Drug Interactions between Biktarvy and Mudrane GG

GENERALLY AVOID: Coadministration with inducers of P-glycoprotein (P-gp) may decrease the oral bioavailability and plasma concentrations of tenofovir alafenamide (TAF), which is a substrate of the efflux transporter. In 26 healthy study subjects, administration of TAF (25 mg once daily) with the P-gp inducer carbamazepine (300 mg twice daily) decreased TAF plasma concentration (Cmax) and systemic exposure (AUC) by an average of 57% and 55%, respectively, compared to TAF administered alone. It is not known if, and to what extent, tenofovir disoproxil fumarate (TDF), another prodrug of tenofovir, may interact with P-gp inducers. The interaction has not been studied with TDF, and no information is found in the labeling of various products containing TDF, although it has been reported to be a P-gp substrate also.

MANAGEMENT: Given the risk of reduced viral susceptibility and resistance development associated with subtherapeutic antiviral drug levels, concomitant use of tenofovir alafenamide fumarate with P-gp inducers is not recommended. Whether this also applies to tenofovir disoproxil fumarate has not been established.

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GENERALLY AVOID: Coadministration with potent inducers of CYP450 3A4, particularly those that can also induce uridine diphosphate glucuronosyltransferase (UGT) 1A1, may significantly decrease the plasma concentrations of bictegravir. According to the product labeling, bictegravir is a substrate of both CYP450 3A4 and UGT1A1; however, the extent to which each enzymatic pathway contributes to the metabolic clearance of bictegravir has not been reported. In healthy study subjects, administration of a single 75 mg dose of bictegravir during treatment with rifampin 600 mg once daily decreased mean bictegravir peak plasma concentration (Cmax) and systemic exposure (AUC) by 28% and 75%, respectively, compared to administration of bictegravir alone. When bictegravir 75 mg once daily was coadministered with rifabutin 300 mg once daily, mean bictegravir Cmax, AUC and trough plasma concentration (Cmin) decreased by 20%, 38% and 56%, respectively. These results are consistent with the fact that rifampin is a more potent inducer of CYP450 3A4 than rifabutin. Rifampin is also a known inducer of UGT1A1.

MANAGEMENT: Given the risk of reduced viral susceptibility and resistance development associated with subtherapeutic antiretroviral drug levels, concomitant use of bictegravir with potent CYP450 3A4 inducers should generally be avoided.

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MONITOR: Barbiturates may decrease serum levels and therapeutic effects of the methylxanthines. The mechanism is barbiturate induction of CYP450 3A4 and 1A2 hepatic metabolism of methylxanthines.

MANAGEMENT: Close observation for clinical and laboratory evidence of decreased methylxanthine effect is indicated if these drugs must be used together. Patients should be advised to notify their physician if they experience a worsening of their respiratory symptoms.

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Ephedrine-methylxanthine combinations are used for the treatment of asthma but the efficacy of the combination has been questioned. This combination may lead to increased xanthine side effects. The mechanism is unknown, but may be related to synergistic pharmacologic effects. Patients using this combination should be closely monitored for side effects such as nausea, vomiting, tachycardia, nervousness, or insomnia. If side effects are noted, the dosage of the xanthine may need to be decreased.

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