Relatro25 mg

Relatro is a direct-acting skeletal muscle relaxant with two well-established, FDA-approved indications:

1. Chronic Spasticity (Established Use)

Used for the treatment of spasticity resulting from upper motor neuron disorders, including:

• Spinal cord injury
• Cerebral palsy
• Multiple sclerosis
• Stroke

Relatro is indicated only when spasticity interferes with function or nursing care and relief is expected to give an overall functional benefit; it is not indicated when spasticity is needed to sustain posture or balance during walking.

2. Malignant Hyperthermia (Established Use)

The intravenous formulation of Relatro is the specific treatment for malignant hyperthermia (MH), a rare, life-threatening hypermetabolic reaction to certain general anesthetic agents. It is also used:

• As preoperative prophylaxis in patients known or suspected to be susceptible to MH
• Following an acute MH crisis, to help prevent recurrence

Off-Label Uses (Not FDA-Approved)

Relatro has also been used off-label, based on case reports and clinical experience, for severe hyperthermic emergencies such as neuroleptic malignant syndrome, exertional heat stroke, and stimulant (e.g., MDMA)-associated hyperthermia when standard cooling and supportive measures are insufficient. Such use should only be undertaken by specialists in a hospital or critical care setting.

Each capsule of Dantrolene Sodium is available in strengths of 25 mg, 50 mg, or 100 mg. Intravenous formulations of Dantrolene Sodium are supplied as a sterile lyophilized powder for reconstitution, commonly as 20 mg per vial (conventional formulation, also containing mannitol) or as a 250 mg per vial nanocrystalline suspension formulation. Exact strengths and presentations may vary by manufacturer and market.

Relatro is a hydantoin derivative that acts as a direct-acting (peripherally acting) skeletal muscle relaxant. Unlike centrally-acting muscle relaxants, Relatro acts directly on skeletal muscle fibers rather than on the central nervous system or the neuromuscular junction, making it uniquely useful for both chronic spasticity and the medical emergency of malignant hyperthermia.

Direct-acting (peripherally acting) skeletal muscle relaxant; Hydantoin derivative; specific antihyperthermic agent for malignant hyperthermia

Dantrolene Sodium acts directly on skeletal muscle by binding to the ryanodine receptor (RyR1) on the sarcoplasmic reticulum, inhibiting the release of calcium ions required for excitation-contraction coupling. This reduces the force of muscle contraction without significantly affecting cardiac or smooth muscle, and without directly blocking neuromuscular transmission.

In malignant hyperthermia, this same mechanism reverses the uncontrolled calcium release from skeletal muscle that drives the hypermetabolic crisis (muscle rigidity, hyperthermia, tachycardia, acidosis).

Pharmacokinetics: Orally, Dantrolene Sodium is adequately absorbed, extensively metabolized in the liver, and eliminated with an average half-life of approximately 8-9 hours after oral dosing. Metabolites are excreted mainly in urine and bile.

Oral capsules of Relatro may be taken with or without food; capsules should be swallowed whole, or may be opened and the contents mixed with juice or a similar vehicle immediately before use for patients unable to swallow capsules. The intravenous formulation of Relatro must be reconstituted (see Reconstitution) and administered only by trained healthcare personnel in a hospital or surgical setting, typically by rapid IV push through a free-flowing line, avoiding extravasation, as the solution is highly alkaline and irritating to tissue.

Relatro has the following well-documented, clinically significant interactions:

• CNS depressants (alcohol, sedatives, opioids, benzodiazepines): additive drowsiness and sedation; combined use should be approached with caution.
• Estrogen-containing therapy: concurrent use, particularly in women over 35, appears to increase the risk of hepatotoxicity associated with Relatro (see Precautions and Warnings).
• Calcium channel blockers (e.g., verapamil): co-administration with intravenous Relatro during treatment of malignant hyperthermia has been associated with cardiovascular collapse and hyperkalemia; this combination should be avoided in that setting.
• Neuromuscular blocking agents (e.g., vecuronium): Relatro may potentiate the degree of neuromuscular blockade.
• Highly protein-bound drugs (e.g., warfarin, clofibrate, tolbutamide): may compete with Relatro for plasma protein binding sites; monitor as clinically indicated.

Always inform the prescribing physician of all other medicines being taken before starting Relatro.

The most common side effects of Relatro, especially during the first two weeks of therapy or with dose increases, include:

• Drowsiness and generalized weakness
• Dizziness and light-headedness
• Fatigue and malaise
• Diarrhea (usually mild and transient; may require temporary dose reduction)

Less common effects include constipation, loss of appetite, speech disturbance, and blurred or double vision.

Serious Side Effects

Serious but less common reactions include liver injury/hepatitis (see Precautions and Warnings for full detail), pleural effusion with pericarditis, blood disorders such as aplastic anemia or leukopenia, and hypersensitivity or photosensitivity reactions. Seek prompt medical attention for yellowing of the skin or eyes, unusual bleeding or bruising, severe breathlessness, or chest pain while taking Relatro.

