Search

The effects of three doses of a special Agnus castus extract (BP1095E1) - extracts from 120 mg, 240 mg and 480 mg of drug per day - were examined within the framework of a placebo-controlled clinical study of tolerance and prolactin secretion in 20 healthy male subjects during a period of 14 days. There was good tolerance during the study as regards the following: adverse effects, the effects on blood pressure and heart rate, blood count, Quick's test, clinical chemistry as well as testosterone, FSH and LH values. During each study phase the 24-hour prolactin secretion profile was measured from the penultimate to the final day, and the amount of prolactin release was monitored an hour after TRH stimulation on the last day. A significant increase in the 24-hour profile was registered with the lowest dose in comparison to placebo, the opposite being the case with the higher doses, i.e. a slight reduction. In contrast to the administration of placebo, the 1-hour AUC after TRH stimulation resulted in a significant increase with the lowest dose and a significant reduction with the highest dese. The results suggest effects of the special Agnus castus extract which are dependent on the dose administered and the initial level of prolactin concentration. more...

In a randomized crossover study on twelve healthy test subjects, the plasma concentration of isosorbide-5-nitrate (IS-5-N) after oral administration of 40 mg IS-5-N daily from two standard preparations (two tablets Ismo 20 or Corangin 20) and two sustained release preparations with 40 mg or 60 mg IS-5-N (one tablet Corangin 40 or Corangin 60) once a day was determined. The concentrations were measured in the first and in the third dose interval (24 hours). The respective pharmacokinetic parameters (AUC, Cmax and tmax) of the first and the third day only differed slightly. The two standard formulations proved to be bioequivalent. With the two sustained release preparations, maximum plasma concentrations attained after five to six hours were measured which were lower by roughly the factor 2. The sustained release preparations showed a low loss of bioavailability of 13-19% as compared to the nonretarded standard formulations. more...

The relative bioavailability of isosorbide dinitrate (ISDN) and its mononitrate metabolites (IS-2-MN, IS-5-MN) was determined under repetitive dose conditions in 8 healthy volunteers using a randomised, crossover design. Reference drugs were non-sustained release ISDN (Isoket 20) and IS-5-MN (Ismo 20). The relative bioavailability of ISDN after Iso Mack Retard was 69%, for two development products 78% and 79%, and 87% for Isoket Retard. The bioavailability of IS-2-MN and IS-5-MN in sustained release preparations was 6-16% and 1-17% lower, respectively. Whereas the sum total for the area under the concentration-time curve (ISDN and metabolites) for Iso Mack Retard 20 mg was also significantly lower, there was no significant difference in this parameter between Isoket retard 20 and Isoket 20. Taking IS-5-MN non-retard as reference, the bioavailability of IS-5-MN and total nitrate in all ISDN preparations examined was significantly lower. more...

The BEACOPP (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine and prednisone) chemotherapy regimen for the treatment of advanced Hodgkin’s lymphoma has a superior outcome, but its toxicity (mainly haematotoxicity) is pronounced and highly variable. The present study was conducted to address the role of pharmacokinetics in individual toxicity. Three plasma samples and a 24-hour urine collection for day 1 of the first three cycles of chemotherapy were analysed in 30 patients, and the pharmacokinetic parameters of the respective drugs were estimated by population pharmacokinetic methods (nonlinear mixed-effects model [NONMEM] software). Demographic data, doses and durations of infusion were also recorded. The effect of these parameters on platelet counts was estimated by analysis of covariance using a general linear model. The pharmacokinetic parameters and respective covariates were similar to the published data. The body surface area, peak concentrations of etoposide, urinary recovery of dechloroethylcyclophosphamide (formed by cytochrome P450 [CYP] 3A4) relative to the cyclophosphamide dose and number of cycles had a significant effect on toxicity. These factors explained 37% of the interindividual variability in the change in platelet counts from day 1 to day 8 of each cycle. The results show that the individual pharmacokinetics of BEACOPP drugs are an important link between dosage and toxicity. Accordingly, individualisation of treatment based on pharmacokinetics may result in more uniform toxicity. Individualisation may also allow escalation of the mean dose, which is probably related to better efficacy. As a consequence of the present study, infusion rates should be standardised, and the potential of a dose reduction in the first cycle and of CYP3A4 phenotyping should be addressed in clinical studies. more...

The inhibition of dansylsarcosine (DS) binding at the benzodiazepine binding site of human serum albumin has been studied in the presence of saturated and unsaturated free fatty acids (FFA) of various chain lengths (C6–C20, C18:1, C18:2). In order to determine the mechanism of displacement, velocity constants for association (k 2) and dissociation (k −2) and binding constants (K A and K A′) have been measured using the stopped-flow method. The inhibitory effect of FFA on DS binding kinetics at site II is dependent of their structure. With increasing amounts of FFA the association velocity constant of DS binding decreases from 520 s−1 (fatty acid free albumin) by a factor of 3–10 and affinity decreases according to FFA chain length. Inhibition is strongest in the presence of caprylic, capric and lauric acid (C8–C12) i.e. with more than one mole FFA per mole albumin, DS association could no longer be measured. Short chain caproic and the long chain FFA C14–C20 showed only a less inhibitory effect since in the presence of a twofold excess k 2 ranged between 100 and 200 s−1. Dissociation velocity of DS from the benzodiazepine binding site could be measured in relationship to FFA chain length using ibuprofene, another drug binding at site II. Dissociation velocity constants k −2 remained constant up to 2 moles FFA per mole albumin (k −2 = 16–18 s−1). A rise in k −2 to 70 s−1 was seen, however, when 2–4 moles capric, lauric, myristic and palmitic (C10–C16) acid were bound, whereas no change was observed when increasing concentrations of caproic, caprylic, stearic and arachic acid. The more compact unsaturated FFA oleic and linoleic acids did not inhibit DS binding to the same extent as their saturated homologue stearic acid. k 2 and k −2 values resembled those when comparable amounts of myristic acid were bound indicating that chain length is the relevant parameter. It can be concluded that two different types of FFA inhibition of binding at the benzodiazepine binding site exist. Short-chain FFA (C6–C8) may be specifically bound at binding site II thereby competitively displacing DS. Longchain FFA (C12–C20), however, occupy their binding sites far from the benzodiazepine binding site. Inhibition occurs via an allosteric mechanism. Capric acid is unique in showing as well as competitive as well as allosteric inhibition characteristics. more...

