Calcium channel blockers + macrolides: elderly patients hospitalised for low blood pressure.

Macrolides that inhibit cytochrome P450 isoenzyme CYP 3A4 can lead to the accumulation of calcium channel blockers metabolised by the same isoenzyme and therefore an increase in their dose-related adverse effects. A Canadian case-control study examined the relationship between macrolide use and hospitalisation for hypotension (including shock) among 7100 elderly patients who were also taking a calcium channel blocker. The results showed more exposure to certain macrolides immediately prior to hospitalisation for hypotension than during an earlier control period; these macrolides included erythromycin (odds ratio (OR) = 5.8; 95% confidence interval: 2.3 to 15) and clarithromycin (OR = 3.7, 95% CI: 2.3 to 6.1). No such increase was found with azithromycin. In practice, patients treated with a calcium channel blocker should not be prescribed erythromycin or clarithromycin, but rather an antibiotic with similar efficacy but a lower risk of interaction.