DANTROLENE: 298 Adverse Event Reports & Safety Profile

DESCRIPTION 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 is supplied in capsules of 25 mg, 50 mg, and 100 mg.

Inactive

Ingredients: Each capsule contains corn starch, lactose monohydrate, magnesium stearate, and talc. The capsule shell contains the following ingredients, D&C Yellow #10, FD&C Red #40, gelatin, titanium dioxide, and yellow iron oxide. Black ink contains the following ingredients, D&C Yellow #10 Aluminum lake, FD&C Blue #1 Aluminum lake, FD&C Blue #2 Aluminum lake, FD&C Red #40 Aluminum lake, n-Butyl alcohol, pharmaceutical glaze (modified) in SD-45, propylene glycol, SDA-3A alcohol and synthetic black iron oxide.

INDICATIONS AND USAGE In Chronic Spasticity 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.

In Malignant Hyperthermia

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.

DOSAGE AND ADMINISTRATION As soon as the malignant hyperthermia reaction is recognized, all anesthetic agents should be discontinued; the administration of 100% oxygen is recommended.

Dantrolene

Sodium for Injection should be administered by continuous rapid intravenous push beginning at a minimum dose of 1 mg/kg, and continuing until symptoms subside or the maximum cumulative dose of 10 mg/kg has been reached. If the physiologic and metabolic abnormalities reappear, the regimen may be repeated. It is important to note that administration of Dantrolene Sodium for Injection should be continuous until symptoms subside. The effective dose to reverse the crisis is directly dependent upon the individual's degree of susceptibility to malignant hyperthermia, the amount and time of exposure to the triggering agent, and the time elapsed between onset of the crisis and initiation of treatment.

Pediatric Dose

Experience to date indicates that the dose of Dantrolene Sodium for Injection for pediatric patients is the same as for adults.

Preoperatively Dantrolene

Sodium for Injection and/or Dantrolene Sodium Capsules may be administered preoperatively to patients judged malignant hyperthermia susceptible as part of the overall patient management to prevent or attenuate the development of clinical and laboratory signs of malignant hyperthermia. The recommended prophylactic dose of Dantrolene Sodium for Injection is 2.5 mg/kg, starting approximately 1-1/4 hours before anticipated anesthesia and infused over approximately 1 hour. This dose should prevent or attenuate the development of clinical and laboratory signs of malignant hyperthermia provided that the usual precautions, such as avoidance of established malignant hyperthermia triggering agents, are followed.

Additional Dantrolene

Sodium for Injection may be indicated during anesthesia and surgery because of the appearance of early clinical and/or blood gas signs of malignant hyperthermia or because of prolonged surgery (see also CLINICAL PHARMACOLOGY , WARNINGS , and PRECAUTIONS ). Additional doses must be individualized.

Oral

Administration of Dantrolene Capsules: Administer 4 to 8 mg/kg/day of oral Dantrolene Sodium in three or four divided doses for 1 or 2 days prior to surgery, with the last dose being given with a minimum of water approximately 3 to 4 hours before scheduled surgery. Adjustment can usually be made within the recommended dosage range to avoid incapacitation (weakness, drowsiness, etc.) or excessive gastrointestinal irritation (nausea and/or vomiting). See also the package insert for Dantrolene Sodium Capsules, USP.

Post Crisis

Follow-Up Dantrolene Sodium Capsules, 4 to 8 mg/kg/day, in four divided doses should be administered 1 to 3 days following a malignant hyperthermia crisis to prevent recurrence of the manifestations of malignant hyperthermia. Intravenous dantrolene sodium may be used postoperatively to prevent or attenuate the recurrence of signs of malignant hyperthermia when oral dantrolene sodium administration is not practical. The intravenous dose of dantrolene sodium in the postoperative period must be individualized, starting with 1 mg/kg or more as the clinical situation dictates.

Preparation

Each vial of Dantrolene Sodium for Injection should be reconstituted by adding 60 mL of sterile water for injection USP (without a bacteriostatic agent), and the vial shaken until the solution is clear. 5% Dextrose Injection USP, 0.9% Sodium Chloride Injection USP, and other acidic solutions are not compatible with Dantrolene Sodium for Injection and should not be used. The contents of the vial must be protected from direct light and used within 6 hours after reconstitution. Store reconstituted solutions between 15°C to 30°C (59°F to 86°F).

