Dantrolene Sodium
Dantrolene Sodium (Hydantoin derivative)
Also known as: Dantrium · Danlene · Dantamacrin · Dantralen · F-440 · F-368 · Dantrolene sodium
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of functional urethral obstruction due to increased external urethral tone | 1-5 mg/kg PO q8-12h | PO | q8-12h | — | 🌎 NA |
| Treatment of functional urethral obstruction due to increased external urethral tone | 1 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Canine stress syndrome (CSS)/Malignant Hyperthermia (MH) - acute attack | 0.2-3 mg/kg IV | IV | Once/PRN | — | 🌎 NA |
| MH-like syndrome associated with hops (Humulus lupulus) ingestion | 2-3 mg/kg IV or 3.5 mg/kg PO as soon as possible after ingestion. | IV/PO | Once | — | 🌎 NA |
| Adjunctive treatment of rhabdomyolysis | 1.5 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Adjunctive treatment of Black Widow Spider bite | 1 mg/kg IV ; followed by 1 mg/kg PO q4h | IV, then PO | q4h | — | 🌎 NA |
- Adjunctive treatment of rhabdomyolysis: From a case report; very intensive drug and supportive therapy used in this case.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of functional urethral obstruction due to increased external urethral tone | 0.5-2 mg/kg PO q12h OR 0.5-1 mg/kg IV | PO/IV | q12h | — | 🌎 NA |
| Treatment of functional urethral obstruction due to increased external urethral tone | 0.5-2 mg/kg PO three times daily | PO | TID | — | 🌎 NA |
| Treatment of functional urethral obstruction due to increased external urethral tone | 2-10 mg (total dose) PO three times daily | PO | TID | — | 🌎 NA |
| Treatment of functional urethral obstruction due to increased external urethral tone | 0.5-1 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
- Treatment of functional urethral obstruction due to increased external urethral tone: IV product very expensive.
- Treatment of functional urethral obstruction due to increased external urethral tone: Given with either prazosin (0.5 mg/cat once to twice daily) or phenoxybenzamine (2.5-7.5 mg/cat once to twice daily).
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of acute rhabdomyolysis | 15-25 mg/kg slow IV four times daily | IV | QID | — | 🌎 NA |
| Treatment of acute rhabdomyolysis | 2-4 mg/kg PO via nasogastric tube once daily | PO | SID | — | 🌎 NA |
| Prevention of recurrent exertional rhabdomyolysis in Thoroughbreds | 4 mg/kg PO in horses fasted (12-hour fast in study) prior to administration. | PO | Once | — | 🌎 NA |
| Prevention of rhabdomyolysis | 2 mg/kg PO once daily for 3-5 days and then every 3rd day for a month | PO | SID then q3d | 1 month | 🌎 NA |
| Prevention of rhabdomyolysis | 300 mg (total dose) PO once daily | PO | SID | — | 🌎 NA |
| Prevention of rhabdomyolysis | 500 mg (total dose) PO for 3-5 days and then 300 mg PO every third day. | PO | SID then q3d | — | 🌎 NA |
| Prevention of rhabdomyolysis | 800 mg (total dose); within 30 minutes prior to administration contents of capsules mixed with 9 mL tap water to make a suspension and given PO one hour before exercise. | PO | Once before exercise | — | 🌎 NA |
| Prevention of post-anesthetic myositis (PAM) | 6 mg/kg enterally (given via NG tube in study) 60 minutes prior to general anesthesia. | Enteral | Once | — | 🌎 NA |
| Prevention of post-anesthetic myositis (PAM) | 10 mg/kg PO (intragastric) 1.5 hours before surgery. | PO | Once | — | 🌎 NA |
| Prevention of post-anesthetic myositis (PAM) | 1.9 mg/kg loading | IV | Once | — | 🌎 NA |
| Prevention of post-anesthetic myositis (PAM) | 4 mg/kg | IV | Once | — | 🌎 NA |
- Prevention of rhabdomyolysis: Drug is diluted in normal saline and given via stomach tube. Monitor hepatic function.
- Prevention of rhabdomyolysis: May be preferable because the drug is hepatotoxic.
- Prevention of post-anesthetic myositis (PAM): Does not appear to prolong recovery time.
- Prevention of post-anesthetic myositis (PAM): Should give peak levels at the time surgery begins and maintain postulated therapeutic levels for an additional 2 hours. Additional doses of 2.5 mg/kg PO (intragastric) q60 minutes can be given.
- Prevention of post-anesthetic myositis (PAM): Will give therapeutic levels but will only persist for about 20 minutes.
- Prevention of post-anesthetic myositis (PAM): Will maintain therapeutic levels for about 2 hours, but peak levels will be quite high.
Swine
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Prevention or treatment of malignant hyperthermia | 3.5 mg/kg IV | IV | Once/PRN | — | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Dantrolene sodium is a unique, direct-acting skeletal muscle relaxant. Unlike centrally acting muscle relaxants (such as methocarbamol or diazepam), dantrolene acts peripherally directly on the muscle fiber itself.
In veterinary medicine, its primary indications include:
- Malignant Hyperthermia (MH): A life-saving intervention for MH and porcine stress syndrome, particularly in swine and dogs.
