inhibited bradykinin-induced venodilation with a log ED50 of 3.74 +/- 0.52 (geometric mean of 5.5 micrograms/min). Responses to bradykinin (0.27-555 ng/min) were tested in veins pre-constricted with the alpha-adrenergic agonist phenylephrine. l-NMMA (25 micrograms/min) decreased bradykinin's maximal venodilatory response from 90 +/- 22% to 39 +/- 15% (p < 0.05). Complete recovery of bradykinin venodilation was obtained within 155 minutes after stopping l-NMMA infusion, indicating that its effects were reversible. In another set of experiments we compared the efficacy of methylene blue to l-NMMA; methylene blue decreased bradykinin-mediated venodilatory response to 53 +/- 17%; when l-NMMA was added, the response was further decreased to 32 +/- 9% (p < 0.002). We conclude that l-NMMA is a very efficacious NO synthase inhibitor in human veins and it is likely functionally reversible.

Objective To examine predictors of magnitude of CD4+ response to treatment of human immunodeficiency virus (HIV) infection with zidovudine. Methods This was a post hoc analysis of randomized placebo-controlled clinical trial in a multicenter trial, 1423 asymptomatic HIV-positive subjects with CD4+ cell counts less than 500 mm−3 were given 500 mg/day zidovudine, 1500 mg/day zidovudine, or placebo. The main outcome measure was change in the CD4+ cell counts over time. Results This study suggests that earlier treatment with zidovudine results in a larger increment in the CD4+ cell count. In addition, the increment in CD4+ cell count is very long lived. However, drug exposure was not found to be a predictor of response to treatment in the dose range studied. Conclusions A parametric model of disease progression can be estimated with use of data collected in a conventionally designed study. These parametric models may provide insight into the optimal use of drugs. This model suggests that zidovudine does not change the underlying course of HIV infection but simply delays the time course. The model also suggests that the magnitude of this delay is larger when treatment is begun earlier in the course of the disease. Clinical Pharmacology and Therapeutics (1993) 54, 556–566; doi:10.1038/clpt.1993.188

BACKGROUND Exercising skeletal muscle releases large amounts of potassium into plasma. beta-adrenergic receptors enhance reuptake of potassium into muscle. Since beta-adrenergic responses decline with aging in many tissues, the elderly might be predisposed to hyperkalemia during exercise. METHODS Venous plasma potassium (K+) was measured during graded bicycle exercise (30 W initial workload with 3-minute 30 W increments) in 18 healthy young men (24.0 +/- 2.9 yrs; mean +/- SD), 18 healthy untrained elderly men (70.0 +/- 3.6 yrs), and 7 elderly master athletes (70.0 +/- 4.6 yrs). Subjects exercised to exhaustion. RESULTS Exercise times and maximal oxygen uptake were: young (N = 14; 19.6 +/- 4.4 min, 42.1 +/- 3.8 ml/kg/min), elderly (N = 13; 11.7 +/- 1.9 min, 26.6 +/- 8.0 ml/kg/min), elderly master athletes (N = 6; 16.8 +/- 2.4 min, 40.2 +/- 10.2 ml/kg/min). The rate of increase in K+ was greater in both elderly (89 +/- 59 mumol/l/min) and elderly master athletes (88 +/- 26) compared with healthy young men (60 +/- 30), p < .05. Despite this greater rate of increase, the elderly group did not achieve higher maximal K+ concentrations than the young because of the much shorter duration of exercise in the elderly group. For subjects performing a maximal exercise test, the maximal increase in K+ was similar in the elderly (1.15 +/- 0.91), but significantly greater in elderly master athletes (1.70 +/- 0.31), compared with healthy young men (1.31 +/- 0.45). CONCLUSIONS Changes in K+ during short-lasting exercise are similar in untrained healthy elderly men compared with healthy young men, but elderly master athletes have greater changes in K+ during exercise. The greater rate of increase in potassium in healthy and athletic subjects supports the hypothesis of an age-related impairment of the beta 2-adrenergic process that mediates potassium flux into skeletal muscle.

The usual objective during long-term pharmacotherapy is, in large part, to maintain continuity of action of the prescribed drug(s). Continuity of action arises from the continuity of execution of a prescribed dosing regimen that is pharmacologically sound in dose quantity and interval between successive doses. Interruptions in dosing can interrupt drug action, but the consequences vary according to length of interruption, drug, drug formulation, length of the patient's prior exposure to the drug, and the disease being treated.

Chronic administration of alpha 1-receptor antagonists is associated with loss of clinical efficacy, especially in congestive heart failure, although the mechanism is uncertain. To evaluate changes in venous alpha 1-adrenoceptor responsiveness during chronic alpha 1-adrenoceptor blockade, dose-response curves to phenylephrine and angiotensin II were constructed in 10 healthy subjects before, during, and after administration of terazosin 1 mg orally for 28 d. Terazosin initially shifted the dose-response curve of phenylephrine to the right, with a significant increase in ED50 for phenylephrine from a control value of 102 to 759 ng/min on day 1 of terazosin (P < 0.001). However, by day 28, the dose-response curve had shifted back towards baseline with an ED50 of 112 ng/min. After discontinuing terazosin, the ED50 for phenylephrine remained near the baseline value, indicating no evidence of supersensitivity to phenylephrine. There was no change in responsiveness to angiotensin II during the course of treatment with terazosin. Plasma terazosin concentrations were stable throughout the period of drug administration. The mean Kd of terazosin was estimated as 11 +/- 15 nM in the first few days of treatment. This study demonstrates that pharmacological tolerance to the alpha 1-adrenoceptor blocking action of terazosin occurs in man and may be responsible for loss in efficacy with chronic therapy.

The aim of this study was to determine whether there is an age-related decline in vascular responsiveness to bradykinin, whose vasodilatory action is mediated chiefly through endothelium-derived relaxing factor (EDRF). Dose-response curves for bradykinin were constructed using the dorsal hand vein compliance technique in veins preconstricted with phenylephrine in 27 volunteers (16 male, 11 female) aged 18 to 81 years. At the end of the bradykinin study, 12 subjects had a single infusion of a high dose of isoproterenol. There was no correlation between age and the EMAX or the log ED50 for bradykinin, although the same subjects showed a correlation between age and EMAX for isoproterenol, as previously found. There was no significant difference in either the EMAX or the log ED50 between male and female subjects. The results suggest that bradykinin-induced vasodilation is independent of age or gender.

