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.
Mecanismo: 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.
Dosificación por especie
- 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 · IV product very expensive.
- Treatment of functional urethral obstruction due to increased external urethral tone · 0.5-2 mg/kg PO three times daily · PO · TID
- Treatment of functional urethral obstruction due to increased external urethral tone · 2-10 mg (total dose) PO three times daily · PO · TID · 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 · 0.5-1 mg/kg PO q12h · PO · q12h
- Treatment of acute rhabdomyolysis · 15-25 mg/kg slow IV four times daily · IV · QID
- Treatment of acute rhabdomyolysis · 2-4 mg/kg PO via nasogastric tube once daily · PO · SID
- Prevention of recurrent exertional rhabdomyolysis in Thoroughbreds · 4 mg/kg PO in horses fasted (12-hour fast in study) prior to administration. · PO · Once
- 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 · Drug is diluted in normal saline and given via stomach tube. Monitor hepatic function.
- Prevention of rhabdomyolysis · 300 mg (total dose) PO once daily · PO · SID · May be preferable because the drug is hepatotoxic.
Vías de administración
Contraindicaciones
- Preexisting liver disease (use with extreme caution)
- Severe cardiac dysfunction (use with caution)
- Pulmonary disease (use with caution)
Efectos adversos
- Weakness
- Sedation
- Dizziness
- Headache
- Nausea
- Vomiting
- Constipation
- Increased urinary frequency
- Hypotension
- Hepatotoxicity (especially with chronic use)
Interacciones farmacológicas
- Benzodiazepines & other CNS depressants · Increased sedation may be seen if tranquilizing agents are used concomitantly.
- Calcium-Channel Blockers · Rare reports of cardiovascular collapse in humans; concomitant use during malignant hyperthermia crises is not recommended. · major
- Estrogens · Increased risks of hepatotoxicity have been seen in women >35 years of age; veterinary significance is unknown.
- Warfarin · Dantrolene may be displaced from plasma proteins by warfarin, resulting in increased effects or adverse reactions.
Monitorización
- 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
Sobredosis
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.
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