- Equine Myopathies: Widely used in horses for the prevention and treatment of exertional rhabdomyolysis ("tying-up") and post-anesthetic myositis (PAM).
- Small Animal Urology: Frequently utilized to manage functional urethral obstruction by decreasing external urethral sphincter tone in dogs and cats.
- Toxin Envenomation: Recommended as an adjunctive treatment for Black Widow spider bites, which cause massive acetylcholine release and severe, painful muscle cramping.
Clinical Pearl: Because the injectable formulation is highly expensive and has a short shelf-life after reconstitution, its use is often reserved for severe, acute crises (like MH), while oral formulations are used for chronic management or prophylaxis.
Mechanism of action
Dantrolene acts intracellularly to uncouple the excitation-contraction process in skeletal muscle.
- It binds specifically to the ryanodine receptor (RyR1) located on the sarcoplasmic reticulum (SR).
- This binding blocks the release of calcium (Ca²⁺) from the SR into the myoplasm.
- Decreased intracellular calcium → prevents the interaction of actin and myosin → produces skeletal muscle relaxation.
Because it specifically targets the RyR1 isoform (found primarily in skeletal muscle) rather than RyR2 (cardiac muscle), it has minimal direct effects on cardiac or smooth muscle at standard therapeutic doses. The exact mechanism for its mild CNS effects (drowsiness, dizziness) remains poorly understood.
Safety & warnings
Contraindications
- Preexisting liver disease (use with extreme caution)
- Severe cardiac dysfunction (use with caution)
- Pulmonary disease (use with caution)
Adverse effects
- Weakness
- Sedation
- Dizziness
- Headache
- Nausea
- Vomiting
- Constipation
- Increased urinary frequency
- Hypotension
- Hepatotoxicity (especially with chronic use)
Precautions
Hepatotoxicity Warning: Dantrolene can cause hepatotoxicity. It should be used with extreme caution in patients with preexisting liver disease. Monitor liver enzymes closely during chronic therapy.
- Use with caution in patients with severe cardiac dysfunction or pulmonary disease.
- Pregnancy: FDA Category C (human); Papich Class C (veterinary). Use cautiously as a last resort when benefits clearly outweigh risks.
- Nursing: Distributed into milk; safe use cannot be assured during nursing.
Drug interactions
Increased sedation may be seen if tranquilizing agents are used concomitantly.
Rare reports of cardiovascular collapse in humans; concomitant use during malignant hyperthermia crises is not recommended.
Increased risks of hepatotoxicity have been seen in women >35 years of age; veterinary significance is unknown.
Dantrolene may be displaced from plasma proteins by warfarin, resulting in increased effects or adverse reactions.
Monitoring
- Baseline and periodic liver function tests (ALT, AST, Alk Phos, etc.) if projecting to be used chronically or using high dosages
- Body temperature (especially for malignant hyperthermia)
- Urine volume, frequency, continence
Pharmacokinetics
Half-life
Absorption
Bioavailability after oral administration is ~35% in humans and ~39% in horses (intragastric). Fairly slowly absorbed; peak levels occur ~5 hours post-oral dose in humans and 1.5 hours in horses. In horses, oral absorption is affected by food and must be given to a fasted horse to achieve therapeutic levels.
Distribution
Substantially bound to plasma proteins (principally albumin). Many drugs may displace it.
Metabolism
Metabolized in the liver.
Elimination
Metabolites are excreted in the urine. Only about 1% of the parent drug is excreted unchanged in the urine and bile.
Overdose
There is no specific antidotal therapy for dantrolene overdoses.
- Decontamination: Remove the drug from the gut if possible (e.g., emesis induction, activated charcoal) if exposure was recent and oral.
- Supportive Care: Treat supportively, monitoring respiratory, cardiovascular, and hepatic function.
Available products
Formulations
- Oral Capsules
- Powder for Injection Solution
Human-labeled
- Dantrolene Sodium Oral Capsules: 25 mg, 50 mg, & 100 mg (Dantrium; generic)
- Dantrolene Sodium Powder for Injection Solution: 20 mg/vial (approx. 0.32 mg/mL dantrolene after reconstitution; with mannitol 3 g/vial) in 70 mL vials (Dantrium Intravenous)
Regulatory status
POM (Prescription Only Medicine)
POM (Prescription Only Medicine)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Capsules should be stored in well-closed containers at room temperature. Powder for injection should be stored at temperatures less than 30°C and protected from prolonged exposure to light. After reconstitution, the powder for injection should be used within 6 hours when stored at room temperature and should be protected from direct light. It is NOT compatible with either normal saline or D5W injection.
Client information
- Expected Effects: Dantrolene can cause mild gastrointestinal upset (vomiting, lack of appetite), increased urinary frequency, and sedation (drowsiness or weakness).
- Liver Warning: Rarely, dantrolene can cause liver toxicity. Contact your veterinarian immediately if your pet develops persistent vomiting, loss of appetite, unexplained profound lethargy, or yellowish discoloration of the whites of the eyes or gums (jaundice).
- Administration: Intravenous use of this drug should only be performed by veterinary professionals familiar with its use and monitoring requirements.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.