Regulation of β-adrenoceptors in animal tissues and human cell cultures has been extensively described; on the other hand, relatively little is known about regulation of β-adrenoceptors in human tissues in vivo. Both β-adrenoceptors and the prostaglandin E1 (PGE1) receptors stimulate vasodilation. We wondered if prolonged infusion of isoproterenol or PGE1 would cause desensitization of smooth muscle relaxation and used the dorsal hand-vein compliance technique to investigate this question. After constructing a dose–response curve to either the β-agonist isoproterenol or to PGE1 in a phenylephrine preconstricted vein, isoproterenol (271 ng/min), PGE1 (956 pg/min), or saline was infused for 4 h in separate experiments. There was no change in the ED50 or Emax for either isoproterenol or PGE1 after saline infusion. After a 4-h infusion of isoproterenol, the maximal vasodilator response to isoproterenol was significantly (p < 0.01) attenuated from 61 ± 33% to 19 ± 10%, while the ED50 significantly increased (p < 0.01) from a geometric mean of 37 to 197 ng/min. After infusion of isoproterenol, the mean maximum PGE1-induced venorelaxation of 129 ± 29% was modestly but significantly (p < 0.05) blunted to 96 ± 35%, while the ED50 of PGE1 increased significantly (p < 0.01) from a geometric mean of 81 to 398 pg/min. A 4-h infusion of PGE1 significantly (p < 0.01) attenuated the maximum response to PGE1 from 73 ± 35 to 28 ± 16%. The maximal vasodilatory response to isoproterenol was also significantly blunted (p < 0.05) from 62 ± 35 to 42 ± 41%, with no change in ED50. Prolonged infusions of either isoproterenol or PGE1 induce heterologous desensitization in human vascular smooth muscle; the dorsal hand-vein provides a useful model for investigating the regulation of receptors and desensitization in humans.

1. Diabetic autonomic neuropathy causes loss of sympathetic cardiovascular control and is associated with increased vascular sensitivity to catecholamines. Supersensitivity to catecholamines could be due to either a postsynaptic increase in vascular sensitivity or to decreased catecholamine uptake into peripheral sympathetic nerve endings. 2. To differentiate between these possible mechanisms we have measured the responsiveness in vivo to noradrenaline and phenylephrine with local infusions into peripheral veins of diabetic patients with and without symptomatic autonomic neuropathy and of healthy control subjects. The dorsal hand vein compliance technique was used. 3. Symptomatic diabetic patients required significantly lower doses of noradrenaline for half-maximal venoconstriction (ED50) (geometric mean 2.14 ng/min) than control subjects (geometric mean 6.61 ng/min, P = 0.032), but there was no difference in the results from the phenylephrine dose-response curves between the groups. Thesre were no differences in venous responsiveness to noradrenaline or phenylephrine between the asymptomatic diabetic group and the control group. However, in the asymptomatic diabetic group, postural blood pressure change (an index of loss of sympathetic control) was correlated with the ED50 for noradrenaline (r = 0.74, P = 0.014), but not with the ED50 for phenylephrine. In the control group the ED50 values for noradrenaline and phenylephrine were correlated with each other (r= 0.81, P= 0.0005). 4. Both vasopressor drugs act on vascular α-adrenoceptors, but only noradrenaline is taken up into peripheral sympathetic nerve endings. Our results suggest that, in diabetic patients, vascular supersensitivity to catecholamines is primarily determined by decreased neuronal catecholamine uptake. A postsynaptic increase in vascular a-adrenoceptor stimulation does not appear to be prominent in diabetic autonomic neuropathy.

Aging is associated with diminished beta-adrenergic responsiveness in a variety of tissues. Desensitization of tissues secondary to the age-associated increase in sympathetic nervous system activity has been proposed as a potential explanation for diminished beta-adrenergic responsiveness. If this hypothesis is correct, then beta-blockade in older people might be expected to reverse the blunted beta-adrenergic responses of tissues having diminished responsiveness. Cardiac chronotropic responses to bolus isoproterenol (ISO) doses and ISO-induced venous smooth muscle dilatation in superficial hand veins were examined in 8 young (26.2 +/- 2.6 yrs) and 9 elderly (68.0 +/- 2.2 yrs) healthy subjects before, during, and 3 and 7 days following 2 weeks of treatment with propranolol. Baseline cardiac chronotropic responsiveness, CD25, was 1.55 +/- 0.77 mcg in the young and 5.97 +/- 2.77 mcg in the elderly subjects (p less than .01), increasing to 84 +/- 56 mcg and 194 +/- 172 mcg during treatment with propranolol. At 3 and 7 days following withdrawal of propranolol, CD25s were respectively 1.24 +/- 0.79 (p = .14) and 1.10 +/- 0.42 (p = .04) in the young and 5.63 +/- 2.34 (p = .31) and 4.85 +/- 2.37 (p = .05) in the elderly subjects. In contrast, there was no decrease in the ED50 or increase in Emax for ISO-induced venodilation of hand veins following propranolol withdrawal. These results demonstrate that both young and elderly subjects have similar increases in cardiac chronotropic responsiveness following discontinuation of beta-blockade and do not support the concept that desensitization is responsible for the diminished beta-adrenergic responsiveness seen with aging.

Data obtained from neonates receiving zidovudine as part of a phase I study were used to estimate the population pharmacokinetic parameters of this drug and to determine the minimum number of data points necessary to provide accurate estimates of the kinetic parameters and their variability. Analysis was performed with 541 concentrations of zidovudine, obtained from 32 infants and with a variety of reduced data sets using NONMEM (nonlinear mixed effect model). The reduced data sets were derived by randomly reducing the number of sampling time points per dosing interval and/or by randomly reducing the number of available subjects. We determined that accurate estimates of pharmacokinetic parameters and their variability were obtained with the inclusion of all 32 patients using only two concentration-time points per dose interval, provided that one of the points was obtained during the first 2 h after administration of the drug. The parameters themselves were adequately estimated with only 24 subjects and two concentration-time points per dose interval. We suggest that NONMEM should be used in addition to the traditional pharmacokinetic analysis to obtain more precise information directly in the population of interest with a minimum of blood sampling from each patient. This is especially critical in infants whose blood volumes are limited.

