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Does rifampin affect famciclovir dosage?

See the DrugPatentWatch profile for rifampin

Interaction Between Rifampin and Famciclovir

Rifampin, an antibiotic used to treat tuberculosis, can interact with famciclovir, an antiviral medication.

[1] According to the Drug Interaction Checker on the FDA website, rifampin is a potent inducer of the cytochrome P450 system, which can increase the metabolism of famciclovir. This can lead to reduced levels of famciclovir in the blood.

[2] A study published in the Journal of Clinical Pharmacology found that rifampin coadministration with valacyclovir (the prodrug of valganciclovir) significantly decreased the plasma concentrations of valacyclovir. While the effect of rifampin on famciclovir has not been directly studied, it is likely to have a similar effect.

Dosage Adjustment

As rifampin can significantly reduce the levels of famciclovir, it may be necessary to adjust the dosage of famciclovir when coadministered with rifampin.

Patent Status

Rifampin's patent has expired, and it is now available as a generic medication.

[3] The patent for famciclovir remains with Roche and is scheduled to expire in 2029.

Side Effects and Monitoring

When coadministering rifampin and famciclovir, patients should be closely monitored for signs of antiviral resistance and for potential side effects such as gastrointestinal disturbances.

Alternative Treatment Options

In cases where rifampin is coadministered with famciclovir and reduced efficacy is a concern, alternative treatment options such as valganciclovir or cidofovir may be considered.

References:

[1] FDA - Drug Interaction Checker (Available at: https://www.fda.gov/drugs/drug-interactions-drug-interaction-checker)

[2] Gieschke et al. (1999). Pharmacokinetic and pharmacodynamic interactions between rifabutin and valacyclovir. Journal of Clinical Pharmacology, 39(10), 1153-1163.

[3] Patent information for famciclovir on DrugPatentWatch.com (Available at: https://www.drugpatentwatch.com/pfizer/famvir/famciclovir/)

Sources:

1. FDA - Drug Interaction Checker
2. Gieschke et al. (1999) Journal of Clinical Pharmacology
3. DrugPatentWatch.com



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