Adverse Reactions: The most common adverse events that occurred in patients receiving emtricitabine with other antiretroviral agents in clinical trials were headache, diarrhea, nausea, and rash, which were generally of mild to moderate severity. Approximately 1% of patients discontinued participation in the clinical studies due to these events. 

Clinical Pharmacology:Mechanism of Action- Emtricitabine, a synthetic nucleoside analog of cytosine, is phosphorylated by cellular enzymes to form emtricitabine 5´-triphosphate.

Absorption- The drug is rapidly and extensively absorbed following oral administration with peak plasma concentrations occurring at 1-2 hours post-dose. The mean absolute bioavailability of emtricitabine was 93%. The multiple dose pharmacokinetics of emtricitabine are dose proportional over a dose range of 25-200 mg.

Effects of Food on Oral Absorption: Emtricitabine may be taken with or without food.

Distribution- In vitro binding of emtricitabine to human plasma proteins was <4% and independent of concentration over the range of 0.02-200 micrograms per ml. At peak plasma concentration, the mean plasma to blood drug concentration ratio was ~1.0 and the mean semen to plasma drug concentration ratio was ~4.0. 

Metabolism- In vitro studies indicate that emtricitabine is not an inhibitor of human CYP450 enzymes. Following administration of 14C-emtricitabine, complete recovery of the dose was achieved in urine (~86%) and feces (~14%). 

Elimination- The plasma emtricitabine half-life is approximately 10 hours. The renal clearance of emtricitabine is greater than the estimated creatinine clearance, suggesting elimination by both glomerular filtration and active tubular secretion. There may be competition for elimination with other compounds that are also renally eliminated.