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Clinical particulars
Target species
Dogs and cats.
Indications for use
- Analgesia in dogs and cats.
- Pre-medication for general anaesthesia or neuroleptanalgesia in dogs and cats in combination with a neuroleptic drug.
Contraindications
Do not use in known cases of hypersensitivity to the active substance or to any of the excipients.
Do not use in animals with advanced respiratory failure.
Do not use in animals with severe liver and renal dysfunction.
Special warnings for each target species
Due to the variable individual response to methadone, animals should be monitored regularly to ensure sufficient efficacy for the desired duration of effect.
Use of the product must be preceded by a thorough clinical examination.
In cats, pupil dilatation is seen long after the analgesic effect has disappeared. It is therefore not an adequate parameter to assess clinical efficacy of the administered dose.
Greyhounds may require higher doses than other breeds to achieve efficacious plasma levels.
Special precautions for use in animals
Methadone may occasionally cause respiratory depression and as with other opioid drugs, care should be taken when treating animals with impaired respiratory function, or animals that are receiving drugs that can cause respiratory depression. To ensure safe use of the product, treated animals should be monitored regularly, including examination of heart rate and respiratory rate.
As methadone is metabolised by the liver, its intensity and duration of action may be affected in animals with impaired liver function. In case of renal, cardiac or hepatic dysfunction, or shock, there may be greater risk associated with the use of the product. The safety of methadone has not been demonstrated in dogs less than 8 weeks and cats less than 5 months of age. The effect of an opioid on head injury is dependent on the type and severity of the injury and the respiratory support supplied. Safety has not been fully evaluated in clinically compromised cats. Due to the risk of excitation, repeated administration in cats should be used with care. The benefit/risk ratio for using the product should be made by the attending veterinarian.
Special precautions to be taken by the person administering the veterinary medicinal product to animals
Methadone can cause respiratory depression following spillage onto the skin or accidental self-injection. Avoid skin, eye and mouth contact and wear impermeable gloves when handling the product. In cases of spillage onto the skin, or splashing into the eyes, wash immediately with large amounts of water. Remove contaminated clothes.
People with known hypersensitivity to methadone should avoid contact with the veterinary medicinal product.
Methadone has the potential to cause stillbirths. Pregnant women are advised not to handle the product.
In the case of accidental self-injection, seek medical advice immediately and show the package leaflet to the physician but DO NOT DRIVE as sedation may occur.
ADVICE TO DOCTORS: Methadone is an opioid whose toxicity may cause clinical effects including respiratory depression or apnoea, sedation, hypotension and coma. When respiratory depression occurs controlled ventilation should be installed. Administration of the opioid antagonist naloxone to reverse the symptoms is recommended.
Adverse reactions
In very common cases (more than 1 in 10 animals displaying adverse reaction(s) during the course of one treatment), the following reactions have been observed after administration of the product:
Cats: Respiratory depression may be seen. Mild excitatory reactions have been observed: lip licking, vocalisation, urination, defaecation, mydriasis, hyperthermia and diarrhoea. Hyperalgesia has been reported. All reactions were transient.
Dogs: Respiratory and bradycardia depression may be seen. Mild reactions have been observed: panting, lip licking, salivation, vocalisation, irregular breathing, hypothermia, fixed stare and body tremors. Occasional urination and defaecation can be seen within the first hour post dose. All reactions were transient.
Use during pregnancy and lactation
Methadone diffuses across the placenta. Studies in laboratory animals have shown adverse effects on reproduction. The safety of the product during pregnancy and lactation has not been assessed in the target species. The use of the product is not recommended during pregnancy or lactation.
Interactions
For concurrent use with neuroleptics refer to Amounts to be administered and administration route. Methadone can potentiate the effects of analgesics, central nervous system inhibitors and substances that cause respiratory depression. Concomitant or subsequent use of the veterinary medicinal product with buprenorphine may lead to lack of efficacy.
Amounts to be administered and administration route
Before administration the body weight should be accurately determined.
Analgesia:
Dogs: 0.5 to 1 mg Methadone HCl per kg body weight, SC, IM or IV (corresponding to 0.05 to 0.1 ml/kg).
Cats: 0.3 to 0.6 mg Methadone HCl per kg body weight, IM (corresponding to 0.03 to 0.06 ml/kg). To ensure accuracy of dosing in cats, an appropriately calibrated syringe should be used to administer the product.
As the individual response to methadone is varied, and depends partly on the dosage, the age of the patient, individual differences in pain sensitivity and general condition, the optimal dosing regimen should be individually based. In dogs, onset of action is 1 hour following subcutaneous administration, approximately 15 minutes following intramuscular injection and within 10 minutes following intravenous injection. Duration of effect is approximately 4 hours following intramuscular or intravenous administration. In cats, onset of action is 15 minutes following administration, and the duration of effect is 4 hours on average. The animal should be examined regularly to assess if additional analgesia is subsequently required.
Pre-medication and/or neuroleptanalgesia:
Dogs:
- Methadone HCl 0.5-1 mg/kg body weight, IV, SC or IM (corresponding to 0.05 to 0.1 ml/kg).
Combinations, e.g.:
- Methadone HCl 0.5 mg/kg body weight, IV (corresponding to 0.05 ml/kg), + e.g. midazolam or diazepam:
Induction with propofol, maintenance on isoflurane in oxygen.
- Methadone HCl 0.5 mg/kg body weight, IV (corresponding to 0.05 ml/kg), + e.g acepromazine:
Induction with thiopentone or propofol to effect, maintenance on isoflurane in oxygen or induction with diazepam and ketamine.
- Methadone HCl 0.5-1.0 mg/kg body weight, IV or IM (corresponding to 0.05 to 0.1 ml/kg), + α2-agonist (e.g. xylazine or medetomidine):
Induction with propofol, maintenance with isoflurane in combination with fentanyl or total intravenous anaesthesia (TIVA) protocol: maintenance with propofol in combination with fentanyl.
TIVA protocol: Induction propofol, to effect. Maintenance with propofol and remifentanil.
Chemical-physical compatibility has only been demonstrated for dilutions 1:5 with the following solutions for infusion: sodium chloride 0.9%, Ringer's solution, and glucose 5%.
Cats:
- Methadone HCl 0.3 to 0.6 mg/kg body weight, IM (corresponding to 0.03 to 0.06 ml/kg):
- Induction with Benzodiazepine (e.g. midazolam) and dissociative (e.g. ketamine);
- With a tranquiliser (e.g. acepromazine) and NSAID (meloxicam) or sedative (e.g. α2-agonist);
- Induction with propofol, maintenance with isoflurane in oxygen.
Doses are dependent on the desired degree of analgesia and sedation, desired duration of effect and the concurrent use of other analgesics and anaesthetics.
When used in combination with other products, lower dosages can be used.
For safe use with other veterinary medicinal products, reference must be made to the relevant product literature.
Overdose
A 1.5 fold overdose resulted in the effects described in Adverse reactions.
Cats: In case of overdoses (>2 mg/kg) the following signs can be observed: increased salivation, excitation, hind leg paralysis and loss of righting reflex. Seizures, convulsion and hypoxia were also recorded in some cats. A dose of 4 mg/kg could be fatal in cats. Respiratory depression has been described.
Dogs: Respiratory depression has been described.
Methadone can be antagonised by naloxone. Naloxone should be given to effect. A starting dose of 0.1 mg/kg intravenously is recommended.