メタドン

動物種別の用量

投与経路

禁忌

• Late-term pregnancy (due to risks of respiratory depression and stillbirths)
• Known hypersensitivity to methadone
• No specific contraindications available in the monograph, but use with caution in patients with severe respiratory compromise or hepatic impairment.

有害事象

• Panting
• Whining or vocalization
• Sedation
• Defecation
• Constipation
• Bradycardia
• Respiratory depression
• Pronounced CNS excitement (in horses at IV doses ≥ 0.1 mg/kg)
• Respiratory depression (primarily under general anaesthesia)
• Transient excitation (when given IV)
• Salivation (when given via oral transmucosal route in cats due to preservatives)
• Constriction of gastrointestinal sphincters (e.g., pyloric sphincter)
• Reduction in gastrointestinal motility (with prolonged use)
• Neonatal sedation (crosses the placenta)

薬物相互作用

• Class I & III Antiarrhythmics (e.g., lidocaine, procainamide, quinidine, amiodarone) · May increase risks for arrhythmias
• Alpha2-Agonists (e.g., medetomidine, xylazine) · Potentiates sedative and analgesic effects; combination with medetomidine may cause severe hypoxemia in dogs breathing room air
• Azole Antifungals (fluconazole, itraconazole, ketoconazole) · May increase methadone levels in humans (does not appear to be true for dogs)
• Calcium Channel Blockers · May increase risks for arrhythmias
• CNS Depressants (anesthetics, antihistamines, phenothiazines, barbiturates, tranquilizers) · May cause increased CNS or respiratory depression
• Corticosteroids (Mineralocorticoids) · May increase potential for electrolyte abnormalities
• Diuretics · Opiates may decrease diuretic efficacy in CHF patients
• Macrolide Antibiotics (erythromycin, clarithromycin) · May inhibit metabolism of methadone and increase levels in humans (does not appear to be true for dogs)
• Monoamine Oxidase Inhibitors (MAOIs) (e.g., amitraz, selegiline) · Potential for severe CNS/behavioral reactions; concomitant use should be avoided
• Skeletal Muscle Relaxants · Methadone may enhance neuromuscular blockade
• Phenobarbital, Phenytoin · May decrease methadone levels in humans (probably does not affect dogs)

モニタリング

• Analgesic or preanesthetic efficacy
• Respiratory rate and depth (monitor for respiratory depression, especially at higher doses)
• Heart rate (bradycardia)
• CNS depression or excitation
• Respiratory rate and depth (especially under general anaesthesia)
• Pain scores (due to individual variation in response)
• Level of sedation
• Gastrointestinal motility (with prolonged use)

過量投与

Overdosage may produce profound **respiratory and/or CNS depression** in most species. Newborns are particularly susceptible. Other toxic effects include cardiovascular collapse, hypothermia, and skeletal muscle hypotonia. **Treatment:** * **Naloxone** is the reversal agent of choice for treating respiratory depression. In massive overdoses, naloxone doses may need to be repeated because naloxone's effects might diminish before sub-toxic levels of methadone are attained. * Mechanical respiratory support should be considered in severe cases. * Dialysis, charcoal hemoperfusion, or forced diuresis do not appear to be beneficial.