Studies on the concentration-effect relationship of levodopa in Parkinson's disease have established that: (1) in patients with a fluctuating response to levodopa, concentration-effect profiles are steeper and markedly shifted to the right (i.e. potency is decreased) compared with those patients whose symptoms are adequately controlled; (2) with controlled-release (CR) preparations, the concentration-effect relationship indicates a decreased potency compared with conventional immediate-release (IR) preparations; and (3) coadministration of a dopamine receptor agonist (even at a subclinical dose) enhances the potency of levodopa. These findings support some current hypotheses on the origin of, and the pathophysiological process underlying, response fluctuations. In patients with response fluctuations, metabolism of levodopa and storage of dopamine in the striatum are reduced. Levodopa is decarboxylated in the extracellular space, with the result that dopamine is released directly to the effect site. Thus, without dopamine storage acting as a buffer between levodopa metabolism and dopaminergic effect, the decline in motor response closely follows the decrease in levodopa concentrations. Even small fluctuations of levodopa concentrations around the EC50 value (the concentration threshold necessary to produce a motor response) might be followed by response fluctuations. Patients with Parkinson's disease who do not have response fluctuations exhibit a residual capacity of production and storage of endogenous dopamine; thus, lower amounts of 'exogenous' dopamine (formed by decarboxylation of levodopa) are required. The storage buffer is responsible for a time lag between decline in peripheral plasma concentrations of levodopa and dopamine-induced motor response. Low doses of a dopamine receptor agonist increase the basal tonus of the striatum, but do not reach the threshold concentration for triggering a motor response. Because of the dichotomic character of the motor response, patients do not switch from an 'off' (not responding) phase to an 'on' (responding) phase. However, lower amounts of exogenous dopamine released in the synaptic cleft will be necessary to induce response. To date, pharmacokinetic-pharmacodynamic modelling does not give a clear answer as to whether response fluctuations are additionally induced by receptor desensitisation or inhibition of the active transport of levodopa across the blood-brain barrier by the main metabolite of levodopa, 3-O-methyldopa. Nevertheless, there is some evidence that higher plasma concentrations of levodopa are required for similar motor effects when CR preparations are compared with IR preparations. Attempts have been made to establish therapeutic drug monitoring of levodopa in patients with response fluctuations. The interindividual variability of EC50 values in single studies is relatively low (10% to a maximum of 50%), which might allow specification of a 'population' threshold plasma concentration (i.e. a minimal effective plasma concentration required to obtain clinical effects). However, considering the short elimination half-life of levodopa, it seems doubtful whether such target drug concentrations can be maintained as steady-state. A marked prolongation of the dosage interval with CR preparations might be limited by the higher threshold concentrations of levodopa necessary to maintain clinical effects. more...

Studies on the concentration/effect relationship of different antihypertensive agents (mainly calcium antagonists and alpha(1)-blockers) in patients confirm a close relation between plasma concentrations and the corresponding fall in blood pressure, but the heterogenity in study objectives and methodology impedes the compiling and differentiation of results. Concentration/effect analysis was established using either the linear or the E(max) model. The studies reviewed here do not speak unequivocally in favor of either one of the methodological approaches (linear or E(max) model, PK/PD modeling, placebo correction) or a certain mode of blood pressure measurement. The responsiveness parameters obtained exhibited a wide intersubject variability; thus, threshold levels derived for any of the investigated compounds can only be used to a limited extent. For drug development, a more integrated protocol should be strived for to design studies on concentration/effect relationship for antihypertensives. Although individualized dose adjustment based on concentration/effect analysis after single-dose application was applied successfully, this approach seems to be an inadequate strategy for conventional treatment of hypertension. more...

The effects of the calcium channel blockers S- and R-verapamil or Ro 40-5967 on penetration processes of peripheral blood lymphocytes (PBL) added to allogenic human vascular endothelial cell (HUVEC) monolayers were studied. Both PBL adhesion and migration were evaluated by combined phase contrast and reflection interference contrast microscopy. PBL adhesion was inhibited by 22% when 100 μg/ml verapamil was added to the cell cultures. PBL migration was completely suppressed with verapamil concentrations above 80 μg/ml (EC50: S-verapamil: 59.7 μg/ml, R-verapamil: 52.3 μg/ml). No differences were seen in the results obtained either with or without cytokine (γ-IFN or IL-1) stimulation. Ro 40-5967 redlfced adhesion completely above concentrations of 40 μg/ml. EC50 for migration was 13 ± 2 or 13 ± 1 μg/ml, respectively. Immunohistochemical analysis of adhesion molecule expression on HUVEC revealed no inhibition of 1CAM-1 and VCAM-1 by verapamil or Ro 40-5967. We concluded that the effects of the calcium channel... more...

Nicotine is rapidly taken up by human keratinocytes (HaCaT cells) and after 3 h the uptake is approximately 50% of maximum. Cotinine, a metabolite of nicotine, was detected, thus demonstrating the metabolism of nicotine in HaCaT cells. Low nicotine concentrations (0.1–200 µg/ml) did not influence the incorporation rate of thymidine into DNA or ami-no acids into proteins. Inhibition of DNA and protein synthesis was only observed at concentrations > 200 µg/ml. After application of 400 µg/ml nicotine, the cells were vacuolated. This process was reversed after nicotine withdrawal. At low nicotine concentrations, no changes in microtubules and actin filaments could be detected. However, in the presence of nicotine (1-10µg/ml), keratin filaments showed a more orderly pattern that controls, and the expression of the suprabasal keratins 1 and 10/11 was induced and increased according to the concentration of nicotine. The number of cornified envelopes also increased markedly. Nicotine concentrations > 100 µg/ml led to a disarrangement of keratin filaments and to a decrease in keratin expression and cornified envelope formation. Our results suggest that nicotine at concentrations up to 100 µg/ml is not an irritant but may induce cornification of the skin. more...

A novel slow release preparation containing 24 mg molsidomine has been investigated in 6 healthy subjects. Individual concentration/time-profiles after the tablet showed two separate concentration peaks at 2.2 h and 15.0 h. The relative bioavailability of the slow release preparation in comparison to an aqueous solution of molsidomine was 0.67. The in vivo dissolution profile revealed either a progressive decrease in dissolution velocity caused by altered physico-chemical conditions in the ileum and the colon or a progressive reduction in the absorption constant. In all subjects deconvolution revealed a punctual increase in absorption about 15 h post-dose, coinciding with the second peak of the concentration/time-profile. Therapeutic plasma levels of molsidomine (greater than 5 ng.ml-1) were not maintained over 24 h by this slow release formulation. more...

