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Antacids: The absorption of gabapentin from the gastrointestinal tract is reduced by antacids containing aluminium with magnesium. It is recommended that gabapentin is taken at least 2 hours after any such antacid.
Morphine: Patients receiving both drugs should be monitored for signs of CNS depression and doses should be reduced accordingly as morphine is reported to reduce the clearance of gabapentin.
Cimetidine: Cimetidine has also been reported to reduce the renal clearance of gabapentin. The decrease in gabapentin excretion is not expected to be of clinical importance.
Hydrocodone: Coadministration increases gabapentin AUC values by 14%. Coadministration decreases hydrocodone Cmax and AUC values in a dose dependent manner Cmax and AUC values were 3% and 4% lower, respectively after administration of 125 mg gabapentin and 27% to 22% lower, respectively after administration of 500 mg gabapentin.
The mechanism for this interaction and the magnitude of interaction at other doses is unknown.
Contraceptive, oral: The Cmax of norethindrone was 13% higher when coadministered with gabapentin; this interaction is not expected to be of clinical importance.
Naproxen: Coadministration (n=18) of naproxen sodium capsules (250 mg) with gabapentin (125 mg) appears to increase the amount of gabapentin absorbed by 12% to 15%. Gabapentin had no effect on naproxen pharmacokinetic parameters. These doses are lower than the therapeutic doses for both drugs. The magnitude of interaction within the recommended dose ranges of either drug is not known.
Other antiepileptic drugs: Gabapentin is not appreciably metabolized nor does it interfere with the metabolism of commonly coadministered antiepileptic drugs.
Lab test interactions: Because false positive readings were reported with the Ames N-Multistix SG dipstick test for urinary protein when gabapentin was added to other antiepileptic drugs, the more specific sulfosalicylic acid precipitation procedure is recommended to determine the presence of urine protein.
