Amlodipine × Rifampicin

Rifampicin is a strong inducer of CYP3A4 and other drug-metabolising enzymes (rifampicin SmPC). CYP3A4 takes part in amlodipine metabolism, so amlodipine levels may fall and its blood pressure effect may weaken (both SmPCs). The documents do not give the size of the fall for amlodipine. For other calcium channel blockers it has been measured: rifampicin reduced exposure to nifedipine by 64% and to verapamil by 93% (rifampicin SmPC).

Blood pressure returns to previous values or rises higher, and headache may appear. In angina, attacks may become more frequent.

The combination is acceptable with blood pressure control. While rifampicin is taken and after it is stopped, measure blood pressure and consider adjusting the amlodipine dose (amlodipine labels). Doses of drugs affected by rifampicin may need adjustment both when it is started and when it is stopped (rifampicin SmPC). Nifedipine, nimodipine, nisoldipine and nitrendipine are contraindicated with rifampicin, so they cannot replace amlodipine (rifampicin SmPC). Rifampicin also reduces exposure to the active metabolite of enalapril, so if a patient is switched to it, the dose is set by clinical response (rifampicin SmPC).