Sera from 17 patients with Type I diabetes and 19 healthy volunteers have been examined to evaluate whether the kinetics of the binding of drugs to Site II of serum albumin is altered in diabetes. Stopped-flow measurements showed that the association velocity and the affinity constants of the fluorescent marker dansylsarcosine were significantly lower in diabetes (160 s-1 and 2.0 x 10(5) l.mol-1) than in non-diabetics (196 s-1 and 4.0 x 10(5) l.mol-1). The dissociation velocity was not different [20.3 s-1 vs. 19.4 s-1]. Although patients with a reduced albumin concentration were excluded the diabetics had significantly lower concentrations than the healthy volunteers. There was a significant correlation between decreased glycosylation of albumin and increased association velocity. The dissociation velocity constants were correlated with the molar concentration ratio of free fatty acids/human serum albumin. Thus, the extent of glycosylation and the amount of fatty acids bound per mole albumin can both affect the kinetics of drug binding to Site II. The lower affinity in patients with Type I diabetes is due to the increased in the glycoalbumin concentration. more...

The antiischemic efficacy of the converting enzyme inhibitor (CEI) benazepril was investigated in a randomized, placebo-controlled double-blind study with intraindividual crossover in 11 normotensive patients with angiographically proven coronary artery disease. Bicycle ergometry and 24-h ambulatory ECG were performed before and after 2-week treatment with placebo and benazepril, respectively. Plasma concentrations of atrial natriuretic peptide (ANP) and plasma renin activity (PRA) were measured before each exercise test. Maximal exercise-induced ST-segment depression was not significantly influenced by benazepril therapy (placebo 2.09 +/- 1.22 mm, benazepril 1.91 +/- 1.00 mm). Systolic blood pressure/heart rate (SBP/HR) product at maximum workload remained almost constant with 253 +/- 43 with placebo and 253 +/- 39 with benazepril treatment. The number of anginal attacks and ischemic episodes detected by ambulatory ECG were not significantly reduced. PRA increased significantly from 2.18 +/- 3.76 to 9.62 +/- 8.49 ng/ml/h after benazepril (p less than 0.005), whereas plasma concentrations of ANP remained unchanged (28.04 +/- 12.39 vs. 26.73 +/- 11.09 pg/ml). Therefore, measurement of ST-segment depression with exercise in 11 normotensive patients with coronary artery disease produced no evidence of an antiischemic action for the CEI benazepril 10 mg twice daily (b.i.d.) for 2 weeks, but an improvement was observed in six patients. more...

Objective: Disorders of steroid hormone metabolism might be related to the etiology of focal nodular hyperplasia of the liver (FNH), a benign tumor, especially prevalent in women. The cytochrome P450 1AI (CYP1A1) enzyme is implicated in the bioactivation of multiple precarcinogens as well as in the metabolism of steroids. Genetic polymorphisms of CYP1A1 have been associated with altered catalytic activity in the hydroxylation of sex hormones and this may account for interindividual variability in exposure to hormone-mediated cell proliferation signals and reactive steroid metabolites. In the study at hand, we aimed to evaluate a possible association between CYP1A1*1, *2A, *2B, and *4 alleles and FNH. Method: Genotyping of 26 affected female patients of Caucasian origin was carried out using PCR/RFLP. Results: Allele frequencies for the CYP1A1 variants *2A, *2B and *4 in 26 female patients with FNH were 0.058, 0.019 and 0.058, respectively. Crude odds ratios for the individual alleles were 0.75 (95% Cl 0.23 - 2.44), 0.72 (95% CI 0.10 - 5.34) and 1.96 (95% CI 0.59 - 6.50), respectively. There were no significant differences between these values and corresponding allele frequencies obtained in a large German sample of unaffected Caucasian women. Conclusion: The present data do not suggest a relevant association between CYP1A1 polymorphisms and focal nodular hyperplasia of the liver in female Caucasians. more...

Objective The mechanism of action of aceclofenac is currently unclear. This study investigated whether biotransformation to metabolites (4′-hydroxy-aceclofenac, diclofenac, 4′-hydroxy-diclofenac) contributes to inhibitory effects on the cyclooxygenase (COX) isozymes in vitro and ex vivo. Methods In vitro investigations were performed with human whole blood and human blood monocytes. A randomized crossover study was performed in volunteers receiving 100 mg aceclofenac or a sustained-release resinate formulation of 75 mg diclofenac to assess the pharmacokinetics and the ex vivo inhibition of COX-1. Results In short-term in vitro assays, neither aceclofenac nor 4′-hydroxy-aceclofenac affected COX-1 or COX-2, whereas diclofenac and 4′-hydroxy-diclofenac inhibited both isoforms. In long-term in vitro assays, aceclofenac and 4′-hydroxy-aceclofenac suppressed both COX isoforms. However, this inhibition was paralleled by a conversion to diclofenac and 4′-hydroxy-diclofenac, respectively. Maximal plasma concentrations of diclofenac after oral administration of aceclofenac (0.39 μmol/L) or diclofenac (1.28 μmol/L) were sufficient for a greater than 97% inhibition of COX-2 (50% inhibitory concentration, 0.024 μmol/L) and a 46% (aceclofenac treatment) or 82% inhibition (diclofenac treatment) of COX-1 (50% inhibitory concentration, 0.43 μmol/L). Moreover, ex vivo COX-1–dependent thromboxane B2 synthesis was inhibited significantly less by aceclofenac than by diclofenac. Conclusions Inhibition of COX isozymes by aceclofenac requires conversion into diclofenac. Although 100 mg aceclofenac yielded diclofenac concentrations substantially lower than 75 mg diclofenac, these were sufficient for a sustained block of COX-2 but caused a minor and shorter inhibition of COX-1 than 75 mg diclofenac. In conclusion, both COX-1–sparing and COX-2–inhibitory actions of aceclofenac may rest in its limited but sustained biotransformation to diclofenac. Clinical Pharmacology & Therapeutics (2003) 74, 222–235; doi: 10.1016/S0009-9236(03)00167-X more...

