PHARMACOKINETICS OF ENROFLOXACIN IN HORSES AFTER SINGLE INTRAVENOUS AND INTRAMUSCULAR ADMINISTRATION

Pharmacokinetic behaviour of enrofloxacin was studied in 6 horses afte r intravenous (i,v.) or intramuscular (i,m,) administration of enroflo xacin (5 mg/kg bwt), Concentrations of enrofloxacin and ciprofloxacin were measured by high performance liquid chromatography in serum, Anti microbial activity of the samples was determined with an agar-diffusio n technique, Reactions at the site of i,m, injection were monitored cl inically and by determination of serum creatine kinase (CK) activity, After i,v. administration, elimination half-life of enrofloxacin was 4 .4 h and volume of distribution was 2.3 l/kg bwt. Enrofloxacin was rap idly metabolised to ciprofloxacin. The half-life of ciprofloxacin para llelled that of the parent drug, its concentration in serum reached 20 -35% of that of the parent drug. After i.m. administration, eliminatio n half-life of enrofloxacin was longer (9.9 h) than after i.v. adminis tration, Mean absorption time of enrofloxacin was also long (9.9 h). N o statistically significant differences were found when half-life and mean residence time of antimicrobial activity were compared with those of enrofloxacin and ciprofloxacin from chemically analysed data, Intr amuscular injection of enrofloxacin was found to be very irritating, A fter i,m, administration, CK activity in serum, compared with pre-inje ction levels, increased over 10-fold. CK activity also stayed high dur ing the 32 h follow-up period, Clinical reactions, such as swelling or tenderness at the i,m, injection sites, were observed in 2 horses.