Pharmacokinetics of lamivudine in cats

Weijiang Zhang Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7390.
Present address is TAP Pharmaceutical Products Incorporated, 675 N Field Dr, Lake Forest, IL 60045.

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Jeffrey K. Mauldin Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7390.
Present address is Culbreth-Carr-Watson Animal Clinic, 1223 E 2nd Ave SW, Rome, GA 30161.

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Chad W. Schmiedt Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7390.
Present address is Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706-1102.

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Charles W. Brockus Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7390.
Present address is Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, IA 50011-1250.

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F. Douglas Boudinot Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7390.
Present address is Department of Pharmaceutics, College of Pharmacy, Virginia Commonwealth University, Richmond, VA 23298.

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M. A. McCrackin Stevenson Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7390.
Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7390.
Present address is Valley Pet Clinic, 1420 S First St, Hamilton, MT 59840.

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Abstract

Objective—To characterize the pharmacokinetics of lamivudine (3TC) in cats.

Animals—6 sexually intact 9-month-old barrier-reared domestic shorthair cats.

Procedure—Cats were randomly alloted into 3 groups, and lamivudine (25 mg/kg) was administered IV, intragastrically (IG), and PO in a 3-way crossover study design with 2-week washout periods between experiments. Plasma samples were collected for 12 hours after drug administration, and lamivudine concentrations were determined by high-performance liquid chromatography. Maximum plasma concentrations (Cmax), time to reach Cmax (Tmax), and bioavailability were compared between IG and PO routes. Area under the curve (AUC) and terminal phase halflife (t½) among the 3 administration routes were also compared.

Results—Plasma concentrations of lamivudine declined rapidly with a t½ of 1.9 ± 0.21 hours, 2.6 ± 0.66 hours, and 2.7 ± 1.50 hours after IV, IG, and PO administration, respectively. Total body clearance and steady-state volume of distribution were 0.22 ± 0.09 L/h/kg and 0.60 ± 0.22 L/kg, respectively. Mean Tmax for IG administration (0.5 hours) was significantly shorter than Tmax for PO administration (1.1 hours). The AUC after IV, IG, and PO administration was 130 ± 55.2 mg·h/L, 115 ± 97.5 mg·h/L, and 106 ± 94.9 mg·h/L, respectively. Lamivudine was well absorbed after IG and PO administration with bioavailability values of 88 ± 45% and 80 ± 52%, respectively.

Conclusions and Clinical Relevance—Cats had a shorter t½ but slower total clearance of lamivudine, compared with humans. Plasma concentrations of lamivudine were maintained above the minimum effective concentration for inhibiting FIV replication by 50% (0.14µM [0.032 µg/mL] for wild-type FIV clinical isolate) for at least 12 hours after IV, IG, or PO administration. (Am J Vet Res 2004;65:841–846)

Abstract

Objective—To characterize the pharmacokinetics of lamivudine (3TC) in cats.

Animals—6 sexually intact 9-month-old barrier-reared domestic shorthair cats.

Procedure—Cats were randomly alloted into 3 groups, and lamivudine (25 mg/kg) was administered IV, intragastrically (IG), and PO in a 3-way crossover study design with 2-week washout periods between experiments. Plasma samples were collected for 12 hours after drug administration, and lamivudine concentrations were determined by high-performance liquid chromatography. Maximum plasma concentrations (Cmax), time to reach Cmax (Tmax), and bioavailability were compared between IG and PO routes. Area under the curve (AUC) and terminal phase halflife (t½) among the 3 administration routes were also compared.

Results—Plasma concentrations of lamivudine declined rapidly with a t½ of 1.9 ± 0.21 hours, 2.6 ± 0.66 hours, and 2.7 ± 1.50 hours after IV, IG, and PO administration, respectively. Total body clearance and steady-state volume of distribution were 0.22 ± 0.09 L/h/kg and 0.60 ± 0.22 L/kg, respectively. Mean Tmax for IG administration (0.5 hours) was significantly shorter than Tmax for PO administration (1.1 hours). The AUC after IV, IG, and PO administration was 130 ± 55.2 mg·h/L, 115 ± 97.5 mg·h/L, and 106 ± 94.9 mg·h/L, respectively. Lamivudine was well absorbed after IG and PO administration with bioavailability values of 88 ± 45% and 80 ± 52%, respectively.

Conclusions and Clinical Relevance—Cats had a shorter t½ but slower total clearance of lamivudine, compared with humans. Plasma concentrations of lamivudine were maintained above the minimum effective concentration for inhibiting FIV replication by 50% (0.14µM [0.032 µg/mL] for wild-type FIV clinical isolate) for at least 12 hours after IV, IG, or PO administration. (Am J Vet Res 2004;65:841–846)

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