Appendix A: Selected Significant Drug Interactions with Rifamycins
| Type of drug | Comments |
|---|---|
| Anticonvulsants | Therapeutic drug monitoring recommended; may require anticonvulsant dose increase. Phenytoin: monitor serum phenytoin concentrations and seizure activity; increase dosage if needed. |
| Antipsychotics | Monitor clinical response; may need to increase haloperidol dose. |
| Antiretrovirals | APV, IDV, LPV/RTV, and NFV should not be used with R. EFV requires a dose increase to 800 mg/day when used with R. |
| Atovaquone | R reduces atovaquone levels by 50%; RFB probably has a similar effect. Consider alternative treatments for PCP. |
| Azole antifungal agents | Itraconazole, ketoconazole, and voriconazole concentrations may be subtherapeutic with any of the rifamycins and should be avoided if possible. Fluconazole has less reduction in serum concentrations vs. other azoles; monitor clinical response and increase fluconazole dose as needed. |
| Benzodiazepines | Monitor clinical response; may need to increase diazepam dose. |
| β-Adrenergic blocking agents | Monitor clinical response; increased propanolol hydrochloride or metoprolol dose may be needed. |
| Chloramphenicol | Monitor serum chloramphenical concentrations; increased chloramphenical dose may be needed; consider an alternative antibiotic. |
| Clarithromycin | RFB level increases by 56% and clarithromycin level decreases by 50%. Avoid R. Monitor signs and symptoms of infection; more study needed. |
| Corticosteroids | Monitor clinical response; may require two- to three-fold increase in corticosteroid dose. |
| Dapsone | Monitor clinical response, including potential hematologic toxic effects; increased dapsone dose may be necessary; additional study needed when used for PCP prophylaxis. |
| Digitoxin | Monitor arrhythmia control, signs and symptoms of heart failure, and serum digitoxin concentrations. |
| Digoxin (oral) | Monitor arrhythmia control, signs and symptoms of heart failure, and serum digoxin concentrations. |
| Doxycycline | Monitor clinical response; increase doxycycline dose if needed; consider an alternative antibiotic. |
| Hypoglycemics | Monitor blood glucose; may require hypoglycemic drug dose increase or change to an alternate hypoglycemic drug. |
| Hypolipidemics | For simvastatin and fluvastatin, monitor hypolipidemic effect; may require use of an alternate hypolipidemic drug. Concurrent use of atorvastatin or pravastatin with rifamycins appears safe. |
| Levothyroxine sodium | Monitor thyrotropin level; increased dose of levothyroxine sodium likely needed (based on case reports). |
| Mefloquine | Consider an alternative malaria prophylaxis/treatment. |
| Methadone hydrochloride | Increase methadone dose with concomitant R therapy; monitor and control withdrawal symptoms. |
| Metronidazole | Monitor for decreased clinical response; increase metronidazole dose if needed; use another agent if possible. |
| Oral anticoagulants | Monitor international normalized ratio; increased anticoagulant dose will likely be needed. |
| Oral contraceptives | Use alternative form(s) of birth control, as rifamycins decrease levels of oral contraceptives. |
| Theophylline | Monitor serum theophylline concentrations; increase theophylline dose if needed. |
| TMP/SMX | Increased levels of TMP/SMX but not considered clinically significant. Can use standard doses safely. |
| Tricyclic antidepressants | Therapeutic drug monitoring recommended; may require dose increase or change to alternative agent. |
Sources: American Thoracic Society, Centers for Disease Control and Prevention, Infectious Diseases Society of America. Treatment of tuberculosis. Am J Respir Crit Care Med 2003;167:603–62.Bartlett JG, Gallant JE. Medical management of HIV infection. Baltimore, MD: Johns Hopkins University, 2005. Finch CK, Chrisman CR, Baciewicz AM, Self TH. Rifampin and rifabutin drug interactions: an update. Arch Intern Med 2002;162:985–92. Gilbert DN, Moellering RC, Eliopoulos GM, Sande MA. The Sanford guide to antimicrobial therapy 2006. 36th ed. Sperryville, VA: Antimicrobial Therapy, Inc., 2006.
This is a partial list of significant drug interactions and the reader is advised to check the drug insert information before prescribing any medications in conjunction with rifamycins.
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