No abstract

Caspofungin, a glucan synthesis inhibitor, is being developed as a parenteral antifungal agent. The pharmacokinetics of caspofungin following 1-h intravenous infusions in healthy men was investigated in four phase I studies. In an alternating two-panel (six men each), rising-single-dose study, plasma drug concentrations increased proportionally with the dose following infusions of 5 to 100 mg. The ␤-phase half-life was 9 to 10 h. The plasma drug clearance rate averaged 10 to 12 ml/min. Renal clearance of unchanged drug was a minor pathway of elimination (ϳ2% of the dose). Multiple-dose pharmacokinetics were investigated in a 2-week, serial-panel (5 or 6 men per panel) study of doses of 15, 35, and 70 mg administered daily; a 3-week, single-panel (10 men) study of a dose of 70 mg administered daily; and a parallel panel study (8 men) of a dose of 50 mg administered daily with or without a 70-mg loading dose on day 1. Moderate accumulation was observed with daily dosing. The degree of drug accumulation and the time to steady state were somewhat dose dependent. Accumulation averaged 24% at 15 mg daily and ϳ50% at 50 and 70 mg daily. Mean plasma drug concentrations were maintained above 1.0 g/ml, a target selected to exceed the MIC at which 90% of the isolates of the most clinically relevant species of Candida were inhibited, throughout therapy with daily treatments of 70 or 50 mg plus the loading dose, while they fell below the target for the first 2 days of a daily treatment of 50 mg without the loading dose. Caspofungin infused intravenously as a single dose or as multiple doses was generally well tolerated. In conclusion, the pharmacokinetics of caspofungin supports the clinical evaluation of once-daily dosing regimens for efficacy against fungal infections.Caspofungin (Cancidas; MK-0991) is an echinocandin that was recently approved by the U.S. Food and Drug Administration for patients with invasive aspergillosis who are refractory to or intolerant of standard therapy. Caspofungin inhibits the synthesis of 1,3-␤-D-glucan, which forms a critical component of many fungal cell walls (3). It has been shown to have potent activity in vitro against many clinically important fungi, including Candida spp. and Aspergillus spp. (2, 7, 9; M. Del Poeta, W. A. Schell, and J. R. Perfect, Abstr. 36th Intersci. Conf. Antimicrob. Agents Chemother., abstr. F33, 1996). In in vivo studies with healthy and immunocompromised animals, prolonged survival in models of disseminated aspergillosis and candidiasis and clearance of Candida spp. from a target organ have been demonstrated with caspofungin treatment (1,5,6 , abstr. 1103, p. 371, 2000).Caspofungin has been developed as a parenteral agent due to its high molecular weight, unfavorable log P (partition coefficient), and extremely poor oral bioavailability in animals. In all the clinical studies, caspofungin has been administered as a constant-rate, 1-h intravenous (i.v.) infusion. This paper describes the results from four phase I studies conducted with healthy male subjects to ...

