Pharmacokinetics of a long-acting formulation of azithromycin in pigs

The pharmacokinetics (pk) of a long acting 20% solution of azithromycin (az-la) in pigs after a single peri-caudal injection at 10 and 20 mg/kg body weight was determined,using an aqueous formulation of the drug administered iv as reference,hplc was used as analytical method. cmax was 1.4 and 2.5 μg/ml,and tmax was 3.1 and 3.4 h,respectively for 10 and 20 mg/kg. both preparations had 99.5% purity. values for mrt were longer in the 10 mg/kg dose group (18.2 h) as compared to the 20 mg/kg group (16.5 h). yet t1/2ß was comparable between both dose levels (8.5 h vs. 7.2 h,for 10 and 20 mg/kg,respectively). no linear increments linked to dose were found in variables such as relative bioavailability,cmax and apparent volume of distribution. values for relative bioavailability (fr) of the higher dose as compared to the lower were 86.81% and absolute bioavailability (f) was 110.5 for the lower dose and 115.9% for the higher. best pk/pd ratios for clinical efficacy of azithromycin describe this antibacterial drug as time-dependent. considering pig's serum concentrations of the az-la preparation here studied after its peri-caudal injection and based on a theoretical minimal therapeutic concentration in plasma of 0.1 μg/ml based on bacteriological testing,a doseinterval of up to 48 h can be achieved. the suitability of this preparation to treat pig respiratory diseases is addressed. © 2014 pvj.