Reconstituted Dantrolene

Sodium for Injection should not be transferred to large glass bottles for prophylactic infusion due to precipitate formation observed with the use of some glass bottles as reservoirs. For prophylactic infusion, the required number of individual vials of Dantrolene Sodium for Injection should be reconstituted as outlined above. The contents of individual vials are then transferred to a larger volume sterile intravenous plastic bag. Stability data on file indicate commercially available sterile plastic bags are acceptable drug delivery devices. However, it is recommended that the prepared infusion be inspected carefully for cloudiness and/or precipitation prior to dispensing and administration. Such solutions should not be used. While stable for 6 hours, it is recommended that the infusion be prepared immediately prior to the anticipated dosage administration time. Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration.

CONTRAINDICATIONS Active hepatic disease, such as hepatitis and cirrhosis, is a contraindication for use of dantrolene sodium capsules. Dantrolene sodium capsules are contraindicated where spasticity is utilized to sustain upright posture and balance in locomotion or whenever spasticity is utilized to obtain or maintain increased function.

REACTIONS Administration to conscious subjects is associated with loss of grip strength and weakness in the legs, drowsiness and dizziness. Other common adverse reactions are: nausea, thrombophlebitis, tissue necrosis secondary to extravasation, urticaria and erythema, and injection site reactions (pain, erythema, swelling) ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Eagle at 1-855-318-2170 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. In a study designed to evaluate the safety and tolerability of RYANODEX, healthy volunteers were randomly assigned to receive treatment with RYANODEX or an active comparator at doses ranging from 1 mg/kg to 2.5 mg/kg. The RYANODEX dose was infused over the course of 1 minute for each of the doses evaluated. The active comparator was an injectable formulation of dantrolene sodium that differed from RYANODEX in that it contained dantrolene sodium and mannitol at concentrations of 0.33 mg/mL and 50 mg/mL, respectively, when reconstituted according to the product's prescribing information. The active comparator was infused at a rate that administered 20 mg of dantrolene per minute for each of the doses evaluated.

Table

1 displays the most common adverse events in this study. These data are not an adequate basis for comparison of the types or frequencies of adverse event types between RYANODEX and the dantrolene sodium comparator. Adverse events increased in frequency with increasing doses in the trial, but did not differ in frequency between the two treatment groups. RYANODEX-treated subjects were more likely to report immediate adverse events of flushing, dystonia, and dysphagia than those receiving the active comparator. In all dose groups, hand grip strength declined after dosing. In general, the decline in hand grip strength was more pronounced and occurred more rapidly in the RYANODEX-treated subjects in the 1.0, 1.75, 2.0 and 2.25 mg/kg treatment groups. In the 2.5 mg/kg treatment group, the decline in hand grip strength both in amount and duration was similar between the two treatment groups.

Table

1: Adverse Events in Healthy Volunteers Number of subjects (%) RYANODEX [N=30] n (%)

Dantrolene Sodium

Comparator [N=31] n (%)

Flushing

8 (27) 1 (3)

Somnolence

5 (17) 4 (13)

Dysphonia

4 (13) 1 (3)

Dysphagia

3 (10) 4 (13)

Nausea

3 (10) 3 (10) Feeling abnormal 3 (10) 3 (10)

Headache

1 (3) 4 (13)

Vomiting

1 (3) 2 (6) Vision blurred 1 (3) 1 (3) Pain in extremity 1 (3) 1 (3) Muscular weakness/Asthenia 1 (3) 1 (3) Atrioventricular block 1 (3) 0 Tachycardia 1 (3) 0 Infusion site pain 1 (3) 0 Dizziness 1 (3) 0

6.2 Postmarketing Experience The following adverse reactions have been identified during postapproval use of another formulation of dantrolene sodium for injection. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Pulmonary Edema

There have been reports of pulmonary edema developing during the treatment of malignant hyperthermia crises with another dantrolene sodium dosage form. The contributory effect of the diluent volume and mannitol in these cases is not known. Thrombophlebitis and Tissue Necrosis There have been reports of thrombophlebitis following administration of intravenous dantrolene. Tissue necrosis secondary to extravasation has been reported [see Warnings and Precautions ( 5.3 )].

Hypersensitivity/Anaphylactic

Reactions There have been reports of urticaria and erythema possibly associated with the administration of dantrolene sodium for injection. Anaphylaxis has been reported.

Injection Site Reactions

Injection site reactions including pain, erythema, and swelling, commonly due to extravasation, have been reported.

