Dantrolene: veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

Dantrium, Revonto, Ryanodex

Species with doses

Dogs, Cats, Horses and Pigs

General dose range

1–5 mg/kg IV as needed (MH crisis) / q8–12h (oral) — check the species tables for the indication

Routes

IV, PO

Last reviewed

1 October 2026

Indications

• Malignant hyperthermia crisis — specific antidote (IV)
• Prevention of MH in known-susceptible patients (pigs) before triggering anaesthesia
• Equine exertional rhabdomyolysis ("tying-up") — prevention/management (oral)
• Functional (reflex dyssynergia) urethral obstruction — external urethral sphincter relaxation

Dantrolene dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Malignant hyperthermia (IV): Papich 5e: prevention 2–3 mg/kg IV; crisis 2.5–3 mg/kg rapid IV bolus (up to 5–10 mg/kg) — canine doses are anecdotal/extrapolated. Plumb’s p.347: acute attack 0.2–3 mg/kg IV (Axlund); hops toxicosis 2–3 mg/kg IV or 3.5 mg/kg PO ASAP (Wismer). Also stop the trigger, cool actively, give 100% oxygen and treat hyperkalaemia/acidosis.
• Functional urethral obstruction (oral): Papich 5e: 1–5 mg/kg PO q8h (or 0.5–1 mg/kg IV). Plumb’s p.347: 1–5 mg/kg PO q8–12h (Lane; Coates); 1 mg/kg PO q8h (Lulich). Relaxes the striated external urethral sphincter — combine with an alpha-blocker (prazosin) for the smooth-muscle component. Hepatotoxic with chronic use.

Cats

• Functional urethral obstruction / muscle relaxation: Papich 5e: muscle relaxation 0.5–2 mg/kg PO q12h; urethral relaxation 1–2 mg/kg PO q8h. Plumb’s p.347: 0.5–2 mg/kg PO q12h or 0.5–1 mg/kg IV (Gunn-Moore); 0.5–2 mg/kg three times daily (Coates); 2–10 mg per cat three times daily with prazosin or phenoxybenzamine (Sparkes). Monitor for weakness and hepatotoxicity.

Horses

• Exertional rhabdomyolysis ("tying-up") prevention: Papich 5e: most commonly 500 mg per horse PO, or 4 mg/kg PO. Plumb’s p.347: 4 mg/kg PO to fasted horses (McKenzie 2003); 2 mg/kg PO once daily for 3–5 days then every 3rd day for a month, or 300 mg per horse daily (MacLeay — efficacy uncertain); 800 mg per horse 1 h before exercise (Edwards). Monitor liver function.
• Post-anaesthetic myopathy prevention: Plumb’s p.347: 6 mg/kg via nasogastric tube 60 min before anaesthesia (McKenzie & Mosley 2009); 10 mg/kg intragastric 1.5 h before surgery, with 2.5 mg/kg q60min if more is needed (Court 1987).

Pigs

• Malignant hyperthermia (treatment): Papich 5e: 1–3 mg/kg IV once. Plumb’s p.347 (Booth 1988): 3.5 mg/kg IV. Obtain a FARAD withdrawal before slaughter.
• Malignant hyperthermia prophylaxis: Papich 5e: 5 mg/kg PO for prophylaxis in susceptible (RYR1) pigs. Obtain a FARAD withdrawal.

Contraindications

Significant hepatic impairment (oral dantrolene is hepatotoxic with chronic use). Known hypersensitivity. (For tying-up prevention, give on an empty stomach for absorption.) Use the IV form promptly in an MH crisis. Avoid extravasation (irritant).

Species-specific warnings

Pigs: Pigs (RYR1/halothane-sensitive) are the classic malignant-hyperthermia species — pre-treat known-susceptible pigs and have IV dantrolene ready for triggered crises.

Adverse effects

• Muscle weakness
• Sedation, lethargy
• Hepatotoxicity (chronic oral use)
• GI upset; phlebitis/irritation (IV)

Drug interactions

• Volatile anaesthetics/succinylcholine: the MH triggers (dantrolene is the antidote)
• Calcium-channel blockers (verapamil/diltiazem) with IV dantrolene: risk of hyperkalaemia/cardiovascular collapse — avoid the combination
• Other CNS depressants/muscle relaxants: additive weakness/sedation
• Hepatotoxic drugs: additive (chronic oral use)

Pregnancy and lactation

Used when needed for an MH crisis (life-threatening); limited routine data otherwise.

Monitoring

• In MH: temperature, EtCO2, ECG/heart rate, potassium and acid–base (treat the crisis comprehensively)
• Muscle strength / respiration (weakness)
• Liver enzymes with chronic oral use
• Response of tying-up/urethral function for those indications

Toxicity and overdose

Overdose causes excessive muscle weakness, sedation, and (chronic oral use) hepatotoxicity. The acute injectable, used appropriately in MH, is lifesaving; the chief chronic concern is dose-related hepatotoxicity with oral therapy.

Management: No specific antidote. Supportive — support ventilation if weakness compromises breathing, monitor and protect the airway; for hepatotoxicity, discontinue and provide hepatoprotection/monitoring. Avoid IV dantrolene + calcium-channel-blocker combination.

Clinical pearls

• THE antidote for malignant hyperthermia — give IV immediately (with stopping the trigger, cooling, 100 % O2, treating hyperkalaemia/acidosis); stock it where volatile anaesthesia/MH-susceptible pigs are involved
• Reconstitution is slow (poorly soluble) — know your product (Ryanodex is faster) and have it ready before a crisis
• Orally, it helps prevent equine "tying-up" (give on an empty stomach before exercise) and relaxes the external urethral sphincter in functional obstruction (pair with an alpha-blocker)
• Avoid IV dantrolene with calcium-channel blockers (hyperkalaemia/collapse); watch the liver on chronic oral use

Mechanism of action

Binds the skeletal-muscle ryanodine receptor (RyR1) on the sarcoplasmic reticulum and inhibits calcium release into the cytoplasm, uncoupling excitation from contraction — directly relaxing skeletal muscle WITHOUT acting at the neuromuscular junction. In malignant hyperthermia, this halts the uncontrolled sarcoplasmic calcium release that drives the hypermetabolic crisis; the same action reduces the muscle hyperactivity of rhabdomyolysis and relaxes the striated urethral sphincter.

Formulations and products

• Injection 20 mg vial (reconstitute) / 250 mg Ryanodex vial
• 25 / 50 / 100 mg capsule (oral)
• Dantrium / Revonto / Ryanodex — 20 mg / 250 mg vial; 25–100 mg capsule, Injection / capsule (human-label)

Storage

IV vials: protect from light; reconstitute per label just before use (poorly soluble — Ryanodex reconstitutes faster). Capsules: 15–30 °C, dry. Have it readily available where MH risk exists.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

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Frequently asked questions