Pharmacokinetics and Bioequivalence of Memantine Tablet and a New Dry Syrup Formulation in Healthy Japanese Males: Two Single-Dose Crossover Studies

INTRODUCTION: Memantine hydrochloride, an N-methyl-D-aspartate receptor antagonist, is used to treat Alzheimer’s disease (AD). A new dry syrup formulation containing memantine hydrochloride has been developed to improve medication adherence in AD patients and to reduce family and caregiver burden. This study was conducted to assess the bioequivalence of this new formulation to the tablet. METHODS: Two single-dose, randomized, open-label, two-period, two-group, crossover studies were conducted to assess the bioequivalence of a test product [dry syrup, 2%, 1 g (containing 20 mg of memantine hydrochloride)] to a reference product (film-coated tablet) under two dosing conditions: administration of the test product as a suspension in water (Study I) and as granules taken with water (Study II). Blood samples were collected at specified time intervals, and memantine plasma concentrations were determined using a validated liquid chromatography tandem mass spectrometry method. The pharmacokinetic parameters of memantine were calculated using non-compartmental analysis. The maximum concentration (C(max)) and area under the concentration–time curve up to the last sampling time (AUC(all)) were used to assess the bioequivalence of the two formulations. RESULTS: The geometric least square mean (GLSM) ratios [90% confidence interval (CI)] of the C(max) and AUC(all) of memantine for the test product to the reference product were 0.981 (0.943–1.020) and 0.978 (0.955–1.001) in Study I, and 0.973 (0.944–1.003) and 1.004 (0.983–1.025) in Study II, respectively. In both studies, the 90% CI values of the GLSM ratios of C(max) and AUC(all) were within the prespecified bioequivalence range (0.80–1.25). The safety of the test product under both dosing conditions and that of the reference product were not different. CONCLUSIONS: The new dry syrup formulation containing memantine hydrochloride showed bioequivalence to the film-coated tablet under the two dosing conditions. Thus, the new dry syrup is suitable under either dosing condition for patients with AD. FUNDING: Daiichi Sankyo Co., Ltd.