Metamizole (Dipyrone) in Cats

What it is

Regulatory status - important caveat

Pharmacokinetics in cats

• Lebkowska-Wieruszewska et al. 2018 (J Vet Pharmacol Ther) gave cats 25 mg/kg IV, IM, and PO in a crossover design. MAA reached mean peak concentrations of ~148.6 µg/mL (IV), ~18.7 µg/mL (IM), and ~20.6 µg/mL (PO), with a half-life of about 7 hours across routes. AA was detectable up to 24 h at lower concentrations. Adverse signs (salivation, vomiting) occurred in all groups: 67% after IV, 34% after IM, 15% after PO.
• de Paula et al. 2023 (Research in Veterinary Science) gave cats 25 mg/kg IV only. Peak MAA was ~29.3 µg/mL (half-life ~5 h) and peak AA was ~1.7 µg/mL (half-life ~14 h, detectable beyond 48 h). Salivation was the main adverse sign noted.

Clinical/toxicology study

• Dipyrone plus tramadol did not provide better analgesia than tramadol alone.
• No clinically meaningful changes in complete blood count, biochemistry, oxidative stress markers (SOD, catalase, lipoperoxidation), or Heinz body percentage were seen, aside from a minor, not clinically relevant myeloperoxidase difference between two dipyrone groups.
• No agranulocytosis or serious hematologic toxicity was observed over this short (5-10 day) monitoring period.

Reported/typical off-label dosing (where used)

• Metamizole (dipyrone): 20-30 mg/kg IV, SC, or IM every 8 hours

Safety concerns

• Agranulocytosis: The principal concern carried over from human medicine. Onset is unpredictable, can follow short-term or long-term use, and is thought to be immune/hypersensitivity mediated rather than dose-dependent; incidence varies by region/genetics and has never been well characterized in cats specifically.
• Anaphylactic/hypersensitivity reactions: injection-site pain/inflammation is common; rare but serious allergic reactions (facial swelling, irregular breathing, fever, rash) can occur and warrant immediate veterinary contact (VCA Animal Hospitals).
• Hemostasis: dipyrone can prolong clotting time, so dosing intervals shorter than 12 h are cautioned against in some species guidance, and it should not be combined with other NSAIDs or corticosteroids (increased GI ulceration/renal risk) - VCA Animal Hospitals.
• Duration of clinical effect is roughly 6-12 hours, longer in cats with hepatic or renal impairment, so caution and dose adjustment/avoidance is warranted in cats with liver or kidney disease.
• No significant impact on renal function or GI tract has been reported in otherwise healthy animals in the available studies, though prolonged use data in cats is sparse.

Bottom line for a clinician or cat owner

1. It is not licensed for cats in most countries and use remains off-label.
2. Robust feline-specific dosing, pharmacodynamic efficacy data, and long-term safety data (particularly regarding agranulocytosis risk) are still lacking - all cited veterinary sources explicitly call for more safety studies before routine clinical use.
3. In the one controlled clinical trial available, adding dipyrone to tramadol did not improve postoperative analgesia over tramadol alone.
4. It should never be combined with other NSAIDs or corticosteroids, and should be used cautiously (or avoided) in cats with hepatic/renal disease, coagulopathy, or known NSAID/pyrazolone hypersensitivity.

Drug of Choice for Pyrexia in Cats

Key principle first

• Very high fever (>41.1°C/106°F) with risk of hyperthermic tissue injury
• Fever causing significant anorexia, lethargy, or patient distress
• Fever of unknown origin where trial anti-inflammatory therapy is used cautiously under close monitoring

If an antipyretic drug is used

• It is one of only two NSAIDs FDA-approved for cats (the other being robenacoxib), and has the best-studied safety/tolerability profile in the species (dvm360; Merck Veterinary Manual; Today's Veterinary Practice).
• An early experimental study (Justus, 1995) found 0.3 mg/kg was the effective dose to prevent endotoxin-induced fever in cats - but this happens to overlap with a dose associated with toxicity (GI ulceration, death at 3-6x this dose over 10 days), so it illustrates the very narrow therapeutic margin of NSAIDs in cats.
• For any clinical use, low doses are preferred: typical dosing is 0.05 mg/kg PO q24h (label maintenance dose in the EU) or even lower (0.02-0.025 mg/kg) for more cautious/chronic use; the US label restricts meloxicam to a single injectable dose because repeated dosing has caused kidney failure and death in cats (FDA).
• Robenacoxib (Onsior) is the other FDA-approved feline NSAID, generally limited to short courses (label max around 3 days in the US).

• Acetaminophen/paracetamol is absolutely contraindicated in cats - they lack sufficient glucuronyl transferase activity, leading to methemoglobinemia, Heinz body hemolytic anemia, and centrilobular hepatic necrosis, which can be fatal even at doses considered safe in dogs or humans (MSD/Merck Veterinary Manual).
• Aspirin can theoretically be used but cats metabolize salicylates very slowly (prolonged half-life due to limited glucuronidation), so it requires markedly extended dosing intervals (roughly every 48-72 hours) and carries real risk of GI ulceration and platelet effects - it is not considered first-line today.
• Dipyrone (metamizole) is used off-label as an antipyretic/analgesic in some countries, but as discussed previously, feline-specific safety and dosing data remain limited, it's not approved for cats in most Western countries, and agranulocytosis risk (though rare) is unpredictable - so it is not a preferred first choice where FDA/EMA-approved options exist.
• Corticosteroids can reduce fever through anti-inflammatory action but should generally be avoided until an infectious cause has been ruled out, since they can worsen infections and confound diagnostic workup - they're used mainly when an immune-mediated cause (e.g., autoagglutination in hemotropic mycoplasmosis) is identified.

Practical bottom line

1. Identify and treat the underlying cause (infection, immune-mediated disease, neoplasia) - this resolves the fever in most cases.
2. If symptomatic fever reduction is truly needed, low-dose meloxicam (or robenacoxib for short courses) under veterinary supervision is the most defensible NSAID choice given its approval status and relatively better-characterized safety in cats - always balanced against the narrow feline NSAID margin, and avoided in cats with renal, hepatic, or GI disease or dehydration.
3. Never give acetaminophen to a cat under any circumstance.

Injection Vetalgin in Cats

What Vetalgin is

Critical safety warning - it is contraindicated in cats

"Do not use in cats. Do not use by subcutaneous route. Vetalgin should not be used in animals with disturbance of the haematopoietic system." - MSD Animal Health India, Vetalgin Vet product label

Species dosing on the approved label (none for cats)

Approved indications (in permitted species)

Why this matters given generic metamizole use in cats

• That off-label use applies to plain metamizole, not necessarily to every branded product formulation.
• Vetalgin specifically carries a "do not use in cats" label warning, likely tied to its excipients (benzyl alcohol/chlorbutol) rather than metamizole alone.
• Contraindications also apply if the animal has any hematopoietic/bone marrow disturbance, given the class-wide (if rare) agranulocytosis risk.
• The product should never be given subcutaneously in any species per the label, and IV injection should be slow to avoid hypotension.

Bottom line