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Recent advances in the management of human immunodeficiency virus (HIV) infection have led to a new perception of the disease and new treatment paradigms (10). These advances include an improved understanding of the pathogenesis of HIV infection (20, 52), the development of reliable assay methodologies for the detection and quantification of viral load (48, 49), the availability of new, potent antiviral agents, and an appreciation that combination antiretroviral therapy reduces disease progression and mortality risks (7, 8, 16, 19, 37). In this context, indinavir, ritonavir, saquinavir, and nelfinavir are the promising new HIV protease inhibitors for the treatment of HIV infection. More potent and sustained suppression of viral replication and durable immunoreconstitution has been shown with the use of dual protease inhibitors or protease inhibitors in combination with nucleoside analogs compared with the suppression achieved with monotherapy (9, 13, 15, 37, 42, 43, 54, 55, 57, 60, 62). Despite these encouraging advances, anti-HIV therapy remains suboptimal. The durability of the antiviral effect is transient in some individuals. Furthermore, effective combination therapies often demand complex regimens that may involve burdensome frequent dosing, side effects, food restrictions, and hydration requirements. These factors reduce the level of patient adherence to the treatment regimen and may ultimately lead to treatment failure. Indinavir is a potent HIV protease inhibitor, with an in vitro 90% inhibitory concentration (IC90) (HIV-1IIIB) of approximately 0.1 μg/ml in a system containing 50% human serum and 10% fetal calf serum (1, 46, 47). Indinavir is rapidly metabolized by cytochrome P-450 3A isoenzymes (CYP3A), the major enzymes present in the liver and gastrointestinal tract, with an elimination half-life of 1.8 h (11, 45). The renal clearance (CLR) of indinavir is reported to be relatively constant over a wide range of concentrations (4, 63). When given as an 800-mg regimen three times a day (t.i.d.) under fasting conditions, the mean steady-state area under the concentration-time curve (AUC) of indinavir for HIV-infected patients over one dose interval was reported to be 18.8 μg · h/ml (37% coefficient of variation [CV]), and the maximum concentration of drug in serum (Cmax) and the minimum concentration in serum (Cmin) were reported to be 7.73 μg/ml (32% CV) and 0.154 μg/ml (71% CV), respectively (45). Meals with high fat and protein contents decreased the indinavir AUC and Cmax by 80 and 85%, respectively (45). To maintain therapeutic concentrations in plasma, indinavir is given at high doses on a strict schedule of once every 8 h (q8h) with rigid meal schedules. Ritonavir has relatively high bioavailability and an elimination half-life of 3 to 5 h (1, 25, 27, 38). Although it is about 99% protein bound when it is given at a dosage of 600 mg twice daily (b.i.d.) concentrations in plasma in excess of the protein binding-adjusted IC90 (2.1 μg/ml) are usually maintained throughout the dosing interval (14). The bioavailability of ritonavir is minimally affected by food (1). Ritonavir is a potent CYP3A inhibitor in vitro (34), with an estimated Ki of 0.085 μg/ml for indinavir in experiments with human liver microsomes (33a). In rats, the combined administration of ritonavir and indinavir (10 mg/kg of body weight for each drug) resulted in an eightfold increase in the indinavir AUC compared to that for indinavir given alone (26, 28). Recently, we described a clinically significant interaction between ritonavir and saquinavir (22). Probably due to the inhibition of the CYP3A metabolism of saquinavir by ritonavir, saquinavir AUC values were greatly enhanced (>50-fold) when saquinavir was coadministered with ritonavir; the combination regimen given b.i.d. with reduced doses of both drugs has been shown to suppress the level of viral RNA to below quantitation limits (

Summary: Purpose: To evaluate the pharmacokinetics and safety of multiple oral doses of tiagabine HC1 in subjects with different degrees of hepatic impairment. Methods: Four subjects with mild hepatic impairment, three subjects with moderate hepatic impairment, and six matched normal subjects received twice daily oral tiagabine HCl for 5.5 days. Serial blood specimens were obtained for 48 h after the final dose. Total and unbound tiagabine plasma concentrations were determined by high-performance liquid chromatography (HPLC) and ultrafiltration, respectively. Pharmacokinetic parameters were compared between the groups by analysis of covariance. Results: For total tiagabine concentrations in normal subjects and subjects with mild and moderate hepatic impairment, Cmax values (mean i SD) were 117 ± 54, 172 ± 40, and 172 ± 28 ng/ml; Cmin values were 13 ± 4,27 ± 4, and 28 ± 6 ng/ml; areas under the plasma concentration-time curve were 396 ± 59, 633 ± 16, and 675 ± 32 ng Wml, and elimination half-lives (harmonic means) were 7, 12, and 16 h, respectively. Unbound tiagabine coricentrations, area under the unbound plasma concentration-time curve, and the free fractions were increased in the hepatically impaired subjects. Reduced serum albumin and α1-acid glycoprotein concentrations may have contributed to increases in the unbound fraction. Adverse events observed included dizziness, tremor, nausea, somnolence, incoordination, and unsteady gait. The frequency of these events was increased in the subjects with liver impairment. Conclusions: Because of the decreased drug elimination caused by liver function impairment, reduced doses or increased dosing interval or both may be needed to attain therapeutic plasma drug concentrations. Time to reach steady state also may be prolonged. The patients should be monitored closely for potential neurologic adverse events.

