Significant interactions may occur between TB medications and other medications (see Chapter 10: Treatment of Active Tuberculosis in Special Populations for information on common drug-drug interactions in TB treatment). The most important TB drug for interactions with other medications is RMP. Most drug interactions can be managed by adjusting the dose of the concomitant medication, based on serum drug concentrations (eg, phenytoin), or by monitoring clinical effect (eg, INR for warfarin) or by substituting drugs (eg, anti-retroviral regimens). It is important to monitor these interactions early in therapy (ie, within 1-to-2 weeks of starting RMP). In some patients, the drug interactions are not manageable and could result in serious adverse consequences (eg, RMP in transplant recipients). It is also important to note that drug-drug interactions will cease within about 2 weeks after RMP is stopped, leading to potential adverse consequences if dosing of other medications is not reassessed (eg, increased clinical effect of methadone or warfarin after withdrawal of RMP).
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