<qa>  What is the dose range of memantine?This is a randomized, placebo-controlled, parallel, double-blind 24-week prospective study of memantine at the dosage range 5-20 mgday in 20 outpatients with idiopathic PD and dementia secondary to PD. Using the dosage escalation regimen approved for Alzheimer disease, subjects will start memantine or comparable placebo at 5 mg daily and advance 5 mgweek to 20 mg day by week 4, with dosing at 10 mg bid. Subjects will undergo 7 clinical visits over the 6-month trial Screen, BaselineWeek 0, and Weeks 4, 8, 14, 20, and 24. The dosage can be titrated downward in increments of 5 mg to a minimum dose of 5 mgday in the event memantine is not tolerated at the scheduled dosages. This broad dose range is being used because 1a favorable cognitive response may be evident at lower doses of memantine than recommended for AD and 2adverse effects could emerge when typical AD dosing recommendations are used, as has been observed when treating PD patients with cholinesterase inhibitors. Subjects will remain on a stable dose of memantineplacebo after Week 8, unless precluded by adverse events. Ten subjects will be assigned to each treatment group. Randomization will be stratified according to whether subjects are taking a concomitant cholinesterase inhibitor. This will enable secondary group comparisons of treatment groups. Results from this initial small study will be used to evaluate the appropriateness of devising a larger-scale multi-site study of memantine for treatment of dementia in PD. 