Although 3TC (lamivudine, Epivir) causes an increase in AZT (zidovudine, Retrovir) levels, no dose adjustment is necessary when these two drugs are taken together. Nevirapine (Viramune) also causes a slight increase in 3TC levels, but no dose adjustment is required.

Drugs that are eliminated in the same way as 3TC may interact with 3TC. These drugs include trimethoprim (Monotrim), an antibiotic which is included in co-trimoxazole (Septrin). Consequently, levels of 3TC may be increased by 40% when it is taken together with co-trimoxazole tablets for Pneumocystis pneumonia (PCP) prophylaxis or toxoplasmosis treatment, although no dose adjustments are necessary.

3TC should not be taken with intravenous foscarnet (Foscavir) or ganciclovir (Cymevene).

There is a risk that taking 3TC alongside hepatitis C treatment including interferon alfa or ribavirin can put patients at risk of side-effects including liver problems. Patients should be monitored regularly, to look out for these problems.