Neuromuscular blocking drugs
Neuromuscular blocking drugsBlock cholinergic transmission between motor nerve ending and the nicotinic receptor on the skeletal muscle they act as antagonist (non depolarizing) and agonist (depolarizing) 1- Enable surgery under light anesthesia 2- Facilitates tracheal intubation 3- Quick induction and quick recovery However: 1- Mechanical ventilation is needed 2- Technical skill are required
They are divided into: 1- Non-depolarizing (competitive ) blockers Tubocurarine, Mivacurium 2- Depolarizing agents Succinylcholine
1- Non-depolarizing (competitive ) blockers
Mechanism of action The drugs interact with the nicotinic receptor to prevent the binding of Ach. These drugs prevent depolarization of the muscle cell membrane and inhibit muscle contraction . The drugs are competitive blocker because they compete Ach on the receptor site. Their action can be overcome by increasing Ach in the synaptic gap by such as neostigmineTherapeutic uses 1- As adjuvant drug with anesthesia during surgery to relax skeletal muscle 2- To facilitate intubation 3- During orthopedic surgery
Side effects 1- Induce histamine release and promote ganglionic blockers 2- Lower blood pressure 3- Increase heart rate 4- Bronchoconstriction 5-Drug interaction (Halothane) , aminoglycoside (Gentamicin ) , Ca channel blocker, increase NM block
2- Depolarizing agents
Mechanism of action Succinylcholine attaches to the nicotinic receptor and acts like Ach to depolarize the junction. Succinylcholine persists at high concentrations in the synaptic cleft, remaining attached to the receptor for a longer time. Continuous depolarization give way gradual repolarization and resistant to depolarizationTherapeutic uses Succinylcholine has rapid onset and short during of action 1- Rapid endotrachial intubation during induction of anesthesia (to avoid aspiration of gastric content during intubation 2- During electroconvulsive shock treatment
Adverse effects 1- Hyperthermia In genetically susceptible patients 2- Apnea In deficient plasma cholinestrase 3- Hyperkalemia In burn patients or patients with massive tissue damage
Skeletal muscle relaxants
Drugs that reduce spasm of the voluntary muscles without impairing voluntary movement can be useful in: Spastic states Low back syndrome Rheumatism with muscle spasmBaclofen It is structurally related to γ-aminobutyric acid (GABA), an inhibitory central nervous system transmitter, it inhibits reflex activity residues mainly in the spinal cord. It reduces spasticity and flexor spasms, but it has no action on voluntary muscle power.It benefits some cases of trigeminal neuralgia.
Dantroline It acts directly on muscle and prevents the release of calcium from sarcopalism stores (benefit in hyperthermia). Diazepam It has skeletal muscle relaxant activity acts centrally. It is less effective than baclfen with less side effects.