The disposition of caspofungin, a parenteral antifungal drug, was investigated. Following a single, 1-h, intravenous infusion of 70 mg (200 Ci) of [ 3 H]caspofungin to healthy men, plasma, urine, and feces were collected over 27 days in study A (n ‫؍‬ 6) and plasma was collected over 26 weeks in study B (n ‫؍‬ 7). Supportive data were obtained from a single-dose [ 3 H]caspofungin tissue distribution study in rats (n ‫؍‬ 3 animals/time point). Over 27 days in humans, 75.4% of radioactivity was recovered in urine (40.7%) and feces (34.4%). A long terminal phase (t 1/2 ‫؍‬ 14.6 days) characterized much of the plasma drug profile of radioactivity, which remained quantifiable to 22.3 weeks. Mass balance calculations indicated that radioactivity in tissues peaked at 1.5 to 2 days at ϳ92% of the dose, and the rate of radioactivity excretion peaked at 6 to 7 days. Metabolism and excretion of caspofungin were very slow processes, and very little excretion or biotransformation occurred in the first 24 to 30 h postdose. Most of the area under the concentration-time curve of caspofungin was accounted for during this period, consistent with distribution-controlled clearance. The apparent distribution volume during this period indicated that this distribution process is uptake into tissue cells. Radioactivity was widely distributed in rats, with the highest concentrations in liver, kidney, lung, and spleen. Liver exhibited an extended uptake phase, peaking at 24 h with 35% of total dose in liver. The plasma profile of caspofungin is determined primarily by the rate of distribution of caspofungin from plasma into tissues.Caspofungin (CANCIDAS; MK-0991) is a parenteral antifungal agent that inhibits 1,3-␤-D-glucan synthesis, which forms a critical component of many fungal cell walls (4). Caspofungin is active against many clinically important fungal species, including Candida spp. and Aspergillus spp. (3,5,7,14), and in clinical trials it has been shown to be efficacious in the treatment of esophageal candidiasis (1, 15, 16), invasive candidiasis (9), and invasive aspergillosis (J. Maertens, I. Raad, G. Petrikkos, et al., Abstr. 42nd Intersci. Conf. Antimicrob. Agents Chemother., abstr. M-868, 2002). This paper describes results from two studies conducted in healthy human subjects to investigate the disposition of caspofungin following intravenous (i.v.) infusion of radiolabeled caspofungin and supportive studies of [ 3 H]caspofungin tissue distribution in rats, in vitro metabolism, and in vitro binding and partitioning in human plasma and blood. The metabolites of caspofungin, a cyclic hexapeptide, in humans have been previously reported (2). Caspofungin is the major component of radioactivity in plasma and urine in the first 24 to 30 h postdose, with a ring-opened form of caspofungin, M0, comprising a minor component. At time points of Ն5 days, M0 was the major component in plasma, and urine radioactivity was largely comprised of the synthetic amino acid dihydoxyhomotyrosine (M1) and its N-acetyl derivative (M2). Caspofungin...

This was a randomized, double-blind, placebo-controlled parallel study in human immunodeficiency virus type 1 (HIV-1)-uninfected healthy subjects to investigate the pharmacokinetic interaction between indinavir (IDV) and ritonavir (RTV). Subjects were allocated to treatment groups of IDV given with RTV in the following milligram doses twice daily: 800 mg of IDV-100 mg of RTV (800-100 mg), 800-200, 800-400, and 400-400 mg, placebo of IDV with RTV doses of 100, 200, and 400 mg, and placebo of both IDV and RTV. Doses of both drugs were administered for 14 days with a low-fat meal and one dose on day 15 with a high-fat meal. Blood was obtained for drug concentration measurements on days 14 and 15. Seventy-three volunteers enrolled in the study: 29 men and 44 women. Fifty-three volunteers completed the study. When compared to standard historical data for 800 mg of IDV every 8 h (q8h), the IDV area under the concentration-time curve for 24 h (AUC 24 ) of IDV-RTV regimens 400-400, 800-100, and 800-200 mg were at least 1.4, 2.3, and 3.3 times higher, respectively, regardless of meal. The concentrations at the end of the dosing interval were 10 to 25 times higher than that observed in the standard regimen of 800 mg of IDV q8h for IDV-RTV 800-100 and 800-200 mg regimens, respectively. RTV at 200 mg maximally enhanced the IDV profile. Improved tolerability was associated with IDV-RTV 800-100 mg versus IDV-RTV 800-200, 800-400, and 400-400 mg q12h. The advantages of IDV-RTV twice daily over 800 mg of IDV q8h include no food restrictions and twice-daily dosing. Also, the regimens achieve levels of IDV that may be helpful in suppressing strains of HIV-1 that have reduced susceptibility to IDV or other protease inhibitors.Pharmacokinetic drug-drug interactions have the potential to enhance drug exposure of protease inhibitors for human immunodeficiency virus (HIV) infection. Indinavir (IDV) plus ritonavir (RTV) is a combination that appears to have a very favorable pharmacokinetic interaction. The metabolic interaction of these drugs results in augmented IDV plasma levels that may prove useful in more convenient dosing intervals and removal of food restrictions. The high IDV levels may be also be active against virus strains with genotypic mutations or phenotypic profiles associated with decreased sensitivity to protease inhibitors at conventional drug concentrations. Thus, a combination regimen of IDV with RTV may be useful in antiretroviral treatment-naive patients, as well as in rescue regimens.A current regimen combines 400 mg of IDV with 400 mg of RTV twice daily (6, 9), but tolerability to RTV is sometimes difficult (NORVIR package circular, Abbott Laboratories, Abbott Park, Ill.). RTV at lower doses is being studied to see if they will provide sufficient metabolic inhibitory activity to permit dosing IDV in a twice-a-day (b.i.d.) regimen and to assess tolerability. The present study was undertaken to characterize the pharmacokinetic profiles of a wider array of dose combinations of IDV plus RTV at steady state (2 weeks)...