Hepatotoxicity

Cases of hepatotoxicity following the use of intravenous dantrolene products have been reported. Elevated liver enzymes have occurred hours to days following use of intravenous dantrolene, though many of these cases were observed in patients with comorbidities (e.g., critical illness).

WARNINGS It is important to recognize that fatal and non-fatal liver disorders of an idiosyncratic or hypersensitivity type may occur with dantrolene sodium therapy. At the start of dantrolene sodium therapy, it is desirable 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 dantrolene sodium hepatotoxicity could be enhanced, although such a possibility has not yet been established. Liver function studies (e.g., SGOT or SGPT) should be performed at appropriate intervals during dantrolene sodium 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. If symptoms compatible with hepatitis, accompanied by abnormalities in liver function tests or jaundice appear, dantrolene sodium should be discontinued. If caused by dantrolene sodium and detected early, the abnormalities in liver function characteristically have reverted to normal when the drug was discontinued. Dantrolene sodium 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 dantrolene sodium and only after previous symptoms and laboratory abnormalities have cleared. The patient should be hospitalized 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. Dantrolene sodium should be used with particular caution in females and in patients over 35 years of age in view of apparent greater likelihood of drug-induced, potentially fatal, hepatocellular disease in these groups. 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). Carcinogenesis, Mutagenesis, Impairment of Fertility Long-term safety of dantrolene sodium 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 tumors compared with concurrent controls. At the highest dose level, there was an increase in the incidence of benign lymphatic neoplasms. In a 30-month study at the same dose levels also in Sprague-Dawley rats, dantrolene sodium produced a decrease in the time of onset of mammary neoplasms. Female rats at the highest dose level showed an increased incidence of hepatic lymphangiomas and hepatic angiosarcomas. The only drug-related effect seen in a 30-month study in Fischer-344 rats was a dose-related reduction in the time of onset of mammary and testicular tumors. A 24-month study in HaM/ICR mice revealed no evidence of carcinogenic activity. 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. Dantrolene sodium has produced positive results in the Ames S. Typhimurium bacterial mutagenesis assay in the presence and absence of a liver activating system.

Pregnancy Pregnancy

Category C Adequate animal reproduction studies have not been conducted with dantrolene sodium. It is also not known whether dantrolene sodium can cause fatal harm when administered to a pregnant woman or can affect reproduction capacity. Dantrolene sodium capsules should be given to a pregnant woman only if clearly needed. Labor and Delivery In one non-randomized open-label study, 21 term pregnant patients received prophylactic oral dantrolene sodium 100 mg per day for 2 to 10 days prior to delivery. Dantrolene readily crossed the placenta with maternal and fetal whole blood levels approximately equal at delivery; neonatal levels then fell approximately 50% per day for 2 days before declining sharply. No neonatal respiratory and neuromuscular side effects were detected at low dose. More data, at higher doses, are needed before more definitive conclusions can be made.

Nursing Mothers

Dantrolene sodium should not be used in nursing mothers. Usage in Pediatric Patients The long-term safety of dantrolene sodium in pediatric patients 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 dantrolene sodium is particularly important in pediatric patients.

Geriatric Use

Clinical studies of dantrolene sodium did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience in the literature has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy. As with all patients receiving dantrolene sodium, it is recommended that elderly patients receive the lowest dose compatible with the optimal response. 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 (for hepatotoxicity details and its management see Black Box and Warnings Sections).

Drug Interactions

Drowsiness may occur with dantrolene sodium therapy, and the concomitant administration of CNS depressants such as sedatives and tranquilizing agents may result in further drowsiness. While a definite drug interaction with estrogen 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 estrogen therapy. Cardiovascular collapse in patients treated simultaneously with verapamil and dantrolene sodium is rare. The combination of therapeutic doses of intravenous dantrolene sodium and verapamil in halothane/α-chloralose anesthetized swine has resulted in ventricular fibrillation and cardiovascular collapse in association with marked hyperkalemia. Until the relevance of these findings to humans is established, the combination of dantrolene sodium and calcium channel blockers is not recommended during the management of malignant hyperthermia. Administration of dantrolene sodium may potentiate vecuronium-induced neuromuscular block.

