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Home > Medications (Drugs) > Naltrexone > More information about Naltrexone

More information about Naltrexone


(nal TREKS one)

U.S. Brand Names



Naltrexone Hydrochloride

Generic Available


Canadian Brand Names



Treatment of ethanol dependence; blockade of the effects of exogenously administered opioids

Pregnancy Risk Factor



Excretion in breast milk unknown


Hypersensitivity to naltrexone or any component of the formulation; narcotic dependence or current use of opioid analgesics; acute opioid withdrawal; failure to pass Narcan® challenge or positive urine screen for opioids; acute hepatitis; liver failure


Dose-related hepatocellular injury is possible; the margin of separation between the apparent safe and hepatotoxic doses appear to be only fivefold or less. May precipitate withdrawal symptoms in patients addicted to opiates, including pain, hypertension, sweating, agitation, irritability; in neonates: shrill cry, failure to feed. Use with caution in patients with hepatic or renal impairment.

Patients who had been treated with naltrexone may respond to lower opioid doses than previously used. This could result in potentially life-threatening opioid intoxication. Patients should be aware that they may be more sensitive to lower doses of opioids after naltrexone treatment is discontinued. Use of naltrexone does not eliminate or diminish withdrawal symptoms.

Adverse Reactions


Central nervous system: Insomnia, nervousness, headache, low energy

Gastrointestinal: Abdominal cramping, nausea, vomiting

Neuromuscular & skeletal: Arthralgia

1% to 10%:

Central nervous system: Increased energy, feeling down, irritability, dizziness, anxiety, somnolence

Dermatologic: Rash

Endocrine & metabolic: Polydipsia

Gastrointestinal: Diarrhea, constipation

Genitourinary: Delayed ejaculation, impotency

<1%: Bad dreams, blurred vision, confusion, depression, disorientation, edema, fatigue, hallucinations, increased blood pressure, itching, rhinorrhea, narcotic withdrawal, nasal congestion, nightmares, palpitation, paranoia, restlessness, sneezing, suicide attempts, tachycardia


Symptoms of overdose include clonic-tonic convulsions and respiratory failure. Patients receiving up to 800 mg/day for 1 week have shown no toxicity. Seizures and respiratory failure have been seen in animals.

Drug Interactions

Narcotic analgesics: Decreased effect of narcotic analgesics; may precipitate acute withdrawal reaction in physically dependent patients; concurrent use is contraindicated

Thioridazine: Lethargy and somnolence have been reported with the combination of naltrexone and thioridazine

Mechanism of Action

Naltrexone (a pure opioid antagonist) is a cyclopropyl derivative of oxymorphone similar in structure to naloxone and nalorphine (a morphine derivative); it acts as a competitive antagonist at opioid receptor sites


Duration: 50 mg: 24 hours; 100 mg: 48 hours; 150 mg: 72 hours

Absorption: Almost complete

Distribution: Vd: 19 L/kg; widely throughout the body but considerable interindividual variation exists

Protein binding: 21%

Metabolism: Extensive first-pass effect to 6-


Half-life elimination: 4 hours; 6-

-naltrexol: 13 hours

Time to peak, serum: ~60 minutes

Excretion: Primarily urine (as metabolites and unchanged drug)


Do not give until patient is opioid-free for 7-10 days as determined by urine analysis

Adults: Oral: 25 mg; if no withdrawal signs within 1 hour give another 25 mg; maintenance regimen is flexible, variable and individualized (50 mg/day to 100-150 mg 3 times/week for 12 weeks); up to 800 mg/day has been tolerated in adults without an adverse effect

Dosing cautions in renal/hepatic impairment:   Caution in patients with renal and hepatic impairment. An increase in naltrexone AUC of approximately five- and 10-fold in patients with compensated or decompensated liver cirrhosis respectively, compared with normal liver function has been reported.


If there is any question of occult opioid dependence, perform a naloxone challenge test; do not attempt treatment until naloxone challenge is negative

Naltrexone is administered orally; to minimize adverse gastrointestinal effects, administer with food or antacids or after meals; advise patient not to self-administer opiates while receiving naltrexone therapy

Monitoring Parameters

For narcotic withdrawal; liver function tests

Patient Education

This medication will help you achieve abstinence from opiates if taken as directed. Do not increase or change dose. Do not use opiates or any medications not approved by your prescriber during naltrexone therapy. You may experience drowsiness, dizziness, or blurred vision (use caution when driving or engaging in tasks requiring alertness until response to drug is known); abdominal cramping, nausea or vomiting (small, frequent meals, frequent mouth care, chewing gum, or sucking lozenges may help); low energy; or decreased sexual function (reversible when drug is discontinued). Report yellowing of skin or eyes, change in color of stool or urine, increased perspiration or chills, acute headache, palpitations, or unusual joint pain. Pregnancy/breast-feeding precautions:   Inform prescriber if you are or intend to become pregnant. Consult prescriber if breast-feeding.

Nursing Implications

Monitor for narcotic withdrawal

Anesthesia and Critical Care Concerns/Other Considerations

May also be used in detoxification with special guidelines

Dental Health: Effects on Dental Treatment

No significant effects or complications reported

Dental Health: Vasoconstrictor/Local Anesthetic Precautions

No information available to require special precautions

Dosage Forms

Tablet, as hydrochloride: 50 mg


Kleber HD, "Naltrexone,"J Subst Abuse Treat, 1985, 2(2):117-22.

Mitchell JE, "Naltrexone and Hepatotoxicity,"Lancet, 1986, 1(8491):1215.

Mokhlesi B, Leikin JB, Murray P, et al, "Adult Toxicology in Critical Care: Part II: Specific Poisonings,"Chest, 2003, 123(3):897-922.

O'Connor PG and Kosten TR, "Rapid and Ultrarapid Opioid Detoxification Techniques,"JAMA, 1998, 279(3):229-34.

International Brand Names

Antaxone® (ES, IT, PT, RU, YU); Antaxon® (HU); Celupan® (ES); Destroxican® (PT); Nalerona® (CL); Nalone® (AT); Nalorex® (BE, FR, GB, IE, IT, NL, PT); Naltrexin® (CH); Narcoral® (IT); Nemexin® (AT, CH, DE, HU); Nodict® (IN); Phaltrexia® (ID); Revez® (AR); Revia® (AT, AU, BR); ReVia® (CA); Revia® (DK, ES, FI); ReVia® (FR); Revia® (HU, IE, IL, NL, NO, NZ, RU, SE, SI, TH)