Naltrexone

Definition

Naltrexone is classified as a pure opiate antagonist. It is sold in the United States under the brand names ReVia and Depade, but is also manufactured and sold under its generic name.

Purpose

Naltrexone is used as part of medically supervised behavior modificationprograms in order to maintain a patient previously addicted to opiates in an opiate-free state following successful opiate detoxification. Naltrexone is also used in the management of alcohol dependence and abstinence in combination with medically supervised behavior modification programs.

Description

Opiates are a group of drugs that are either derived from opium (i.e. morphine, hydromorphone, oxymorphone, heroin, codeine, hydrocodone, oxycodone) or chemically resemble these opium derivatives (such as meperidine). They are commonly referred to as narcotics. Some opiates have medically valid uses, while others are recreational drugs of abuse. All are physically addictive.

The drug naltrexone is an opiate antagonist. This means that it blocks and reverses the physical effects of drugs such as morphine, hydromorphone, oxymorphone, heroin, meperidine, codeine, hydrocodone, oxycodone and other drugs classified as narcotics. When given to patients who have been successfully treated for opiate addiction, it not only decreases craving for these types of drugs, it also prevents patients who use opiates while taking naltrexone from experiencing the euphoria associated with their use. In these two ways, naltrexone helps prevent re-addiction to opiates.

Chemically, naltrexone is not an alcohol antagonist. However, when it is used in combination with behavior modification in the recovering alcoholic, naltrexone decreases the craving for alcohol. This helps to prevent a return to alcohol use, or it decreases the severity of relapse by reducing the amount of alcohol consumed during the relapse or decreasing the length of the relapse.

Naltrexone is available in 50-mg oral tablets.

Recommended dosage

After a person has been successfully detoxified from opiates, he or she will receive a test dose of 25 mg of naltrexone, then be observed for one hour for symptoms of opiate withdrawal. If no problems occur after this test dose, another 25 mg test dose is administered.

Getting a person to comply with treatment for opiate addiction is the single most important aspect in maintaining an opiate-free state. Different schedules for taking naltrexone have been developed to help meet the needs of individuals in order to make taking the drug easier. Following successful initiation of therapy, naltrexone may be administered in one of the following ways:

• 50 mg daily Monday through Friday and 100 mg Saturday
• 100 mg every other day
• 150 mg every third day
• 100 mg on Monday and Wednesday and 150 mg on Friday
• 150 mg on Monday and 200 mg on Thursday

The duration of treatment with naltrexone for opiate dependence varies with patient need, although most patients will require at least six months of treatment.

The usual dose of naltrexone for alcohol dependence is 50 mg daily, although a few patients may require only 25 mg daily. The proper duration of therapy is not known, as studies of the use of naltrexone in alcohol dependence did not go beyond 12 weeks.

Precautions

In a very small number of patients, naltrexone may be toxic and cause damage to the liver. Before starting naltrexone and throughout treatment, patients should receive monthly liver function tests to assess the drug's effect on the liver.

Patients should be free of all opiates for seven to 10 days before starting naltrexone. Naltrexone may cause opiate withdrawal symptoms in people whose bodies are not free from opiates. Patients should be observed for opiate withdrawal immediately following the first dose of the drug.

Patients may have a false sense of security that the presence of naltrexone in their system makes them immune from the effects of opiates. In fact, the opiate antagonism caused by naltrexone is not absolute and patients can still experience both analgesia (suppression of pain) and euphoria by administration of larger-than-normal amounts of opiates. Consequently, patients receiving naltrexone who continue to use or receive opiates may take larger doses and should be monitored for signs and symptoms of opiate overdose.

Side effects

The following represents the most common side effects associated with naltrexone:

• nausea, vomiting, diarrhea, cramps
• headache, insomnia, anxiety, irritability, depression, dizziness
• joint and muscle pain
• rash

Interactions

Because naltrexone is an opiate antagonist, opiate derivatives that are used for medicinally in treating cough, diarrhea, and pain may no longer be effective.

The combination of naltrexone and disulfiram, a drug that is also used for alcohol abuse, may cause increased liver toxicity and liver damage when taken together. This combination should be avoided unless in consultation with a physician, it is decided that the potential benefits of this combination outweigh the risks.

BOOKS

American Society of Health-System Pharmacists. AHFS Drug Information 2002.Bethesda: American Society of Health-System Pharmacists, 2002.

O'Brien, Charles P. "Drug Addiction and Drug Abuse." In Goodman & Gillman's The Pharmacological Basis of Therapeutics Tenth Editionedited by Joel G. Hardman, Ph.D. and Lee E. Limbird, Ph.D. New York: McGraw-Hill, 2001.

Jack Raber, Pharm.D.