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Morphine: When a 60-mg controlled-release morphine capsule was administered 2 hours prior to a 600-mg Gabapentin capsule, mean Gabapentin AUC increased compared to Gabapentin administered without morphine. This was associated with an increased pain threshold (cold pressor test). The clinical significance of such changes has not been defined. Morphine pharmacokinetic parameter values were not effected by administration of Gabapentin 2 hours after morphine. The observed opioid-mediated side effects associated with morphine plus Gabapentin did not differ significantly from morphine plus placebo. The magnitude of interaction at other doses is not known. (See PRECAUTIONS).
No interaction between Gabapentin and phenobarbital, phenytoin, valproic acid, or carbamazepine.
Coadministration of Gabapentin with oral contraceptives containing norethindrone and/or ethinyl estradiol, does not influence the steady-state pharmacokinetics of either component.
Coadministration of Gabapentin with antacids containing aluminum and magnesium, reduced Gabapentin bioavailability. It is recommended that Gabapentin be taken about two hours following antacid administration.
Renal excretion of Gabapentin is unaltered by probenecid.
A slight decrease in renal excretion of Gabapentin that is observed when it is coadministered with cimetidine is not expected to be of clinical importance.
Alcohol or centrally acting drugs of abuse may exaggerated some Gabapentin central nervous system side effects (e.g. somnolence and ataxia).
Laboratory test: False positive readings were reported with the Ames N-Multistix SG dipstick test when Gabapentin was added to other anticonvulsant drugs. To determine urinary protein, the more specific sulfosalicylic acid precipitation procedure is recommended.
