Absorption and Distribution: Cesamet (nabilone) appears to be completely absorbed from the human gastrointestinal tract when administered orally. Following oral administration of a 2 mg dose of radiolabeled nabilone, peak plasma concentrations of approximately 2 ng/mL nabilone and 10 ng equivalents/mL total radioactivity are achieved within 2.0 hours. The plasma half-life (T½) values for nabilone and total radioactivity of identified and unidentified metabolites are about 2 and 35 hours, respectively. The initial rapid disappearance of radioactivity represents uptake and distribution of nabilone into tissue and the slower phase elimination by metabolism and excretion. The apparent volume of distribution of nabilone is about 12.5 L/kg.

Nabilone exhibits dose linearity within its therapeutic range. Clinical data suggests that the intake of food does not significantly affect either the rate or extent of absorption.

Metabolism: Metabolism of nabilone is extensive and several metabolites have been identified. Precise information concerning the metabolites that may accumulate is not available. The relative activities of the metabolites and the parent drug have not been established. There are at least two metabolic pathways involved in the biotransformation of nabilone. A minor pathway is initiated by the stereospecific enzymatic reduction of the 9-keto moiety of nabilone to produce the isomeric carbinol metabolite. The peak concentrations of nabilone and its carbinol metabolites are comparable, but their combined exposures in plasma do not account for more than 20% of that of total radioactivity. Secondly, a metabolite of nabilone in feces has been identified as a diol formed by reduction of the 9-keto group plus oxidation at the penultimate carbon of the dimethylheptyl side chain. In addition, there is evidence of extensive metabolism of Cesamet by multiple P450 enzyme isoforms. In vitro P450 inhibition studies using human liver microsomes showed that nabilone did not significantly inhibit CYP1A2, 2A6, 2C19, 2D6, and 3A4 (using midazolam and nifedipine as substrates). Nabilone had a weak inhibitory effect on CYP 2E1 and 3A4 (testosterone; IC50> 50 µM) and had a moderate inhibitory effect on CYP2C8 and 2C9 (IC50> 10 µM). However, in clinical use, the very low nabilone plasma concentration is unlikely to interfere with the P450-mediated degradation of co-administered drugs. Chronic oral administration of 1 mg t.i.d. for 14 days to 3 subjects gave no indication there was any significant accumulation of nabilone. Available evidence suggests that one or more of the metabolites has a terminal elimination half-life that exceeds that of nabilone. Consequently, in repeated use, the metabolites may accumulate at concentrations in excess of the parent drug.

Elimination: The route and rate of the elimination of nabilone and its metabolites are similar to those observed with other cannabinoids, including delta-9-THC (dronabinol). When nabilone is administered intravenously, the drug and its metabolites are eliminated mainly in the feces (approximately 67%) and to a lesser extent in the urine (approximately 22%) within 7 days. Of the 67% recovered from the feces, 5% corresponded to the parent compound and 16% to its carbinol metabolite. Following oral administration about 60% of nabilone and its metabolites were recovered in the feces and about 24% in urine. Therefore, it appears that the major excretory pathway is the biliary system.

The effects of age, gender, hepatic dysfunction, and renal insufficiency on the metabolism and elimination of nabilone have not been determined.

Special Populations: The pharmacokinetic profile of Cesamet has not been investigated in either pediatric (see PRECAUTIONS, Pediatric Use) or geriatric patients (see PRECAUTIONS, Geriatric Use).