Basic Information
Dantrolene sodium (DS) is a non-centrally acting skeletal muscle relaxant. It interferes with normal excitation/contraction coupling. Although the mechanism of action is not understood completely, it is thought to interfere with the release of calcium from the sarcoplasmic reticulum by interfering with a specific receptor. DS does not interfere with cardiac and smooth-muscle contraction because the mechanism of calcium release in these types of muscle is under different control. DS is used in humans primarily for upper motor neuron disorders. It is metabolized by the liver and excreted in urine.
Dogs and Cats
DS may be used to treat functional urethral obstruction due to urethral spasm in both dogs and cats. It is used for a similar purpose in the emergency care of acute spinal cord injury when the patient has decreased urinary function.
DS is an integral part of the treatment for malignant hyperthermia and canine stress syndrome. In contrast to equine exercise induced rhabdomyolysis, pretreatment with DS is not protective in dogs prone to canine stress syndrome. DS also is mentioned as an adjunct treatment for black widow spider bite.
Horses
DS is used as a treatment and as a preventive measure for exertional rhabdomyolysis. In treating exertional rhabdomyolysis, DS decreases muscle spasm and possibly helps prevent further muscle necrosis. Other drugs used concurrently to treat exertional rhabdomyolysis include sedatives, such as Acepromazine or Xylazine, NSAIDs, intravenous fluids, and possibly DMSO. When DS is used within a preventive program, it should be given on an empty stomach prior to exercise. Oral absorption of DS takes about one and one half hours and the half-life is slightly more than two hours. Some clinicians also use DS in the management of horses with back and sacroiliac pain.
Dantrolene Sodium Side Effects
- Hepatotoxicity is a rare but serious side-effect. In humans, this occurs most frequently with chronic use but has been seen after a short course of therapy.
- Sedation, dizziness, lethargy, and other signs of CNS depression are the most common side-effects. Muscle weakness has been reported in dogs. Other side-effects include increased urinary frequency and hypotension.
- In human patients, nausea, vomiting, and constipation all have been reported.
Precautions
- DS should not be used or should be used with extreme caution in animals with decreased liver, cardiac, or pulmonary function.
- DS is excreted in milk. It should be used in pregnant or lactating animals only when the benefits of therapy outweigh the potential risk.
- Drug Interactions
- Additive CNS depression may result when DS is used with benzodiazepines or other tranquilizers.
- DS should not be used with calcium channel blockers due to rare reports of cardiac collapse in humans.
- Co-administration of DS and estrogens may increase the risk of hepatotoxicity.
- DS is highly protein bound. Warfarin may displace DS from plasma proteins, increasing the possibility of adverse reactions.
Overdose
Oral overdose may cause increased severity of side effects. If recognized promptly, gut emptying protocols should be attempted.