CYP3A4 is involved in about 50% of drug metabolism, so there is a high risk of drug-to-drug interactions with this enzyme. Ritonavir (trade name Norvir - Abbott Laboratories) is an antiretroviral drug from the protease inhibitor class used to treat HIV infection and AIDS and is a potent inhibitor of CYP3A4.
Substrates of CYP2D6 include tricyclic antidepressants, antipsychotics (eg, haloperidol), MDMA, SSRIs, beta blockers, and opiates. Drug-to-drug interactions can occur with all of these drugs when taken in combination with CYP2D6 inhibitors.
One of the key jobs of a pharmacist is to notice and prevent drugs that can negatively interact and thus prevent adverse drug reactions in patients. Enzyme induction and inhibition as well as drugs that compete for phase I and phase II reactions are the most common drug-drug interactions that are reviewed by pharmacists.
