1. Pharmacokinetics: tolcapone

Tolcapone differs from entacapone in that the former penetrates the blood-brain barrier and inhibits COMT in the CNS. However, the inhibition of COMT in the periphery appears to be the primary therapeutic action. Tolcapone has a relatively long duration of action (probably due to its affinity for the enzyme) compared to entacapone, which requires more frequent dosing. Both drugs are extensively metabolized and eliminated in feces and urine. Dosage may need to be adjusted in patients with moderate or severe cirrhosis.