Aceclofenac [[2-(2',6'-dichlorophenyl)amino]phenylacetoxyacetic acid] is a phenylacetic acid derivative with potent analgesic and anti-inflammatory properties and an improved gastro-intestinal tolerance. In the present study, a liquid-liquid extraction-based reversed-phase HPLC method with UV detection was validated and applied for the analysis of aceclofenac and three of its metabolites (4'-hydroxy-aceclofenac, diclofenac, 4'-hydroxy-diclofenac) in human plasma. The analytes were separated using an acetonitrile-phosphate buffer gradient at a flow rate of 1 mL/min, and UV detection at 282 nm. The retention times for aceclofenac, diclofenac, 4'-hydroxy-aceclofenac, 4'-hydroxy-diclofenac and ketoprofen (internal standard) were 69.1, 60.9, 46.9, 28.4 and 21.2 min, respectively. The validated quantitation range of the method was 10-10000 ng/mL for aceclofenac, 4'-hydroxy-aceclofenac and diclofenac, and 25-10000 ng/mL for 4'-hydroxy-diclofenac. The developed procedure was applied to assess the pharmacokinetics of aceclofenac and its metabolites following administration of a single 100 mg oral dose of aceclofenac to three healthy male volunteers. more...

Objective We investigated the effect of polymorphisms in the P-glycoprotein (P-gp) MDR1 gene on steady-state pharmacokinetics of digoxin in Caucasians. According to earlier data, homozygous TT of the exon 26 complementary deoxyribonucleic acid (cDNA) 3435C>T polymorphism was associated with low P-gp expression in the human intestine. Methods Eight healthy male homozygous carriers of the wild-type exon-26 3435C>T (CC), 8 heterozygous subjects (CT), and 8 homozygous mutant (TT) subjects were selected. Seven further MDR1 polymorphisms were determined. Digoxin was administered orally twice daily on the first two study days; on days 3 to 5, 0.25 mg was given in the morning. On day 5, kinetic parameters were analyzed for genotype-phenotype and haplotype-phenotype relationships. Results The area under the plasma concentration-time curve from time zero to 4 hours [AUC(0–4)] (P = .042) and Cmax (P = .043) values of digoxin were higher in subjects with the 3435TT genotype than in those with the 3435CC. No influence of other single nucleotide polymorphisms (SNPs) on digoxin parameters was detected. Comparison of genotypes deduced from SNPs 2677G>T (exon 21) and 3435C>T revealed significant differences for AUC(0–4) (P = .034) and Cmax (P = .039), which were substantiated by haplotype analysis. Haplotype 12 (2677G/3435T), which had a frequency of 13.3% in a randomly drawn Caucasian sample (n = 687), was associated (Mann-Whitney test) with higher AUC(0–4) values (P = .009) than were found in noncarriers (mean ± SD, 5.7 ± 0.9 μg · h/L [n = 7] versus 4.8 ± 0.9 μg · h/L [n = 17]). Haplotype 11 (2677G/3435C) had lower AUC(0–4) values (P = .013) compared with those of noncarriers (mean ± SD, 4.7 ± 0.9 μg · h/L [n = 16] versus 5.6 ± 0.9 μg · h/L [n = 8]). Results of haplotype analysis match data of other MDR1 studies. Conclusion Haplotype 12 codes for high values of AUC(0–4) and Cmax of orally administered digoxin. Analysis of MDR1 haplotypes is superior to unphased SNP analysis to predict MDR1 phenotype. Clinical Pharmacology & Therapeutics (2002) 72, 584–594; doi: 10.1067/mcp.2002.129196 more...

Silibinin, the main constituent of silymarin, a flavonoid drug from silybum marianum used in liver disease, was tested for inhibition of human cytochrome P-450 enzymes. Metabolic activities were determined in liver microsomes from two donors using selective substrates. With each substrate, incubations were carried out with and without silibinin (concentrations 3.7-300 microM) at 37 degrees in 0.1 M KH2PO4 buffer containing up to 3% DMSO. Metabolite concentrations were determined by HPLC or direct spectroscopy. First, silibinin IC50 values were determined for each substrate at respective K(M) concentrations. Silibinin had little effect (IC50>200 microM) on the metabolism of erythromycin (CYP3A4), chlorzoxazone (CYP2E1), S(+)-mephenytoin (CYP2C19), caffeine (CYP1A2) or coumarin (CYP2A6). A moderate effect was observed for high affinity dextromethorphan metabolism (CYP2D6) in one of the microsomes samples tested only (IC50=173 microM). Clear inhibition was found for denitronifedipine oxidation (CYP3A4; IC50=29 microM and 46 microM) and S(-)-warfarin 7-hydroxylation (CYP2C9; IC50=43 microM and 45 microM). When additional substrate concentrations were tested to assess enzyme kinetics, silibinin was a potent competitive inhibitor of dextromethorphan metabolism at the low affinity site, which is not CYP2D6 (Ki.c=2.3 microM and 2.4 microM). Inhibition was competitive for S(-)-warfarin 7-hydroxylation (Ki,c=18 microM and 19 microM) and mainly non-competitive for denitronifedipine oxidation (Ki,n=9 microM and 12 microM). With therapeutic silibinin peak plasma concentrations of 0.6 microM and biliary concentrations up to 200 microM, metabolic interactions with xenobiotics metabolised by CYP3A4 or CYP2C9 cannot be excluded. more...

Background and objectives The activity of the human cytochrome P450 CYP1A2 is decreased by female sex hormones during pregnancy or treatment with oral contraceptives. However, the influence of menstrual cycle on CYP 1A2 activity is not clear. Methods CYP1A2 activity was monitored in 15 women (13 with confirmed ovulatory cycles, 2 smokers, age (mean +/- SD) 27.8 +/- 3.8 years, body mass index 23.8 +/- 3.8 kg x m-2) using the specific substrate caffeine (mean doses 149 mg). After a run-in period started one week prior to expected onset of menses, daily saliva samples were taken 7.3 +/- 0.7 hours after caffeine intake throughout the cycle, and caffeine clearance was estimated from the paraxanthine to caffeine ratio therein. Ovulation was confirmed by progesterone serum concentration above 3 ng/ml in the second half of the cycle. Results Initial (day 2) caffeine clearance (n = 15, geometric mean) was 1.37 ml/min/kg body weight (coefficient of variation (CV) 48%). The ratio of caffeine clearance for the luteal (day -9 to -4 prior to onset of the next menses) to the follicular phase (days 5-10) was (n = 13, point estimate) 1.03 (90% CI 0.95-1.12), indicating that there was no difference in CYP1A2 activity between these cycle phases. The median intraindividual CV in ovulatory cycles (n = 13) was 23% (range 11% to 39%). As an additional finding, there was evidence for long-term fluctuations of CYP1A2 activity in most individuals. Conclusions A dose adaptation according to the phase of menstrual cycle based on pharmacokinetics is not required for CYP1A2 substrates. more...

