Memantine plasma concentration-time course for the respective treatment regimens A–D (mean±s.e. mean). (•) Regimen A: Acidic urine pH, low urinary flow; (○) Regimen B: Acidic urine pH, high urinary flow; (▪) Regimen C: Alkaline urine pH, low urinary flow; (□) Regimen D: Alkaline urine pH, high urinary flow. 24 h after the intake of memantine, statistically significant differences (*P < 0.05) were detected between regimens with acidic and alkaline urine pH (A vs C, A vs D, B vs C, B vs D).