The purpose of this study was to evaluate the feasibility of intrapulmonary delivery of ABT-431, a selective D1 receptor agonist. Following intratracheal instillation of the drug solution, the lung bioavailability was found to be approximately 75% in dogs. An aerosol suspension formulation was then developed by dispersing the drug in tetrafluoroethane, HFC-134a, with the aid of poloxamer 124 and vitamin E. This ABT-431 MDI aerosol formulation showed about 40% of the particles emitted from the valve and actuator system to be under 5 μm in diameter. Also, the primary package (15 mL aluminum container, DF10/ACT-150 valve, and Micron-4-actuator with the orifice 0.4 mm) was satisfactory for accurate and reproducible dosimetry. Using tracheostomized beagle dogs, the C max following tracheal administration of 5 mg aerosolized ABT-431 was found to be 13.3±0.9 ng ml −1 and the AUC 0–24 was estimated at 33.2±10.6 h ng ml −1 . The lung bioavailability of the aerosolized drug was 34% compared to intravenous injection in dogs. In humans, results from a single rising dose study demonstrated that rapid absorption of ABT-431 following oral inhalation administration resulted in a dose-dependent increase in the area under the plasma-time curve at dosage levels between 3.3 and 13.2 mg. There is a possibility of up to 25% absorption of the drug from human lung. Thus, pulmonary bioavailability of ABT-431 is significantly greater than that of oral administration. Also, these findings suggest that small and lipophilic compounds, especially with hepatic first pass effect, may be effectively delivered systemically using oral inhalation aerosols.

Summary: Purpose: We wished to determine the effect of renal impairment on the pharmacokinetics and tolerability of the new antiepileptic drug tiagabine (TGB). Methods: We assessed TGB pharmacokinetics and tolerability in 25 subjects with various degrees of renal function (based on creatinine clearance, n = 4–6 per group) from healthy (group I) to requiring hemodialysis (group V) in a single and multiple dose (every 12h), one-period (groups I-IV) or a single dose, two-period (group V) study (4-mg oral doses of TGB · HCl). Blood samples were collected after the first dose (both periods for group V) and after the last dose on day 5 (groups I-IV). TGB plasma concentrations and plasma protein binding were determined by high-performance liquid chromatography (HPLC) and ultrafiltration, respectively. Results: TGB was well tolerated by all study subjects. The pharmacokinetics of TGB were similar in all subjects; no pharmacokinetic parameter (based on either total or unbound concentrations) was statistically correlated with creatinine clearance. For total TGB in plasma, single-dose mean values of the maximum plasma concentration, clearance, and half-life (t1/2) ranged from 52 to 108 ng/ml, from 7.14 to 11.02 I/h, and from 6.4 to 8.4 h, respectively. Conclusions: TGB pharmacokinetics and tolerability were independent of renal function; therefore, dosage adjustment is unnecessary for epilepsy patients with renal impairment.

The pharmacokinetics of single oral doses of zileuton 200 to 800mg, its R(+) and S(-) enantiomers, and its N-dehydroxylated and glucuronide metabolites have been investigated in a randomised study in 16 normal male healthy volunteers. Zileuton was 93.4% bound to plasma proteins. The overall dispositional pharmacokinetics of zileuton racemate appeared to be linear. The mean dose-normalised area under the concentration-time curve from zero to infinity (AUC0-infinity) remained constant, while the mean dose-normalised peak plasma concentration (Cmax) decreased with the increase in dose, possibly because of dissolution rate-limited absorption at the higher doses. The R(+) and S(-) enantiomers of zileuton may have similar absorption profiles, although the apparent total plasma clearance of the S(-) enantiomer was 49 to 76% higher than the corresponding values for the R(+) enantiomer. The AUC0-infinity of each enantiomer increased proportionately with dose. The pharmacokinetics of the N-dehydroxylated metabolite of zileuton were highly variable, with a more than dose-proportional increase in the mean dose-normalised Cmax and area under the concentration-time curve from zero to 24 hours. The elimination of the glucuronide metabolites of the R(+) and S(-) enantiomers of zileuton was formation rate-limited. The mean percentage of the administered zileuton dose recovered in urine as glucuronide metabolites ranged from 73.1 to 76.5% and showed no dose-related differences. The renal clearance of the glucuronide metabolites of zileuton exceeded the normal glomerular filtration rate, suggesting that these metabolites may be excreted through renal tubular secretion in addition to filtration.