PRECAUTIONS General Care must be taken to prevent extravasation of dantrolene sodium solution into the surrounding tissues due to the high pH of the intravenous formulation and potential for tissue necrosis. When mannitol is used for prevention or treatment of late renal complications of malignant hyperthermia, the 3 g of mannitol needed to dissolve each 20 mg vial of intravenous dantrolene sodium should be taken into consideration. Information for Patients Based upon data in human volunteers, perioperatively, it is appropriate to tell patients who receive Dantrolene Sodium for Injection that symptoms of muscle weakness should be expected postoperatively (i.e. decrease in grip strength and weakness of leg muscles, especially walking down stairs). In addition, symptoms such as "lightheadedness" may be noted. Since some of these symptoms may persist for up to 48 hours, patients must not operate an automobile or engage in other hazardous activity during this time. Caution is also indicated at meals on the day of administration because difficulty swallowing and choking has been reported. Caution should be exercised in the concomitant administration of tranquilizing agents.

Drug Interactions

Dantrolene sodium is metabolized by the liver, and it is theoretically possible that its metabolism may be enhanced by drugs known to induce hepatic microsomal enzymes. However, neither phenobarbital nor diazepam appears to affect dantrolene sodium metabolism. 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. Cardiovascular collapse in association with marked hyperkalemia has been reported in patients receiving dantrolene in combination with calcium channel blockers. It is recommended that the combination of intravenous dantrolene sodium and calcium channel blockers, such as verapamil, not be used together during the management of malignant hyperthermia crisis. Administration of dantrolene may potentiate vecuronium-induced neuromuscular block. Carcinogenesis, Mutagenesis, and Impairment of Fertility 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 tumors compared with concurrent controls. At the highest dose level (approximately the same as the maximum recommended daily dose on a mg/m 2 basis), there was an increase in the incidence of benign hepatic lymphatic neoplasms. In a 30-month study in Sprague-Dawley rats fed dantrolene sodium, the highest dose level (approximately the same as the maximum recommended daily dose on a mg/m 2 basis) produced a decrease in the time of onset of mammary neoplasms. Female rats at the highest dose level showed an increased incidence of hepatic lymphangiomas and hepatic angiosarcomas. The only drug-related effect seen in a 30-month study in Fischer-344 rats was a dose-related reduction in the time of onset of mammary and testicular tumors. A 24-month study in HaM/ICR mice revealed no evidence of carcinogenic activity. The significance of carcinogenicity data relative to use of dantrolene sodium in humans is unknown. Dantrolene sodium has produced positive results in the Ames S. Typhimurium bacterial mutagenesis assay in the presence and absence of a liver activating system. Dantrolene sodium administered to male and female rats at dose levels up to 45 mg/kg/day (approximately 1.4 times the maximum recommended daily dose on a mg/m 2 basis) showed no adverse effects on fertility or general reproductive performance.

Pregnancy Pregnancy

Category C Dantrolene sodium has been shown to be embryocidal in the rabbit and has been shown to decrease pup survival in the rat when given at doses seven times the human oral dose. There are no adequate and well-controlled studies in pregnant women.

Dantrolene

Sodium for Injection should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Labor and Delivery In one uncontrolled study, 100 mg per day of prophylactic oral dantrolene sodium was administered to term pregnant patients awaiting labor and delivery. Dantrolene readily crossed the placenta, with maternal and fetal whole blood levels approximately equal at delivery; neonatal levels then fell approximately 50% per day for 2 days before declining sharply. No neonatal respiratory and neuromuscular side effects were detected at low dose. More data, at higher doses, are needed before more definitive conclusions can be made.

Nursing Mothers

Dantrolene has been detected in human milk at low concentrations (less than 2 micrograms per mL) during repeat intravenous administration over 3 days. Because of the potential for serious adverse reactions in nursing infants from dantrolene, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Geriatric Use

Clinical studies of Dantrolene Sodium for Injection did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Drug Interactions: Drowsiness may occur with dantrolene sodium therapy, and the concomitant administration of CNS depressants such as sedatives and tranquilizing agents may result in further drowsiness. While a definite drug interaction with estrogen 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 estrogen therapy. Cardiovascular collapse in patients treated simultaneously with verapamil and Dantrolene Sodium is rare. The combination of therapeutic doses of intravenous Dantrolene Sodium and verapamil in halothane/ α -chloralose anesthetized swine has resulted in ventricular fibrillation and cardiovascular collapse in association with marked hyperkalemia. Until the relevance of these findings to humans is established, the combination of Dantrolene Sodium and calcium channel blockers is not recommended during the management of malignant hyperthermia. Administration of dantrolene sodium may potentiate vecuronium-induced neuromuscular block.