OBJECT DRUGS

Calcium Channel Blockers:

• Amlodipine (Norvasc)
• Bepridil (Vascor)
• Diltiazem (Cardizem, etc.)
• Felodipine (Plendil)
• Isradipine (DynaCirc, etc.)
• Nicardipine (Cardene, etc.)
• Nifedipine (Procardia, etc.)
• Nimodipine (Nimotop)
• Nisoldipine (Sular)
• Nitrendipine (Baypress)
• Verapamil (Isoptin, etc.)

PRECIPITANT DRUGS

Enzyme Inducers:

• Barbiturates
• Bosentan (Tracleer)
• Carbamazepine (Tegretol, etc.)
• Cloxacillin (Cloxapen)
• Dabrafenib (Tafinlar)
• Dicloxacillin (Dynapen)
• Griseofulvin (Grisactin, etc.)
• Nafcillin (Unipen)
• Oxcarbazepine (Trileptal, etc.)
• Phenytoin (Dilantin, etc.)
• Primidone (Mysoline)
• Rifabutin (Mycobutin)
• Rifampin (Rifadin, etc.)
• Rifapentine (Priftin)
• St. John's Wort

Comment:

Rifampin markedly reduces the plasma concentrations of verapamil, diltiazem, nifedipine, and nisoldipine; the effect probably occurs with most other combinations of calcium channel blockers (CCBs) and enzyme inducers. The effect is greater with oral than with parenteral administration of the CCB.

Class 3: Assess Risk & Take Action if Necessary

• Consider Alternative: It may be difficult to achieve therapeutic serum concentrations of oral CCBs in the presence of enzyme inducers. Thus, if at all possible, use an alternative to either the CCB or the enzyme inducer. Avoid barbiturates if a non-barbiturate alternative is suitable (e.g., benzodiazepine). Theoretically, amlodipine would be less affected than other CCBs, since it undergoes less first-pass metabolism.
• Monitor:Monitor for altered CCB effect if inducer is initiated, discontinued, or changed in dosage. Keep in mind that enzyme induction is usually gradual and may take days to weeks for onset and offset, depending on the specific inducer.