Dantrolene Sodium

Skeletal Muscle Relaxant Hydantoin derivative

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IV 1-2 mg/kg (for malignant hyperthermia, may repeat up to 10 mg/kg cumulative) As needed, usually every 5-10 minutes until signs resolve Duration: Acute management; may be followed by oral therapy
Notes: For malignant hyperthermia, administer rapidly as a bolus. For muscle spasticity, oral dosing is preferred.
Dog PO 2-5 mg/kg q8h to q12h Duration: Variable, depending on condition
Notes: Start at lower end and titrate to effect. May cause sedation.
Cat IV 1-2 mg/kg (for malignant hyperthermia) As needed, may repeat Duration: Acute management
Notes: Use with caution; cats may be more sensitive to adverse effects.
Cat PO 1-2 mg/kg q12h Duration: Variable
Notes: Off-label use; monitor for hepatotoxicity.
Horse IV 2-4 mg/kg (for malignant hyperthermia) As needed, may repeat Duration: Acute management
Notes: Administer slowly; monitor cardiovascular status.
Horse PO 2-4 mg/kg q12h Duration: Variable
Notes: Used for exertional rhabdomyolysis; may take several days to see effect.
Cattle IV 2-4 mg/kg (for malignant hyperthermia) As needed Duration: Acute management
Notes: Extra-label; observe withdrawal times.
Small Ruminants IV 2-4 mg/kg (for malignant hyperthermia) As needed Duration: Acute management
Notes: Extra-label; use with caution.
Rabbit IV 1-2 mg/kg (for malignant hyperthermia) As needed Duration: Acute management
Notes: Extra-label; monitor closely.

Clinical Indications & Species Uses

General Indications
  • Treatment of malignant hyperthermia
  • Management of skeletal muscle spasticity
Dog (Canine)
  • Treatment of malignant hyperthermia
  • Management of skeletal muscle spasms due to upper motor neuron disorders
  • Adjunct in the treatment of tetanus
Cat (Feline)
  • Treatment of malignant hyperthermia
  • Management of skeletal muscle spasms (off-label)
Horse (Equine)
  • Treatment of malignant hyperthermia
  • Management of exertional rhabdomyolysis (off-label)
Cattle (Bovine)
  • Treatment of malignant hyperthermia (off-label)
  • Management of muscle spasms (off-label)
Small Ruminants (Sheep / Goat)
  • Treatment of malignant hyperthermia (off-label)
  • Management of muscle spasms (off-label)
Rabbit & Small Mammals
  • Treatment of malignant hyperthermia (off-label)
  • Management of muscle spasms (off-label)
Exotic & Other Species
  • Treatment of malignant hyperthermia in susceptible species (off-label)

Pharmacology & Mechanism of Action

Drug Class: Skeletal Muscle Relaxant | Pharmacological Group: Hydantoin derivative

Mechanism of Action: Dantrolene sodium acts peripherally on skeletal muscle by inhibiting the release of calcium ions from the sarcoplasmic reticulum. It binds to the ryanodine receptor (RyR1) and stabilizes the channel in a closed state, thereby preventing the excessive calcium release that leads to muscle contraction. This action reduces the excitation-contraction coupling, resulting in muscle relaxation without affecting the neuromuscular junction or the central nervous system.

Pharmacodynamics: Dantrolene produces skeletal muscle relaxation by directly interfering with the contractile mechanism. It decreases the force of contraction in response to neural stimulation, and its effects are more pronounced on fast-twitch (type II) muscle fibers than on slow-twitch (type I) fibers. It does not significantly affect cardiac or smooth muscle at therapeutic doses. The drug is used to treat malignant hyperthermia, a hypermetabolic state triggered by volatile anesthetics or succinylcholine, by reducing the massive calcium release that causes muscle rigidity and hyperthermia.

⚡ Pharmacokinetics Summary

Absorption: Dantrolene is poorly absorbed after oral administration, with a bioavailability of approximately 70% in dogs. Absorption is variable and may be affected by food. The onset of action after oral dosing is usually within 1-2 hours, but peak plasma concentrations may take 4-6 hours. For intravenous administration, the onset is rapid, within minutes.
Distribution: Dantrolene is widely distributed in the body. It crosses the placenta and is distributed into milk. It is highly bound to plasma proteins (approximately 90%). The volume of distribution is relatively small, reflecting its high protein binding and limited tissue penetration.
Metabolism: Dantrolene is extensively metabolized in the liver, primarily by hydroxylation to 5-hydroxydantrolene, which has similar pharmacological activity. The metabolism is mediated by cytochrome P450 enzymes, particularly CYP3A4. There is some enterohepatic recirculation.
Excretion: Dantrolene and its metabolites are excreted primarily in the urine (approximately 70-80%) and to a lesser extent in bile and feces. The elimination half-life is approximately 4-8 hours in dogs, but may be longer in other species.
Half-Life: Dogs: 4-8 hours; Cats: approximately 5-6 hours; Horses: approximately 2-3 hours; Humans: 8-12 hours
Bioavailability: Oral bioavailability is approximately 70% in dogs, but may be lower in other species. Intravenous administration provides 100% bioavailability.
Protein Binding: Approximately 90% bound to plasma proteins, primarily albumin.

