[Pharmacokinetics and pharmacodynamics of anti-Parkinson drugs in geriatric patients : Key for optimization of treatment].

Levodopa in combination with a decarboxylase inhibitor has an elimination half-life (t1/2) in older people of 1.8 h. The pharmacokinetics are complex and depend on galenics, body weight, sex, gastrointestinal motility and accompanying diseases. Levodopa plasma concentrations after oral dosing vary intraindividually and interindividually. The decarboxylase inhibitors benserazide and carbidopa possess different t1/2. In advanced Parkinson's disease, intrajejunal levodopa or subcutaneous foslevodopa combined with a decarboxylase inhibitor infusion can maintain constant levodopa plasma levels during daytime. To rapidly reach steady state, an adequate morning bolus is required. Absorption and elimination of entacapone and opicapone are similar to levodopa. Entacapone as a reversible catechol O‑methyltransferase (COMT) inhibitor must be administered concomitant to levodopa. Opicapone as irreversible COMT inhibitor is administered once daily at night. Rasagiline and selegiline are irreversible inhibitors of monoamine oxidase B. Therefore, in spite of their short t1/2 they are dosed once daily. Absorption of rasagiline is independent of meals. Clinically established dopamine agonists activate D1/D5 dopamine motor receptors less strongly than the dopaminergic receptors of D2/D3/D4group. This is a probable reason for their numerous adverse effects particularly in older people with Parkinson's disease.