There is a growing awareness that simply saying that a drug is effective (ie, the p value is less than 0.05) is not adequate information for the optimal treatment of patients. It is increasingly appreciated that drugs act differently in different populations, for example the elderly, and at different doses or serum concentrations. These relationships should be defined to optimize use of drugs in different populations. Techniques are discussed that allow investigators to better describe the pharmacokinetic and pharmacodynamics response for individual patients. The term population pharmacokinetic/pharmacodynamic analysis (population PK/PD) has been applied to a collection of these techniques. The role of population PK/PD in the drug development process remains to be defined, but should be expanded.

The increasing burden of HIV care threatens to overwhelm health-care providers and systems in the developing world. Clinical pharmacologists, applying the training that they possess in regulatory science, rational prescribing, and teaching therapeutics, could improve the delivery of care in that setting. However, the shortage of clinical pharmacologists and the emigration of health-care providers limit the ability to take advantage of this approach. Possible solutions are outlined in this Commentary. Clinical Pharmacology & Therapeutics (2009); 85, 6, 579–581 doi:10.1038/clpt.2009.54

delta-Aminolevulinic acid-4-[14C] and [3H]-bilirubin were administered intravenously to five patients with Gilbert's syndrome and four healthy control subjects on two occasions: before and on days 10 through 14 of a course of phenobarbital (2.5 mg/kg/day). The resulting curves of [3H]-bilirubin and [14C]-bilirubin in plasma were analyzed by computer to determine a number of parameters of physiological interest. As expected, phenobarbital produced a highly significant fall in the plasma concentration of unconjugated bilirubin as a result of a significant increase in hepatic bilirubin clearance in all subjects; plasma bilirubin turnover was unaltered. Surprisingly, the drug produced no change in the incorporation of [14C]-delta-aminolevulinic acid into [14C]-early labeled bilirubin. To explain this unexpected finding, the effects of phenobarbital (75 mg/kg/day for 6 days) on incorporation of [14C]-delta-aminolevulinic acid and 2-[14C]-glycine into [14C]-early labeled bilirubin and on the activity of the enzyme delta-aminolevulinic acid synthase were studied in nonfasted, adult, male Sprague-Dawley rats. At the dose and duration of treatment used, phenobarbital administration increased total hepatic delta-aminolevulinic acid synthase activity and produced a significant increase of 70% in the incorporation of [14C]-glycine into early labeled bilirubin. By contrast, no increase in the incorporation of [14C]-delta-aminolevulinic acid into early labeled bilirubin was observed. These data suggest that delta-aminolevulinic acid is an inappropriate precursor for studies of the rate of heme biosynthesis, presumably because it bypasses delta-aminolevulinic acid synthase, the physiological rate-limiting enzyme in the heme biosynthetic pathway.

Essential hypertension is more prevalent among blacks than whites although the explanation is unknown. It is possible that an altered vascular adrenoceptor responsiveness in blacks may play a role in the etiology of this racial difference. To test this hypothesis, we have compared the diameter changes in superficial veins in response to phenylephrine, an alpha-adrenergic agonist, and to isoproterenol, a beta-adrenergic agonist, in black and white young normotensive males using the dorsal hand vein compliance technique. The maximal venoconstriction after phenylephrine (Emax) was 92 +/- 9% (mean +/- SD) in the whites but only 74 +/- 12% in the blacks (p = 0.00046). The ED50 of phenylephrine was 342 ng/min (geometric mean) in whites and 245 ng/min in blacks (p = 0.50). The Emax and ED50 for isoproterenol-mediated venodilation was not significantly different between the racial groups. These results indicate a decreased maximal responsiveness to alpha-adrenergic stimulation in normotensive blacks. How these changes relate to cardiovascular alterations in hypertensive blacks requires further study.

Fluconazole, a potent bis-triazole antimycotic drug, has been demonstrated to inhibit antipyrine metabolism, a cytochrome P-450 dependent process, in vivo in mice. Cyclosporine is metabolized by the cytochrome P-450 enzyme system in both mice and man. We investigated whether fluconazole had any effects on the metabolism of cyclosporine in vivo in mice. The effects of three different doses of fluconazole (1, 5, and 20 mg/kg) on the metabolism of cyclosporine in CD-1 mice were studied in single-dose experiments. Fluconazole produced significant dose-dependent decreases in the elimination rate constant and increases in the terminal half-life of cyclosporine. The 1 mg/kg dose caused a 26% prolongation of the terminal half-life and the 5 and 20 mg/kg dose prolonged the half-life by 72 and 187%, respectively. Fluconazole doses in the 1–5 mg/kg range are effective in mouse models of fungal infections. These results provide further in vivo evidence that fluconazole is a potent inhibitor of the cytochrome P-450 dependent enzyme system in mice. Future experimental studies in animals and humans are needed to evaluate possible metabolic drug–drug interactions involving fluconazole.Key words: cyclosporine, drug metabolism, drug–drug interaction, fluconazole, cytochrome P-450, animal, antifungal.

