The purpose of this study is to determine the safety and effectiveness of memantine, an experimental drug, in improving AIDS dementia complex (ADC). The symptoms of ADC can be improved with zidovudine (ZDV). However, ZDV therapy has been associated with significant toxicities, and the effectiveness of ZDV seems to decrease during the second and third years of therapy. The effectiveness of other antiretroviral drugs as treatment for ADC is not known, so it is important to explore alternative therapies.

The signs and symptoms of the AIDS Dementia Complex can be alleviated by zidovudine (ZDV). However, ZDV therapy has been associated with significant toxicities, particularly bone marrow suppression. The efficacy of ZDV appears to decrease during the second and third years of therapy. It is not known whether this reflects cumulative toxicity. In addition, the efficacy of other antiretroviral agents remains uncertain. Hence, adjunctive therapy for cognitive and motor symptoms of AIDS is important. Patients will be randomized to one of the following 2 arms: Arm 1 receives memantine plus concurrent antiretroviral therapy; Arm 2 receives placebo plus concurrent antiretroviral therapy. The initial dose of memantine is increased each week for the next 3 weeks, unless a maximum tolerated dose is reached. Following a 16-week evaluation period there is a 4-week washout prior to re-assessment. After the washout period, all patients, including those formerly randomized to the placebo arm, are given the opportunity to receive an open-label, 12-week administration of memantine. \[AS PER AMENDMENT 4/6/99: The open-label phase is extended by 48 weeks to a total of 60 weeks of therapy. Patients who did not receive the initial 12 weeks of open-label treatment are eligible still for the 48-week open-label treatment phase.\]