The purpose of this study is to determine the efficacy, safety, and population pharmacokinetics and determinants of drug responses to buspirone in children with autism using a randomized, double blind, cross over study in children ages 2 to 6 years.

Autism is a neurodevelopmental disorder defined as qualitative impairment in social interaction and communication and restrictive stereotype patterns of behavior, interests and activities. Pharmacological agents are being increasingly used off label in very young autistic children, and there is virtually no data regarding the pharmacokinetics, safety or efficacy of these agents in young children.

The approach in this study differs from pharmacotherapy studies of autism carried out thus far in several ways:

• the rationale underlying our approach is based upon an attempt to alter synaptic plasticity during postnatal development, focusing on very young children
• are integrating our drug trial with a PG study evaluating whether buspirone response is related to expression of genes involved in serotoninergic neurotransmission
• will assess these variables together with in vivo assessment of serotonin synthesis capacity with PET.

This is a prospective, randomized, double blind, crossover study where children will be stratified by age into two groups. Treatment will last for 12 weeks with dosing twice a day. Parent ratings, cognitive tests and blood sampling will occur throughout the study period.

Inclusion Criteria:

• Meet study definition for the diagnosis of autistic disorder
• Age 2 to 6 (male or female)
• Informed Consent

Exclusion Criteria:

• Clinical or lab evidence of renal or hepatic disease
• Treatment with any medication known to alter the activity of the CYP3A4 enzyme including ketoconazole, itraconazole, grapefruit juice, erythromycin, clarithromycin, cimetidine, verapamil, diltiazem, rifampin, phenytoin, phenobarbital, or carbamazepine within the previous 3 months
• Use of centrally acting drugs during the 6 weeks prior or during the study
• Presence or history of neurological disorders, including seizure disorders