Objective The aim of this study was to determine whether pharmacokinetic interactions between the protease inhibitors saquinavir soft gel, nelfinavir, and ritonavir are affected by the timing of administration. Study design We used an open-label, 6-period, incomplete Latin square crossover study in 18 human immunodeficiency virus–negative subjects. Each received single oral doses of 2 of the 3 protease inhibitors during each of 6 periods. Single doses were given either simultaneously or separated by 4 hours. The order of the periods was balanced, and periods were separated by 2 days. We measured protease inhibitor concentrations over a 24-hour period by HPLC and estimated pharmacokinetic parameters by noncompartmental methods. Results Median saquinavir area under the curve (AUC) increased by 62-fold when ritonavir was coadministered, by 50-fold when ritonavir was given 4 hours earlier, and by 16-fold when saquinavir preceded ritonavir by 4 hours. Saquinavir AUC increased by 7-fold when nelfinavir was coadministered. Nelfinavir AUC increased by 2.5-fold with coadministration of ritonavir and by 1.8- and 2.1-fold when ritonavir was administered before nelfinavir and after nelfinavir, respectively. Ritonavir AUCs were unaffected by coadministration of the other drugs. The effect of ritonavir on the kinetics of saquinavir persisted for at least 48 hours after a single dose of ritonavir, suggesting the possibility of metabolic intermediates that form inhibitory complexes. Conclusion Except for saquinavir followed by ritonavir, there is little difference in protease inhibitor exposure for simultaneous or staggered doses. The persistent effect of ritonavir suggests the possibility that lower doses and longer dosing intervals might be effective when ritonavir is used to boost concentrations of other protease inhibitors. Clinical Pharmacology & Therapeutics (2003) 73, 406–416; doi: 10.1016/S0009-9236(03)00006-7

A particular instability phenomenon as well as the countermeasure in a voltage source inverter-fed synchronous machine with a field orientation control circuit without using a position sensor. A superposed control circuit generates the reference values of the rotor current and the field-oriented stator voltage vector. The necessary signals for the generation of these reference values are calculated using a current model which is fed by the reference values of the currents. Due to the utilization of the load angle signal calculated in this way, the torque component of the stator current is strongly coupled with the flux, which results in an operation range where, under normal excitation, the machine is not able to work stably at the desired operation point. This instability is independent of the parameter tuning and the orientation correctness. The required decoupling is realized by feeding back of the actual flux signal to the control unit, and the unstable operation range will be eliminated. >

Objective: Lipid lowering therapy is used increasingly in persons with HIV infection in the absence of safety data or information on drug interactions with antiretroviral agents. The primary objectives of this study were to examine the effects of ritonavir (RTV) plus saquinavir soft-gel (SQVsgc) capsules on the pharmacokinetics of pravastatin, simvastatin, and atorvastatin, and the effect of pravastatin on the pharmacokinetics of nelfinavir (NFV) in order to determine clinically important drug-drug interactions. Design: Randomized, open-label study in healthy, HIV seronegative adults at AIDS Clinical Trials Units across the USA. Methods: Three groups of subjects (arms 1, 2, and 3) received pravastatin, simvastatin or atorvastatin (40 mg daily each) from days 1-4 and 15-18. In these groups, RTV 400 mg and SQVsgc 400 mg twice daily were given from days 4-18. A fourth group (arm 4) received NFV 1250 mg twice daily from days 1-14 with pravastatin 40 mg daily added from days 15-18. Statin and NFV levels were measured by liquid chromatography/tandem mass spectrometry. Results: Fifty-six subjects completed both pharmacokinetic study days. In arms 1-3, the median estimated area under the curves (AUC) 0-24 for the statins were: pravastatin (arm 1, n = 13), 151 and 75 ng.h/ml on days 4 and 18 (decline of 50% in presence of RTV/SQVsgc), respectively (P = 0.005); simvastatin (arm 2, n = 14), 17 and 548 ng.h/ ml on days 4 and 18 (increase of 3059% in the presence of RTV/SQVsgc), respectively (P < 0.001); and total active atorvastatin (arm 3, n = 14), 167 and 289 ng.h/ml on days 4 and 18 (increase of 79% in the presence of RTV/SQVsgc), respectively (P < 0.001). In arm 4, the median estimated AUC 0-8 for NFV (24 319 versus 26 760 ng.h/ml; P = 0.58) and its active M8 metabolite (15565 versus 14571 ngh/m; P = 0.63) were not statistically different from day 14 to day 18 (without or with pravastatin). Conclusions: Simvastatin should be avoided and atorvastatin may be used with caution in persons taking RTV and SQVsgc. Dose adjustment of pravastatin may be necessary with concomitant use of RTV and SQVsgc. Pravastatin does not alter the NFV pharmacokinetics, and thus appears to be safe for concomitant use.

A method was developed and validated for measuring the free fraction of nelfinavir in plasma employing equilibrium dialysis for the separation of free (unbound) drug and liquid chromatography/tandem mass spectrometry for quantitation. Nelfinavir, widely used to treat HIV infection, is a highly bound HIV protease inhibitor with the fraction bound in plasma being greater than 98%. Thus variations in the free fraction may be clinically important when interpreting total drug concentrations. Optimization of the method was carried out considering the influence of sample matrix and physicochemical and absorptive properties of nelfinavir. Nelfinavir free fraction averaged 0.41 +/- 0.094, 0.43 +/- 0.087 and 0.41 +/- 0.063% at nelfinavir plasma concentrations of 1000, 2000 and 3000 ng/ml, respectively. Free nelfinavir concentrations were underestimated with this assay by approximately 25% because of unavoidable losses to adsorption. However, the adsorptive loss was reproducible and consistent across the concentration range of the assay. Within-day and between-day precisions ranged from 6.0 to 9.4% and 15.2 to 27.3%, respectively. The lower limit of quantitation of the unbound concentration of nelfinavir was 1.0 ng/ml, permitting analysis of samples with total concentrations of nelfinavir in plasma that areor = 400 ng/ml. This developed method proves reproducible and sensitive and its application to patient plasma samples is also reported.

