OBJECT DRUGS

Antipsychotics:

• Aripiprazole (Abilify, etc.)
• Clozapine (Clozaril, etc.)
• Iloperidone (Fanapt)
• Olanzapine (Zyprexa, etc.)
• Paliperidone (Invega, etc.)
• Risperidone (Risperdal, etc.)

PRECIPITANT DRUGS

Enzyme Inhibitors: (CYP2D6)

• Amiodarone (Cordarone, etc.)
• Cinacalcet (Sensipar)
• Diphenhydramine (Benadryl, etc.)
• Haloperidol (Haldol)
• Propafenone (Rythmol, etc.)
• Propoxyphene^*
• Quinidine (Quinidex)
• Ritonavir (Norvir)
• Terbinafine (Lamisil, etc.)
• Thioridazine (Mellaril)

^* Propoxyphene (Darvon) was withdrawn from the US market.

Comment:

These antipsychotics are metabolized by CYP2D6. Drugs that inhibit CYP2D6 may lead to accumulation of the antipsychotic. People with "normal" CYP2D6 activity (Extensive Metabolizers) are at the greatest risk. Note that because terbinafine has an extraordinarily long terminal half-life, the inhibitory effect of terbinafine on CYP2D6 may last for many weeks after terbinafine is discontinued.

Class 3: Assess Risk & Take Action if Necessary

• Consider Alternative:
• Diphenhydramine: Other antihistamines such as desloratadine (Clarinex), fexofenadine (Allegra), loratadine (Claritin), and cetirizine (Zyrtec) are not known to inhibit CYP2D6.
• Monitor: Be alert for altered effect of the antipsychotic if CYP3A4 inhibitors are started, stopped, or changed in dosage. Due to the long half-lives of some of these drugs, the onset and offset of these interactions may take one to two weeks.