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An integrative population pharmacokinetics (PPK)-based approach was used to characterize the effect of hepatic impairment on clobazam PK and its major metabolite in systemic circulation, N-desmethylclobazam (N-CLB). At therapeutic clobazam dosages, N-CLB plasma concentrations are 3-5 times greater than the parent compound. PK data from clinical trials in patients with Lennox-Gastaut syndrome (LGS; OV-1002 and OV-1012), healthy participants (OV-1016), and participants with and without renal impairment (OV-1032), as well as those from a publication describing the effects of hepatic impairment on clobazam PK, were merged to create the PPK model. Individual patient clobazam PK parameters from the publication were used to generate patient plasma-concentration data. Clobazam PK was linear and the formation of N-CLB was elimination-rate limited. Hepatic impairment did not affect the total apparent clearance of clobazam but may affect the PK of N-CLB. Because the formation of N-CLB is elimination-rate limited and the total apparent clearance of clobazam is unaffected by hepatic impairment, the PPK model suggests that patients with LGS and hepatic impairment may not require clobazam dosage modification.

Amphotericin B (AmB) in small unilamellar liposomes (AmBisome) provides higher plasma concentrations and greater safety than the conventional deoxycholate formulation. The authors compared the disposition of the liposome's drug and cholesterol components by measuring AmB and radioactivity in plasma, urine, and feces for 1 week after a single 2-hour infusion of 14C-cholesterol-labeled AmBisome (2 mg/kg, 1 microgCi/kg) in healthy adults (4 males, 1 female). The plasma profile of 14C-cholesterol differed from that of AmB, lacking an initial rapid disappearance phase, having a lower total clearance, and having a volume of distribution (0.13 L/kg) close to that of the plasma compartment. The biphasic disappearance and long plasma half-life (147 h) of 14C-cholesterol were similar to those of other low-clearance liposomes. This and the low clearance of 14C-cholesterol from the plasma compartment suggest that it served as a liposome marker. The plasma drug-lipid ratio fell during the study, showing that AmB was cleared from plasma more rapidly than cholesterol or liposomes and suggesting that the composition of the liposomes changed over time. 14C-radioactivity was recovered mainly in the feces (9.5% of dose), consistent with the catabolism of cholesterol to bile salts. Combined fecal and renal clearances were < 18% of total clearance, suggesting that most of the liposomal drug and lipid remained in the body 1 week after dosing. Thus, AmBisome remains in the circulation for an extended period of time while releasing AmB, resulting in its markedly altered pharmacokinetic and safety profiles.

Cyclosporine is a marketed immunosuppressive agent and a known substrate for CYP3A. Micafungin is an antifungal agent and a mild inhibitor of CYP3A-mediated metabolism in vitro. The objectives of this study were to evaluate the pharmacokinetics of cyclosporine and micafungin before and with concomitant administration. The pharmacokinetics of single-dose oral cyclosporine (5 mg/kg) were estimated on days 1, 9, and 15 (n = 27). Subjects received micafungin (100 mg/d over 1 hour) on days 7, 9, and 11 through 15. Micafungin pharmacokinetics were estimated on days 7, 9, and 15. Mean apparent oral cyclosporine clearances were estimated to be 645 ± 236 mL/h/kg, 546 ± 101 mL/h/kg (P = .01), and 540 ± 104 mL/h/kg (P = .02) for days 1, 9, and 15, respectively. Micafungin appears to be a mild inhibitor of cyclosporine metabolism.

Tacrolimus (FK506, Prograf) is a macrolide lactone antibiotic widely used by the oral route for the prophylaxis of organ rejection in patients who have received allogenic liver or kidney transplants. This study investigated the influence of a high- versus a low-fat meal, relative to the fasting state (three treatments total), on the rate and extent of tacrolimus absorption following a single 5 mg oral dose. The protocol employed a three-period, randomized, crossover design employing 5 x 1 mg capsules in 15 healthy male nonsmoking, drug-free volunteers, 20 to 45 years of age, who were within 15% of their ideal body weight. Food had a clinically significant effect in reducing relative bioavailability, as well as slowing absorption, but did not affect terminal exponential half-life (approximately 34 hours). Mean maximum tacrolimus blood concentration (Cmax) values were 25.6, 5.88, and 9.03 ng/mL for the fasting, high-fat, and low-fat treatments, respectively; mean area under the blood concentration-time curve (AUC(0-infinity) values were 272, 181, and 201 (ng/mL)-h, respectively; and mean time of Cmax (tmax) values were 1.37, 6.47, and 3.20 hours, respectively. Differences in parameters between the fasting and each fed treatment were statistically significantly different (p < 0.05). Statistically significant differences also existed in tmax between the two meals. Results also indicated the safety of single 5 mg oral tacrolimus doses administered to healthy volunteers.