Neointima formation involves tissue expression of matrix proteins and growth factors. The role of alphavbeta3, but not alphavbeta5 integrin in vascular cells has been sufficiently investigated. The aim of the present study was to determine and compare the function of alphavbeta3 and alphavbeta5 integrins in rat aortic (RASMC) and human coronary vascular smooth muscle cells (HCSMC) and to characterize their expression accompanying neointima formation in vivo. RASMC and HCSMC express alphavbeta3 and alphavbeta5 integrin subunits. The alphavbeta5 integrin predominantly mediated adhesion of RASMCs to vitronectin and spreading on vitronectin via RGD-binding sequences. In contrast, the alphavbeta3 integrin did not contribute to the adhesion and spreading on fibronectin, vitronectin, gelatin or collagen I coated layers. PDGF-directed migration through gelatin coated membranes involved both alphavbeta3 and alphavbeta5 integrins. Selective blocking antibodies for alphavbeta3 and alphavbeta5 inhibited migration of RASMC and HCSMC by more than 60 % (p0.01). Integrin expression was studied in vivo in thoracic aorta of Sprague Dawley rats before and after balloon injury. In situ hybridization demonstrated low signals for alphav, beta3 and beta5 mRNA in uninjured aorta, which increased significantly at 14 days, localized predominantly in the neointima. Northern analysis of aorta after 14 days of injury also demonstrated an upregulation of alphav, beta3 and beta5 mRNA compared to uninjured aorta. Consistent with the increase in message levels, increased integrin protein expression was seen in the neointima after 7 and 14 days. This study provides evidence that alphavbeta3 and alphavbeta5 are elevated during neointima formation in the rat and indicates a novel role for alphavbeta5 participating in mechanisms regulating smooth muscle cell migration.

High-performance capillary electrophoresis (HPCE) with UV absorbance detection (254 nm) has been applied for analyzing intracellular free ribonucleotides. The nucleotide profiles obtained from peripheral blood lymphocytes differ from those obtained from Molt4 human leukemic cells. With a 140 mM borate buffer, pH 9.4, a nearly complete profile can be obtained in 25 min. HPCE has comparable resolution to that of high-performance liquid chromatography (HPLC) but is faster in terms of time per sample run (25 min vs 45 min) and requires much less sample (nanoliter range for HPCE vs microliter range for HPLC).

Protease inhibitors are very effective in treating patients infected with HIV. However, many drugs in this class penetrate poorly into the central nervous system (CNS) and may permit this site to be a sanctuary from which resistant virus can emerge. Previous studies have shown that the protease inhibitor saquinavir (SQV) interacts with the multidrug transport system, P-glycoprotein (P-gp), expressed in epithelial cells in the gut mucosa and at the blood-brain barrier, and thus might affect both the oral absorption and the penetration of SQV into the CNS. To determine whether SQV is a substrate for P-gp, its uptake was determined in cancer cells, which do (Dx5) and do not (MES-SA) express P-gp. The distribution of SQV between brain tissue and plasma was also investigated in rats and in normal and P-gp-deficient mdr1a(-/-) mice. The distribution ratio of SQV in plasma:brain:cerebrospinal fluid was approximately 100:10:0.2 in rats. The accumulation of SQV was enhanced in MES-SA cells (P-gp-negative) versus Dx5 cells (P-gp-positive). Bolus i.v. injection of [(14)C]SQV (2 and 5 mg/kg) into mdr1a(-/-) and normal mice (n = 3 or 4) resulted in 3-fold higher radioactivity in brains from mdr1a(-/-) mice. Similarly, oral administration of [(14)C]SQV (500 mg/kg) resulted in a 5-fold increase in systemic exposure and a 10-fold increase in brain levels in mdr1a(-/-) mice. These data demonstrate that saquinavir is a substrate for P-gp and that this transport system may play a role in limiting oral absorption and CNS exposure to this protease inhibitor.

Background Cigarette smoking is associated with impaired endothelium-dependent dilatation in human veins and arteries. An in vivo study in animals suggests that nicotine may contribute to this abnormality. We tested the hypothesis that local administration of nicotine at a dose reproducing the plasma concentration observed during smoking would impair endothelium-dependent vasodilatation in human veins in vivo. Methods We studied 11 healthy nonsmokers with the dorsal hand vein compliance technique. After 70% to 80% preconstriction with phenylephrine, endothelium-dependent venous relaxation was assessed by infusion of bradykinin (1 to 278 ng/min), a potent vasodilator acting primarily in this model through endothelial release of nitric oxide and prostanoids. Sodium nitroprusside (0.0001 to 3166 ng/min) was used to test endothelium-independent relaxation. Dose-response curves were constructed before and during nicotine coinfusion at a rate of 40 ng/min, reproducing a plasma concentration of 15 ng/mL. Results After a 10-minute preinfusion, nicotine administration was associated with a loss in sensitivity to bradykinin (P < .001). After 30 and 60 minutes of preinfusion with nicotine, the venorelaxant effect of bradykinin was further reduced (P < .001). A similar inhibition of the response to bradykinin by nicotine persisted in the presence of indomethacin (INN, indometacin). Coinfusion of nicotine did not attenuate sodium nitroprusside–induced venodilation. Conclusion The results show that acute local exposure to nicotine in vivo is associated with an impaired response to endothelium-derived nitric oxide in human veins. This finding may provide further insight into the pathophysiology of smoking-induced endothelial dysfunction. (Clin Pharmacol Ther 2000;67:391-7.) Clinical Pharmacology & Therapeutics (2000) 67, 391–397; doi: 10.1067/mcp.2000.105153

Abstract —Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is elevated in hypercholesterolemia. This study was designed to determine the role of ADMA in the increased mononuclear cell adhesiveness observed in human hypercholesterolemia. In patient studies, plasma ADMA levels were determined by high-performance liquid chromatography. Functional mononuclear leukocyte adhesion assays were performed in parallel, and flow cytometry was used to characterize bound monocytes and T lymphocytes. Hypercholesterolemic patients were then placed on an oral l -arginine regimen of 14 or 21 g/d and studied over 12 weeks. In cell culture studies, bovine aortic endothelial cells were incubated with varied concentrations of ADMA. Monocytoid cells were cocultured with these bovine aortic endothelial cells, and their adhesiveness was assessed by use of a binding assay. Flow cytometry was used to quantify adhesion molecule expression. Plasma ADMA levels and adhesiveness of mononuclear cells (specifically, monocytes and T lymphocytes) were elevated in hypercholesterolemic patients. Adhesiveness was inversely correlated with the plasma l -arginine/ADMA ratio. Oral administration of l -arginine normalized plasma l -arginine/ADMA ratios and attenuated monocyte and T-lymphocyte adhesiveness. ADMA had no direct effect on the adhesiveness of mononuclear cells. However, monocytes became hyperadhesive when cocultured with ADMA-exposed endothelial cells. In human hypercholesterolemia, the plasma l -arginine/ADMA ratio is inversely correlated with mononuclear cell adhesiveness. Restoration of the l -arginine/ADMA ratio to control levels normalizes mononuclear cell adhesiveness. Our studies suggest that the elaboration of endothelium-derived nitric oxide affects the behavior of circulating T lymphocytes and monocytes.

