Episode 948: CYP Inducers and Inhibitors

Mar 17, 2025

CYP enzymes play a crucial role in the metabolism of many medications. Discover how CYP inducers can lower drug concentrations, while inhibitors like grapefruit juice can increase them. The podcast delves into real-life implications, particularly for patients on multiple medications. It discusses the risks associated with interactions involving common drugs like Bactrim and Paxlovid, showcasing the need for awareness in polypharmacy. This episode is a must-listen for anyone interested in the nuances of medication management!

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INSIGHT

CYP Enzymes Metabolize Most Drugs

CYP enzymes metabolize around 70 to 80% of drugs and medications we take.\n- Understanding enzyme interactions helps predict drug metabolism changes.

ANECDOTE

Rifampin Reduces Birth Control Effectiveness

Rifampin induces CYP enzymes and reduces the effectiveness of birth control.\n- This led to a case where a medical student on rifampin got pregnant due to reduced birth control efficacy.

INSIGHT

Impacts of CYP Inducers and Inhibitors

CYP inhibitors increase medication concentrations, risking side effects like bleeding with warfarin.\n- CYP inducers lower medication effectiveness, increasing risks such as clotting with warfarin.

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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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