Dantrolene Sodium
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: 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 (Caยฒโบ)** from the SR into the myoplasm. * Decreased intracellular calcium โ prevents the interaction of actin and myosin โ 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.
Dosing by species
- Treatment of functional urethral obstruction due to increased external urethral tone ยท 0.5-2 mg/kg PO q12h OR 0.5-1 mg/kg IV ยท PO/IV ยท q12h ยท IV product very expensive.
- Treatment of functional urethral obstruction due to increased external urethral tone ยท 0.5-2 mg/kg PO three times daily ยท PO ยท TID
- Treatment of functional urethral obstruction due to increased external urethral tone ยท 2-10 mg (total dose) PO three times daily ยท PO ยท TID ยท Given with either prazosin (0.5 mg/cat once to twice daily) or phenoxybenzamine (2.5-7.5 mg/cat once to twice daily).
- Treatment of functional urethral obstruction due to increased external urethral tone ยท 0.5-1 mg/kg PO q12h ยท PO ยท q12h
- Treatment of acute rhabdomyolysis ยท 15-25 mg/kg slow IV four times daily ยท IV ยท QID
- Treatment of acute rhabdomyolysis ยท 2-4 mg/kg PO via nasogastric tube once daily ยท PO ยท SID
- Prevention of recurrent exertional rhabdomyolysis in Thoroughbreds ยท 4 mg/kg PO in horses fasted (12-hour fast in study) prior to administration. ยท PO ยท Once
- Prevention of rhabdomyolysis ยท 2 mg/kg PO once daily for 3-5 days and then every 3rd day for a month ยท PO ยท SID then q3d ยท 1 month ยท Drug is diluted in normal saline and given via stomach tube. Monitor hepatic function.
- Prevention of rhabdomyolysis ยท 300 mg (total dose) PO once daily ยท PO ยท SID ยท May be preferable because the drug is hepatotoxic.
Routes of administration
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)
Drug interactions
- Benzodiazepines & other CNS depressants ยท Increased sedation may be seen if tranquilizing agents are used concomitantly.
- Calcium-Channel Blockers ยท Rare reports of cardiovascular collapse in humans; concomitant use during malignant hyperthermia crises is not recommended. ยท major
- Estrogens ยท Increased risks of hepatotoxicity have been seen in women >35 years of age; veterinary significance is unknown.
- Warfarin ยท 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
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.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.