Recently, we cloned a human organic cation transporter, hOCT1, which is expressed primarily in the liver. hOCT1 plays an important role in the cellular uptake and elimination of various xenobiotics including therapeutically important drugs. HIV protease inhibitors are a new class of therapeutic agents. The purpose of this study was to elucidate the interactions of HIV protease inhibitors with hOCT1 and to determine whether hOCT1 is involved in the elimination of these compounds. We studied the interactions of HIV protease inhibitors with hOCT1 in a transiently transfected human cell line, HeLa. Uptake studies were carried out 40 h post-transfection using the radiolabeled model organic cation, [(14)C]tetraethylammonium (TEA), under different experimental conditions. In cis-inhibition studies, all of the HIV protease inhibitors tested, i.e., indinavir (IC(50) of 62 microM), nelfinavir (IC(50) of 22 microM), ritonavir (IC(50) of 5.2 microM), and saquinavir (IC(50) of 8.3 microM) inhibited TEA uptake in HeLa cells expressing hOCT1. However, none of the HIV protease inhibitors trans-stimulated [(14)C]TEA uptake, suggesting that they are poorly translocated by hOCT1. Nelfinavir, ritonavir, and saquinavir demonstrated an apparent "trans-inhibition" effect. No enhanced uptake of [(14)C]saquinavir was observed in hOCT1 DNA-transfected cells versus empty vector-transfected cells. These data suggest that HIV protease inhibitors are potent inhibitors, but poor substrates, of hOCT1. Some HIV protease inhibitors may potently inhibit the uptake and elimination of cationic drugs that are substrates for hOCT1, leading to potential drug-drug interactions. Other transporters, e.g., MDR1 and MRP1, in HIV-targeted cells may control the intracellular concentrations of HIV protease inhibitors.

The obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular disease and systemic hypertension. Because systemic arterial blood pressure is proportional to venodilation and venous return to the heart, we hypothesized that altered vascular responsiveness might exist in the veins of subjects with OSAS. We therefore investigated venodilator responses in awake, normotensive subjects with and without OSAS, using the dorsal hand vein compliance technique. Dose-response curves to bradykinin and nitroglycerin were obtained from 12 subjects with OSAS and 12 matched control subjects. Maximal dilation (E(max)) to bradykinin was significantly lower in the OSAS group (62.1% +/- 26.1%) than in the control group (94.3% +/- 10.7%) (p0.005). Vasodilation to nitroglycerin tended to be lower in the OSAS group (78.6% +/- 31.8%) than the control group (100.3% +/- 12.9%), but this effect did not reach statistical significance. When six of the OSAS subjects were retested after 60 d of treatment with nasal continuous positive airway pressure (CPAP), E(max) to bradykinin rose from 60.3% +/- 20. 3% to 121.4% +/- 26.9% (p0.01). Vasodilation to nitroglycerin also increased, but this effect did not reach statistical significance. These results demonstrate that a blunted venodilatory responsiveness to bradykinin exists in OSAS. This effect appears to be reversible with nasal CPAP therapy.

Objective In arteries and veins smoking is associated with impaired nitric oxide–mediated relaxation to endothelium-dependent agonists such as bradykinin. We investigated whether acute local angiotensinconverting enzyme (ACE) inhibition, achieved by enalaprilat, could influence bradykinin-induced vasodilation in veins of smokers. Methods We studied 7 smokers and 7 nonsmokers with the hand vein technique. After preconstriction with phenylephrine was performed, endothelium-dependent and independent relaxations were assessed by infusing bradykinin (1 to 278 ng/min) and sodium nitroprusside (0.0001 to 3166 ng/min), respectively. Dose-response curves were constructed before and during enalaprilat coinfusion (1 μg/min for 40 minutes). Results Smokers had impaired venodilation to bradykinin compared with nonsmokers (P < .01). Apparent maximal relaxation induced by bradykinin was 78% ± 9% in the control group and 48% ± 9% in smokers (mean ± SD). ACE inhibition shifted the bradykinin dose-response curve to the left in both groups (P < .001) and was associated with a minimal increase in apparent maximal venodilation in nonsmokers (78% ± 9% to 83% ± 18%). In contrast, in smokers ACE inhibition augmented the magnitude of apparent maximal venodilation to values comparable to those observed in the control group (48% ± 9% to 102% ± 21%). In both groups the response to sodium nitroprusside was not affected by enalaprilat. Conclusions This study shows that acute local ACE inhibition restores bradykinin-induced relaxation in smokers to values found in nonsmokers. This observation suggests that increased vascular metabolism of bradykinin exists in veins of smokers and that the vascular renin-angiotensin system may play a key role in smoking-induced endothelial dysfunction. Clinical Pharmacology & Therapeutics (1999) 65, 295–303; doi

Acute administration of L-arginine, the precursor of endothelial nitric oxide, has been shown to improve endothelial function in hypercholesterolaemic rabbits and humans. Animal studies suggest that this beneficial effect, which is thought to be related to the increased availability of nitric oxide, may not be sustained during chronic oral administration. Pharmacokinetic alterations may contribute to this observation. The present study was designed to examine the disposition of L-arginine in hypercholesterolaemic subjects during long-term administration. Plasma L-arginine concentrations were determined by HPLC in 10 patients (eight women and two men; mean age 46±16 years) after an intravenous dose of 10 or 30 g and an oral dose of 5 or 7 g. Pharmacokinetic studies were performed at regular intervals (4 weeks) during a 12-week period of oral L-arginine administration (14–21 g/day). The average plasma L-arginine concentrations before (baseline) and during administration were 16.1±1.2 and 22.5±1.3 μg/ml respectively (P< 0.05). Plasma concentrations of L-arginine remained above baseline throughout weeks 2–12. The L-arginine exposure, expressed as a normalized area-under-the-curve for 8 h (AUC0–8) after oral or intravenous doses during the first visit, was 894.4±118.7 and 1837.8±157.0 units respectively. There were no significant changes in peak plasma L-arginine concentrations or in the AUC0–8 after oral and intravenous doses during subsequent visits (P> 0.05). The mean non-renal clearance of L-arginine during the four visits remained constant. Knowledge of the pharmacokinetics of L-arginine may be useful in the design of clinical trials involving this agent, as well as in the interpretation of the pharmacodynamics of this important precursor of nitric oxide.

