Generic Name : Dantrolene.

Trade Name    : DantRelax.

Drug Class      : Skeletal Muscle Relaxants.

Forms of The Drug

  1. Capsule: 25mg, 50mg, 100mg.
  2. Powder for injection: 20mg/vial, 250mg/vial.

Mechanism of Action

Its mechanism of action is distinct from other muscle relaxants as it acts directly on skeletal muscle cells rather than exerting its effects on the central nervous system. Here’s how dantrolene works:

  1. Inhibition of Calcium Release: Dantrolene acts by inhibiting the release of calcium ions (Ca^2+) from the sarcoplasmic reticulum, a specialized structure within skeletal muscle cells where calcium is stored. Calcium ions play a crucial role in muscle contraction: when released from the sarcoplasmic reticulum into the muscle cell cytoplasm, calcium binds to the protein complex troponin, initiating a series of events that lead to muscle contraction.
  2. Blockade of Excitation-Contraction Coupling: By inhibiting calcium release from the sarcoplasmic reticulum, dantrolene disrupts the process known as excitation-contraction coupling, which is essential for muscle contraction. Without sufficient calcium ions in the cytoplasm, the muscle cell is unable to contract effectively.
  3. Selective Action on Skeletal Muscle: Dantrolene selectively targets skeletal muscle cells and does not affect smooth muscle or cardiac muscle. This specificity is due to the unique structure and function of the sarcoplasmic reticulum in skeletal muscle cells, which differs from that in smooth muscle and cardiac muscle cells.
  4. Reduction of Muscle Spasticity and Hyperactivity: By inhibiting calcium release and interfering with excitation-contraction coupling in skeletal muscle cells, dantrolene reduces muscle spasticity and hyperactivity. This leads to relaxation of the affected muscles, alleviating symptoms such as muscle stiffness, tightness, and involuntary muscle contractions.
  5. Use in Malignant Hyperthermia: Dantrolene is also used in the treatment and prevention of malignant hyperthermia, a rare but potentially life-threatening condition triggered by certain anesthetic agents. In this context, dantrolene acts by inhibiting excessive calcium release from the sarcoplasmic reticulum in skeletal muscle cells, which helps to prevent or reverse the dangerous increase in body temperature and muscle rigidity characteristic of malignant hyperthermia.

Indications

  1. Spasticity Associated with Neurological Disorders: such as multiple sclerosis, cerebral palsy, spinal cord injury, or stroke.
  2. Various musculoskeletal conditions, such as muscle strains, sprains, or injuries.
  3. Malignant Hyperthermia.
  4. Certain neuromuscular disorders: such as hereditary spastic paraplegia, stiff person syndrome, or neuromyotonia (Isaacs syndrome).
  5. Used off-label for the management of conditions involving muscle hyperactivity or spasms not specifically listed in the approved indications.

Contraindications

  1. Hypersensitivity
  2. Active Liver Disease.
  3. Previous History of Hepatitis.
  4. Pregnancy and Breastfeeding.
  5. Preexisting Muscle Weakness: such as myasthenia gravis or muscular dystrophy. Dantrolene can exacerbate muscle weakness or fatigue.
  6. Chronic Respiratory Disease: such as chronic obstructive pulmonary disease (COPD) or severe asthma.
  7. Myopathy

Side Effects

  1. Muscle Weakness.
  2. 1. Muscle Weakness.
  3. Drowsiness.
  4. Fatigue.
  5. Dizziness.
  6. Nausea, vomiting, diarrhea, or abdominal discomfort.
  7. Jaundice, dark urine, or abdominal pain.
  8. Shallow breathing or difficulty breathing.
  9. Rash, itching, swelling of the face or throat, difficulty breathing, or severe dizziness.

Drug Interaction

  1. Other CNS depressants, such as opioids, benzodiazepines, alcohol, and certain antipsychotic medications.
  2. Calcium Channel Blockers.
  3. Estrogen-containing Hormonal Contraceptives.
  4. Succinylcholine
  5. CYP450 Enzyme Inhibitors: such as fluvoxamine, ciprofloxacin, and fluoroquinolone antibiotics.
  6. CYP450 Enzyme Inducers: such as rifampin, phenytoin, and carbamazepine.

Precautions

  1. Pregnancy: Category C.
  2. Lactation: Dantrolene is excreted into human breast milk, and therefore caution is advised when considering its use in breastfeeding women.

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