Trospium chloride, an atropine derivative used for the treatment of urge incontinence, was tested for inhibitory effects on human cytochrome P450 enzymes. Metabolic activities were determined in liver microsomes from two donors using the following selective substrates: dextromethorphan (CYP2D6), denitronifedipine (CYP3A4), caffeine (CYP1A2), chlorzoxazone (CYP2E1), S-(+)-mephenytoin (CYP2C19), S-(-)-warfarin (CYP2C9) and coumarin (CYP2A6). Incubations with each substrate were carried out without a possible inhibitor and in the presence of trospium chloride at varying concentrations (37-3000 microM) at 37 degrees in 0.1 M KH2PO4 buffer containing up to 3% DMSO. Metabolite concentrations were determined by high-performance liquid chromatography (HPLC) in all cases except CYP2A6 where direct fluorescence spectroscopy was used. First, trospium chloride IC50 values were determined for each substrate at respective K(M) concentrations. Trospium chloride did not show relevant inhibitory effects on the metabolism of most substrates (IC50 values considerably higher than 1 mM). The only clear inhibition was seen for the CYP2D6-dependent high-affinity O-demethylation of dextromethorphan, where IC50 values of 27 microM and 44 microM were observed. Therefore, additional dextromethorphan concentrations (0.4-2000 microM) were tested. Trospium chloride was a competitive inhibitor of the reaction with Ki values of 20 and 51 microM, respectively. Thus, trospium chloride has negligible inhibitory effects on CYP3A4, CYP1A2, CYP2E1, CYP2C19, CYP2C9 and CYP2A6 activity but is a reasonably potent inhibitor of CYP2D6 in vitro. Compared to therapeutic trospium chloride peak plasma concentrations below 50 nM, the 1000-times higher competitive inhibition constant Ki however suggests that inhibition of CYP2D6 by trospium chloride is without any clinical relevance. more...

Several quinolone antibacterial agents are known to inhibit the metabolism of theophylline, with the potential to cause adverse events due to raised theophylline concentrations during coadministration. A randomized crossover study was therefore conducted with 12 healthy male volunteers (ages, 23 to 34 years; body weight, 64 to 101 kg) to evaluate a possible interaction between rufloxacin and theophylline. Both drugs were administered at steady state. Following the administration of an oral loading dose of 400 mg on day 1, rufloxacin was given orally at 200 mg once daily on days 2 to 7 during one period only. During both periods, 146 mg of theophylline was administered orally twice daily for 3 days (which were days 4 to 6 of the rufloxacin coadministration period) and intravenously once the next morning to test for an interaction. Theophylline and rufloxacin concentrations were measured by reversed-phase high-pressure liquid chromatography, the pharmacokinetics of theophylline at steady state following administration of the last dose were calculated by compartment-model-independent methods. To compare the treatments, analysis of variance-based point estimates and 90% confidence intervals (given in parentheses) were calculated for the mean ratios of the pharmacokinetic parameters from the test (rufloxacin coadministration) over those from the reference (theophylline without rufloxacin) period. These were as follows: maximum concentration at steady state, 1.01 (0.96 to 1.07); area under the concentration-time curve from 0 to 12 h, 0.98 (0.94 to 1.02); half-life, 0.99 (0.95 to 1.03); total clearance at steady state, 1.02 (0.99 to 1.06); and volume of distribution in the elimination phase, 1.01 (0.97 to 1.05). In conclusion, rufloxacin did not affect theophylline pharmacokinetics at steady state. Therefore, therapeutic coadministration of rufloxacin and theophylline is not expected to cause an increased incidence of theophylline-related adverse events. more...

1. The relationship between plasma concentration of levodopa and motor-response was investigated in 12 patients with Parkinson's disease who showed marked response fluctuations, after a single oral dose of an immediate release (IR) formulation (100 mg levodopa/25 mg genserazide) and a controlled release (CR) formulation (300 mg levodopa/75 mg benserazide), using a double-blind, randomized, cross-over design. 2. The sum score of the Columbia University Rating Scale (CURS sigma) was used for pharmacodynamic assessment. A sigmoidal Emax-model was fitted to the data using a semiparametric pharmacokinetic/dynamic approach. 3. The dose-corrected AUC of levodopa after the IR-formulation was 27.5 (+/- 9.1 s.d.) ng ml-1 h per mg and 23.2 (+/- 4.6 s.d.) ng ml-1 h per mg after the CR-formulation. Cmax was 1714 (+/- 1027 s.d.) ng ml-1 after the IR-formulation and 1494 (+/- 383 s.d.) ng ml-1 after the CR-formulation. 4. With both preparations, the maximal response to levodopa (Emax) was a decrease in the CURS sigma rating of about 27 scores. Estimates of the EC50 of levodopa were 495 (+/- 144 s.d.) ng ml-1 (IR) and 1024 (+/- 502 s.d.) ng ml-1 (CR), respectively (95%-CI: 1.51-2.66, point estimator 1.95). The mean duration of the motor response was 1.9 (+/- 0.5 s.d.) h (IR) and 2.8 (+/- 0.7 s.d.) h (CR), respectively (95%-CI: 1.12-2.04, point estimator 1.53).(ABSTRACT TRUNCATED AT 250 WORDS) more...

The importance of smoking as a possible factor in coronary heart disease (CHD) may be related to the effect of carbon monoxide (CO) on oxygen exchange at the hemoglobin molecule (Hb). We examined the kinetics of this process in vitro and ex vivo using a fast-reaction technique (stopped-flow) whereby the dissociation-rate constant of oxygen was determined in the blood of smokers and non-smokers and at fixed HbCO-concentrations in non-smokers blood. In non-smokers, carbon monoxide saturated blood was obtained by gassing with carbon monoxide and mixing the samples with appropriate carbon monoxide free blood to achieve HbCO-concentration in the range of 10–60%. The reaction time course for the oxygen-dissociation was divided into a non-linear-initial phase (loss of the first oxygen molecule) and a subsequent linear phase. The oxygen-dissociation velocity decreased from 96.5 × 103 ms−1 to 42.7 × 103 ms−1 in the linear phase at pH 7.4 and decreased from 29.2 × 103 ms−1 to 20.9 × 103 ms−1 at pH 9.2 when the HbCO-concentration was increased to 63%. For the initial phase at pH 7.4, the dissociation velocity decreased depending on the HbCO-concentration. In non-smokers 50% of the bound oxygen was released in 17.5±2.3 ms (n = 13) whereas in smokers 19.4±1.8 ms (n = 14) (p more...

