This study has been designed to confirm, in healthy subjects, the lack of a clinically important pharmacokinetic interaction between Dimebon, at the proposed maximum commercial dose of 20 mg TID (administered every 8 hours), and digoxin (Lanoxin®) 0.125 mg QD, a sensitive P-gp substrate recommended by FDA.

Inclusion Criteria:

• Healthy male and/or female subjects between the ages of 18 and 55 years, inclusive (Healthy is defined as no clinically relevant abnormalities identified by a detailed medical history, full physical examination, including blood pressure and pulse rate measurement, 12-lead ECG and clinical laboratory tests).
• Body Mass Index (BMI) of 17.5 to 30.5 kg/m2; and a total body weight >50 kg (110 lbs).

Exclusion Criteria:

• A known history of hypersensitivity or previous intolerance to Dimebon or digoxin.
• 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) disease or clinical findings at screening.
• Pregnant or nursing women; women of childbearing potential (WOCBP) who are unwilling or unable to use an acceptable method of contraception as outlined in the protocol from at least 14 days prior to the first dose of study medication.