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Cesamet (Nabilone) - Drug Interactions, Contraindications, Overdosage, etc

 
 



DRUG INTERACTIONS

Drug Interactions

Potential interactions between Cesamet 2 mg, and diazepam 5 mg; sodium secobarbital 100 mg; alcohol 45 mL (absolute laboratory alcohol); or codeine 65 mg, were evaluated in 15 subjects. Only a single combination was utilized at any one time. The subjects were evaluated according to physiologic (i.e., heart rate and blood pressure), psychometric, psychomotor, and subjective parameters. In this study, as expected, the depressant effects of the combinations were additive. Psychomotor function was particularly impaired with concurrent use of diazepam. Caution must thus be used when administering nabilone in combination with any CNS depressant.

Nabilone is purportedly highly bound to plasma proteins, and therefore, might displace other protein-bound drugs. Therefore, practitioners should monitor patients for a change in dosage requirements when administering nabilone to patients receiving other highly protein-bound drugs. Published reports of drug-drug interactions involving cannabinoids are summarized in the following table.

CONCOMITANT DRUG CLINICAL EFFECT(S)
Amphetamines, cocaine, other sympathomimetic
agents
Additive hypertension, tachycardia, possibly cardiotoxicity
Atropine, scopolamine, antihistamines, other
anticholinergic agents
Additive or super-additive tachycardia, drowsiness
Amitriptyline, amoxapine, desipramine, other
tricyclic antidepressants
Additive tachycardia, hypertension, drowsiness
Barbiturates, benzodiazepines, ethanol, lithium,
opioids, buspirone, antihistamines, muscle relaxants,
other CNS depressants
Additive drowsiness and CNS depression
Disulfiram A reversible hypomanic reaction was reported in a 28 y/o
man who smoked marijuana; confirmed by dechallenge and
rechallenge
Fluoxetine A 21 y/o female with depression and bulimia receiving 20
mg/day fluoxetine X 4 wks became hypomanic after
smoking marijuana; symptoms resolved after 4 days
Antipyrine, barbiturates Decreased clearance of these agents, presumably via
competitive inhibition of metabolism
Theophylline Increased theophylline metabolism reported with smoking of
marijuana; effect similar to that following smoking tobacco
Opioids Cross-tolerance and mutual potentiation
Naltrexone Oral THC effects were enhanced by opioid receptor
blockade.
Alcohol Increase in the positive subjective mood effects of smoked
marijuana

OVERDOSAGE

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).

CONTRAINDICATIONS

Cesamet is contraindicated in any patient who has a history of hypersensitivity to any cannabinoid.

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 delta-9-THC in the production of cannabis-like effects, thus demonstrating that Cesamet has a high 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.

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