ingle-dose data. Tramadol is a mild inducer of selected drug metabolism pathways measured in animals.
Use with Carbamazepine
Patients taking carbamazepine may have a significantly reduced analgesic effect of tramadol hydrochloride. Because carbamazepine increases tramadol metabolism and because of the seizure risk associated with tramadol, concomitant administration of tramadol hydrochloride and carbamazepine is not recommended.
Use with Quinidine
Tramadol is metabolized to M1 by the CYP2D6. Quinidine is a selective inhibitor of that isoenzyme, so that concomitant administration of quinidine and tramadol hydrochloride results in increased concentrations of tramadol and reduced concentrations of M1. The clinical consequences of these findings are unknown. In vitro drug interaction studies in human liver microsomes indicate that tramadol has no effect on quinidine metabolism.
Use with Inhibitors of CYP2D6
In vitro drug interaction studies in human liver microsomes indicate that concomitant administration with inhibitors of CYP2D6 such as fluoxetine, paroxetine, and amitriptyline could result in some inhibition of the metabolism of tramadol.
Use with Cimetidine
Concomitant administration of tramadol hydrochloride with cimetidine does not result in clinically significant changes in tramadol pharmacokinetics. Therefore, no alteration of the tramadol hydrochloride dosage regimen is recommended.
Use with MAO Inhibitors
Interactions with MAO inhibitors, due to interference with detoxification mechanisms, have been reported for some centrally acting drugs (seeWARNINGS, USE WITH MAO INHIBITORS).
Use with Digoxin and Warfarin
Post-marketing surveillance has revealed rare reports of digoxin toxicity and alteration of warfarin effect, including elevation of pro-thrombin times.
Carcinogenesis, Mutagenesis, Impairment of Fertility
A slight, but statistically significant, increase in two common murine tumors, pulmonary and hepatic, was observed in a mouse carcinogenicity study, particularly in aged mice. Mice were dosed orally up to 30 mg/kg (90 mg/m2 or 0.36 times the maximum daily human dosage of 246 mg/m2) for approximately two years, although the study was not done with the Maximum Tolerated Dose. This finding is not believed to suggest risk in humans. No such finding occurred in a rat carcinogenicity study (dosing orally up to 30 mg/kg, 180 mg/m2, or 0.73 times the maximum daily human dosage).
Tramadol was not mutagenic in the following assays: Ames Salmonella microsomal activation test, CHO/HPRT mammalian cell assay, mouse lymphoma assay (in the absence of metabolic activation), dominant lethal mutation tests in mice, chromosome aberration test in Chinese hamsters, and bone marrow micronucleus tests in mice and Chinese hamsters. Weakly mutagenic results occurred in the presence of metabolic activation in the mouse lymphoma assay and micronucleus test in rats. Overall, the weight of evidence from these tests indicates that tramadol does not pose a genotoxic risk to humans.
No effects on fertility were observed for tramadol at oral dose levels up to 50 mg/kg (300 mg/m2) in male rats and 75 mg/kg (450 mg/m2) in female rats. These dosages are 1.2 and 1.8 times the maximum daily human dosage of 246 mg/m2, respectively.
Pregnancy
Teratogenic Effects
Pregnancy Category C
Tramadol has been shown to be embryotoxic and fetotoxic in mice, (120 mg/kg or 360 mg/m2), rats (≥25 mg/kg or 150 mg/m2) and rabbits (≥75 mg/kg |
