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
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