Disclosed herein is an oral dosage formulation suitable for treating a neurodegenerative disorder. The oral dosage formulation contains both sustained-release and immediate-release drugs. The sustained-release drug in the oral dosage formulation is memantine, and the immediate-release drug in the oral dosage formulation is donepezil and/or memantine, and the formulation is characterized in having a pH-independent dissolution profile of memantine at a pH range from about 1.0 to about 7.0.
