: DANTRIUM is available for the continuing management of patients whose treatment was initiated in a hospital or other institution recognised as a special centre for rehabilitation.

DESCRIPTION

DANTRIUM is dantrolene sodium, chemically 1-{[5-(p-nitrophenyl) furfurylidene] amino} hydantoin sodium hydrate. 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: DANTRIUM is supplied in capsules of 25 mg and 50 mg.

PHARMACOLOGY

In isolated nerve-muscle preparations, DANTRIUM has been shown to produce relaxation of the contractile state of the skeletal muscle by an effect beyond the myoneural junction and directly on the muscle itself. In these preparations DANTRIUM uncouples the excitation and contraction of the skeletal muscle, probably by interfering with the release of calcium ions from the sarcoplasmic reticulum. This effect appears to be more pronounced in fast muscle fibres as compared to slow ones, but generally affects both. A central nervous system effect occurs with drowsiness, dizziness and generalised weakness in some 20% of cases. The extent of the involvement of the CNS in DANTRIUM-induced muscle relaxation is unknown. The absorption of DANTRIUM 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 biological half-life of DANTRIUM in adults is 8.7 hours after a 100 mg dose. Specific metabolic pathways in the degradation and elimination of DANTRIUM in human subjects have been established. Metabolic patterns are similar in adults and children. 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 analogue and the acetamido analogue. Approximately 20 to 25% of an oral dose appears in the urine in the metabolised form and 1% or less is excreted unchanged. About 45 to 50% of the same oral dose appears in the bile. Since DANTRIUM is probably metabolised by hepatic microsomal enzymes, enhancement of its metabolism by other drugs is possible. However, neither phenobarbital nor diazepam appears to affect DANTRIUM metabolism. Based on assays of whole blood and plasma, slightly greater amounts of dantrolene are associated with red blood cells than with the plasma fraction of blood. Significant amounts of dantrolene are bound to plasma proteins, mostly albumin, and this binding is readily reversible. Binding to plasma protein is not significantly altered by diazepam, diphenylhydantoin, or phenylbutazone. Binding to plasma proteins is reduced by warfarin and clofibrate and increased by tolbutamide.

INDICATIONS

DANTRIUM is indicated in controlling the manifestations of clinical spasticity resulting from serious chronic disorders such as 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. There is no evidence that patients with contractures will benefit. DANTRIUM is not indicated in the treatment of skeletal muscle spasm resulting from rheumatic disorders or electroconvulsive therapy. If improvement occurs, it will ordinarily occur within the dosage titration schedule (see DOSAGE AND ADMINISTRATION), as manifested by a decrease in the severity of spasticity and the ability to resume a daily function not quite attainable without DANTRIUM. Occasionally, subtle but meaningful improvements in spasticity may occur with DANTRIUM 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 DANTRIUM for a period of 2 to 4 days will frequently demonstrate exacerbation of the manifestation of spasticity and may serve to confirm a clinical impression. A decision to continue the administration of DANTRIUM 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 an annoying manifestation of spasticity considered important by the patient himself.

CONTRAINDICATIONS

Active hepatic disease, such as acute hepatitis and active cirrhosis, is a contraindication for use of DANTRIUM. DANTRIUM is contraindicated where spasticity is utilised to sustain upright posture and balance in locomotion or whenever spasticity is utilised to obtain or maintain increased function.

WARNINGS

It is important to recognise that DANTRIUM 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. Hepatotoxicity appears to be dose-related above 200 mg/day and this is the maximum recommended dose. Patients receiving higher doses should be closely monitored. Even sporadic short courses of doses above 400 mg/day 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 DANTRIUM 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. If symptoms compatible with hepatitis, accompanied by abnormalities in liver function tests or jaundice appear, DANTRIUM should be discontinued. If caused by DANTRIUM and detected early, the abnormalities in liver function characteristically have reverted to normal when the drug was discontinued. Long-term safety of DANTRIUM in humans has not been established. Chronic studies in rats, dogs and monkeys at dosages greater than 30 mg/kg/day showed growth or weight depression and signs of hepatopathy and possible occlusion nephropathy, all of which were reversible upon cessation of treatment. Sprague-Dawley female rats fed dantrolene sodium for 18 months at dosage levels of 15, 30 and 60 mg/kg/day showed an increased incidence of benign and malignant mammary tumours compared with concurrent controls and, at the highest dosage an increase in the incidence of hepatic lymphangiomas and hepatic angiosarcomas. These effects were not seen in 2 1/2-year studies in Sprague-Dawley or Fischer 344 rats or in 2-year studies in mice of the HaM/ICR strain. Carcinogenicity in humans cannot be fully excluded, so that this possible risk of chronic administration must be weighed against the benefits of the drug (i.e. after a brief trial) for the individual patient.

