Methadone Hydro Chloride

methadone hydrochloride (meth' a done) Dolophine, Methadone HCl Diskets, Methadone HCl Intensol, Methadose Pregnancy Category C Controlled Substance C-II Drug class

Opioid agonist analgesic Therapeutic actions

Acts as agonist at specific opioid receptors in the CNS to produce analgesia, euphoria, sedation; the receptors mediating these effects are thought to be the same as those mediating the effects of endogenous opioids (enkephalins, endorphins); when used in approved methadone maintenance programs, can substitute for heroin, other illicit opioids in patients who want to terminate a drug use. Indications

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Relief of severe pain Detoxification and temporary maintenance treatment of opioid addiction (ineffective for relief of general anxiety)

Contraindications and cautions

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Contraindicated with hypersensitivity to opioids, diarrhea caused by poisoning (before toxins are eliminated), bronchial asthma, COPD, cor pulmonale, respiratory depression, anoxia, kyphoscoliosis, acute alcoholism, increased intracranial pressure. Use cautiously with acute abdominal conditions, CV disease, supraventricular tachycardias, myxedema, seizure disorders, delirium tremens, cerebral arteriosclerosis, ulcerative colitis, fever, Addison's disease, prostatic hypertrophy, urethral stricture, recent GI or GU surgery, toxic psychosis, pregnancy prior to labor (crosses placenta; neonatal withdrawal observed in infants born to drugusing mothers; safety for use in pregnancy before labor not established), labor or delivery (administration of opioids to mother can cause respiratory depression of neonate—risk greatest for prematures), renal or hepatic dysfunction, lactation.

Available forms

Tablets—5, 10 mg; oral solution—5 mg/5 mL, 10 mg/5 mL; oral concentrate— 10 mg/mL; injection—10 mg/mL; dispersible tablets—40 mg Dosages

Oral methadone is approximately one-half as potent as parenteral methadone. ADULTS

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Relief of pain: 2.5–10 mg IM, SC, or PO q 3–4 hr as necessary. IM route is preferred to SC for repeated doses (SC may cause local irritation). Individualize

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dosage; patients with excessively severe pain and those who have become tolerant to the analgesic effect of opioids may need higher dosage. Detoxification: Initially, 15–20 mg PO or parenteral; PO preferred. Increase dose to suppress withdrawal signs. 40 mg/day in single or divided doses is usually an adequate stabilizing dose for those physically dependent on high doses. Continue stabilizing doses for 2–3 days, then gradually decrease dosage every day or every 2 days. A daily reduction of 20% of the total dose may be tolerated. Provide sufficient dosage to keep withdrawal symptoms at tolerable level. Treatment should not exceed 21 days and may not be repeated earlier than 4 wk after completion of previous course. Detoxification treatment continued longer than 21 days becomes maintenance treatment, which may be undertaken only by approved programs (addicts hospitalized for other medical conditions may receive methadone maintenance treatment). Maintenance treatment: For patients who are heavy heroin users up until hospital admission, initial dose of 20 mg 4–8 hr after heroin is stopped or 40 mg in a single dose PO. For patients with little or no opioid tolerance, half this dose may suffice. Dosage should suppress withdrawal symptoms but not produce acute narcotic effects of sedation, respiratory depression. Give additional 10 mg doses if needed to suppress withdrawal syndrome. Adjust dosage, up to 120 mg/day.

PEDIATRIC PATIENTS

Not recommended for relief of pain in children due to insufficient documentation. GERIATRIC PATIENTS OR IMPAIRED ADULTS

Use caution. Respiratory depression may occur in the elderly, the very ill, those with respiratory problems. Reduced dosage may be necessary. Pharmacokinetics Route PO IM SC

Onset 30–60 min 10–20 min 10–20 min

Peak 1.5–2 hr 1–2 hr 1–2 hr

Duration 4–12 hr 4–6 hr 4–6 hr

Metabolism: Liver; T1/2: 25 hr Distribution: Crosses placenta and enters breast milk Excretion: Bile and feces Adverse effects

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CNS: Light-headedness, dizziness, sedation, euphoria, dysphoria, delirium, insomnia, agitation, anxiety, fear, hallucinations, disorientation, drowsiness, lethargy, impaired mental and physical performance, coma, mood changes, weakness, headache, tremor, seizures, miosis, visual disturbances, suppression of cough reflex CV: Facial flushing, peripheral circulatory collapse, arrhythmia, palpitations, chest wall rigidity, hypertension, hypotension, orthostatic hypotension, syncope Dermatologic: Pruritus, urticaria, laryngospasm, bronchospasm, edema, hemorrhagic urticaria (rare) GI: Nausea, vomiting, dry mouth, anorexia, constipation, biliary tract spasm; increased colonic motility in patients with chronic ulcerative colitis

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GU: Ureteral spasm, spasm of vesical sphincters, urinary retention or hesitancy, oliguria, antidiuretic effect, reduced libido or potency Local: Tissue irritation and induration (SC injection) Major hazards: Respiratory depression, apnea, circulatory depression, respiratory arrest, shock, cardiac arrest Other: Sweating (more common in ambulatory patients and those without severe pain), physical tolerance and dependence, psychological dependence

Interactions

Drug-drug • Potentiation of effects of methadone with barbiturate anesthetics—decrease dose of meperidine when coadministering • Decreased effectiveness of methadone with hydantoins, rifampin, urinary acidifiers (ammonium chloride, potassium acid phosphate, sodium acid phosphate) • Increased effects and toxicity of methadone with cimetidine, ranitidine Drug-lab test • Elevated biliary tract pressure (opioid effect) may cause increases in plasma amylase, lipase; determinations of these levels may be unreliable for 24 hr after administration of opioids Nursing considerations Assessment

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History: Hypersensitivity to opioids, diarrhea caused by poisoning, bronchial asthma, COPD, cor pulmonale, respiratory depression, kyphoscoliosis, acute alcoholism, increased intracranial pressure; acute abdominal conditions, CV disease, supraventricular tachycardias, myxedema, seizure disorders, delirium tremens, cerebral arteriosclerosis, ulcerative colitis, fever, Addison's disease, prostatic hypertrophy, urethral stricture, recent GI or GU surgery, toxic psychosis; pregnancy; labor; lactation Physical: T; skin color, texture, lesions; orientation, reflexes, bilateral grip strength, affect, pupil size; pulse, auscultation, BP, orthostatic BP, perfusion; R, adventitious sounds; bowel sounds, normal output; frequency and pattern of voiding, normal output; ECG; EEG; thyroid, liver, kidney function tests

Interventions

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Give to lactating women 4–6 hr before the next feeding to minimize the amount in milk. Keep opioid antagonist and equipment for assisted or controlled respiration readily available during parenteral administration. Use caution when injecting SC into chilled areas of the body or in patients with hypotension or in shock—impaired perfusion may delay absorption; with repeated doses, an excessive amount may be absorbed when circulation is restored.

Teaching points

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Take drug exactly as prescribed. Avoid alcohol—serious adverse effects may occur. Do not take leftover medication for other disorders; do not let anyone else take the prescription. Avoid pregnancy while taking this drug; using barrier contraceptives is advised. These side effects may occur: Nausea, loss of appetite (take with food, lie quietly, eat frequent small meals); constipation (laxative may help); dizziness, sedation, drowsiness, impaired visual acuity (avoid driving, performing other tasks that require alertness, visual acuity). Report severe nausea, vomiting, constipation, shortness of breath, or difficulty breathing.

Adverse effects in Italic are most common; those in Bold are life-threatening.