Contributor: Jorge Chalit-Hernandez, OMS3 Educational Pearls: CYP enzymes are responsible for the metabolism of many medications, drugs, and other substances CYP3A4 is responsible for the majority Other common ones include CYP2D6 (antidepressants), CYP2E1 (alcohol), and CYP1A2 (cigarettes) CYP inducers lead to reduced concentrations of a particular medication CYP inhibitors effectively increase concentrations of certain medications in the body Examples of CYP inducers Phenobarbital Rifampin Cigarettes St. John's Wort Examples of CYP inhibitors -azole antifungals like itraconazole and ketoconazole Bactrim (trimethoprim-sulfamethoxazole) Ritonavir (found in Paxlovid) Grapefruit juice Clinical relevance Drug-drug interactions happen frequently and often go unrecognized or underrecognized in patients with significant polypharmacy A study conducted on patients receiving Bactrim and other antibiotics found increased rates of anticoagulation in patients receiving Bactrim Currently, Paxlovid is prescribed to patients with COVID-19, many of whom have multiple comorbidities and are on multiple medications Paxlovid contains ritonavir, a powerful CYP inhibitor that can increase concentrations of many other medications A complete list of clinically relevant CYP inhibitors can be found on the FDA website: https://www.fda.gov/drugs/drug-interactions-labeling/drug-development-and-drug-interactions-table-substrates-inhibitors-and-inducers References Glasheen JJ, Fugit RV, Prochazka AV. The risk of overanticoagulation with antibiotic use in outpatients on stable warfarin regimens. J Gen Intern Med. 2005;20(7):653-656. doi:10.1111/j.1525-1497.2005.0136.x Lynch T, Price A. The effect of cytochrome P450 metabolism on drug response, interactions, and adverse effects. Am Fam Physician. 2007;76(3):391-396. PAXLOVID™. Drug interactions. PAXLOVIDHCP. Accessed March 16, 2025. https://www.paxlovidhcp.com/drug-interactions Summarized & Edited by Jorge Chalit, OMS3 Donate: https://emergencymedicalminute.org/donate/