PRECAUTIONS

DANTRIUM 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 DANTRIUM after a total of 45 days, therapy should be discontinued. The lowest possible effective dose for the individual patient should be prescribed. At the start of DANTRIUM therapy, it is essential to do liver function studies (SGOT, SGPT, alkaline phosphatase, total bilirubin) for a baseline or to establish whether there is pre-existing liver disease. If baseline liver abnormalities exist and are confirmed, there is a clear possibility that the potential for DANTRIUM hepatotoxicity could be enhanced. Liver function studies (e.g. SGOT or SGPT) should be performed at appropriate intervals during DANTRIUM therapy. If such studies reveal abnormal values, therapy should generally be discontinued. Only where benefits of the drug have been of major importance to the patient, should reinitiation or continuation of therapy be considered. Some patients have revealed a return to normal laboratory values in the face of continued therapy while others have not. DANTRIUM therapy has been reinstituted in a few patients who have developed clinical and/or laboratory evidence of hepatocellular injury. If such reinstitution of therapy is done, it should be attempted only in patients who clearly need DANTRIUM and only after previous symptoms and laboratory abnormalities have cleared. The patient should be hospitalised and the drug should be restarted in very small and gradually increasing doses. Laboratory monitoring should be frequent and the drug should be withdrawn immediately if there is any indication of recurrent liver involvement. Some patients have reacted with unmistakable signs of liver abnormality upon administration of a challenge dose, while others have not. DANTRIUM should be used with particular caution in females and in patients over 35 years of age in view of the apparently greater likelihood of drug-induced, potentially fatal, hepatocellular disease in these groups. In view of the above, careful consideration should be given to the possible risks involved in the concurrent use of hormonal oral contraceptives with DANTRIUM (see INTERACTIONS). DANTRIUM should be used with caution in patients with impaired pulmonary function, particularly those with obstructive pulmonary disease, and in patients with severely impaired cardiac function due to myocardial disease. It should be used with caution in patients with a history of previous liver disease or dysfunction (see WARNINGS). Patients should be cautioned against driving a motor vehicle or participating in hazardous occupations while taking DANTRIUM. Dantrolene causes dizziness, drowsiness, and weakness; alcohol and other CNS depressants may intensify this effect. DANTRIUM might possibly evoke a photosensitivity reaction; patients should be cautioned about exposure to sunlight while on therapy. In patients with impaired renal function, dosage may have to be significantly reduced and the possibility of a drug related further impairment borne in mind (see ADVERSE REACTIONS).

(Category B2) The safety of DANTRIUM for use in women who are or who may become pregnant has not been established; hence it should be given only when the potential benefits have been weighed against possible hazard to mother and child. Dantrolene crosses the placenta.

DANTRIUM should not be used by nursing mothers. Dantrolene has been detected in human breast milk.

The long-term safety of DANTRIUM in children under the age of 5 years has not been established. Because of the possibility that adverse effects of the drug could become apparent only after many years, a benefit-risk consideration of the long-term use of DANTRIUM is particularly important in paediatric patients.

INTERACTIONS WITH OTHER MEDICINES

While a definite drug interaction with oestrogen therapy has not yet been established, caution should be observed if the two drugs are to be given concomitantly. Hepatotoxicity has occurred more often in women over 35 years of age receiving concomitant oestrogen therapy. There are very rare reports of cardiovascular collapse in patients treated simultaneously with verapamil and dantrolene sodium. The combination of therapeutic doses of intravenous dantrolene sodium and verapamil in halothane/-chloralose anaesthetised swine has resulted in ventricular fibrillation and cardiovascular collapse in association with marked hyperkalaemia. Until the relevance of these findings to humans is established, the combination of dantrolene sodium and calcium channel blockers, such as verapamil, is not recommended. The effects of non-depolarising muscle relaxants may be potentiated in patients administered dantrolene. Dantrolene causes dizziness, drowsiness, and weakness; alcohol and other CNS depressants may intensify this effect.

ADVERSE EFFECTS

The most frequently occurring side effects of DANTRIUM have been drowsiness, dizziness, weakness, general malaise, fatigue, and diarrhoea. (These have been experienced by approximately 20% of patients). They are generally transient, occurring early in treatment, and can often be obviated by beginning with a low dose and increasing dosage gradually until an optimal regimen is established. Diarrhoea may be severe and may necessitate temporary withdrawal of DANTRIUM therapy. If diarrhoea recurs upon readministration of DANTRIUM, therapy should probably be withdrawn permanently. Other less frequent side effects, listed according to system, are:

Gastrointestinal

Constipation, rarely progressing to signs of intestinal obstruction, GI bleeding, anorexia, swallowing difficulty, gastric irritation, abdominal cramps, vomiting, nausea, dry mouth, saliva hypertension, dyspepsia, dysphagia.

