Abstract
Dear Editor
Concerns have recently been raised about the concomitant use of calcium-channel blockers and macrolide antibiotics, particularly clarithromycin. Two recent cases of deliberate amlodipine overdose, complicated by community-acquired pneumonia, managed on our intensive care unit have highlighted to us this significant, potential drug interaction. Both received benzyl penicillin and clarithromycin as per hospital protocol alongside organ support in the form of inotropes. One patient required positive pressure ventilation, and both showed evidence of hepatic and renal dysfunction, one requiring haemofiltration.
Clarithromycin is a potent liver enzyme inhibitor and thus potentiates the action of amlodipine. An increased risk of acute kidney injury, hypotension and all-cause mortality amongst patients in whom these drugs are co-prescribed has been suggested. 1 This is surely all the more concerning in cases of amlodipine overdose, particularly in the context of hepato-renal injury.
Hospital protocols promote the routine use of clarithromycin in the treatment of community-acquired pneumonia, and dosing regimes of other drugs with the potential for interaction such as warfarin are judiciously adjusted. In our experience, clinicians and pharmacists often neglect amlodipine when considering these potentially deleterious interactions. We feel more needs to be done to raise awareness of this important patient safety issue.