Paracetamol (acetaminophen) is a widely used analesic and antipyretic agent. It is metabolize primarily by glucuronide and sulphate conjugation and has therefore been used as a "model" substrate for examining conjugation mechanisms. Oxidation is quantitatively less important than glucuronidation and sulphation is mediated by the cytochrome P450 microsomal system to the N-acetyl-p-benzoquinoneimine (NABQI).

The aim of this study was to compare of pharmacokinetics of paracetamol in calves black-and-white (BW) breed and cross-breed calves black-and-white x holstein-friesian (BW x HF). The effect of age on "interbreed" differences in the values of selected pharmacokinetic parameters of this model drug was examined.

The experiment was carried out on 20 health calves : 10 of CB. breed and 10. cross-breed. The paracetamol test was performed in calves aged 10., 20 and 40. day of life. The animals received paracetamol "per os" in the dose of 10 mg/kg body weight. Blood samples was collected before and at 0.25, 0.5, 1, 2, 3, 4, 6 and 8 hours after model drug administration. The concentration of paracetamol in plasma was determined by the spectrophotometric method. The pharmacokinetics of paracetamol : volume of distribution (V_d), mean residence time (MRT), biological half-life (T_0.5) and metabolic clearance (Cl_m) were calculated through a non-compartmental method using the TopFit computer software.

The obtained results indicate that the age of calves influenced on the estimated values of pharmacokinetic parameters of paracetamol. We observed that pharmacokinetic parameters of this model drug differed significantly between 10., 20. and 40. day-old calves(P<0.05; P<0.01) : increase of volume of distribution (from 27.09 to 39.20 l) and metabolic clearance (from 288.2 to 588.5 ml/min) and decrease of mean residence time (from 100 to 83 min.) and biological half-life (from 85 to 68 min.) values. It was also stated that pharmacokinetic parameters of paracetamol in black-and-white and black-and-white x holstein-friesian cross breed calves differ not significantly (P>0.05) : BW -

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