title: Mechanistic study of the azithromycin dosage-form-dependent food effect.
abstract: OBJECTIVE
  Azithromycin capsules are known to exhibit a negative food effect, manifest as a decrease in azithromycin bioavailability in the fed state. Azithromycin tablets are known to be bioequivalent to capsules in the fasted state, but do not exhibit a food effect. In the present study, the involvement of gastric degradation of azithromycin to des-cladinose azithromycin (DCA) has been investigated as a possible mechanism for the observed capsule food effect.
  
  
  METHODS
  Healthy volunteers were dosed with azithromycin tablets and capsules, fasted and fed, in a four-way randomized crossover study. Serum levels of DCA were measured as a function of time post-dose. Natural log-transformed PK parameters were statistically analyzed using an ANOVA model appropriate for the study design.
  
  
  RESULTS
  When capsules were dosed to fed subjects, the systemic AUC for DCA was 243% of the value observed after fasted-state dosing, and the DCA C(max) was 270% of the value observed after fasted-state dosing. When azithromycin tablets were dosed in the fasted and fed states, there was no significant difference in systemic DCA.
  
  
  CONCLUSIONS
  Gastric degradation of azithromycin to DCA is the likely mechanism for the observed negative food effect observed for azithromycin capsules. This effect is not observed for tablets. These observations suggest that azithromycin capsules exhibit slow and/or delayed disintegration in the fed stomach, resulting in extended gastric residence and degradation of a portion of the gastrically retained azithromycin.
authors.affiliation: Pharmaceutical Sciences, PharmaTherapeutics, Pfizer Global R&D, MS-4124, Groton, Connecticut 06340, USA. william.j.curatolo@pfizer.com
authors.forename: William
authors.initials: W
authors.lastname: Curatolo
authors.forename: George
authors.initials: G
authors.lastname: Foulds
authors.forename: Robert
authors.initials: R
authors.lastname: Labadie
mesh_terms: D000328:Adult; D019540:Area Under Curve; D017963:Azithromycin / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*; D001682:Biological Availability; D002214:Capsules; D002851:Chromatography, High Pressure Liquid; D018592:Cross-Over Studies; D004304:Dosage Forms; D005215:Fasting; D005260:Female; D018565:Food-Drug Interactions; D006801:Humans; D008297:Male; D015394:Molecular Structure
chemical_list: D002214:Capsules; D004304:Dosage Forms; D017963:Azithromycin