The absolute bioavailability F and response (prolongation of the PR interval) of verapamil after single doses of the same oral formulation administered on two different days were investigated in 16 male subjects with an 80 mg fast dissolving and a 240 mg controlled-release preparation and compared with a bolus injection of 5 mg of verapamil. The absolute bioavailability was 23% in both investigations for the 80 mg preparation and 32% in both investigations for the 240 mg dosage form. The individual values obtained for tmax, cmax, F, and AUC0-alpha showed a wide intersubject variability; therefore, no significant differences could be observed between the two trials for each dosage, but significant differences existed between the investigations of the two preparations. After intravenous administration, concentration-effect curves were about twofold left shifted when compared with the 80 mg tablet and about threefold left shifted when compared with the 240 mg tablet. Estimation of the drug input rate showed significantly (p less than 0.05) smaller values when the controlled-release tablet was given (80 mg tablet: 95.1 and 107.7 mg/h; 240 mg tablet; 55.8 and 46.3 mg/h). Thus, the effect and bioavailability of verapamil show sufficient intersubject reproducibility if the same formulation is given. The differences between the responses and the bioavailability after administration of different preparations may be related as well to the drug absorption rate and the stereoselective first pass of verapamil as to saturation of first-pass metabolism. more...

The concentrations of isosorbide dinitrate (ISDN), isosorbide-5-mononitrate (IS-5-MN) and isosorbide-2-mononitrate (IS-2-MN) were determined in plasma (PL), saphenous vein wall (SV) and pectoral muscle (PM) from 8 patients undergoing coronary bypass surgery. The patients were pretreated for 2 days with ISDN 240 mg per day (standard release formulation) in 4 doses of 40 mg and one dose of 80 mg. The plasma and tissue samples were obtained during the operation, 10-12 h after the last dose. Isosorbide-2-mononitrate and isosorbide-5-mononitrate were present in plasma and tissues in the same concentration ranges with molar concentration ratios of 0.88 (IS-2-MN: PM/PL), 0.85 (IS-5-MN: PM/PL), 0.99 (IS-2-MN: SV/PL) and 1.06 (IS-5-MN: SV/PL). Mean ISDN concentrations in tissue were considerably higher than in plasma; the molar concentration ratios were 4.9 (SM/PL) and 7.21 (SV/PL). The accumulation of ISDN in vessel walls may contribute to its greater vascular action compared to the mononitrates, but it may also facilitate the development of tolerance during long-term treatment. more...

Ten patients with essential hypertension (WHO grade I-II) were treated in an open dose-adjustment study with the standard regimen of slow-release nifedipine 20 mg b.d. for 2 weeks and with an individualized dose for 6 weeks. The optimum dose, defined as that producing a pre-dose diastolic blood pressure (dBP) of 90 mm Hg at steady state, was determined from the individual concentration-effect relationship after a test-dose of 20 mg. On standard therapy, the reduction in pre-dose dBP was inadequate in 4 patients and it was excessive in 1 patient. After 2 weeks of individualized treatment, the required pre-dose antihypertensive effect was obtained in all patients. The individual doses required were 10 mg b.d., 10 mg t.d.s. 20 mg b.d., 20 mg t.d.s. and 20 mg q.d.s. One patient dropped out of the study because of side effects. Loss of the antihypertensive effect was observed in one patient after 6 weeks of treatment. On the optimized dose, the average value of the pre- and 2 h post-dose steady state nifedipine concentrations (27.6 micrograms/l) compared well with model-derived optimum concentrations (28.6 microliters/l) (r = 0.9210). The results show that the dose of nifedipine can be accurately predicted using the individual concentration-effect relationship after a single dose. more...

Background/Aims The BEACOPP chemotherapy regimen (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, prednisone) used for Hodgkin's disease has a superior outcome, but pronounced and variable toxicity (mainly hematotoxicity). The present study was carried out to identify the impact of individual pharmacokinetics on the degree of hematotoxicity. Methods In 30 patients treated with BEACOPP, three plasma samples and urine collected over 24h on the first day of the first three cycles were analysed. Demographic data, doses, infusion times and blood cell counts were recorded. Pharmacokinetics parameters of the antineoplastic agents were estimated with population pharmacokinetic methods (NONMEM software); factors with potential influence on platelet counts were identified by ANOVA using a general linear model. Results Pharmacokinetic parameters could be calculated successfully for cyclophosphamide, etoposide, doxorubicin, and procarbazine. Creatinine clearance, infusion rates of etoposide and urinary excretion rates of N-dechloroethylcyclo-phosphamide and carboxycyclophosphamide had a significant effect on the decrease in platelet count from day 1 to day 8 of each cycle, explaining 46% of the interindividual variability of this parameter. Conclusions Individualization of treatment based on the factors identified here may decrease toxicity of the BEACOPP polychemotherapy regimen. Clinical Pharmacology & Therapeutics (2005) 77, P18–P18; doi: 10.1016/j.clpt.2004.11.070 more...

first aim is to pro- duce pharmacologists who will work in various capacities in academia and industry, with the major goal of maintaining a sufficient number of pharmacologists to keep the field viable and creative. In this sense, education functions to maintain pharmacology for its own purpose and prevent it from merging com- pletely into the big melting pot of molecular biology. A second purpose reaches beyond its own needs and is directed at a group of people who are not pharmacologists, namely phar- macists and medical doctors. In par- ticular, the pharmacologist teaches the medical student the scientific basis of pharmacology. Furthermore, there is the need to teach therapeutics with the aim of obtaining conscien- tious and therapeutically proficient medical doctors. This goal has been accomplished in various countries with variable success, but the pre- scribing habits of German medical doctors have been criticized both nationally and intemationallyr,2. This criticism mainly reflects the lack of successful education in pharma- cology and therapeutics in Germany. At present, the state-dictated cur- riculum in Germany requires only education in pharmacology and has led to the afore-mentioned dismal results. Consequently, the need for a much better education in therapeutics in Germany has been recognized”. It is now clear that it is necessary to have a separate and in-depth education in therapeutics in addition to a basic course in pharmacology, and the teaching of therapeutics falls into the natural competence of the clinical pharmacologM+. The current trends of some pharmacological depart- ments in Germany to add a ‘little’ clinical pharmacology by appointing a junior level faculty member to take care of this field or, as has been suggested by Habermannr in his re- sponse to the article of Page ef RI!, to confer this duty to ‘any able and eager competitor’ is, in our opinion, a grave mistake and will not result in the desired improvement in the pre- scribing habits of the medical doc- tors. Whoever creates such a ‘chal- lenge cup’ of clinical pharmacologists ignores that this discipline is in- volved in various aspects of human medicine from basic science to hu- man pathophysiology, drug develop- ment, pharmacoeconomics and regu- latory function. Education in clinical pharmacology has been defined in various ways in different countries. In Germany, clinical pharmacology has finally been established as a field separate from pharmacology, and an essential part of the curriculum is ward experience. In addition, the educational experience includes years of consulting activity on the wards, running of the drug-assay laboratory and conducting studies in Phases 1 through 4, thus preparing the clinical pharmacologist to ultimately teach therapeutics. In summary, pharmacology has failed in Germany more...

