Chemical formula: C₂₁H₂₇NO Molecular mass: 309.445 g/mol PubChem compound: 4095
There is no evidence of safety in human pregnancy. A careful risk/benefit assessment should be made before administration to pregnant women because of possible adverse effects on the foetus and neonate including respiratory depression, low birth weight, neonatal withdrawal syndrome and increased rate of stillbirths. However, methadone has not been associated with congenital malformations.
It may be necessary to increase the dose of methadone if withdrawal symptoms develop. Increased clearance and reduced plasma levels have been reported during pregnancy.
Female addicts who are pregnant will require specialised care from obstetric and paediatric staff with experience in such management.
During labour there is a risk of gastric stasis and inhalation pneumonia in the mother and foetal distress. Methadone should not be used in labour.
Methadone is excreted in breastmilk at low levels. The decision to recommend breast-feeding should take into account clinical specialist advice and consideration should be given to whether the woman is on a stable maintenance dose of methadone and any continued use of illicit substances. If breastfeeding is considered, the dose of methadone should be as low as possible. Prescribers should advise breastfeeding women to monitor the infant for sedation and breathing difficulties and to seek immediate medical care if this occurs. Although the amount of methadone excreted in breast milk is not sufficient to fully suppress withdrawal symptoms in breast-fed infants, it may attenuate the severity of neonatal abstinence syndrome. If it is necessary to discontinue breastfeeding it should be done gradually, as abrupt weaning could increase withdrawal symptoms in the infant.
Specialist care for obstetric and paediatric staff with experience in such management is required. If breast feeding is considered, the dose of methadone should be as low as possible and the infant monitored to avoid sedation. Breastfed infants may develop physical dependence and exhibit withdrawal symptoms.
Reports of visual disorders have been reported in neonates following exposure to methadone during pregnancy. However, other factors have also been present and a definitive causal link to methadone has not been established.
The ability to drive or operate machinery may be severely effected during and after treatment with methadone. The time after which such activities can be safely resumed is extremely patient dependant and must be decided by the physician.
Methadone may cause drowsiness and reduce alertness and the ability to drive. after the administration of methadone.
This medicine can impair cognitive function and can affect a patient’s ability to drive safely. This class of medicine is in the list of drugs included in regulations under 5a of the Road Traffic Act 1988. When prescribing this medicine, patients should be told:
The adverse effects of methadone are generally the same as with other opioids, most commonly nausea and vomiting, which are observed in approximately 20% of the patients who undergo methadone outpatient treatment, where the medicinal control is often unsatisfactory.
The most serious adverse effect of methadone is respiratory depression, which may emerge during the stabilisation phase. Apnoea, shock and cardiac arrest have occurred.
Adverse reactions listed below are classified according to frequency and system organ class. These reactions are more frequently observed in non opioid tolerant individuals. Frequency groupings are defined according to the following convention: very common (≥1/10), common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), rare (≥1/10,000 to <1/1,000), very rare (<1/10,000), not known (cannot be estimated from the available data).
Not known: Hyperprolactinaemia.
Common: Euphoria, hallucinations.
Uncommon: Dysphoria, dependence, agitation, insomnia, disorientation, reduced libido.
Unknown: Drug dependence.
Common: Sedation.
Uncommon: Headache, syncope.
Common: Blurred vision, miosis, dry eyes.
Not Known: Nystagmus.
Common: Vertigo.
Rare: Bradycardia, palpitations, cases of prolonged QT interval and torsade de pointes have been reported, especially with high doses of methadone.
Uncommon: Facial flush, hypotension.
Uncommon: Pulmonary oedema, exacerbation of asthma, dry nose, respiratory depression particularly with large doses.
Very common: Nausea, vomiting.
Common: Constipation.
Uncommon: Xerostomia, glossitis.
Uncommon: Bile duct dyskinesia.
Common: Transient rash, sweating.
Uncommon: Pruritis, urticaria, other rash and in very uncommon cases bleeding urticaria.
Uncommon: Urinary retention, antidiuretic effect.
Uncommon: Reduced potency, galactorrhoea, dysmenorrhoea and amenorrhoea.
Common: Fatigue, drowsiness.
Uncommon: Oedema of the lower extremities, asthenia, oedema, hypothermia, drug withdrawal syndrome.
Common: Weight increase.
Methadone is associated with undesirable effects similar to other opioid analgesics. There are no modern clinical studies available that can be used to determine the frequency of undesirable effects. Therefore, all the undesirable effects listed are classed as “frequency unknown”.
Endocrine Disorders: Hyperprolactinaemia.
Psychiatric Disorders: Confusion, mood change including euphoria and dysphoria, hallucinations, restlessness, sleep disturbances. Drug dependence.
Nervous System Disorders: Drowsiness, dizziness, vertigo.
Eye Disorders: Dry eyes, visual disturbances such as miosis.
Cardiac Disorders: Bradycardia, tachycardia, palpitations, QT prolongation, torsades de pointes.
Vascular Disorders: Orthostatic hypotension.
Respiratory, Thoracic & Mediastinal Disorders: Respiratory depression, dry nose.
Gastrointestinal Disorders: Nausea, vomiting (particularly at the start of treatement), constipation, biliary spasm, dry mouth.
Skin & Subcutaneous tissue Disorders: Sweating, facial flushing, rashes (urticaria, pruritus), oedema.
Musculoskeletal, Connective Tissue & Bone Disorders: Muscle rigidity
Renal & Urinary Disorders: Micturition difficulties, urinary retention, ureteric spasm
Reproductive System & Breast Disorders: Decreased libido, dysmenorrhoea, amenorrhoea, sexual dysfunction
Metabolism and nutrition disorders SOC: Hypoglycaemia (frequency not known).
General & Administration Site Disorders: Hypothermia, drug withdrawal syndrome.
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