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.

>10%:

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

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

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--naltrexol

Half-life elimination: 4 hours; 6--naltrexol: 13 hours

Time to peak, serum: ~60 minutes

Excretion: Primarily urine (as metabolites and unchanged drug)

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.

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

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.