Haematologic

Aplastic anaemia, leukopenia, lymphocytic lymphoma.

Hepatobiliary

Liver function test disturbances, hepatitis (see WARNINGS).

Neurologic

Speech disturbance, seizure, headache, nausea, light-headedness, visual disturbance, diplopia, alteration of taste, insomnia

Cardiovascular

Tachycardia, erratic blood pressure, heart failure, phlebitis, exacerbation of cardiac insufficiency.

Psychiatric

Mental depression, mental confusion, increased nervousness, insomnia.

Urogenital

Increased urinary frequency, crystalluria, haematuria, difficult erection, urinary incontinence and/or nocturia, difficult urination, chromaturia and/or urinary retention. A transient lowering of G.F.R. and renal plasma flow after 8 weeks' therapy has been reported.

Integumentary

Abnormal hair growth, acne-like rash, pruritus, urticaria, eczematoid eruption, sweating.

Musculoskeletal

Myalgia, backache.

Respiratory

Feeling of suffocation, respiratory failure.

Special Senses

Excessive tearing.

Hypersensitivity

Pleural effusion with associated eosinophilia, pericarditis, anaphylaxis.

Other

Chills and fever.

DOSAGE AND ADMINISTRATION

Prior to the administration of DANTRIUM consideration should be given to the potential response to treatment. A decrease in spasticity sufficient to allow a daily function not otherwise attainable should be the therapeutic goal of treatment with DANTRIUM. Refer to the INDICATIONS section for a description of the response to be anticipated. It is important to establish a therapeutic goal (regain and maintain a specific function such as therapeutic exercise program, utilisation of braces, transfer manoeuvres, etc.) before beginning DANTRIUM therapy. Dosage should be increased until the maximum performance compatible with the dysfunction due to underlying disease is achieved. No further increase in dosage is then indicated.

It is important that the dosage be titrated and individualised for maximum effect. The lowest dose compatible with optimal response is recommended.

In view of the potential for liver damage in long-term DANTRIUM use, therapy should be stopped if benefits are not evident within 45 days.

Begin therapy with 25 mg once daily; increase to 25 mg two, three, or four times daily and then by increments of 25 mg up to as high as 50 mg two, three or four times daily if necessary. The maximum recommended dose is 200 mg/day. As most patients will respond to this or a lower dose, and hepatotoxicity appears to be dose-related above 200 mg/day, higher doses should be used only rarely and with close monitoring. (See WARNINGS). Doses higher than 400 mg/day should not be used.

Each dosage level should be maintained for four to seven days to determine the patient's response. The dose should not be increased beyond, and may even have to be reduced to, the amount at which the patient received maximal benefit without adverse effects.

A similar approach should be utilised starting with 0.5 mg/kg of body weight twice daily; this is increased to 0.5 mg/kg three or four times daily and then by increments to a maximum of 2 mg/kg three times a day. Doses higher than 50 mg four times daily should not be used in children.

OVERDOSAGE

Fatal poisoning with this agent is rare, and lethal doses are not established. There is no known set of symptoms with acute overdose. Signs and symptoms are likely to be an extension of those under ADVERSE REACTIONS. The primary toxic effect is CNS depression and in severe cases coma. Respiratory depression may occur in patients with significant CNS depression. Total skeletal paralysis is unlikely in conscious patients. Symptoms that may occur include, but are not limited to, muscular weakness, alterations in the state of consciousness (e.g., lethargy, coma), vomiting, diarrhoea and crystalluria. Mild tachycardia and hypotension may develop. Oral dantrolene may cause lethargy, but is likely to resolve uneventfully. Monitor and support respiratory and cardiovascular function. Intravenous fluids should be administered in fairly large quantities to avert the possibility of crystalluria. Consider central venous pressure monitoring to guide further fluid therapy. Fluids and electrolytes should be monitored closely. Monitor patients with significant CNS depression for respiratory insufficiency and rhabdomyolysis. Emesis is NOT recommended due to risk of CNS and respiratory depression. Excretion of the active compounds is NOT known to be enhanced by fluid diuresis. Contact the Poisons Information Centre for advice on the management of an overdose.

PRESENTATION AND STORAGE CONDITIONS

Capsules 25 mg: (Orange and tan, opaque, coded "DANTRIUM 25mg", "0149" and "0030" with a single line all in black): 100's. Capsules 50 mg: (Orange and tan, opaque, coded "DANTRIUM 50mg", "0149" and "0031" with a double line all in black): 100's. Store below 25oC

NAME OF THE MEDICINE