Muscle relaxants depolarizing

According to whether receptor occupancy leads to a blockade or an excitation of the endplate, one distinguishes nondepolarizing from depolarizing muscle relaxants (p. 186). As adjuncts to general anesthetics, muscle relaxants help to ensure that surgical procedures are not disturbed by muscle contractions of the patient (p. 216). 

When anaesthetics are given it is common practice to give succinylcholine, a depolarizing muscle relaxant with normally a short duration of action. 

Table 27-2 Comparison of a Typical Nondepolarizing Muscle Relaxant (Rocuronium) and a Depolarizing Muscle Relaxant (Succinylcholine). ...

The local anesthetics procaine and lidocaine enhance the neuromuscular block produced by nondepolarizing and depolarizing muscle relaxants. 

In large doses, most local anesthetics block neuromuscular transmission. However, in smaller doses, they enhance the neuromuscular block produced by both nondepolarizing and depolarizing muscle relaxants. In small doses, local anesthetics depress posttetanic potentiation, and this is thought to be a prejunctional neural effect. With higher doses, local anesthetics block acetylcholine-induced... 

DONEPEZIL SUXAMETHONIUM Possible t efficacy of suxamethonium Suxamethonium is metabolized by cholinesterase parasympatho-mimetics inhibit cholinesterase and so prolong the action of suxamethonium Avoid co-administration. Ensure that the effects of suxamethonium have worn off before administering a parasympathomimetic to reverse non-depolarizing muscle relaxants. A careful risk-benefit analysis should be made before considering the use of suxamethonium for emergency anaesthesia in patients taking parasympathomimetics. The short half-life of edrophonium means that it can be used to diagnose suspected dual block with suxamethonium... 

PANCURONIUM THEOPHYLLINE Antagonism of neuromuscular blockade Uncertain Larger doses of pancuronium may be needed to obtain the desired muscle relaxation during anaesthesia other non-depolarizing muscle relaxants do not seem to be affected... 

NON-DEPOLARIZING CALCIUM CHANNEL BLOCKERS T effect of non-depolarizing muscle relaxants with parenteral calcium channel blockers the effect is less certain with oral therapy. In two cohort studies, vecuronium requirements were halved in patients on diltiazem. Nimodipine does not seem to share this effect Uncertain postulated that ACh release at the synapse is calcium dependent. L calcium concentrations at the nerve ending may l ACh release, which in turn prolongs the nerve blockade Monitor nerve blockade carefully in patients on calcium channel blockers, particularly near to the end of surgery, when muscle relaxation may be prolonged and difficult to reverse... 

NON-DEPOLARIZING PARASYMPATHOMIMETICS 1 efficacy of non-depolarizing muscle relaxants Anticholinesterases oppose the action of non-depolarizing muscle relaxants Used therapeutically... 

Figure 9.14. Stmctures of muscle-relaxants. a d-Tubocu-rarine (top) and pancuronium. The two acetylcholine moieties in the pancuronium molecule are highlighted, b Stmctures of the depolarizing muscle relaxants succinylcholine (top) and de-camethonium (bottom).

Basta SJ, Ali HH, Savarese JJ, Sunder N, Gionfriddo M, Cloutier G, Lineberry C, Cato AE. Clinical pharmacology of atracurium besylate (BW 33A) a new non-depolarizing muscle relaxant. Anesth Analg 1982 61(9) 723-9. 

Tryba M. Wirkungsverstarkung nicht-depolarisierender Muskelrelakantien durch AcylaminopenciUine. Untersuchungen am Beispiel von Vecuronium. [Potentiation of the effect of non-depolarizing muscle relaxants by acylami-nopenicillins. Studies on the example of vecuronium.] Anaesthesist 1985 34(12) 651-5. 

Gallamine is a non-depolarizing muscle relaxant. For intubation about 2 mg/kg (some authors say 3-4 mg/kg) are necessary, and the duration of effect is then similar to the usual intubating doses of D-tubocurarine or pancuronium. A dose of 1-1.5 mg/kg is usually sufficient to produce apnea and adequate abdominal relaxation. Such doses are said to be short-acting (20 minutes) but can provide clinical relaxation (75% or more depression of twitch height) for some 30-40 minutes. Individual variation is considerable, and complete spontaneous reversal of blockade is relatively slow. 

Metronidazole can potentiate the effects of non-depolarizing muscle relaxants (41). 

Mivacurium chloride is a non-depolarizing muscle relaxant, a benzylisoquinolinium diester compound with a duration of approximately twice that of suxamethonium. In vitro (1), it is metabolized to a significant extent by plasma cholinesterase, and minimally by acetylcholinesterase. The rate of metabolism in vitro is directly related to plasma cholinesterase activity. In pooled human plasma the rate of hydrolysis of mivacurium was 70% that of suxamethonium. Its half-life is 5-10 minutes compared with 2-5 minutes for suxamethonium. The in vitro hydrolysis of mivacurium by purified human plasma cholinesterase occurs at 88% of the rate for suxamethonium (2). There was a poor correlation between the duration of action of bolus doses of mivacurium and the plasma cholinesterase activity in individual patients (2), a finding that has also been reported by others (3). However, the average infusion rate to maintain around 95 % blockade in individual patients correlated significantly with the patients plasma cholinesterase activities (4). While metabolites have been detected in both urine and bile, mivacurium seems to depend principally on ester hydrolysis for its plasma clearance, so that reduced activity of plasma cholinesterase is likely to result in a prolonged duration of action. 

Goudsouzian NG, Liu LM, Cote CJ. Comparison of equipotent doses of non-depolarizing muscle relaxants in children. Anesth Analg 1981 60(12) 862-6. 

Many efforts have been made to find a technique to prevent the suxamethonium-associated increase in intraocular pressure. Some attenuation of the pressure response has been demonstrated with defasciculation doses of non-depolarizing muscle relaxants (122), but this could not be reproduced in subsequent studies (100-102,123). The same is true for self-taming, that is... 

Quinidine potentiates not only non-depolarizing muscle relaxants but also depolarizing drugs (276). 

Brim VD. Denervation supersensitivity the response to depolarizing muscle relaxants. Br J Anaesth 1973 45(2) 222-6. 

Moorthy SS, HUgenberg JC. Resistance to non-depolarizing muscle relaxants in paretic upper extremities of patients with residual hemiplegia. Anesth Analg 1980 59(8) 624-7. 

Clinically important, potentially hazardous interactions with aminophylline, atracurium, cisatracurium, doxacurium, epinephrine, ergometrine, mivacurium, non-depolarizing muscle relaxants, oxprenolol, oxytocin, pancuronium, rapacuronium, rifampin, vecuronium, xanthines... 

---