Binding kinetics at the benzodiazepine binding site of albumin have been determined as a function of age and fatty acid concentration in serum from 32 neonates (umbilical cord blood), 28 adults aged 23-65 years and 24 adults aged 66-101 years using fluorescence-time curves obtained in a Durrum-Gibson stopped-flow apparatus and the specific marker ligand dansylsarcosine. The binding reaction can be described by a 2-step mechanism characterised by four constants: the association rate constant k2 and dissociation rate constant k-2 for the rate limiting step-2; the affinity constant KA' for the formation of an unstable intermediate complex in step-1; the affinity constant KA for the overall reaction. There were marked differences in k2 between the three groups of subjects with highest values occurring in neonates (mean: 296 s-1), intermediate values in adults aged 23-65 years (mean: 200 s-1, P less than 0.001) and lowest values in adults aged 66-101 years (mean: 144 s-1, P less than 0.001). The dissociation rate constants (k-2) averaged 18.5 s-1 overall, showed only minor changes with increasing age and corresponded to dissociation half-lives of 42 ms, 38 ms and 33 ms for neonates, adults 23-65 years and adults 66-101 years respectively. KA' in neonates and in the group of elderly subjects were lower than in adults aged 23-65 years.(ABSTRACT TRUNCATED AT 250 WORDS) more...

Cytostatic drugs reduce the rate and extent of beta-acetyldigoxin absorption attributable to reversible damage of the gastrointestinal mucosa. As beta-acetyldigoxin verapamil is an agent rapidly absorbed in the proximal small bowel, plasma concentrations and apparent absorption of verapamil administered orally (160 mg) have been determined in nine patients with nongastrointestinal cancer before and 24 h after cytostatic treatment. The cytostatic therapy reduced the area under the plasma verapamil concentration-time curve in eight of the patients, with a mean reduction of 35% (p less than 0.05). It is concluded that, as previously found for digoxin, the absorption of verapamil is diminished owing to impairment of the absorptive capacity of the mucosa of the upper small intestine. more...

To obtain true half lives, glycoside elimination from six healthy subjects was studied for 14 days after multiple intravenous doses or oral administration of a daily maintenance dose of beta-methyldigoxin 0.3 mg. After oral or intravenous administration of beta-methyldigoxin ceased, the plasma concentrations declined from the 14th to the 16th days with a half life of 1.7 days. From the 16th to the 20th day a change from a shorter to a longer half life of 2.8 and 2.9 days was observed. Similar half lives were found in urine: after the last dose the initial slope from the 14th to the 16th day had a half life of 1.8 days, and the terminal slope had one of 3.2 days. The results indicate release of the glycoside from slowly equilibrating tissues. more...

The kinetics of intravenous and oral dihydroergotoxine mesylate determined in eight healthy male subjects with a radioimmunoassay method incorporating a plasma extraction step to obtain maximal sensitivity and specificity. The intravenous plasma concentration-time curve showed an initial rapid decline (half-life[t1/2] = 3.5 min) and could be fitted to a three-compartment model. The high systemic clearance (20.2 to 28.8 ml x min-1 x kg-1) and large distribution volume, (9.9 to 20.41 x kg-1) were associated with a terminal t1/2 of 9.5 to 18.4 hr. The oral absorption was rapid. (t1/2 = 14.8 min). Absolute bioavailability was 5.3% to 12.4%. The terminal t1/2 and bioavailability were considerably lower than earlier estimates and this can be attributed to the use in these investigations of a more sensitive and specific dihydroergotoxine assay method. more...

The absorption characteristics of dihydroergotoxine administered as an oral solution, tablet and retard capsule have been determined in a randomised cross-over investigation in 12 healthy males. The plasma concentrations of dihydroergotoxine produced by the three preparations, measured using a specific and sensitive radioimmuno-assay method over 24 h, exceeded 200 pg ml-1 for approximately 5 h and decayed in a biphasic manner with a slowest measured half-life of 12-14 h. The retard capsule differs from the other two preparations in having a low Cmax (50% of that recorded for the solution) and a clearly defined plateau. The bioavailability of the retard capsule was similar to that for the solution indicating that first-pass metabolism is not significantly increased following a three-fold prolongation in the absorption rate constant. The 20-40% greater bioavailability of dihydroergotoxine solution and retard capsule in comparison with the standard tablet may be due to a reduced contact time with gastric secretions achieved by means of rapid absorption from the stomach (solution) or delayed release at pH 1.5 (retard capsule). more...

Four patients with a biliary fistula received 0.5 mg 3H-methylproscillaridin as a single oral dose. 55% of the dose was excreted in bile, 16% in urine and 3% in faeces. More than 60% of the radioactivity excreted in bile and urine appeared within the first 24 hours. 78% of the radioactivity in bile consisted of CHCl3-insoluble metabolites of methylproscillaridin, incubation of which with beta-glucuronidase led to splitting off glucuronic acid from almost 80%. Methylproscillaridin can be regarded as the principal conjugated compound. TLC-separation of CHCl3-soluble compounds from bile showed identical running of radioactivity with methylproscillaridin, proscillaridin and scillarenin and three unknown metabolites P1, P2, and P3. In urine the CHCl3-soluble fraction averaged 16% to 34% of the total amount and was identified as methylproscillaridin, proscillaridin, scillarenin, P2 and P3. The relative composition of the total radioactivity in faeces amounted to 77% methylproscillardidin, 4% scillarenin and 12% polar metabolites. more...

