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Diagonal Method to Measure Synergy Among Any Number of Drugs
Published on: June 21, 2018
Possible interaction of ranitidine with phenytoin
1Department of Pharmacy, University Hospital, Vancouver, Canada.
Drug Intelligence & Clinical Pharmacy
|December 1, 1988
Summary
Ranitidine can increase phenytoin levels in patients. Monitoring serum phenytoin is crucial when starting ranitidine to prevent toxicity.
Area of Science:
- Pharmacology
- Drug Metabolism
- Clinical Toxicology
Background:
- Cimetidine and ranitidine are known to inhibit hepatic cytochrome P-450 enzymes.
- This inhibition affects the metabolism of various co-administered drugs.
- Ranitidine's inhibitory effect is generally less potent than cimetidine's at standard therapeutic doses.
Observation:
- A 66-year-old male patient experienced a 40% increase in serum phenytoin concentration.
- This increase occurred over one month after initiating ranitidine 150 mg twice daily for postsurgical prophylaxis.
- Phenytoin levels returned to baseline after discontinuing ranitidine, with no other changes in medication or dosage.
Findings:
- Ranitidine, even at common doses, can significantly inhibit phenytoin metabolism.
- This drug interaction can lead to supratherapeutic phenytoin serum concentrations.
- The case highlights a potential for clinically relevant drug-drug interactions with ranitidine.
Implications:
- Clinicians should monitor serum phenytoin concentrations in patients starting ranitidine therapy.
- Close monitoring is recommended during the initial month of co-administration.
- Further research is needed to understand inter-individual variability in ranitidine's drug interaction potential.
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