This study will evaluate four different modified release formulation to estimate the amount of dimebon available to the body relative to the current dimebon formulation that is given three times a day. The results of this study will help inform and guide further formulation development efforts with the ultimate goal of reducing dose frequency to once-a-day or twice-a-day.

Inclusion Criteria:

• Healthy male and/or female subjects between the ages of 18 and 55 years, inclusive.

Body Mass Index (BMI) of 17.5 to 30.5 kg/m2; and a total body weight >50 kg (110 lbs).

Exclusion Criteria:

• Evidence or history of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurologic, or allergic disease (including drug allergies, but excluding untreated, asymptomatic, seasonal allergies at time of dosing).
• Subjects with any history of a previous seizure (including childhood febrile seizures) or convulsion or significant head trauma.
• Subjects with hypersensitivity reactions to dimebon or other antihistamines.
• Any condition possibly affecting drug absorption (eg, gastrectomy).
• Smokers who use greater than 5 cigarettes per day.
• Use of proton pump inhibitors, antacids, and H2-blockers are prohibited for the duration of the study.
• Pregnant or nursing females; females of childbearing potential who are unwilling or unable to use an acceptable method of non-hormonal contraception.