Entacapone (EN) improves the efficacy of levodopa/dopadecarboxylase inhibitor (LD/DDI) formulations by inhibition of the enzyme catechol-O-methyltransferase (COMT). COMT inhibition also promotes the synthesis of basic LD metabolites, whereas DDI support the composition of acidic LD derivatives. LD metabolism correlates to the one of (13)C-sodium-octanoate, which is employed in breath tests to measure gastric emptying velocity. Objectives were to investigate the impact of COMT inhibition on the recovery rate of (13)C-sodium-octanoate in parkinsonian patients, who received first 100 mg LD/Carbidopa (CD) and the next day 100 mg LD/CD/EN combined with (13)C-sodium-octanoate in each case. The recovery rate of (13)C-sodium-octanoate was significant higher during the LD/CD/EN-compared with the LD/CD condition. COMT inhibition combined with LD/DDI improves absorption of a co-administered salt probably due to a COMT inhibition induced basic environment in gastrointestinal membranes. This improves dissolution and absorption of acids and salts. Thus it may enhance absorption of LD itself.
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