Metamizole for Dogs - Usage, Dosage and Side Effects

Metamizole or dipyrone is a drug belonging to the group of pyrazolone derivatives that is used as an analgesic, antipyretic and spasmolytic agent. It is not a type of non-steroidal anti-inflammatory drug (NSAID), but it does have a weak anti-inflammatory effect in some cases.

Availability of metamizole

Although Metamizole can be purchased over the counter in some countries, it should only ever be given to dogs under veterinary supervision. Since metamizole is the active ingredient, it is often sold under trade names such as Novalgin.

In the United Kingdom and Unites States, it is usually referred to as dipyrone as approved or adopted names, respectively. Although it has been used previously as a solution for injection, metamizole is no longer approved in the United States or the United Kingdom. This is due to the potential development of a side effect known as agranulocytosis. This is a blood disorder which can be fatal.

Like any other drug, metamizole must be prescribed by a veterinarian. Since it requires parenteral administration (intravenous or intramuscular route), it must also be administered by a veterinarian or veterinary assistant.

As we have stated in the previous section, metamizole has three fundamental effects: analgesic, antipyretic and spasmolytic. We will explain each of these effects and the specific situations in which their administration can be beneficial.

Analgesic effect

Metamizole is a drug with an analgesic effect that is used to relieve moderate to severe pain. This effect is produced thanks to the strong blockade of the enzyme cyclo-oxygenase (COX-3) and the activation of the opioid and cannabinoid systems.

Its analgesic effect allows this drug to be used within multimodal analgesia which consists of the simultaneous use of different classes of analgesics that act on different receptors and transmission pathways. The aim of their usage is to provide better pain control. Specifically, metamizole in dogs can be combined with NSAIDs and opioids, allowing the dose of each drug to be reduced. It has also been shown to have a synergistic effect with other pain relievers, such as morphine or ketoprofen.

Specifically, metamizole is used to control:

• Visceral pain (especially colicky pain)
• Pain due to cancer
• Postoperative pain
• Pain associated with the musculoskeletal system (e.g. in arthritis, rheumatic conditions, neuralgia or low back pain)

A noteworthy aspect of metamizole is that its action does not involve blocking the production of prostaglandins. For this reason, it does not produce the characteristic adverse effects of NSAIDs (such as gastrointestinal ulcers or kidney failure). Therefore, it can be considered a good alternative for those patients in whom the use of NSAIDs is contraindicated.

Learn more about other painkillers for canine use with our article on dexketoprofen for dogs.

Antipyretic effect

Metamizole also has an antipyretic effect, i.e. it reduces fever in dogs. Although the antipyretic mechanism of action is not well defined, there is evidence showing that this effect occurs through pathways independent of prostaglandin blocking.

In general, metamizole can be used in any febrile episode, especially in cases that are refractory to other antipyretic drugs.

Spasmolytic or antispasmodic effect

Last but not least, metamizole in dogs has a spasmolytic or antispasmodic effect. This means that it relaxes smooth muscle in the digestive tract, urinary tract, bile duct, etc. This antispasmodic effect is explained by the decrease in the synthesis of inositol phosphate, which produces a reduction in the release of intracellular calcium.

Because of its antispasmodic properties, metamizole is often used in dogs with gastrointestinal, biliary, or urinary colic.

Currently, metamizole for dogs is only available as an injectable solution for intravenous or intramuscular administration.

The dose of metamizole for dogs should be 20 to 50 mg of metamizole per kilogram of body weight. This dose can be administered either slowly intravenously or deep intramuscularly, but not subcutaneously. This is due to the susceptibility of local irritation at the injection site. Learn more about this process with our article on giving a dog shots under the skin.

Metamizole overdose in dogs

Cases of dipyrone overdose in dogs have been reported at very high doses, from 1,000 to 4,000 mg/kg body weight. Metamizol poisoning in dogs affects the central nervous system, causing symptoms such as sedation and seizures. In cases of overdose, it will be necessary to establish supportive treatment and control the convulsive crisis with intravenous diazepam for dogs.

Although cases of leukopenia, agranulocytosis and aplastic anemia have been reported in people due to the use of metamizol, in veterinary medicine there are no reports on the presence of these or other hematological toxic effects caused by metamizole. In fact, the data sheet for metamizole does not describe any adverse reaction associated with the use of this drug. This does not mean side effects do not exist, but that they are poorly reported in veterinary medicine.

Although metamizole can be fairly safe drug, there are certain situations in which its administration can be counterproductive. Specifically, metamizole in dogs is contraindicated in the following cases:

• Allergy or hypersensitivity to metamizole or to any excipient that accompanies the active ingredient
• Dogs with heart, liver or kidney failure
• Dogs with gastric or intestinal ulcers

It should be noted that studies in animals have not shown that metamizole produces teratogenic or toxic effects on fetuses. However, it is recommended to use it with caution in pregnant and lactating bitches since more evidence is required to prove the safety of the drug in these stages.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

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