For many years, it has been considered dogma that drug biotransformation capability is limited at best in the fetus and newborn but increases over the first year of life to levels in toddlers and young children that generally exceed adult capacity. There are several situations where examination of clinical PK data has revealed discernable patterns of drug clearance that can be attributed to developmental differences in drug biotransformation. It has become apparent that there are developmental differences in expression among drug metabolizing enzyme families (cytochromes P450 or "CYPs", etc.) Furthermore, individual drug metabolizing enzymes with in a family may have unique developmental profiles that influence the therapeutic response, desired or undesired, to a given agent.

The specific aim of this proposal is to extend the current longitudinal investigation into the preschool age group (1 to 5 years of age). The developmental profile of CYPs, 1A2, 2D6, and 3A4 will be determined by caffeine and dextromethorphan phenotyping procedures.

Accepts Healthy Volunteers

Inclusion Criteria:

• Healthy children 12 months of age at enrollment

Exclusion Criteria:

• Height and weight ratio outside of the 5th to 100th percentile for adjusted age
• Historical and/or biochemical evidence of hepatic, renal, or hematopoetic dysfunction
• Historical or physical evidence of a neurologic disease/condition (excluding simple, febrile seizures)
• Historical or physical evidence of any disorder associated with swallowing and/or gastrointestinal function
• Concomitant therapy with drugs or other products known to alter the activity of hepatic or intestinal microsomal enzymes(e.g., inducers or inhibitors of CYPs 1A2, 2D6, and/or 3A4), P-glycoprotein or potential competing substrates for the CYPs, under study within 7 days of a scheduled phenotyping evaluation
• Evidence of behavioral, developmental, or psychosocial conditions in the subjects and/or parents/caregivers that, in the opinion of the investigator, would have the potential to adversely impact the level of compliance required for successful study completion
• Evidence of geographic instability (i.e., moving of primary residence within last 24 months) that would adversely influence compliance with repeated study visits necessary for completion of the protocol
• Lack of telephone access required to insure adequate subject contact/follow-up
• Inability to obtain written informed consent from the subject''''s parents/guardians