nucleoside analogs which inhibit human and simian immunodeficiency virus in vitro. The pharmacokinetic properties of these compounds in rhesus monkeys after intravenous, oral, and subcutaneous administration of the drug were compared. Half-lives, total clearances, and steady-state volumes of distribution for the two drugs were determined. The half-lives for the drugs by the different routes were between 0.58 and 1.4 h. Oral bioavailabllity of 3'-deoxy-2',3'-didehydrothymidine was incomplete, with an average of 42% ± 15% of the dose reaching the systemic circulation. Absorption of 3'-fluoro-3'-deoxythymidine after oral administration was variable, with bioavailability ranging from 21 to 95%. Bioavailability after subcutaneous administration ranged from 59 to 77% for 3'-deoxy-2',3'-didehydrothymidine and from 52 to 59% for 3'-fluoro-3'-deoxythymidine. The ratio of concentrations in cerebrospinal fluid and serum for the drugs was about 0.15 at 1 h after drug administration and was independent of the route of administration, suggesting that a nucleoside carrier-mediated process is involved in the transport of these compounds to the central nervous system. Because of the similar metabolism of nucleoside analogs in monkeys and humans, the potential glucuronide formation was assessed. Whereas the glucuronide of 3'-fluoro-3'-deoxythymidine was readily detected in urine, the amount of 3'-deoxy-2',3'-didehydrothymidine glucuronidated was small or not detectable in one-half of the urine samples. Pharmacokinetic parameters for the two drugs were similar to each other and analogous to those for 3'-azido-3'-deoxythynidine in monkeys, suggesting that the same dose and scheduling of the drug can be used for all three compounds in prophylactic and therapeutic efficacy drug studies in rhesus monkeys.

The pharmacokinetics of the anti-human immunodeficiency virus type 1 nucleosides, 3'-azido-2',3'-dideoxyuridine (AzddU) and 3'-azido-3'-deoxythymidine (AZT) were characterized in rhesus monkeys. Half-life, total clearance, and steady-state volume of distribution were similar for both compounds. The observed pharmacokinetic parameters for AZT were comparable to those previously reported in humans. Oral absorption of AzddU and AZT was virtually complete after 60 mg/kg. However, bioavailability of both nucleosides was markedly lower (less than 50%) after 200 mg/kg, possibly indicating the involvement of a saturable absorption mechanism. The nucleosides were also well absorbed after subcutaneous administration. AzddU and AZT penetrated the cerebrospinal fluid (CSF) with concentration ratios in CSF:serum ranging from 0.05 to 0.25 one hour after drug administration. The glucuronides of AZT and AzddU were readily detected in urine. Hemogram and blood chemistry values for animals receiving short-term treatment (3 doses) with either AZT or AzddU did not exhibit any significant changes when compared with untreated control monkeys. The similar pharmacokinetic characteristics of AzddU compared with AZT suggest that clinical trials of AzddU are warranted.

The pharmacokinetics of primaquine (PQ) and its major carboxylic acid metabolite (PQC) have been studied in seven Indian patients with P. vivax malaria following PQ 15 mg/day p.o. for 14 days. After a single oral dose on Day 1, a mean peak blood concentration of 50.7 ng/ml PQ was attained after 2.3 h, which declined monoexponentially with a half-life of 5.6 h. The mean total body clearance was 37.6 l/h and the volume of distribution was 292 l. The mean renal excretion (0-24 h) of the drug was only 0.54% of the dose and renal clearance was 0.189 l/h. Following chronic administration, none of the pharmacokinetic parameters was affected, and a steady state blood concentration of 2.5-4.2 ng/ml PQ was attained. After the first dose of PQ, PQC had a mean area under the blood concentration - time curve 11-fold higher than that of the parent drug. In contrast to the rapid distribution and elimination of PQ, the metabolite showed a longer mean residence time and accumulation in the body. The mean Cmax and AUC of the metabolite on Day 14 were 48 and 40% higher than the corresponding Day 1 values. The metabolite could not be detected in urine at any time in any patient. PQ and its metabolite did not show any accumulation in blood cells.

A significant number of patients with AIDS and AIDS-related complex develop neurological complications. Therefore, it is critical that anti-HIV agents penetrate the blood-brain barrier and suppress viral replication in the brain. In an effort to increase the brain delivery of anti-HIV nucleosides, in vitro and in vivo pharmacokinetics of dihydropyridine derivatives of 3'-azido-2',3'-dideoxyuridine (AzddU, AZDU, or CS-87) and 3'-azido-3'-deoxythymidine (AZT, Zidovudine) have been studied. In vitro studies of the prodrugs (AzddU-DHP and AZT-DHP) in human serum, mouse serum, and mouse brain homogenate indicated that the rates of serum conversion from prodrugs to parent drugs are species dependent: mouse brain homogenate greater than mouse serum greater than human serum. Half-lives in human serum, mouse serum, and mouse brain homogenate are 4.33, 0.56, 0.17 h, respectively, for AzddU and 7.70, 1.40, and 0.18 h, respectively, for AZT. In vivo studies of AzddU-DHP and AZT-DHP showed that the prodrugs have areas under the serum concentration-time curves (AUC) similar to those of the parent drugs. The AUC in serum for AzddU following prodrug administration is 25.79 micrograms h/mL, which is similar to the value of 25.83 micrograms h/mL when AzddU was administered. Analogously, the serum AUCs for AZT when AZT-DHP and AZT were administered are 25.38 and 26.64 micrograms h/mL, respectively. However, the brain AUCs for both AzddU and AZT derived from prodrugs, being 11.43 and 11.28 micrograms h/mL, respectively, are greater than the brain AUCs for AzddU (2.09 micrograms h/mL) and AZT (1.21 micrograms h/mL) when the parent drugs were administered. Thus, the relative brain exposure (re) for AzddU (5.47) and AZT (9.32) indicate a significant increase in exposure to the anti-HIV nucleosides following prodrug administrations. The results of extended half-lives of the synthesized prodrugs in human serum along with the higher re values in vivo warrant studies in larger animals to determine the potential usefulness of the prodrugs in humans.

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