Assessment of the bioequivalence of different formulations containing azithromycin (tablets and suspension).

Azithromycin (CAS 11772-70-0) is an orally administered macrolide antimicrobial drug, structurally related to erythromycin, with a similar spectrum of antimicrobial activity. The aim of the present studies, performed in two different groups of volunteers, was to compare the bioavailability of azithromycin (Azro) 500 mg tablets (study 1) and azithromycin (Azro) 200 mg/5 mL suspensions (study 2) with originator products. Each study was conducted according to an open, randomized, single-dose, two-period cross-over design in 24 healthy volunteers with a wash-out period from 14 to 21 days. Blood samples were taken up to 96 h post dosing, and concentrations of azithromycin were determined by HPLC method. In the first study, the 90% confidence interval for intra-individual ratios (test vs. reference) of AUC0-t and Cmax of azithromycin were between 0.82 and 1.04 for AUC0-t and 0.81 and 1.11 for Cmax, and thus within the acceptance ranges for bioequivalence trials. The 90% confidence interval for intra-individual ratios of AUC0-t and Cmax of azithromycin administered as suspension were between 0.89 and 1.22 and 0.91 and 1.23, respectively. These values were also within the acceptance range. Concerning the secondary parameter tmax the 90% confidence interval for the intra-individual differences for azithromycin were between -0.49 - 0.50 in the first and between -0.50 - 0.25 in the second study, respectively. In the light of the results of the studies reported here it can be concluded that azithromycin test formulations, i.e. tablet and suspension are bioequivalent to the respective reference formulations.