Pharmacokinetics[edit]
Typical dose of tolcapone is 100 or 200 mg, orally administered three times daily.[10] The half life of tolcapone is 2–3 hours, volume of distribution (Vd) being 0.3 L/kg (21 L in average 70 kg person) and bioavailability about 60%.[11]
Tolcapone has the ability to cross the blood–brain barrier and thus exerts its COMT inhibitory effects in the central nervous system (CNS) as well as in the periphery.
99% of tolcapone is in monoanionic form when in body because the physiological pH is 7.4. Tolcapone penetrates the blood-brain barrier better than two other nitrocatechols such as nitecapone and entacapone because it has higher lipophilicity due to its R substituent.[vague] Partition coefficients quantify the ability of the molecule to cross the blood-brain barrier. LogPIdce= 0.2, -1.4, -0.4 for tolcapone, nitecapone and entacopone respectively. Partition coefficients in this case were measured in 1,2-dichloroethane / H2O solution which caused molecules to be in ionized form. There is no current explanation for how these charged molecules permeate the blood-brain barrier.