Pregnancy: Relatro crosses the placenta. Human reproductive safety data are limited, and Relatro should be used during pregnancy only if the potential benefit clearly justifies the potential risk to the fetus, under close physician supervision — particularly for the emergency, life-saving treatment of malignant hyperthermia.

Lactation: Use of Relatro is contraindicated in breastfeeding mothers, as it is excreted into breast milk and may affect the nursing infant (see Contraindications). A physician should be consulted regarding infant feeding if Relatro is required.

Boxed Warning: Liver Injury (Hepatotoxicity)

Relatro carries a boxed warning for potentially fatal, symptomatic liver injury (hepatitis), which can occur at any dose but is more common with:

• Daily doses above 400 mg (risk rises further at doses of 800 mg per day or more)
• Prolonged therapy (generally beyond 60 days)
• Female sex and age over 35 years
• Concurrent use of other hepatotoxic medications or estrogens

Baseline liver function tests (e.g., AST/SGOT, ALT/SGPT) are required before starting Relatro for chronic use, and periodic liver function monitoring should continue throughout treatment. Relatro should be discontinued if liver function abnormalities occur, if there is no clear clinical benefit within 45 days, or if continued therapy is no longer indicated after the lowest effective dose has been established.

Other Precautions

• Relatro commonly causes drowsiness and dizziness; avoid driving or operating hazardous machinery until effects are known.
• Use with caution in patients with pre-existing cardiac or pulmonary dysfunction, especially with long-term oral use.
• Avoid co-administration of intravenous Relatro with calcium channel blockers during malignant hyperthermia treatment (see Interactions).
• Photosensitivity reactions have been reported; minimize prolonged sun exposure.
• Intravenous solutions are highly alkaline; avoid extravasation, as it may cause tissue damage.

Overdose with Relatro may cause muscle weakness, lethargy, altered consciousness or coma, vomiting, diarrhea, and crystalluria.

There is no specific antidote. Management is supportive and should take place in a hospital setting, and may include maintaining a clear airway, intravenous fluids to maintain adequate urine output and help prevent crystalluria, and cardiac and respiratory monitoring. If overdose is suspected, seek immediate medical attention or contact your local emergency services or poison control center right away; do not attempt to manage a suspected overdose at home.

Store Relatro capsules at room temperature (below 30°C), protected from light and moisture. Store unreconstituted injectable powder as directed on the label; once reconstituted, protect the solution from light and use within the time specified by the manufacturer (typically within 6 hours). Keep out of reach of children.

Hepatic impairment: Active liver disease is a contraindication to Relatro (see Contraindications). In patients without active liver disease, liver function must still be monitored closely throughout treatment.

Renal impairment: Specific dose-adjustment guidance is not well established; use with caution and monitor clinically, since metabolites are partly renally excreted.

Elderly (geriatric) patients: May be more susceptible to hepatotoxicity and CNS effects (drowsiness, dizziness); start at the lower end of the dosing range and monitor liver function and clinical response closely.

Cardiac or pulmonary dysfunction: Use with caution, particularly with long-term oral therapy for spasticity (see Precautions and Warnings).

For chronic spasticity, an adequate trial of Relatro is generally considered to be 45 days at an optimized dose; if no meaningful functional benefit is seen by then, treatment should be discontinued. If beneficial, Relatro may be continued long-term at the lowest effective dose with regular reassessment and periodic liver function monitoring. For malignant hyperthermia, treatment is acute and continues only until the crisis is controlled, with post-crisis prophylaxis typically continued for 1 to 3 days. Preoperative prophylaxis in at-risk patients is generally given for 1 to 2 days before surgery.

The intravenous powder formulations of Relatro must be reconstituted immediately before use. Each vial is reconstituted by adding the volume of sterile water for injection specified by the manufacturer (without a bacteriostatic agent, for conventional formulations) and shaking the vial until the solution is clear, as Relatro dissolves slowly; conventional formulations typically require vigorous mixing for a minute or more. The reconstituted solution should be protected from light, used promptly (generally within 6 hours), and administered only by trained healthcare personnel via a patent intravenous line, avoiding extravasation.

Skeletal muscle relaxants (direct-acting/peripherally acting); Hydantoin derivatives

Dantrolene Sodium binds to the ryanodine receptor (RyR1) on the sarcoplasmic reticulum of skeletal muscle cells, inhibiting calcium ion release into the muscle cytoplasm. Because calcium release is essential for excitation-contraction coupling, this action directly weakens skeletal muscle contraction — including the uncontrolled contraction and heat production seen in malignant hyperthermia — without significantly affecting the heart, smooth muscle, or the neuromuscular junction.

Category C (FDA legacy pregnancy category)

Relatro is approved for chronic spasticity in children 5 years of age and older, using a weight-based starting dose (approximately 0.5 mg/kg once daily) titrated gradually as tolerated; safety and efficacy for chronic spasticity have not been established in children under 5 years. For the treatment of malignant hyperthermia, intravenous Relatro is used in pediatric patients of any age, dosed by body weight, since this is a life-threatening emergency where treatment cannot be withheld.