Combivir Drug Interactions

Combivir contains lamivudine and zidovudine, therefore any interactions identified for these individually are relevant to Combivir. Clinical studies have shown that there are no clinically significant interactions between lamivudine and zidovudine.
Zidovudine is primarily metabolised by UGT enzymes; co-administration of inducers or inhibitors of UGT enzymes could alter zidovudine exposure. Lamivudine is cleared renally. Active renal secretion of lamivudine in the urine is mediated through organic cation transporters (OCTs); co-administration of lamivudine with OCT inhibitors or nephrotoxic drugs may increase lamivudine exposure.
Lamivudine and zidovudine are not significantly metabolised by cytochrome P₄₅₀ enzymes (such as CYP 3A4, CYP 2C9 or CYP 2D6) nor do they inhibit or induce this enzyme system. Therefore, there is little potential for interactions with antiretroviral protease inhibitors, non-nucleosides and other medicinal products metabolised by major P₄₅₀ enzymes.
Interaction studies have only been performed in adults. The list as follows should not be considered exhaustive but is representative of the classes studied. (See table.)

Click on icon to see table/diagram/image


Click on icon to see table/diagram/image

Exacerbation of anaemia due to ribavirin has been reported when zidovudine is part of the regimen used to treat HIV although the exact mechanism remains to be elucidated. The concomitant use of ribavirin with zidovudine is not recommended due to an increased risk of anaemia (see Precautions).
Consideration should be given to replacing zidovudine in a combination ART regimen if this is already established. This would be particularly important in patients with a known history of zidovudine induced anaemia.
Concomitant treatment, especially acute therapy, with potentially nephrotoxic or myelosuppressive medicinal products (e.g. systemic pentamidine, dapsone, pyrimethamine, co-trimoxazole, amphotericin, flucytosine, ganciclovir, interferon, vincristine, vinblastine and doxorubicin) may also increase the risk of adverse reactions to zidovudine. If concomitant therapy with Combivir and any of these medicinal products is necessary then extra care should be taken in monitoring renal function and haematological parameters and, if required, the dosage of one or more agents should be reduced. Limited data from clinical trials do not indicate a significantly increased risk of adverse reactions to zidovudine with co-trimoxazole (see interaction information relating to lamivudine and co-trimoxazole as previously mentioned), aerosolised pentamidine, pyrimethamine and acyclovir at doses used in prophylaxis.