Methadone HCl

 Action Relieves pain by stimulating opiate receptors in CNS; also causes respiratory depression, peripheral vasodilation, inhibition of intestinal peristalsis, sphincter of Oddi spasm, stimulation of chemoreceptors that cause vomiting and increased bladder tone.

 Indications Management of severe pain; detoxification and temporary maintenance treatment of narcotic addiction.

 Contraindications Standard considerations.

 Route/Dosage

Pain

ADULTS: IM/SC/PO 2.5–10 mg q 3–4 hr prn. May need higher doses in patients with severe pain or tolerance.

Detoxification

ADULTS: PO 15–20 mg initially to suppress withdrawal symptoms. Additional doses may be needed. PATIENTS PHYSICALLY DEPENDENT ON HIGH DOSES OF NARCOTICS: PO 40 mg/day may be given for 2–3 days; decrease dose q 1–2 days. MAINTENANCE: PO 20–40 mg initially to suppress withdrawal symptoms in patients who are heavy heroin users. Additional 10 mg doses can be given prn. Adjust dose as tolerated and required, up to 120 mg/day.

 Interactions

Barbiturate anesthetics: Drug actions may be additive. Cimetidine, protease inhibitors: Monitor for increased respiratory and CNS depression. CNS depressants (eg, tranquilizers, sedatives, alcohol): Additive CNS depression. Fluvoxamine: Monitor for increased CNS depression when taken with methadone. Monitor for signs and symptoms of withdrawal when fluvoxamine is discontinued. Hydantoins, rifampin, barbiturates: May decrease effectiveness of methadone. Urinary acidifiers: May increase renal clearance of methadone.

 Lab Test Interferences Increased amylase and lipase may occur up to 24 hr after dose.

 Adverse Reactions

CV: Hypotension; palpitations; bradycardia; tachycardia. CNS: Lightheadedness; euphoria; dysphoria; headache; insomnia; dizziness; edation; disorientation; incoordination. DERM: Sweating; pruritus; urticaria. GI: Nausea; vomiting; constipation; abdominal pain; dry mouth. GU: Urinary retention or hesitancy. HEMA: Thrombocytopenia. RESP: Laryngospasm; depression of cough reflex. OTHER: Tolerance; psychological and physical dependence with chronic use.

 Precautions

Pregnancy: Pregnancy category undetermined. Methadone use has been associated with low infant birthweight. Lactation: Excreted in breast milk. Children: Not recommended for children; dosage is not well defined. Special risk patients: Use drug with caution in patients with myxedema, acute alcoholism, acute abdominal conditions, ulcerative colitis, decreased respiratory reserve, head injury or increased intracranial pressure, hypoxia, supraventricular tachycardia, depleted blood volume or circulatory shock. Drug dependence: Methadone has abuse potential. Hepatic or renal impairment: May need to decrease dose. Obstetrical analgesia: Do not use methadone for obstetrical analgesia. Its long duration of action increases the probability of neonatal respiratory depression. Treatment of drug addiction: Methadone for detoxification should not be given for > 21 days and treatment should not be repeated within 4 wk. More than 3 wk in methadone treatment of narcotic dependence is considered maintenance therapy; only approved programs can provide this therapy.

 Administration/Storage

• If GI upset occurs, give with food.
• Adjust dose as tolerated and required (up to 120 mg/day) or adequate pain relief. When withdrawing methadone, decrease by 10% every 1–2 days.
• Use reduced dose in elderly or debilitated patients.
• IM administration is preferred over SC injection, which can cause local irritation.
• Rotate injection sites.
• Store at room temperature in light-resistant container.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Monitor vital signs, especially respirations.
• Monitor bowel function and treat constipation as indicated.
• Monitor I&O. Observe for urinary retention.
• Assess for pain relief.
• Have patient turn, cough and deep breathe every 2 hr.
• Watch for additive CNS effects when used with other CNS depressants.
• Carefully monitor patients with acute abdominal problems, acute alcoholism, myxedema, respiratory disease, supraventricular tachycardia or shock.
• Document and notify physician of any side effects, including hypotension, bradycardia, tachycardia, laryngospasm, decreased cough reflex, dizziness, disorientation, nausea and vomiting, constipation, urinary retention, sweating, pruritus, physical and psychological dependence with long-term use.

 Patient/Family Education

• Tell patient to take methadone regularly, as prescribed. If dose is missed, tell patient to take as soon as possible. If close to next dose, wait and take next regularly scheduled dose.
• Advise patient that drug may cause dizziness, drowsiness, or blurred vision and to use caution while driving or performing other hazardous tasks.
• Caution patient to avoid intake of alcoholic beverages or other CNS depressants.
• If constipation occurs, tell patient to increase fluids and fiber or to use fiber laxative.
• Explain that use of methadone before pain becomes acute will allow it to alleviate pain better.
• Caution patient to avoid sudden position changes to prevent orthostatic hypotension.
• Explain types and potential significance of sympathomimetic side effects.