Dose-dependent stimulation of gallbladder contraction by intravenous erythromycin in man

We have previously shown that a single oral dose of 500 mg erythromycin causes gallbladder contraction. The effect of intravenous erythromycin on antroduodenal motility is dose-dependent; < 3 mg/kg body weight stimulates propagated contractions in a fashion similar to motilin while doses > 7 mg/kg cause giant non-propagated antral contractions not seen with motilin. Using ultrasound, we have examined the effect of differing doses of intravenous erythromycin on gallbladder motility in man. Erythromycin (1 mg/kg) caused fasting gallbladder contraction to 52% of basal gallbladder volume (P < 0.001), and increased gallbladder emptying following a liquid meal (maximal percentage emptied 75 +/- 6.8% vs. 58 +/- 9.0% following saline, P < 0.05). Erythromycin (7 mg/kg) however, had no effect on gallbladder fasting or post-prandial motor activity. We conclude that the effect of erythromycin on gallbladder motility is dose-dependent, with higher doses having no effect. It is possible that at higher doses erythromycin stimulates other receptors in addition to the motilin receptor, and that the combined effect is different to the stimulation of the motilin receptor alone.