The bioavailability of levonorgestrel is approximately 95% (range 85 to 100%). The plasma protein binding of levonorgestrel is about 98%. It is bound 50% to albumin and 48% to SHBG. Levonorgestrel is metabolized in the liver, via reduction, hydroxylation, and conjugation (specifically glucuronidation and sulfation). Oxidation occurs primarily at the C2α and C16β positions, while reduction occurs in the A ring. 5α-Dihydrolevonorgestrel is produced as an active metabolite of levonorgestrel by 5α-reductase. The elimination half-life of levonorgestrel is 24 to 32 hours, although values as short as 8 hours and as great as 45 hours have been reported. About 20 to 67% of a single oral dose of levonorgestrel is eliminated in urine and 21 to 34% in feces.