Dantrolene
Dantrium · Ryanodex
Skeletal muscle ryanodine receptor antagonist
Blocks RYR1 (ryanodine receptor) → ↓ Ca²⁺ release from sarcoplasmic reticulum → muscle relaxation. The only drug for malignant hyperthermia.
Indications
- •Malignant hyperthermia
- •Neuroleptic malignant syndrome (off-label)
- •Spasticity (chronic, oral)
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| MH crisis | 2.5 mg/kg IV bolus, repeat q5 min until symptoms resolve (≥ 10 mg/kg often) | Same: 2.5 mg/kg IV |
Pharmacokinetics
Onset 5 min IV. Half-life 4–8 h. Hepatic.
Side effects
- !Muscle weakness (especially with repeat dosing)
- !Hepatotoxicity (chronic oral)
- !Phlebitis (very alkaline; large vein preferred)
- !Mannitol load (3 g per 20 mg vial of original formulation; Ryanodex is mannitol-poor)
Contraindications
- ×None for MH crisis
Clinical pearls
- ★Ryanodex (250 mg/vial, reconstitutes in 5 mL) — fast for MH crisis vs. older 20 mg vial in 60 mL water.
- ★Stock at MH cart in any facility using volatile anesthetics or sux.
- ★Avoid CCBs concurrently — severe hyperkalemia risk.
Other drugs in Others
- Lipid Emulsion 20%
Theory: 'Lipid sink' sequesters lipophilic drugs (especially LAs), shifts to better Ca²⁺ handling, fatty acid metabolic support.
- Hydroxocobalamin
Vitamin B12a precursor; cyanide binds to cobalt center of hydroxocobalamin → forms cyanocobalamin (B12) → renal excretion. Also scavenges nitric oxide → vasoconstriction.
- Octreotide
Long-acting somatostatin analogue → suppresses splanchnic blood flow, GI/pancreatic secretions, GH, glucagon, insulin, and serotonin/vasoactive-peptide release.
- Alvimopan
Blocks GI mu-opioid receptors WITHOUT crossing the blood-brain barrier → reverses opioid-induced gut slowing while preserving central analgesia. Accelerates return of bowel function.
- Phentolamine
Competitive, reversible α1 + α2 blockade → vasodilation. Short-acting.
- Inhaled Nitric Oxide
Inhaled NO diffuses to pulmonary vascular smooth muscle → ↑ cGMP → SELECTIVE pulmonary vasodilation only in VENTILATED lung units (improves V/Q matching). Inactivated by hemoglobin before reaching systemic circulation → no systemic hypotension.
- Digoxin Immune Fab
Ovine Fab fragments bind free digoxin → the complex is renally excreted → rapidly reverses digoxin/digitoxin toxicity.
- Aminophylline
Nonselective PDE inhibition (↑ cAMP) + adenosine-receptor antagonism → bronchodilation, respiratory stimulation, mild inotropy/chronotropy.
Browse all classes: /reference/drugs
Suggested reading
- •MHAUS malignant hyperthermia treatment protocol
- •FDA package insert
- •Miller's Anesthesia, 9e