Objective To characterize drug-taking behavior using continuous electronic monitoring in an AIDS clinical trial. Setting This was a substudy of AIDS Clinical Trials Group (ACTG) protocol 175, a phase II/III study of dideoxynucleoside monotherapy versus combination therapy in asymptomatic HIV-positive subjects. Participants were required to comply with regimens containing zidovudine, zalcitabine and didanosine, or matching placebos; the total daily pill count was 16. Design For participants at two ACTG 175 sites, electronic devices were used to monitor drug-taking behavior of all study medications over a period of approximately 90 days. Measurements Four indices of drug-taking behavior were calculated and their distributions and relationship to the prescribed regimen were examined. Results Data from 41 subjects were analyzed. Of the prescribed doses of zidovudine, zalcitabine and didanosine, 88, 84 and 82%, respectively, were taken. Of these, 55, 66 and 79%, respectively, were taken at the prescribed dosing frequency. The median percentage of days on which participants failed to take any of the doses was 2-5%. There was a trend towards lower adherence in the combination therapy arms compared with those assigned to receive monotherapy. In this analysis, older patients demonstrated better adherence, although patient characteristics, in general, were poorly predictive of adherence. Conclusion Drug-taking behavior for all three active study medications differed from that prescribed. One result of this erratic adherence was that study participants sustained little antiretroviral effect during more than 25% of the monitoring period.

Patient compliance (adherence) with prescribed medication is often erratic, while clinical outcomes are causally linked to actual, rather than nominal medication dosage. We propose here a hierarchical Markov model for patient compliance. At the first stage, conditional upon individual random effects and a set of individual-specific nominal daily dose times, we assume that (i) the subject-specific probability of taking zero, one, or more than one dose associated with a given nominal dose time depends on the value of certain covariates, and on the number of doses associated with the immediate previous time, but is independent of any other previous or future dosing events (the Markov hypothesis); and (ii) the set of 'errors' between actual dose times associated with each nominal time is multivariate normally distributed, conditional on covariates and the number of such actual dose times, as in (i). At the second stage, a multivariate normal distribution is assumed for the individual random effects. We fit this model by maximum likelihood to data collected over three months using an electronic system for recording actual dose times in HIV-positive patients assigned to a regimen of zidovudine thrice daily. Beyond its value for describing and quantifying compliance behaviour, as illustrated here, the model may prove useful for explanatory analyses of clinical trials.

The anti-HIV protease inhibitors represent a new class of agents for treatment of HIV infection. Saquinavir, ritonavir, indinavir, and nelfinavir are the first drugs approved in this class and significantly reduce HIV RNA copy number with minimal adverse effects. They are all substrates of cytochrome P450 3A4, and are incompletely bioavailable. The drug transporting protein, P-glycoprotein (P-gp), which is highly expressed in the intestinal mucosa, could be responsible for the low oral bioavailability of these and other drugs which are substrates for this transporter. To determine whether these protease inhibitors are modulators of P-gp, we studied them in cell lines which do and do not express P-gp. Saquinavir, ritonavir and nelfinavir significantly inhibited the efflux of [3H]paclitaxel and [3H]vinblastine in P-gp-positive cells, resulting in an increase in intracellular accumulation of these drugs. However, similar concentrations of indinavir did not affect the accumulation of these anticancer agents. In photoaffinity labeling studies, saquinavir and ritonavir displaced [3H]azidopine, a substrate for P-gp, in a dose-dependent manner. These data suggest that saquinavir, ritonavir, and nelfinavir are inhibitors and possibly substrates of P-gp. Because saquinavir has a low bioavailability, its interaction with P-gp may be involved in limiting its absorption.

Background —Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of nitric oxide (NO) synthase. Because endothelial NO elaboration is impaired in hypercholesterolemia, we investigated whether plasma concentrations of ADMA are elevated in young, clinically asymptomatic hypercholesterolemic adults. We further studied whether such elevation of ADMA levels was correlated with impaired endothelium-dependent, NO-mediated vasodilation and urinary nitrate excretion. In a randomized, double-blind, placebo-controlled study, we investigated whether these changes could be reversed with exogenous l -arginine. Methods and Results —We measured plasma levels of l -arginine, ADMA, and symmetrical dimethylarginine (SDMA) by high-performance liquid chromatography in 49 hypercholesterolemic (HC) and 31 normocholesterolemic (NC) humans. In 8 HC subjects, endothelium-dependent forearm vasodilation was assessed before and after an intravenous infusion of l -arginine or placebo and compared with 8 NC control subjects. ADMA levels were significantly elevated by >100% (2.17±0.15 versus 1.03±0.09 μmol/L; P l -Arginine levels were similar, resulting in a significantly decreased l -arginine/ADMA ratio in HC subjects (27.7±2.4 versus 55.7±5.4; P l -arginine significantly increased the l -arginine/ADMA ratio and normalized endothelium-dependent vasodilation and urinary nitrate excretion. ADMA levels were inversely correlated with endothelium-mediated vasodilation ( R =0.762, P R =0.534, P Conclusions —We find that ADMA is elevated in young HC individuals. Elevation of ADMA is associated with impaired endothelium-dependent vasodilation and reduced urinary nitrate excretion. This abnormality is reversed by administration of l -arginine. ADMA may be a novel risk factor for endothelial dysfunction in humans.

