Methadone


Thông tin thuốc gốc
Chỉ định và Liều dùng
Oral
Analgesia
Adult: Initially 2.5-10 mg every 6-8 hr as required. Titrate dose slowly and according to response. May also be given via IM or SC inj. Not more than twice daily dosing for prolonged use.
Child: 0.7 mg/kg/day in divided doses every 4-6 hr as required, max 10 mg/dose. Dose should be titrated carefully according to individual requirements.

Oral
Neonatal abstinence syndrome
Child: 100 mcg/kg increased by 50 mcg/kg every 6 hr until symptoms are controlled. Daily dose should be given in 2 divided doses during prolonged use.

Oral
Intractable cough associated with lung cancer
Adult: 1-2 mg every 4-6 hr. Reduce to 12 hrly during prolonged use.

Oral
Opioid dependence
Adult: Initial dose of 20-30 mg as a single dose. Additional doses of 5-10 mg may be used if withdrawal symptoms are not suppressed or if they reappear. Total dose should not exceed 40 mg on the 1st day. Usual stabilising dose: 40 mg daily in single or divided doses. Once patient has stabilised for 2 or 3 days, dosage may be gradually reduced daily or at 2-day intervals. Dosage must be individualised and adjusted to keep withdrawal symptoms at a tolerable level.
Child: Dose should be individualised according to opiate tolerance. After a period of maintenance treatment, withdrawal should be slow, with doses reduced by <10% at a time with 10-14 day intervals between dose reductions.
Hepatic Impairment
Dosage may need to be reduced.
Cách dùng
May be taken with or without food.
Chống chỉ định
Acute respiratory depression; acute bronchial asthma; acute alcoholism; risk of paralytic ileus; raised intracranial pressure or head injury.
Thận trọng
Dose should be individualised. Prolonged QT interval; CV disease; hepatic impairment; electrolyte abnormalities; concommitant use of QT prolonging drug; respiratory disease; elderly. May impair ability to drive or operate machinery.
Phản ứng phụ
Nausea; vomiting; constipation; anorexia; abdominal pain; drowsiness; respiratory depression; hypotension; bradycardia; euphoria; headache; dysphoria; urinary retention; miosis; visual disturbances; impotence; dizziness; sweating; pruritis; asthenia; arrythmias; QT prolongation.
Potentially Fatal: Cardiac arrest; respiratory arrest; shock.
IM/IV/Parenteral/PO/SC: C
Quá liều
Respiratory and CV depression may occur. Oxygen, IV fluids, vasopressors and other supportive measures may be used. In non-opioid dependant patients, opioid antagonists can be used but, as they may precipitate an acute withdrawal syndrome, they should be used with caution in opioid dependant patients
Tương tác
Withdrawal symptoms may be experienced with naloxone, naltrexone, pentazocine, nalbuphine, butorphanol, and buprenorphine. Increased clearance and possible reduced efficacy with some antiretrovirals (abacavir, amprenavir, efavirenz, nelfinavir, nevirapine, ritonavir, lopinavir); rifampin; phenytoin; phenobarbital; carbamazepine. Decreased clearance and possibly increased toxicity with CYP3A4 inhibitors (e.g. ketoconazole, voriconazole, sertraline, fluvoxamine). Increased chance of cardiac toxicity with other QT prolonging drugs. Increased CNS depression with alcohol, other opioids or CNS depressants. Methadone may increase plasma levels of desipramine, zidovudine.
Food Interaction
Grapefruit juice may increase oral methadone bioavailability. St John's wort may decrease methadone plasma levels.
Tác dụng
Description: Methadone is a synthetic opioid mu-agonist which binds to opiate receptors in CNS, decreasing the perception and response to pain. It is used principally as an analgesic and for treatment of opioid addiction.
Onset: Oral: 0.5-1 hr for analgesic effect. Parenteral: 10-20 minutes.
Duration: Oral: 6-8 hr, but increases to 22-48 hr with repeated doses.
Pharmacokinetics:
Absorption: Rapidly absorbed from GI tract.
Distribution: Widely distributed, 60-90% protein bound. Crosses placenta and is distributed in milk.
Metabolism: Hepatic metabolism to inactive metabolites.
Excretion: Eliminated in the faeces and urine as metabolites and unchanged drug. Elimination half life varies between individuals.
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