Autism is a disorder that appears during the first three years of a child's life. Children with autism hear, feel and sense themselves, others and their environment in a way that scientists are seeking more ways to understand.

The main purpose of this study is to understand how the study drug, memantine, is absorbed and eliminated in children and adolescents with autistic spectrum disorders. This study will also look for any side effects that happen as the drug is processed through the body.

Memantine is approved for the treatment of moderate to severe Alzheimer's disease. The use of memantine in this study is considered experimental. While there will be no direct benefit to participants, investigators hope the study will contribute to the understanding of the effects of memantine in the treatment of autism in the future.