Dantrolene

Dantrolene is a directly acting skeletal-muscle relaxant used for disorders involving excessive skeletal-muscle calcium release or contraction. Its most important emergency application is malignant hyperthermia. In horses, it is also used for selected rhabdomyolysis and peri-anesthetic muscle disorders; selected urethral-relaxation uses in small animals are largely empirical.

Group

Direct skeletal muscle relaxant

Mechanism of Action

Dantrolene inhibits calcium release from the sarcoplasmic reticulum, principally through effects on the skeletal-muscle ryanodine receptor RyR1. Reduced cytosolic calcium weakens excitation–contraction coupling and decreases skeletal-muscle contraction. During malignant hyperthermia, this interrupts excessive calcium-driven contraction and hypermetabolism, reducing heat production and muscle injury. Its action is primarily peripheral rather than suppression of central motor signaling.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Malignant hyperthermia prevention	2–3 mg/kg	IV		Canine regimens are empirical; pharmacokinetic studies question whether these doses achieve effective muscle concentrations. Higher 5–10 mg/kg doses have been cited but are not routine escalation targets.
Malignant hyperthermia crisis	2.5–3 mg/kg	IV		Canine regimens are empirical; pharmacokinetic studies question whether these doses achieve effective muscle concentrations. Higher 5–10 mg/kg doses have been cited but are not routine escalation targets.
Muscle relaxation	1–5 mg/kg	PO	Every 8 h	Canine regimens are empirical; pharmacokinetic studies question whether these doses achieve effective muscle concentrations. Higher 5–10 mg/kg doses have been cited but are not routine escalation targets.
Urethral relaxation	1–5 mg/kg	PO	Every 8 h	Canine regimens are empirical; pharmacokinetic studies question whether these doses achieve effective muscle concentrations. Higher 5–10 mg/kg doses have been cited but are not routine escalation targets.
Urethral relaxation	0.5–1 mg/kg	IV		Canine regimens are empirical; pharmacokinetic studies question whether these doses achieve effective muscle concentrations. Higher 5–10 mg/kg doses have been cited but are not routine escalation targets.
Hops-associated hyperthermia	2–3 mg/kg	IV		As soon as possible after ingestion; intensive supportive treatment is also required.
Hops-associated hyperthermia	3.5 mg/kg	PO		Alternative route reported for hops-associated syndrome; not an additional dose on top of IV treatment.
Rhabdomyolysis case report	Reference only	PO		A published case used 1.5 mg/kg every 8 hours alongside intensive multidrug and supportive care; not a general-purpose regimen.
Urethral relaxation	1–5 mg/kg	PO	Every 8–12 h
Urethral relaxation	1 mg/kg	PO	Every 8 h
Malignant hyperthermia	0.2–3 mg/kg	IV
Black widow envenomation	Reference only	IV		Adjunctive regimen: 1 mg/kg IV, then 1 mg/kg orally every 4 hours.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Muscle relaxation	0.5–2 mg/kg	PO	Every 12 h
Urethral relaxation	1–2 mg/kg	PO	Every 8 h
Urethral relaxation	1 mg/kg	IV
Urethral relaxation	0.5–2 mg/kg	PO	Every 12 h
Urethral relaxation	0.5–1 mg/kg	IV
Urethral relaxation	0.5–2 mg/kg	PO	Every 8 h
Urethral relaxation	0.5–1 mg/kg	PO	Every 12 h
Urethral relaxation with alpha blockade	Reference only	PO		Dantrolene 2–10 mg/cat every 8 hours combined with either prazosin 0.5 mg/cat every 12–24 hours or phenoxybenzamine 2.5–7.5 mg/cat every 12–24 hours.

Horse

Use / stage	Dose	Route	Schedule	Instructions
Muscle relaxation	500 mg/animal	PO		Common empirical fixed amount; optimum preanesthetic and rhabdomyolysis regimens are not established.
Muscle relaxation	4 mg/kg	PO		Alternative studied weight-based regimen; clinical efficacy evidence is limited.
Acute rhabdomyolysis	2–4 mg/kg	PO	Every 24 h	Administered through a nasogastric tube in the cited regimen.
Recurrent exertional rhabdomyolysis prevention	4 mg/kg	PO		Studied in Thoroughbreds after a 12-hour fast; efficacy is condition dependent.
Rhabdomyolysis prevention taper	Reference only	PO		One regimen uses 2 mg/kg daily for 3–5 days, then every third day for one month. Fixed-dose alternatives use 300 mg daily, or 500 mg daily for 3–5 days followed by 300 mg every third day; choose a regimen rather than combining them.
Pre-exercise rhabdomyolysis prevention	800 mg	PO		Give one hour before exercise; disperse in 9 mL water and administer within 30 minutes.
Perianesthetic myopathy prevention	Reference only	PO		Reported alternatives: 6 mg/kg by nasogastric tube 60 minutes before anesthesia; or 10 mg/kg 90 minutes beforehand with further 2.5 mg/kg doses hourly. IV alternatives were 1.9 mg/kg for about 20 minutes of anesthesia or 4 mg/kg for about 2 hours. These distinct procedural regimens are not interchangeable.
High-dose acute rhabdomyolysis protocol	Reference only	IV		The additional text reports 15–25 mg/kg slowly IV four times daily. This is markedly inconsistent with other supplied equine doses; the amount is not enabled for calculation pending resolution.

Pig

Use / stage	Dose	Route	Schedule
Malignant hyperthermia crisis	1–3 mg/kg	IV	Once
Malignant hyperthermia prevention	5 mg/kg	PO
Malignant hyperthermia	3.5 mg/kg	IV

Indications

Treatment of malignant hyperthermia and related skeletal-muscle hypermetabolic crises in susceptible veterinary patients.
Prevention of malignant hyperthermia in selected high-risk animals undergoing anesthesia.
Adjunctive management of recurrent exertional rhabdomyolysis in horses, with limited controlled clinical evidence.
Selected peri-anesthetic use in horses to reduce muscle injury or manage post-anesthetic myopathy, based on limited evidence.
Empirical treatment of functional urethral obstruction associated with excessive striated urethral-sphincter tone in selected cats or dogs; efficacy is incompletely established.

Contraindications

Hepatic disease; use cautiously with weakness or debilitation

Interactions

Acidic solutions are incompatible with the IV preparation.

Adverse effects

Weakness
Hyperkalemia, bradycardia and arrhythmias
Hepatic injury

Preparations

Preparation	Form	Strength	Route
Dantrolene 100 mg capsule	Capsule	100 mg / capsule	PO
Dantrolene conventional injection 0.33 mg/mL Conventional 20 mg vial after prescribed reconstitution.	Injection	0.33 mg / mL	IV
Dantrolene concentrated injection 50 mg/mL 250 mg presentation after prescribed reconstitution; not interchangeable by volume with conventional injection.	Injection	50 mg / mL	IV

Monitoring and Administration

Monitor temperature, acid–base status, potassium, ECG and hepatic enzymes.

Oral administration is usually on an empty stomach. Equine capsules may be dispersed in water or made into a paste.

Reconstituted conventional injection has a short use period; reject cloudy or precipitated solution. Concentrated and conventional vials require different reconstitution instructions.

Monitor baseline and serial liver enzymes during chronic or high-dose treatment; assess urinary function when used for urethral relaxation.

Older high-dose equine IV and peri-anesthetic protocols differ substantially from routine regimens; they require separate clinical verification before use.