Cigarette smoking has been shown to impair endothelium-dependent dilation in arteries. We tested the hypothesis that cigarette smoking also impairs endothelium-dependent venodilation and evaluated changes in this response after smoking cessation in a time-course study using the dorsal hand vein technique. Dose-response curves were constructed in smokers and nonsmokers by infusing bradykinin (1–278 ng/min), an endothelium-dependent vasodilator, and nitroglycerin (0.006–1,583 ng/min), an endothelium-independent vasodilator, into hand veins preconstricted with the selective α1-adrenergic agonist phenylephrine. The maximal venodilation induced by bradykinin was 89 ± 5% in controls ( n = 16) and 61 ± 7% in smokers ( n = 18; P = 0.02). No difference in nitroglycerin-induced venodilation was observed between the two groups. Coinfusion of l-arginine (0.33 mg/min) markedly improved the bradykinin-induced venodilation in smokers (52 ± 7 to 90 ± 9%; P < 0.01). After acute smoking cessation ( n = 7), restoration to normal bradykinin-induced venodilation was observed within 24 h, whereas no change in the response to a maximally effective dose of nitroglycerin (1,583 ng/min) was detected. In a human vein model appropriate for testing vascular functional alterations, this study demonstrates that smoking impairs endothelium-dependent venodilation in heavy smokers. Moreover, this endothelial dysfunction appears to be rapidly reversible after smoking cessation. This model may be useful in studies evaluating mechanisms of endothelial dysfunction and interventions to modify it.

We propose a semiparametric method to estimate model-independent pharmacokinetic (PK) measures such as area under concentration-time, peak concentration and time to peak concentration (Tpeak), for noisy population PK data from a sparsely sampled prospectively designed trial. The method is developed within the mixed-effect model framework, for the single-dose and steady-state case. We describe individual concentration vs. time using a longitudinal spline, consisting of a template spline, common to all individuals, and an individual-specific distortion spline accounting for individual differences. We impose a number of constraints on the longitudinal spline, including (i) it has a decreasing tail, (ii) its typical Tpeak is near the modal Tpeak observed in the population data, and (iii) its value is zero at time zero (single dose), or the same nonzero value at the beginning and end of a dosing interval (steady state). We test our method using simulated data and compare its performance to that of a parametric and a nonparametric method. An actual data example is also shown. The performance of the method is as good or better than that of a standard nonparametric method, and when the analysis model is misspecified, the method is superior to a standard parametric one. Since it is often not apparent that an analysis model is correct, we propose this approach as a general method for analysis.

The relationship of CD4+ cell response, level of RNA in plasma, and quantitative peripheral blood mononuclear cell (PBMC) titer to apparent drug exposure was investigated by using data from AIDS Clinical Trial Group protocol 229, a multicenter randomized study. Patients received either saquinavir, zalcitabine, or a combination of both, along with open-label zidovudine. Approximately 100 patients were enrolled in each arm, and the primary study duration was 24 weeks. Individual drug exposure, the area under the concentration-time curve, was estimated by using population-based pharmacokinetic methods. Response was defined as the maximum increase in CD4+ cell count or the maximum decrease in RNA in plasma or PBMC titer adjusted for baseline CD4+ cell count, RNA in plasma, and PBMC titer, respectively. Regression of responses on exposure demonstrated an exposure effect for saquinavir which was significant for the maximum increase in CD4+ cell count and the decrease in RNA in plasma. For the PBMC titer, no significant relationship could be demonstrated but the results suggested a trend similar to that of the other response variables. For all three response variables, the slope of the saquinavir exposure response was greater with the triple combination (saquinavir, zidovudine, and zalcitabine) than with the combination of saquinavir and zidovudine, suggesting possible synergism between saquinavir and zalcitabine.

Objective Hypotension induced by parenteral administration of chloroquine is a common and serious adverse effect of this drug. Our aim was to investigate whether chloroquine produces venodilation in vivo and to explore the underlying mechanisms. Methods Vascular effects of chloroquine were studied in healthy volunteers with use of the dorsal hand vein technique at the Geriatric Research Education and Clinical Center, Veterans Affairs Palo Alto Health Care System. We studied 22 healthy volunteers (19 men and three women). Venous responsiveness was determined with the dorsal hand vein technique, which measures the diameter of the vein. Results Chloroquine was found to produce a dose-dependent relaxation of hand veins preconstricted with the α1-receptor selective agonist phenylephrine. The venodilatory response to chloroquine ranged from 15% ± 19% at an infusion rate of 0.75 μg/min to 61% ± 24% at 48 μg/min. Venodilation was attenuated by the nitric-oxide synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) so that the dose of chloroquine required to produce 20% venodilation was increased from 3.7 μg/min to 15 μg/min (p < 0.01). In the presence of a combination of histamine receptor antagonists, there was also a diminution of the vasodilatory response to chloroquine from 72% ± 5% to 44% ± 5% at the infusion rate of 96 μg/min. The response was further reduced to 33% ± 7% by the coinfusion of H1-/H2-receptor antagonists with L-NMMA. Conclusion Chloroquine produces venodilation at infusion rates that achieve local concentrations likely similar to those observed systematically after clinically relevant intravenous doses. The data also suggest a role for nitric oxide and histamine release in mediating this response. Clinical Pharmacology & Therapeutics (1997) 61, 677–683; doi

▪ Abstract Well-designed clinical trials maximize the information that can be obtained regarding the clinical pharmacology of a drug and, in turn, can streamline and enhance the drug development process. Until recently, little emphasis has been placed on integrating the role of variability in individual patterns of drug-taking into the drug development process. With the use of electronic monitoring, the temporal relationship between an individual's pattern of dosing and the prescribed regimen may be examined, and individual drug exposure may be estimated based on the actual history of dosing. As a result, accurate estimation of exposure-response relationships (or surrogate markers of response) can be obtained. Considerations in the design of clinical trials must therefore be expanded to include appropriate methods to measure compliance, sufficient frequency of monitoring to allow the time course of response to be mapped, and the use of statistically valid methods of data analysis.