Zeffix Drug Interactions

Interaction studies have only been performed in adults.
The likelihood of metabolic interactions is low due to limited metabolism and plasma protein binding and almost complete renal elimination of unchanged substance.
Lamivudine is predominantly eliminated by active organic cationic secretion. The possibility of interactions with other medicinal products administered concurrently should be considered, particularly when their main route of elimination is active renal secretion via the organic cationic transport system e.g. trimethoprim. Other medicinal products (e.g. ranitidine, cimetidine) are eliminated only in part by this mechanism and were shown not to interact with lamivudine.
Substances shown to be predominately excreted either via the active organic anionic pathway, or by glomerular filtration are unlikely to yield clinically significant interactions with lamivudine.
Administration of trimethoprim/sulphamethoxazole 160 mg/800 mg increased lamivudine exposure by about 40%. Lamivudine had no effect on the pharmacokinetics of trimethoprim or sulphamethoxazole. However, unless the patient has renal impairment, no dosage adjustment of lamivudine is necessary.
A modest increase in C_max (28%) was observed for zidovudine when administered with lamivudine, however overall exposure (AUC) was not significantly altered. Zidovudine had no effect on the pharmacokinetics of lamivudine (see Pharmacology: Pharmacokinetics under Actions).
Lamivudine has no pharmacokinetic interaction with alpha-interferon when the two medicinal products are concurrently administered. There were no observed clinically significant adverse interactions in patients taking lamivudine concurrently with commonly used immunosuppressant medicinal products (e.g. cyclosporin A). However, formal interaction studies have not been performed.
Emtricitabine: Due to similarities, Zeffix should not be administered concomitantly with other cytidine analogues, such as emtricitabine. Moreover, Zeffix should not be taken with any other medicinal products containing lamivudine (see Precautions).
Cladribine: In vitro lamivudine inhibits the intracellular phosphorylation of cladribine leading to a potential risk of cladribine loss of efficacy in case of combination in the clinical setting. Some clinical findings also support a possible interaction between lamivudine and cladribine. Therefore, the concomitant use of lamivudine with cladribine is not recommended (see Precautions).