title: Effect of ionized calcium on the neuromuscular blocking actions of atracurium and vecuronium in the cat.
abstract: We have determined neuromuscular blocking effects of atracurium and vecuronium at normal, high and low plasma concentrations of ionized calcium ( [Ca2+] ) in the cat. Twitch responses were measured bilaterally in the anterior tibialis muscles, using intact central innervation in one preparation. Plateaus of high and low [Ca2+] were created by infusions of calcium chloride and citrate, respectively. The interactions with changes in [Ca2+] were similar for atracurium and vecuronium, and were unaffected by central muscle innervation. The median increase in [Ca2+] from 1.21 to 1.59 mmol litre-1 shifted the dose-response curves of the drugs to the right, increasing ED50 by 7-13%, whereas the decrease to median 0.78 mmol litre-1 potentiated the drugs by a similar order. This indicates a lesser influence of [Ca2+] on the action of neuromuscular blockers than reported in a previous in vitro study. Even though the interactions were statistically significant, their moderate magnitude suggests minor clinical significance.
authors.affiliation: Department of Anaesthesia, Rikshospitalet, University Hospital, Oslo, Norway.
authors.forename: L
authors.initials: L
authors.lastname: Gramstad
authors.forename: E S
authors.initials: ES
authors.lastname: Hysing
mesh_terms: D000818:Animals; D001279:Atracurium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009121:Muscle Denervation; D009469:Neuromuscular Junction / Q000187:drug effects; D014673:Vecuronium Bromide / Q000494:pharmacology*
chemical_list: D001279:Atracurium; D014673:Vecuronium Bromide; D002118:Calcium