Synthadon 5 mg/ml Solution for Injection for Cats and Dogs

Due to the variable individual response to methadone, animals should be regularly
monitored to ensure sufficient efficacy for the desired effect duration. Use of the
veterinary medicinal product must be preceded by a thorough clinical examination. In
cats pupil dilatation is seen long after the analgesic effect has disappeared. It is

Revised: December 2024
AN: 00064/2023
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 veterinary medicinal 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
veterinary medicinal 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. Use in the above mentioned cases should be in accordance with a benefit/risk
assessment by the responsible veterinarian.
Special precautions to be taken by the person administering the veterinary medicinal
product to animals
Methadone can cause respiratory depression following spillage on the skin or
accidental self-injection. Avoid skin, eyes and mouth contact and personal protective
equipment consisting of impermeable gloves should be worn when handling the
veterinary medicinal product. In case of spilling on the skin or splashing in 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 veterinary medicinal product.
In case of accidental self-injection, seek medical advice immediately and show the
package leaflet or the label to the physician but DO NOT DRIVE as sedation may
occur.
To the physician:
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 initiated. Administration of the
opioid antagonist naloxone to reverse the symptoms is recommended.
Special precautions for the protection of the environment
Not applicable.
Other precautions
Not applicable.

Revised: December 2024
AN: 00064/2023