Five healthy volunteers received digoxin 0.4 mg or beta-methyldigoxin 0.4 mg i.v., daily for 14 days, in a randomized cross-over arrangement. By monitoring minimal plasma concentrations during multiple dosing, it was found that the steady state pharmacokinetics of digoxin and beta-methyldigoxin could be estimated even better by a one-compartment than by a two-compartment model. The following mean parameters were calculated: the half life of digoxin of 1.54 +/- 0.31 days was significantly shorter than the half life of 2.29 +/- 0.34 days for beta-methyldigoxin. The distribution volume of 807 +/- 187 liters for digoxin was not significantly larger than the 735 +/- 227 liters for beta-methyldigoxin. Renal digoxin clearance of 191 +/- 25 ml/min was significantly higher than both the renal clearance of beta-methyldigoxin of 111 +/- 23 ml/min and also the creatinine clearance, which indicates tubular secretion of digoxin. There was a 2.8-fold accumulation of beta-methyldigoxin injected once a day, which was significantly higher than the 1.80-fold accumulation of digoxin. more...

Binding curves obtained by the stopped-flow method for the association of warfarin and human serum albumin (HSA) at pH 6.0 and 9.0 have been analysed with digital- and analog computers. The first association product (WHSA') at pH 6-9 does not contribute to the observed fluorescence enhancement during warfarin-HSA complex formation. A similar consecutive relaxation process leads to a more stable warfarin-HSA complex, with HSA in the neutral (N)-form (pH 6) and base (B)-form (pH 9). This rearrangement can be measured by stopped-flow (k 2 = 31 s-1 at pH 6; K'2 = 63 s-1 at pH 9). At pH 6 a further concentration dependent relaxation process has been observed indicating that the complex of warfarin with the N-form of HSA gets partially converted into its B-form with a half-time for this N leads to B transition in the range of 0.2-0.4 s. A drug such as warfarin can act as effector molecule for conformational changes of the HSA tertiary and quaternary structure during the formation of a high affinity complex. more...

Color discrimination ability of 53 patients with congestive heart failure and 32 healthy volunteers treated with digoxin, digitoxin, or pengitoxin was determined with the Farnworth's Munsell 100 hue test. The patients had been treated with digitalis glycosides for several months prior to color vision testing. The volunteers received glycosides until a steady-state plasma concentration was reached. Glycoside plasma levels were measured by radioimmunoassay on the 3 days prior to color vision testing. The total error scores, indices of color discrimination, increased with the glycoside plasma levels. Subjects treated with digitoxin or pengitoxin exhibited no marked elevation in total error score at therapeutic concentrations, whereas 17 of 28 subjects with therapeutic digoxin plasma concentrations (less than 2.0 ng/ml) showed disturbed color discrimination. At toxic plasma levels all 5 digoxin-treated subjects, 7 of 13 digitoxin-treated subjects, and 3 of 8 pengitoxin-treated subjects showed impairment of color discrimination. The greater tendency of digoxin to impair color vision in comparison with digitoxin and pengitoxin may be related to a higher uptake or different distribution in the retina. more...

After oral administration of 25 μg/kg 3 H-labelled digitoxin (sp. act. 26.2 mCi/mg) to female rats, the total radioactivity in blood and in urine was eliminated with a half-life time of 2 and 1.7 days, respectively. The fecal elimination half-life time had a. biphasic course. The chloroform-soluble and chloroform-insoluble metabolites excreted in urine and feces were determined in order to explain the much shorter half-life time of 0.4 days in feces during the early phase of elimination. In the feces, 45 per cent of the dose excreted within 5 days consisted of chloroform-soluble substances. In this fraction, the main excretion product was digoxigenin-bis-digitoxoside (20 per cent), whereas the percentages of the other glycosides, after the last collection period, amounted to significantly less: 9% digitoxin, 9% digoxin. 5% digitoxigenin-bis-digitoxoside, and 2% digitoxigenin-mono-digitoxoside. The Chromatographic analysis of the chloroform-insoluble fraction, which accounted for 15 per cent of the dose. revealed a conjugation of glucuronic and sulfuric acid with digoxin, and digoxin, 5% digitoxigenin-bis-digitoxosidc. and 2% digitoxigenin-mono-digitoxoside. The contrast, sulfuric acid alone was the main conjugation partner of 3-epi-digitoxigenin. In urine, 4.6 per cent of the administered radioactivity was represented by digoxin, 2 per cent by digitoxin, 1 per cent by digoxigenin-bis-digitoxoside, and 1.4 per cent by polar metabolites. Only traces of digitoxigenin-bis-digitoxoside cind digoxigenin-mono-digitoxoside were detected. The much shorter half-life time of the eliminated radioactivity in feces seems to be due to the higher portion of poorly reabsorbed conjugation products and digoxigeninbis-digitoxoside. more...

The tissue distribution after repeated intravenous administration of tritium-labelled digoxin, β-methyldigoxin and ouabain was examined in heart and brain of 6 beagle dogs. In addition, the (Na++K+)-ATPase activity was measured in various heart and brain areas, and its affinity to the cardiac glycosides was determined. The glycoside concentrations in the atria are lower than in the ventricles, and the left heart areas show higher concentrations than the right areas. Significant differences in the (Na++K+)-ATPase activity or its binding capacity in the various heart areas, which could be responsible for this characteristic distribution pattern, were not found. In agreement with its greater lipid-solubility, β-methyldigoxin shows a higher accumulation in the brain than digoxin and ouabain. However, while β-methyldigoxin is evenly distributed throughout all brain areas, concentration differences are found for digoxin and ouabain in the telencephalon, cerebellum and brain stem. This characteristic distribution of the more polar glycosides may be partly determined by the different structure of the capillaries in the central nervous system. In addition, the binding affinities for digoxin and ouabain also differ in the various crude brain preparations. In the diencephalon, pons, cerebellum and medulla the dissociation constants as a reciprocal measure of the binding affinity were lower for digoxin with 7.5 to 9.9×10−9 than in the telencephalon, mesencephalon and spinal cord with dissociation constants of 1.1 to 1.45×10−8 M. Since, in these brain areas higher glycoside concentrations per g wet weight were also measured, the glycoside accumulation in the various brain areas could be dependent on the higher receptor affinity of these brain areas. On the other hand, the binding affinities for β-methyldigoxin were the same in all brain areas, with a mean dissociation constant of 1.45×10−8 M. more...