Available Formulations & Strengths

Oral Capsule 25 mg, 50 mg, 100 mg (PO)
Injectable Solution 20 mg/70 mL (reconstituted with sterile water) (IV)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to dantrolene or any component of the formulation
  • Hepatic disease (active or history of hepatitis)
  • Concurrent use with verapamil or other calcium channel blockers (risk of hyperkalemia and cardiac depression)
  • Use in patients with compromised cardiac function (relative contraindication)
Warnings & Clinical Precautions:
  • Hepatotoxicity: Dantrolene can cause severe hepatic injury, especially with prolonged oral use. Monitor liver enzymes periodically.
  • Muscle weakness: May cause generalized weakness, especially in animals with pre-existing weakness or myasthenia gravis.
  • Sedation and ataxia: Common at higher doses; caution when animals need to ambulate.
  • Pregnancy: Use with caution; safety not established. Dantrolene crosses the placenta.
  • Lactation: Dantrolene is excreted in milk; use with caution in nursing animals.
  • Renal impairment: Use with caution; dose adjustment may be necessary.
  • Malignant hyperthermia: Dantrolene is the drug of choice but should be used as part of a comprehensive treatment protocol including cooling, supportive care, and discontinuation of triggering agents.
  • Extravasation: IV formulation is alkaline; avoid extravasation as it can cause tissue necrosis.
  • Rapid IV administration may cause thrombophlebitis.

Adverse Effects & Reactions

Common:

  • Sedation
  • Drowsiness
  • Weakness
  • Ataxia
  • Vomiting
  • Diarrhea

Serious / Severe:

  • Hepatotoxicity (elevated liver enzymes, jaundice, hepatic failure)
  • Respiratory depression (especially with high doses or concurrent CNS depressants)
  • Cardiac arrhythmias (with rapid IV administration)
  • Hyperkalemia (especially with concurrent verapamil)
  • Anaphylaxis (rare)

Rare:

  • Pleural effusion with pericarditis (reported in humans)
  • Eosinophilia
  • Lymphocytic lymphoma (in long-term human use)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Calcium channel blockers (e.g., verapamil, diltiazem) May cause hyperkalemia, cardiac depression, and cardiovascular collapse. Avoid concurrent use. High
CNS depressants (e.g., barbiturates, opioids, tranquilizers) Additive sedation and respiratory depression. Moderate
Neuromuscular blocking agents (e.g., atracurium, vecuronium) May enhance neuromuscular blockade, leading to prolonged paralysis. Moderate
Hepatotoxic drugs (e.g., azathioprine, NSAIDs) Increased risk of hepatotoxicity. Moderate
Digoxin Potential for increased risk of arrhythmias. Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe muscle weakness
  • Respiratory depression
  • Cardiac arrhythmias
  • Hypotension
  • Seizures (in severe cases)
  • Coma

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Maintain airway, breathing, and circulation. Administer oxygen and assist ventilation if needed. Monitor cardiac function and treat arrhythmias. Use intravenous fluids to maintain blood pressure. Consider activated charcoal if recent oral ingestion. In severe cases, consider extracorporeal removal (hemodialysis) but efficacy is limited due to high protein binding.

Food Animal Withdrawal Times

🥩 Meat: 7 days🥛 Milk: 3 days

Withdrawal times are not established for dantrolene in food animals. The values provided are conservative estimates based on pharmacokinetic data. Always consult regulatory guidelines and use extra-label with caution. For cattle, a meat withdrawal of 7 days and milk withdrawal of 3 days is suggested. For other species, follow local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F); excursions permitted between 15-30°C (59-86°F).

Handling & Special Conditions: Protect from moisture. The reconstituted IV solution should be used within 6 hours and protected from light. Do not freeze.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary species; approved for human use. Veterinary use is extra-label.

Extra-Label (Off-Label) Use: In the US, dantrolene is not FDA-approved for veterinary use, but it can be used extra-label under the Animal Medicinal Drug Use Clarification Act (AMDUCA) when a valid veterinarian-client-patient relationship exists. For food animals, extra-label use requires a withdrawal period established by the veterinarian, and the drug must not be used in an extra-label manner that results in violative residues.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Dantrolene sodium is a critical drug for the management of malignant hyperthermia, a life-threatening condition that can be triggered by volatile anesthetics (e.g., halothane, sevoflurane) and succinylcholine. It is also used for the treatment of skeletal muscle spasticity due to upper motor neuron lesions, and off-label for conditions like exertional rhabdomyolysis in horses. The drug should be used with caution due to its potential for hepatotoxicity, especially with prolonged oral therapy. Liver function tests should be monitored before and during treatment. In emergency situations, IV administration is preferred for rapid onset. For chronic conditions, oral dosing is used, but the dose should be titrated to the lowest effective dose to minimize adverse effects. Dantrolene is not a substitute for treating the underlying cause of muscle spasticity. In food animals, extra-label use requires careful attention to withdrawal times to avoid residues. Always consult the most current veterinary drug references and regulatory guidelines.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)