Aim:To investigate the influence of omeprazole on the pharmacokinetics ofdomperidone given as free base and maleate salt.Methods:An open,randomized,2-period crossover study with a washout period of 7 d was conducted in 10healthy Chinese,male patients.In each study period,the patients were adminis-tered a single oral dose of 10 mg domperidone as free base or maleate salt on d 1,20 mg omeprazole twice daily on d 2 and 3,and once on d 4.A single dose of 10 mgdomperidone as free base or maleate salt was taken at 4 h after administration ofomeprazole on d 4.Plasma samples were collected on d 1 and 4 after the adminis-tration of domperidone,and the plasma concentrations of domperidone were de-termined by a sensitive liquid chromatography-tandem mass spectrometry method.Results:For free-base domperidone,pretreatment with omeprazole resulted in a16% decrease in maximum concentration(C_(max)),compared with administrationalone(P<0.05).However,for maleate salt,with the exception of an increase in t_(1/2),no pharmacokinetic parameters were significantly changed.When the free baseand maleate salt were administered alone,no differences were found in any param-eters between the 2 formulations.In contrast,when they were administered in thepresence of omeprazole,the C_(max)of domperidone given as free base was lower(25.9%)than that given as maleate salt(P<0.05).Conclusion:Pretreatment ofomeprazole does not affect the absorption of domperidone maleate,but leads to amoderately decreased rate of absorption of the free base. Aim: To investigate the influence of omeprazole on the pharmacokinetics ofdomperidone given as free base and maleate salt. Methods: An open, randomized, 2-period crossover study with a washout period of 7 d was conducted in 10 heathy Chinese, male patients. study period, the patients were adminis-tered a single oral dose of 10 mg domperidone as free base or maleate salt on d 1, 20 mg omeprazole twice daily on d 2 and 3, and once on d 4. A single dose of 10 mgdomperidone as free base or maleate salt was taken at 4 h after administration ofomeprazole on d 4. Plasma samples were collected on d 1 and 4 after the adminis- tration of domperidone, and the plasma concentrations of domperidone were de-termined by a sensitive liquid chromatography -tandem mass spectrometry method. Results: For free-base domperidone, pretreatment with omeprazole resulted in a 16% decrease in maximum concentration (C max), compared with administrationalone (P <0.05) of an increase in t_ (1/2), no pharmacokinetic parameters were significantly changed.When the free baseand maleate salt were administered alone, no differences were found in any param-eters between the two formulations.In contrast, when they were administered in the presence of omeprazole, The C max (max) of domperidone given as free base was lower (25.9%) than that given as maleate salt (P <0.05) .Conclusion: Pretreatment ofomeprazole does not affect the absorption of domperidone maleate, but leads to amoderately decreased rate of absorption of the free base.