Prolonged mivacurium infusion in young and elderly adultsPurpose: This study was designed to evaluate pharmacoclynamically and pharmacokinetically if the ds-cis isomer of mivacurium contributed to neuromuscular block during prolonged infusions lasting more than four hours in young adult and elderly (> 60 yr) patients. Methods: The mechanomyogramic neuromuscular response of the adductor potlids was recorded in 32 adults 18-59 yr. and 19 elderly (> 60 yr.) patients during N20:O2:opioid anaesthesia. The mivacudum infusion rate was adjusted to maintain single twitch depression at 95 --+-496 of control. Blood samples were taken every 30 min to determine the plasma concent~tion of ds-cis isomer of mivacufium. At the end of the surgical procedure, patients were allowed to recover spontaneously to at least 25% of control twitr~ response. gemflts: The mean mivacurium infusion requirement to maintain 97 +_ I (mean +__ SD)% depression of the twitch response was 6.0 -+ 0.4 pg.kg-l-min -t in young adults, and 4.3 +_ 0.3 pg-kgUmin -~ in elderly paEents (P < 0.001), The infusion requirement in patients with low plasma cholinesterase activity was the lowest 2.4 _.+ 1.2 /Jg.kg -~.min -j. Plasma ds-cis isomer concentrations reached peak levels wi~in one-two hours and remained relatively constant throughout the duration of infusion even in patients with low cholinesterase actMty. There was no relationship between duration of infusion, plasma concentrations of ds-ds isomer and the early recovery indices of mivacurium (up to 25%). Neuromuscular transmission recovered adequately with or without antagonism in all patients. Condusiom When the mivacudum infusion was ~ to maintain 95 ---4% twitch deprmsion, the plasma concentration of the ds-cis isomer did not increase during prolonged infusions (four hours) and neuromuscular transmission recovers satisfactorily.Objectif : Cette Etude pharmacoclynamique et pharmacocinEtique visait A determiner si risomEre dc-cis du mivacurium contribualt au bloc neuromusculalre pendant des perfusions de quatre heures et plus, chez des jeunes adultes el: chez des sujets plus ~gEs (>60 ans). M6thodes : La r6ponse m6canomyographique neuromusculaire a 6t6 enregistr~ae ,~ I'adducteur du pouce chez 32 patients adultes de 18 ~ 59 ans et chez 19 patients plus ~g6s (>60 ans) pendant une anesth~ie associant N20/O2 un morphinique. La vitesse de peffusion du mivacurium 6talt r~glEe de fagon ~ maintenir un twitch sous 95 -496 du contr61e. La concentration plasmatique de I'isorn6re cis-cis du mivacurium 6tait d6termin6e sur des ~-hantillons de sang pr~lev~s aux 30 min. Une fois la chirurgie termir~,e, on laissait les patients r6cup~rer spontan6ment jusqu',~ une r6ponse d'au moins 25% au twitch. ll~ultats : [. perfusion moyenne de mivacurium n~cessaire pour maintenir la r~ponse au twitch sous 97 + 1% (moyenne + El') ~talt de 6,0 + 0,4 pg-kg -~.min -~ chez les jeunes adultes et de 4,3 _+ 0,3 #g'kg -~-min -~ chez les patients plus ~s (P < 0,001). Les patients dont I'activit6 de la cholinest~rase plasmatique ~ faible avai...