Losartan drug interactions
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Losartan Drug Interactions: A Comprehensive Overview
Introduction to Losartan and Its Pharmacokinetics
Losartan is a widely used angiotensin-receptor antagonist primarily prescribed for hypertension and various cardiovascular conditions. It is rapidly absorbed after oral administration, reaching peak concentrations within 1-2 hours. Approximately 14% of losartan is metabolized into its more potent active metabolite, E 3174, which has a half-life of 6-9 hours. The drug is metabolized mainly by cytochrome P450 (CYP) enzymes, specifically CYP3A4, CYP2C9, and CYP2C10.
Losartan and Cytochrome P450 Enzymes
The metabolism of losartan involves significant interactions with the CYP450 enzyme system. Studies have shown that losartan's pharmacokinetic interactions are primarily mediated by CYP2C9 and CYP3A4. This interaction profile suggests that drugs affecting these enzymes could alter losartan's efficacy and safety. For instance, combining losartan with drugs like phenobarbital, rifampin, or fluconazole requires careful monitoring due to potential pharmacokinetic interactions.
Herb-Drug Interactions with Losartan
Herbal supplements can also influence losartan's pharmacokinetics and pharmacodynamics. For example, Shengmai injection (SMI) has been shown to enhance losartan's antihypertensive effects by increasing its plasma concentration and bioavailability, likely through the inhibition of CYP3A4 and drug transporters like P-gp and BCRP. Similarly, Curcuma longa (CUR) and Lepidium sativum (LS) have been found to potentiate losartan's blood pressure-lowering effects and increase its plasma concentration in hypertensive rats.
Drug-Drug Interactions with Losartan
Commonly Studied Drug Interactions
- Hydrochlorothiazide: Studies indicate no significant pharmacokinetic interaction between losartan and hydrochlorothiazide, making their combination safe and effective for hypertension treatment.
- Amlodipine: While amlodipine does not significantly affect the pharmacokinetics of losartan's active metabolite, it does decrease losartan's exposure and increase its clearance. However, the combination is generally well-tolerated and provides additive hemodynamic benefits.
- Sucroferric Oxyhydroxide: This phosphate binder does not significantly alter the pharmacokinetics of losartan, suggesting a low risk of interaction.
Other Notable Interactions
Losartan has been shown to have no significant interactions with warfarin, digoxin, or omeprazole, indicating its favorable interaction profile with these commonly used medications. However, it is crucial to avoid losartan during pregnancy due to the risk of serious fetal toxicity.
Conclusion
Losartan is a well-tolerated antihypertensive agent with a favorable drug interaction profile. Its interactions with the CYP450 enzyme system and various drugs and herbs highlight the importance of monitoring and potential dose adjustments. Understanding these interactions ensures the safe and effective use of losartan in managing hypertension and other cardiovascular conditions.
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