Antacids: Antacids may reduce the bioavailability of gabapentin by up to 20%. It is recommended that gabapentin be taken about two hours after antacid administration.
Cimetidine: Gabapentin's mean apparent oral clearance and creatinine clearance decreased by 14% and 10%, respectively, in the presence of cimetidine 300 mg. Thus, cimetidine appeared to alter the renal excretion of both gabapentin and creatinine which is an endogenous marker of renal function.
Hydrocodone: Concomitant use of gabapentin (125-500 mg) decreases hydrocodone Cmax and AUC values in a dose-dependent manner relative to the use of hydrocodone alone; Cmax and AUC values are 3% to 4% lower, respectively, after administration of gabapentin 125 mg and 21-22% lower, respectively, after administration of gabapentin 500 mg. Hydrocodone increases gabapentin AUC values by 14%.
Morphine: Concomitant use of morphine and gabapentin may result in increased plasma concentrations of gabapentin. Patients who experience symptoms of CNS depression such as somnolence may require a decrease in morphine or gabapentin dosage.
Naproxen: Concomitant use of naproxen sodium and gabapentin increases the amount of absorbed gabapentin by 12% to 15%.
Oral contraceptives: Multiple-dose pharmacokinetic profiles (based on AUC and half-life) of norethindrone and ethinyl estradiol after administration of norethindrone acetate 2.5 mg and ethinyl estradiol 50 mcg were similar with and without concomitant use of gabapentin 400 mg.
Probenecid: Gabapentin pharmacokinetic parameters with and without probenecid were comparable. This indicates that gabapentin does not undergo renal tubular secretion by the pathway that is blocked by probenecid.
Anticonvulsants: Pharmacokinetics of gabapentin were unchanged after administration of other anticonvulsants such as valproic acid, carbamazepine, phenobarbital, or phenytoin.