NALTREXONE HYDROCHLORIDE

NALTREXONE HYDROCHLORIDE (nal-trex'one) ReVia, Vivitrol Classifications: narcotic (opiate) antagonist; Therapeutic: narcotic antagonist Prototype: Naloxone HCl Pregnancy Category: C

Availability

25 mg, 50 mg, 100 mg tablets; 380 mg injection

Action

Pure opioid antagonist with prolonged pharmacologic effect, structurally and pharmacologically similar to naloxone. Mechanism of action not clearly delineated, but it appears that its competitive binding at opioid receptor sites reduces euphoria and drug craving without supporting the addiction.

Therapeutic Effect

Weakens or completely and reversibly blocks the subjective effects (the "high") of IV opioids and analgesics possessing both agonist and antagonist activity.

Uses

Adjunct to the maintenance of an opioid-free state in detoxified addicts who are and desire to remain narcotic free. Management of alcohol dependence as an adjunct to social and psychotherapeutic methods.

Unlabeled Uses

Obesity.

Contraindications

Patients receiving opioid analgesics or in acute opioid withdrawal; opioid-dependent patient; acute hepatitis, liver failure. Also contraindicated in any individual who (1) fails naloxone challenge, (2) has a positive urine screen for opioids, or (3) has a history of sensitivity to naltrexone; pregnancy (category C), lactation. Safe use in children <18 y is not established.

Route & Dosage

Treatment of Opiate Cessation Adult: PO 25 mg followed by another 25 mg in 1 h if no withdrawal response; maintenance regimen is individualized (max: 800 mg/d) Alcohol Dependence Adult: PO 50 mg once/d IM 380 mg qmo

Administration

Challenge Test

Give the naloxone challenge test (administered IV of SC) before starting the abstinence program with naltrexone.

• SC dose: The SC dose is followed by an observation period of 45 min for symptoms of withdrawal (see below).
• IV dose: A portion of the IV dose is injected and, with the needle left in place, the patient is observed for 30 sec for withdrawal symptoms. If none are observed, remainder of dose is injected and patient is observed for the next 20 min.
• Withdrawal symptoms: Stuffiness or runny nose; tearing; yawning; sweating; tremors; vomiting; gooseflesh; feeling of temperature change; bone, joint, and muscle pains; abdominal cramps.
• Interpretation: Evidence of withdrawal symptoms indicates that the patient is a potential risk and should not enter a naltrexone program.
• Do not give naltrexone until patient is opiate free for at least 7–10 d.

Oral

• Give without regard to food.

Adverse Effects (≥1%)

GI: Dry mouth, anorexia, nausea, vomiting, constipation, abdominal cramps/pain, hepatotoxicity. Musculoskeletal: Muscle and joint pains. CNS: Difficulty sleeping, anxiety, headache, nervousness, reduced or increased energy, irritability, dizziness, depression. Skin: Skin rash. Body as a Whole: Chills.

Interactions

Drug: Increased somnolence and lethargy with phenothiazines; reverses analgesic effects of narcotic (opiate) agonists and narcotic (opiate) agonist-antagonists.

Pharmacokinetics

Absorption: Rapidly from GI tract; 20% reaches systemic circulation (first pass effect). Onset: 15–30 min. Peak: 1 h. Duration: 24–72 h PO; 4 wk IM. Metabolism: In liver to active metabolite. Elimination: In urine. Half-Life: 10–13 h PO, 5–10 d IM.

Nursing Implications

Assessment & Drug Effects

• Lab tests: Check liver function before the treatment is started, at monthly intervals for 6 mo, and then periodically as indicated.

Patient & Family Education

• Note: Naltrexone therapy may put you in danger of overdosing if you use opiates. Small doses even at frequent intervals will give no desired effects; however, a dose large enough to produce a high is dangerous and may be fatal.
• It may be possible to transfer from methadone to naltrexone. This can be done after gradual withdrawal and final discontinuation of methadone.
• Report promptly onset of signs of hepatic toxicity (see Appendix F) to physician. The drug will be discontinued.
• Do not self-dose with OTC drugs for treatment of cough, colds, diarrhea, or analgesia. Many available preparations contain small doses of an opioid. Consult physician for safe drugs if they are needed.
• Tell a doctor or dentist before treatment that you are using naltrexone.
• Wear identification jewelry indicating naltrexone use.

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Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug