Ultrasonographic evaluation of the effects of azithromycin on antral motility and gastric emptying in healthy cats

Background Erythromycin, a macrolide antibiotic with motilin agonist properties, shortens gastric emptying (GE) time in healthy cats. Azithromycin, another macrolide antibiotic, is effective for treatment of gastric paresis in people. Objectives To evaluate the effects of azithromycin on GE and gastric motility in healthy cats in comparison with erythromycin (positive control) and placebo. Animals Eight healthy purpose-bred cats. Methods Prospective, blinded, crossover study. Cats received either azithromycin (3.5 mg/kg PO q24h), erythromycin (1 mg/kg PO q8h), or placebo for 24 hours before and during evaluation of GE. A validated method using ultrasound for sequential measurements of antral area as well as amplitude and frequency of contractions was used to assess GE and evaluate gastric antral motility postprandially over an 8-hour period. Results GE was significantly faster (P < .05) after administration of azithromycin and erythromycin when compared to placebo in the late phase of fractional emptying from 75% (mean +/- SD: 327 +/- 51 minutes, 327 +/- 22 minutes, and 367 +/- 29 minutes, respectively), to 95% fractional emptying (399 +/- 52 minutes, 404 +/- 11 minutes, and 444 +/- 24 minutes, respectively). The drugs had no significant effect on antral motility variables at any time point. Conclusions and Clinical Importance Azithromycin and erythromycin shorten GE time in a comparable manner in healthy cats. Evaluation of their efficacy in cats with gastric dysmotility is warranted.