NALTREXONE HYDROCHLORIDE (Page 3 of 5)

Special Risk Patients


Renal Impairment: Naltrexone hydrochloride and its primary metabolite are excreted primarily in the urine, and caution is recommended in administering the drug to patients with renal impairment.

Hepatic Impairment: An increase in naltrexone AUC of approximately 5-and 10-fold in patients with compensated and decompensated liver cirrhosis, respectively, compared with subjects with normal liver function has been reported. These data also suggest that alterations in naltrexone bioavailability are related to liver disease severity.

Information for Patients

It is recommended that the prescribing physician relate the following information to patients being treated with naltrexone hydrochloride:

You have been prescribed naltrexone hydrochloride tablets as part of the comprehensive treatment for your alcoholism or drug dependence. You should carry identification to alert medical personnel to the fact that you are taking naltrexone hydrochloride. A naltrexone hydrochloride medication card may be obtained from your physician and can be used for this purpose. Carrying the identification card should help to ensure that you can obtain adequate treatment in an emergency. If you require medical treatment, be sure to tell the treating physician that you are receiving naltrexone hydrochloride therapy. You should take naltrexone hydrochloride as directed by your physician.

  • Advise patients that if they previously used opioids, they may be more sensitive to lower doses of opioids and at risk of accidental overdose should they use opioids after naltrexone hydrochloride treatment is discontinued or temporarily interrupted. It is important that patients inform family members and the people closest to the patient of this increased sensitivity to opioids and the risk of overdose.
  • Advise patients that because naltrexone hydrochloride can block the effects of opioids, patients will not perceive any effect if they attempt to self-administer heroin or any other opioid drug in small doses while on naltrexone hydrochloride tablets. Further, emphasize that administration of large doses of heroin or any other opioid to try to bypass the blockade and get high while on naltrexone hydrochloride may lead to serious injury, coma, or death.
  • Patients on naltrexone hydrochloride tablets may not experience the expected effects from opioid-containing analgesic, antidiarrheal, or antitussive medications.
  • Patients should be off all opioids, including opioid-containing medicines, for a minimum of 7 to 10 days before starting naltrexone hydrochloride tablets in order to avoid precipitation of opioid withdrawal. Patients transitioning from buprenorphine or methadone may be vulnerable to precipitation of withdrawal symptoms for as long as two weeks. Ensure that patients understand that withdrawal precipitated by administration of an opioid antagonist may be severe enough to require hospitalization if they have not been opioid-free for an adequate period of time, and is different from the experience of spontaneous withdrawal that occurs with discontinuation of opioid in a dependent individual. Advise patients that they should not take naltrexone hydrochloride tablets if they have any symptoms of opioid withdrawal. Advise all patients, including those with alcohol dependence, that it is imperative to notify healthcare providers of any recent use of opioids or any history of opioid dependence before starting naltrexone hydrochloride to avoid precipitation of opioid withdrawal.
  • Advise patients that naltrexone hydrochloride tablets may cause liver injury. Patients should immediately notify their physician if they develop symptoms and/or signs of liver disease.
  • Advise patients that they may experience depression while taking naltrexone hydrochloride tablets. It is important that patients inform family members and the people closest to the patient that they are taking naltrexone hydrochloride and that they should call a doctor right away should they become depressed or experience symptoms of depression.
  • Advise patients that naltrexone hydrochloride has been shown to be effective only when used as part of a treatment program that includes counseling and support.
  • Advise patients that dizziness may occur with naltrexone hydrochloride treatment, and they should avoid driving or operating heavy machinery until they have determined how naltrexone hydrochloride affects them.
  • Advise patients to notify their physician if they:
    • become pregnant or intend to become pregnant during treatment with naltrexone hydrochloride.
    • are breast-feeding.
    • experience other unusual or significant side effects while on naltrexone hydrochloride therapy.

Laboratory Tests


Naltrexone hydrochloride does not interfere with thin-layer, gas-liquid, and high pressure liquid chromatographic methods which may be used for the separation and detection of morphine, methadone or quinine in the urine. Naltrexone hydrochloride may or may not interfere with enzymatic methods for the detection of opioids depending on the specificity of the test. Please consult the test manufacturer for specific details.

Drug Interactions


Studies to evaluate possible interactions between naltrexone hydrochloride and drugs other than opiates have not been performed. Consequently, caution is advised if the concomitant administration of naltrexone hydrochloride and other drugs is required.

The safety and efficacy of concomitant use of naltrexone hydrochloride and disulfiram is unknown, and the concomitant use of two potentially hepatotoxic medications is not ordinarily recommended unless the probable benefits outweigh the known risks.

Lethargy and somnolence have been reported following doses of naltrexone hydrochloride and thioridazine.

Patients taking naltrexone hydrochloride may not benefit from opioid containing medicines, such as cough and cold preparations, antidiarrheal preparations, and opioid analgesics. In an emergency situation when opioid analgesia must be administered to a patient receiving naltrexone hydrochloride, the amount of opioid required may be greater than usual, and the resulting respiratory depression may be deeper and more prolonged (see PRECAUTIONS).

Carcinogenesis, Mutagenesis and Impairment of Fertility


The following statements are based on the results of experiments in mice and rats. The potential carcinogenic, mutagenic and fertility effects of the metabolite 6-β-naltrexol are unknown.

In a two-year carcinogenicity study in rats, there were small increases in the numbers of testicular mesotheliomas in males and tumors of vascular origin in males and females. The incidence of mesothelioma in males given naltrexone at a dietary dose of 100 mg/kg/day (600 mg/m2 /day; 16 times the recommended therapeutic dose, based on body surface area) was 6%, compared with a maximum historical incidence of 4%. The incidence of vascular tumors in males and females given dietary doses of 100 mg/kg/day (600 mg/m2 /day) was 4% but only the incidence in females was increased compared with a maximum historical control incidence of 2%. There was no evidence of carcinogenicity in a two-year dietary study with naltrexone in male and female mice.

There was limited evidence of a weak genotoxic effect of naltrexone in one gene mutation assay in a mammalian cell line, in the Drosophila recessive lethal assay, and in non-specific DNA repair tests with E. coli. However, no evidence of genotoxic potential was observed in a range of other in vitro tests, including assays for gene mutation in bacteria, yeast, or in a second mammalian cell line, a chromosomal aberration assay, and an assay for DNA damage in human cells. Naltrexone did not exhibit clastogenicity in an in vivo mouse micronucleus assay.

Naltrexone (100 mg/kg/day [600 mg/m2 /day] PO; 16 times the recommended therapeutic dose, based on body surface area) caused a significant increase in pseudopregnancy in the rat. A decrease in the pregnancy rate of mated female rats also occurred. There was no effect on male fertility at this dose level. The relevance of these observations to human fertility is not known.

Pregnancy

Teratogenic Effects: Pregnancy Category C: Naltrexone has been shown to increase the incidence of early fetal loss when given to rats at doses ≥ 30 mg/kg/day (180 mg/m2 /day; 5 times the recommended therapeutic dose, based on body surface area) and to rabbits at oral doses ≥ 60 mg/kg/day (720 mg/m2 /day; 18 times the recommended therapeutic dose, based on body surface area). There was no evidence of teratogenicity when naltrexone was administered orally to rats and rabbits during the period of major organogenesis at doses up to 200 mg/kg/day (32 and 65 times the recommended therapeutic dose, respectively, based on body surface area).

Rats do not form appreciable quantities of the major human metabolites, 6-β-naltrexol; therefore, the potential reproductive toxicity of the metabolite in rats is not known.

There are no adequate and well-controlled studies in pregnant women. Naltrexone hydrochloride should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

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