Clarithromycin is an inhibitor of the cytochrome P453A4, the enzyme that metabolizes calcium-channel blockers. The antibiotic can send blood concentrations of calcium-channel blockers soaring by as much as 500% leading to severe hypotension.
Patients on regular treatment with calcium channel blockers like Amlodipine, Felodipine, Nifedipine, Diltiazem or Verapmil were prescribed Clarithromycin or Azithromycin. These macrolide antibiotics are commonly used for upper respiratory infection, pneumonia, eradication of H. Pylori, and atypical mycobacteria.
Because azithromycin is only a weak inhibitor of CYP34A, the type of intensification of the calcium-channel blocker that occurs with clarithromycin is not expected.
Also, due to the role of the kidneys in eliminating clarithromycin, guidelines call for reduced dosing of the antibiotic in patients with chronic kidney disease.
Thus, it is highly advisable, in patients suffering from high blood pressure and on regular medications, to be wary of the antibiotics prescribed or used over the counter.
Published: November 9 in JAMA