Animal Pharmacology and/or Toxicology
Monkeys treated with Cesamet at doses as high as 2 mg/kg/day for a year experienced no significant adverse events. This result contrasts with the findings in a planned 1-year dog study that was prematurely terminated because of deaths associated with convulsions in dogs receiving as little as 0.5 mg/kg/day. The earliest deaths, however, occurred at 56 days in dogs receiving 2 mg/kg/day. The unusual vulnerability of the dog to Cesamet is not understood; it is hypothesized, however, that the explanation lies in the fact that the dog differs markedly from other species in its metabolism of Cesamet.
Carcinogenesis, Mutagenesis, Impairment of Fertility
No long-term studies in animals have been performed to evaluate the carcinogenic potential of nabilone.
Nabilone was not genotoxic in the Ames test, the rat hepatocyte unscheduled DNA synthesis (UDS) test, the Chinese hamster bone marrow cell sister chromatid exchange (SCE) test, the male rat dominant lethal tests nor the rat micronucleus test.
Dietary administration of nabilone up to 4 mg/kg/day (about 6 times the recommended maximum human dose based on body surface area) was found to have no effect on fertility and reproductive performance of male and female rats.
Teratogenic Effects. Pregnancy Category C
Teratology studies conducted in pregnant rats at doses up to 12 mg/kg/day (about 16 times the human dose on a body surface area basis) and in pregnant rabbits at doses up to 3.3 mg/kg/day (about 9 times the human dose on a body surface area basis) did not disclose any evidence for a teratogenic potential of nabilone. However, there was dose related developmental toxicity in both species as evidenced by increases in embryo lethality, fetal resorptions, decreased fetal weights and pregnancy disruptions. In rats, postnatal developmental toxicity was also observed. There are no adequate and well-controlled studies in pregnant women. Because animal studies cannot rule out the possibility of harm, Cesamet should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Signs and Symptoms - Signs and symptoms of overdosage are an extension of the psychotomimetic and physiologic effects of Cesamet.
Treatment - To obtain up-to-date information about the treatment of overdose, a good resource is your certified Regional Poison Control Center. Telephone numbers of certified poison control centers are listed in the Physicians' Desk Reference (PDR). In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in your patient.
Overdosage may be considered to have occurred, even at prescribed dosages, if disturbing psychiatric symptoms are present. In these cases, the patient should be observed in a quiet environment and supportive measures, including reassurance, should be used. Subsequent doses should be withheld until patients have returned to their baseline mental status; routine dosing may then be resumed if clinically indicated. In such instances, a lower initiating dose is suggested. In controlled clinical trials, alterations in mental status related to the use of Cesamet resolved within 72 hours without specific medical therapy.
In overdose settings, attention should be paid to vital signs, since both hypertension and hypotension have been known to occur; tachycardia and orthostatic hypotension were most commonly reported.
No cases of overdosage with more than 10 mg/day of nabilone were reported during clinical trials. Signs and symptoms that would be expected to occur in large overdose situations are psychotic episodes, including hallucinations, anxiety reactions, respiratory depression, and coma.
If psychotic episodes occur, the patient should be managed conservatively, if possible. For moderate psychotic episodes and anxiety reactions, verbal support and comforting may be sufficient. In more severe cases, antipsychotic drugs may be useful; however, the utility of antipsychotic drugs in cannabinoid psychosis has not been systematically evaluated. Support for their use is drawn from limited experience using antipsychotic agents to manage cannabis overdoses. Because of the potential for drug-drug interactions (e.g., additive CNS depressant effects due to nabilone and chlorpromazine), such patients should be closely monitored.
Protect the patient's airway and support ventilation and perfusion. Meticulously monitor and maintain, within acceptable limits, the patient's vital signs, blood gases, serum electrolytes, as well as other laboratory values and physical assessments. Absorption of drugs from the gastrointestinal tract may be decreased by giving activated charcoal, which, in many cases, is more effective than emesis or lavage; consider charcoal instead of or in addition to gastric emptying. Repeated doses of charcoal over time may hasten elimination of some drugs that have been absorbed. Safeguard the patient's airway when employing gastric emptying or charcoal.
The use of forced diuresis, peritoneal dialysis, hemodialysis, charcoal hemoperfusion, or cholestyramine has not been reported. In the presence of normal renal function, most of a dose of nabilone is eliminated through the biliary system.
Treatment for respiratory depression and comatose state consists in symptomatic and supportive therapy. Particular attention should be paid to the occurrence of hypothermia. If the patient becomes hypotensive, consider fluids, inotropes, and/or vasopressors.
The estimated oral median lethal dose in female mice is between 1,000 and 2,000 mg/kg; in the female rat, it is greater than 2,000 mg/kg, (See CLINICAL PHARMACOLOGY).
DRUG ABUSE AND DEPENDENCE
Controlled Substance — Cesamet, a synthetic cannabinoid pharmacologically related to Cannabis sativa L. (Marijuana; (delta-9-THC) is a highly abusable substance. Cesamet is controlled under Schedule II (CII) of the Controlled Substances Act. Prescriptions for Cesamet should be limited to the amount necessary for a single cycle of chemotherapy (i.e., a few days). Cesamet may produce subjective side effects which may be interpreted as a euphoria or marijuana-like "high" at therapeutic doses.
It is not known what proportion of individuals exposed chronically to Cesamet or other cannabinoids will develop either psychological or physical dependence. Long term use of these compounds has, however, been associated with disorders of motivation, judgment, and cognition. It is not clear, though, if this is a manifestation of the underlying personalities of chronic users of this class of drugs or if cannabinoids are directly responsible for these effects. An abstinence syndrome has been reported following discontinuation of delta-9-THC at high doses of 200 mg per day for 12 to 16 consecutive days. The acute phase was characterized by psychic distress, insomnia, and signs of autonomic hyperactivity (sweating, rhinorrhea, loose stools, hiccups). A protracted abstinence phase may have occurred in subjects who reported sleep disturbances for several weeks after delta-9-THC discontinuation.
Abuse — Cesamet may produce subjective side effects that may be interpreted as a euphoria or marijuana-like "high" at therapeutic doses. Cesamet was shown to be qualitatively and quantitatively similar to approved oral delta-9-THC in the production of cannabis-like effects, thus demonstrating its potential for abuse.
Preclinical studies performed in both dogs and monkeys demonstrated that Cesamet was cannabinoid-like. As with delta-9-THC, tolerance develops rapidly to the pharmacological effects in both the dog and the monkey. Cross-tolerance between Cesamet and delta-9-THC was demonstrated in the monkey.
Dependence — The physical dependence capacity of Cesamet is unknown at this time. Patients who participated in clinical trials of up to 5 days' duration evidenced no withdrawal symptoms on cessation of dosing.