DANTROLENE SODIUM- dantrolene sodium capsule
(25 mg, 50 mg and 100 mg)
Dantrolene sodium has a potential for hepatotoxicity, and should not be used in conditions other than those recommended. Symptomatic hepatitis (fatal and non-fatal) has been reported at various dose levels of the drug. The incidence reported in patients taking up to 400 mg/day is much lower than in those taking doses of 800 mg or more per day. Even sporadic short courses of these higher dose levels within a treatment regimen markedly increased the risk of serious hepatic injury. Liver dysfunction as evidenced by blood chemical abnormalities alone (liver enzyme elevations) has been observed in patients exposed to dantrolene sodium for varying periods of time. Overt hepatitis has occurred at varying intervals after initiation of therapy, but has been most frequently observed between the third and twelfth month of therapy. The risk of hepatic injury appears to be greater in females, in patients over 35 years of age, and in patients taking other medication(s) in addition to dantrolene sodium. Spontaneous reports suggest a higher proportion of hepatic events with fatal outcome in elderly patients receiving dantrolene sodium. However, the majority of these cases were complicated with confounding factors such as intercurrent illnesses and/or concomitant potentially hepatotoxic medications (see Geriatric Use subsection). Dantrolene sodium should be used only in conjunction with appropriate monitoring of hepatic function including frequent determination of SGOT or SGPT. If no observable benefit is derived from the administration of dantrolene sodium after a total of 45 days, therapy should be discontinued. The lowest possible effective dose for the individual patient should be prescribed.
The chemical formula of dantrolene sodium is hydrated 1-[[[5-(4-nitrophenyl)-2-furanyl]methylene] amino]-2, 4-imidazolidinedione sodium salt. It is an orange powder, slightly soluble in water, but due to its slightly acidic nature the solubility increases somewhat in alkaline solution. The anhydrous salt has a molecular weight of 336. The hydrated salt contains approximately 15% water (3-1/2 moles) and has a molecular weight of 399. The structural formula for the hydrated salt is:
Dantrolene sodium, USP is supplied in capsules of 25 mg, 50 mg, and 100 mg.
Inactive Ingredients: Each capsule contains croscarmellose sodium, gelatin, lactose monohydrate, magnesium stearate, pharmaceutical ink, pregelatinized starch, titanium dioxide, and yellow iron oxide. In addition, the 25 mg capsule contains D&C Yellow #10 and FD&C Green #3, the 50 mg capsule contains FD&C Blue #1, and the 100 mg capsule contains FD&C Red #40 and FD&C Yellow #6.
In isolated nerve-muscle preparation, dantrolene sodium has been shown to produce relaxation by affecting the contractile response of the skeletal muscle at a site beyond the myoneural junction, directly on the muscle itself. In skeletal muscle, dantrolene sodium dissociates the excitation contraction coupling, probably by interfering with the release of Ca++ from the sarcoplasmic reticulum. This effect appears to be more pronounced in fast muscle fibers as compared to slow ones, but generally affects both. A central nervous system effect occurs, with drowsiness, dizziness, and generalized weakness occasionally present. Although dantrolene sodium does not appear to directly affect the CNS, the extent of its indirect effect is unknown. The absorption of dantrolene sodium after oral administration in humans is incomplete and slow but consistent, and dose-related blood levels are obtained. The duration and intensity of skeletal muscle relaxation is related to the dosage and blood levels. The mean biologic half-life of dantrolene sodium in adults is 8.7 hours after a 100-mg dose. Specific metabolic pathways in the degradation and elimination of dantrolene sodium in human subjects have been established. Metabolic patterns are similar in adults and pediatric patients. In addition to the parent compound, dantrolene, which is found in measurable amounts in blood and urine, the major metabolites noted in body fluids are the 5-hydroxy analog and the acetamido analog. Since dantrolene sodium is probably metabolized by hepatic microsomal enzymes, enhancement of its metabolism by other drugs is possible. However, neither phenobarbital nor diazepam appears to affect dantrolene sodium metabolism.
Clinical experience in the management of fulminant human malignant hyperthermia, as well as experiments conducted in malignant hyperthermia susceptible swine, have revealed that the administration of intravenous dantrolene, combined with indicated supportive measures, is effective in reversing the hypermetabolic process of malignant hyperthermia. Known differences between human and swine malignant hyperthermia are minor. The prophylactic administration of oral or intravenous dantrolene to malignant hyperthermia susceptible swine will attenuate or prevent the development of signs of malignant hyperthermia in a manner dependent upon the dosage of dantrolene administered and the intensity of the malignant hyperthermia triggering stimulus. Limited clinical experience with the administration of oral dantrolene to patients judged malignant hyperthermia susceptible, when combined with clinical experience in the use of intravenous dantrolene for the treatment of malignant hyperthermia and data derived from the above cited animal model experiments, suggests that oral dantrolene will also attenuate or prevent the development of signs of human malignant hyperthermia, provided that currently accepted practices in the management of such patients are adhered to (see INDICATIONS AND USAGE); intravenous dantrolene should also be available for use should the signs of malignant hyperthermia appear.
Dantrolene sodium capsules are indicated in controlling the manifestations of clinical spasticity resulting from upper motor neuron disorders (e.g., spinal cord injury, stroke, cerebral palsy, or multiple sclerosis). It is of particular benefit to the patient whose functional rehabilitation has been retarded by the sequelae of spasticity. Such patients must have presumably reversible spasticity where relief of spasticity will aid in restoring residual function. Dantrolene sodium capsules are not indicated in the treatment of skeletal muscle spasm resulting from rheumatic disorders.
If improvement occurs, it will ordinarily occur within the dosage titration (see DOSAGE AND ADMINISTRATION), and will be manifested by a decrease in the severity of spasticity and the ability to resume a daily function not quite attainable without dantrolene sodium capsules.
Occasionally, subtle but meaningful improvement in spasticity may occur with dantrolene sodium capsule therapy. In such instances, information regarding improvement should be solicited from the patient and those who are in constant daily contact and attendance with him. Brief withdrawal of dantrolene sodium capsules for a period of 2 to 4 days will frequently demonstrate exacerbation of the manifestations of spasticity and may serve to confirm a clinical impression.
A decision to continue the administration of dantrolene sodium capsules on a long-term basis is justified if introduction of the drug into the patient’s regimen:
- produces a significant reduction in painful and/or disabling spasticity such as clonus, or
- permits a significant reduction in the intensity and/or degree of nursing care required, or
- rids the patient of any annoying manifestation of spasticity considered important by the patient himself.
Oral dantrolene sodium capsules are also indicated preoperatively to prevent or attenuate the development of signs of malignant hyperthermia in known, or strongly suspect, malignant hyperthermia susceptible patients who require anesthesia and/or surgery. Currently accepted clinical practices in the management of such patients must still be adhered to (careful monitoring for early signs of malignant hyperthermia, minimizing exposure to triggering mechanisms and prompt use of intravenous dantrolene sodium and indicated supportive measures should signs of malignant hyperthermia appear); see also the package insert for intravenous dantrolene sodium.
Oral dantrolene sodium capsules should be administered following a malignant hyperthermic crisis to prevent recurrence of the signs of malignant hyperthermia.
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