STUDIES ON THE PHARMACOKINETICS OF CEFTRIAXONE IN GOATS
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Date
2004
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AAU, Anand
Abstract
Ceftriaxone, a third generation semisynthetic cephalosporin has excellent activity against aerobic gram negative and gram positive bacteria including moderate activity against many strains of Pseudomonas aeruginosa. The present study was designed to study pharmacokinetics of ceftriaxone in goats following single dose intravenous administration at the dose rate of 20 mg kg-1 of body weight. Following administration of drug the blood samples were collected at predetermined time intervals. Drug concentration in plasma was determined using High Performance Liquid Chromatography (HPLC). After intravenous administration, the plasma concentration- time curve was characteristic of a two compartment open model whereas; it was best fitted to one compartment open model following intramuscular administration. Based on the plasma drug concentration time curve various rate constants and pharmacokinetic parameters were calculated by least square regression analysis. Following intravenous administration the mean plasma ceftriaxone level of 235.02 ± 42.1 µg ml-1 was observed at 0.033 h (2 minutes), which rapidly declined to 38.49 ± 3.53 µg ml-1 at 0.533 h (32 minutes). The distribution half-life (t1/2α) and elimination half-life (t1/2β) were 0.12 + 0.004 hand 1.50 ± 0.05 h, respectively. The mean values of apparent volume of distribution [Vd(area)] and volume of distribution of drug at steady-state (Vdss) were calculated to be 0.58 ± 0.04 and 0.28 ± 0.05 L Kg-1, respectively. The mean value of total body clearance (CIB) was 4.50 ± 0.43 ml min-1 kg-1 Following single dose intramuscular administration of ceftriaxone at the rate of 20 mg kg-1 of body weight in goats, the therapeutically effective plasma concentration was detectable at 0.0833 hours (5 minutes) and maintained for 12 hours. Peak plasma concentration (8.34 ± 0.81 µg ml-1) was obtained at 0.5 hours after intramuscular administration. After rapid absorption of drug from the site of administration (t1/2ka: 0.08 ± 0.01 hours), it is slowly eliminated from the body (t1/2β: 2.03 ± 0.09 hours). The bioavailability of ceftriaxone was 0.59 + 0.04 (59 ± 4.0 per cent) following intramuscular administration. Based on the pharmacokinetic parameters obtained, dosage regimens of ceftriaxone were calculated. An appropriate intravenous dosage regimen of ceftriaxone in goats would be 7.0 mg kg-1 of body weight to be repeated every 12- hour interval. Intramuscular dosing of the drug at the dose rate of 20 mg kg-1 of body weight every 12 hours is suggested for mass medication of goats. A more practical approach would be to give the drug intravenous (7.0 mg kg-1) followed by intramuscular (20.0 mg kg-1) repeated at every 12 hours.
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VETERINARY PHARMACOLOGY, A STUDY