Efficacy and Safety of Memantine for Parkinson's Disease Dementia (PDD) and Dementia With Lewy Bodies (DLB)

Inclusion Criteria: * a diagnosis of Parkinson's disease (Larsen and Dupont, 1994) and dementia (DSM IV(1987; 1994), or Dementia with Lewy bodies (McKeith et al. Neurology 2005) * mild-to-moderate or moderate dementia (i.e. MMSE 12-26, inclusive) * the subject has given a written informed consent * the subject is able and willing to comply with the study procedures and has a reliable caregiver (i.e. relative or nurse/nurse assistant who sees the patient at least weekly) Exclusion Criteria: * other brain disease of sufficient severity to cause dementia * mental retardation * terminal illness with life expectancy shorter than 6 months * recent major changes in health status * known epilepsy or previous convulsive seizure * major depression * severe dementia as defined by a Mini-mental State Examination score of 12 or lower * moderate to severe renal impairment (i.e. serum creatinine \> 1,5 upper limit normal (ULN) or creatinin clearance \< 40ml/minute/1,73 m2 * moderate or severe heart disease (NYHA III-IV) * moderate or severe pulmonal disease * moderate to severe hepatic impairment (bilirubin or transaminases \> 2 times ULN * women of childbearing potential (i.e. not post-menopausal and not taking contraceptive * the subjects is lactating * any laboratory value(s) exceeding the limits of normality if deemed to be clinically relevant by the study physician * known allergies to the investigational product