Avonza Drug Interactions

Interactions relevant to lamivudine: Co-administration with trimethoprim/sulfamethoxazole results in a 40% increase in lamivudine area under the concentration curve. No dose adjustment of Tenofovir Disoproxil Fumarate/Lamivudine/Efavirenz 300 mg/300 mg/400 mg Tablets is necessary. Lamivudine has no effect on the pharmacokinetics of trimethoprim or sulfamethoxazole.
Interactions relevant to tenofovir: Didanosine: Co-administration of tenofovir disoproxil fumarate and didanosine is not recommended (see Precautions and the table as follows).
Renally eliminated medicinal products: Since tenofovir is primarily eliminated by the kidneys, co-administration of tenofovir disoproxil fumarate with medicinal products that reduce renal function or compete for active tubular secretion via transport proteins hOAT 1, hOAT 3 or MRP 4 (e.g. cidofovir) may increase serum concentrations of tenofovir and/or the co-administered medicinal products.
Tenofovir disoproxil fumarate should be avoided with concurrent use of a nephrotoxic medicinal product, such as aminoglycosides, amphotericin B, foscarnet, ganciclovir, pentamidine, vancomycin, cidofovir or interleukin-2 (see Precautions).
Given that tacrolimus can affect renal function, close monitoring is recommended when it is co-administered with tenofovir disoproxil fumarate.
Interactions relevant to efavirenz: Efavirenz is eliminated through hepatic metabolism, mainly catalyzed by the genetically polymorphic cytochrome (CYP) 450 isoform CYP2B6, but also by CYP3A. Therefore, agents that alter the activity of CYP2B6 or CYP3A may alter the plasma concentration of efavirenz.
Efavirenz is a clinically important inducer of cytochrome P450 enzymes, such as CYP3A4; therefore interactions with medicinal products metabolized by this pathway may occur. In vitro, efavirenz is also an inhibitor of UDP-glucuronosyl transferases, CYP3A4, CYP2C9 and CYP2C19. In the great majority of cases where efavirenz interacts in vivo with known CYP3A substrates, the net result after multiple doses is a decreased systemic exposure of the drug interacting with efavirenz. Though efavirenz might act in vivo as a net inhibitor of CYP3A4 after the first doses, it has not been demonstrated that this happens once CYP3A4 induction has set in.
Efavirenz should not be administered concurrently with terfenadine, astemizole, cisapride pimozide, bepridil or ergot derivatives, since this may result in altered plasma concentrations of these drugs. (See table.)

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