AIM To investigate the effect of oral roxithromycin on serum concentrations at steady state and its pharmacokinetics of aminophylline in New Zealand rabbits. METHODS The experiment was divided into 2 stages: (Ⅰ) The subjects only received a four-day course of oral aminophylline until steady-state; (Ⅱ) aminophylline and roxithromycin were coadministrated from the d 5～10. After the last dose of aminophylline at the end of each study stage, serum theophylline concentrations were determined with HPLC. RESULTS Compared to stage Ⅰ, AUC、CL/Fs、 K a、 K e、 T 1/2(ka) 、 T max had significantly changed or very significantly changed at stage Ⅱ ( P

Penicillins are one type of the most important antibiotics used in the clinic.Control of drug impurity profiles is an important part of ensuring drug safety.This is particularly important in penicillins where polymerization can lead to polymers as elicitors of passive cutaneous anaphylaxis.The current under-standing of penicillin polymerization is based on reactions with amino groups,but no comprehensive mechanistic understanding has been reported.Here,we used theoretical calculations and column switching-LC/MS techniques to study penicillin dimerization.Ampicillin and benzylpenicillin were selected as representative penicillins with or without amino groups in the side chain,respectively.We identified four pathways by which this may occur and the energy barrier graphs of each reaction process were given.For benzylpenicillin without an amino group in the 6-side chain,dimerization mode A is the dominant mode,where the 2-carboxyl group of one molecule reacts with the β-lactam of another molecule.However,ampicillin with an amino group in the 6-side chain favors dimerization mode C,where the amino group of one molecule attacks the β-lactam of another molecule.These findings can lead to a polymer control approach to maintaining penicillin antibiotics in an active formulation.