Investigators hypothesize that gabapentin will reduce opioid analgesic requirements and pain scores up to 36 hours post adenotonsillectomy without increased adverse effects such as emergence delirium, respiratory complications or bleeding. The clinical effect may depend on the individual's pharmacogenetic profile to look for a specific set of genetic polymorphisms that relate to the metabolism and effect of the study drug, gabapentin, and opioid analgesic pain medications.