Pharmacokinetic interaction between shuanghuanglian and azithromycin injection: A nonlinear mixed-effects model analysis in rats.

1. This study aimed to evaluate the pharmacokinetic interaction of shuanghuanglian (SHL) and azithromycin in rats, and to provide experimental support for rational drug use in clinics. 2. HPLC-UV and HPLC-MS/MS approaches were respectively developed to detect the forsythiaside (active component of SHL) and azithromycin concentrations. Both non-compartmental and compartmental analyses were employed to calculate pharmacokinetic parameters. A nonlinear mixed-effects modelling method was applied to fit the drug concentration-time data. The influence of drug coadministration on pharmacokinetic parameters was tested using forward inclusion and backward elimination procedures. 3. After drug co-administration, areas under the drug concentration-time curve (AUC) and half-lives (T1/2 ) of both azithromycin and forsythiaside increased significantly, meanwhile, the drug clearance (CL) decreased compared to single drug administration. Both forsythiaside and azithromycin exposures increased after coadministration. Two-compartment models were suitable to describe the in vivo behavior of both azithromycin and forsythiaside. The coadministration of SHL could significantly decrease the central volume of azithromycin (VCA ), and forsythiaside clearance (CLF ) decreased after co-intravenous administration of azithromycin. 4. Co-intravenous administration of forsythiaside and azithromycin could significantly increase drug exposures for both drugs. Lower dose can provide sufficient drug exposure to obtain antibacterial activity. The coadministration may be a potential method to increase therapy efficiency while decrease adverse drug reactions.