The potential for interactions between caspofungin and nelfinavir or rifampin was evaluated in two parallelpanel studies. In study A, healthy subjects received a 14-day course of caspofungin alone (50 mg administered intravenously [IV] once daily) (n ‫؍‬ 10) or with nelfinavir (1,250 mg administered orally twice daily) (n ‫؍‬ 9) or rifampin (600 mg administered orally once daily) (n ‫؍‬ 10). In study B, 14 subjects received a 28-day course of rifampin (600 mg administered orally once daily), with caspofungin (50 mg administered IV once daily) coadministered on the last 14 days, and 12 subjects received a 14-day course of caspofungin alone (

This report investigated safety and dosing recommendations of intravenous caspofungin in hepatic insufficiency. In the single-dose study, 8 patients each with mild and moderate hepatic insufficiency received 70 mg of caspofungin. In the multiple-dose study, 8 patients with mild hepatic insufficiency and 13 healthy matched controls received 70 mg on day 1 and 50 mg daily on days 2 through 14. Eight patients with moderate hepatic insufficiency received 70 mg on day 1 and 35 mg daily on days 2 through 14. Caspofungin was generally well tolerated with no discontinuations due to serious or nonserious adverse experiences. The area under the concentration-time profile over the interval of last quantifiable point to infinity (AUC(0-infinity)) geometric mean ratio (GMR) (90% confidence interval [CI]) for mild hepatic insufficiency/historical controls was 1.55 (1.32-1.86) in the single-dose study and for mild hepatic insufficiency/concurrent controls was 1.21 (1.04-1.39) for day 14 area under the concentration-time profile calculated over the interval 0 to 24 hours (AUC(0-24h)) following multidose. The AUC(0-infinity) GMR (90% CI) for moderate hepatic insufficiency/historical controls was 1.76 (1.51-2.06) following 70 mg; AUC(0-24h) GMR (90% CI) for moderate hepatic insufficiency/concurrent controls was 1.07 (0.90-1.28) on day 14 after 35 mg daily. No dosage adjustment is recommended for patients with mild hepatic insufficiency. A dosage reduction to 35 mg daily following the 70-mg loading dose is recommended for patients with moderate hepatic insufficiency.

Indinavir dry-filled capsules are relatively well tolerated by children with HIV infection, although hematuria occurs at higher doses. Future studies need to evaluate the efficacy of indinavir when combined de novo with zidovudine and lamivudine.

The pharmacokinetics and bioavailability of cyclobenzaprine, a widely used muscle relaxant, were investigated in four clinical studies, and the effects of age, gender, and hepatic insufficiency were characterized. Cyclobenzaprine plasma clearance was 689 ml/min, and the bioavailability of a 5 mg oral dose was 0.55. Following oral doses of 2.5 to 10 mg tid in healthy young subjects, cyclobenzaprine pharmacokinetics were linear, and plasma concentrations generally increased proportional to dose. There was about a fourfold accumulation of the drug in plasma on multiple dosing, corresponding to an effective half-life of 18 hours. Steady-state plasma concentrations of cyclobenzaprine in elderly subjects were twice as high as in young subjects following oral doses of 5 mg tid. Steady-state plasma concentration also appeared to be up to twofold higher in subjects with mild hepatic insufficiency compared to healthy controls. The magnitude of any difference in steady-state plasma concentration between males and females appears to be small relative to intersubject variability. A reduction in dose or dosing frequency should be considered in the elderly and in patients with liver disease.