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Volume 2 (2002), Pages 1369-1378
Research Article

Variable Absorption of Clavulanic Acid After an Oral Dose of 25 mg/kg of Clavubactin® and Synulox® in Healthy Cats

1Institute for Anaesthesiology, University Medical Center Sint Radboud, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
2DADA Consultancy, Dennenstraat 109, 6543 JR Nijmegen, The Netherlands
3Regivet BV, Boswinde 113, 2496 WG Den Haag, The Netherlands

Received 25 February 2002; Revised 25 March 2002; Accepted 28 March 2002

Copyright © 2002 Tom B. Vree et al.


The aims of this investigation were to calculate the pharmacokinetic parameters and to identify parameters, based on individual plasma concentration-time curves of amoxicillin and clavulanic acid in cats, that may govern the observed differences in absorption of both drugs. The evaluation was based on the data from plasma concentration-time curves obtained following a single-dose, open, randomised, two-way crossover phase-I study, each involving 24 female cats treated with two Amoxi-Clav formulations (formulation A was Clavubactin® and formulation was B Synulox® ; 80/20 mg, 24 animals, 48 drug administrations). Plasma amoxicillin and clavulanic acid concentrations were determined using validated bioassay methods. The half-life of elimination of amoxicillin is 1.2 h (t1/2 = 1.24 ± 0.28 h, Cmax = 12.8 ± 2.12 μg/ml), and that of clavulanic acid 0.6 h (t1/2 = 0.63 ± 0.16 h, Cmax = 4.60 ± 1.68 μg/ml). There is a ninefold variation in the AUCt of clavulanic acid for both formulations, while the AUCt of amoxicillin varies by a factor of two. The highest clavulanic acid AUCt values indicate the best absorption; all other data indicate less absorption. Taking into account that the amoxicillin–to–clavulanic acid dose ratio in the two products tested was 4:1, the blood concentration ratios may actually vary much more, apparently without compromising the products’ high efficacy against susceptible microorganisms.