Prolonged mivacurium infusion in young and elderly adults

Area of Science:

• Anesthesiology
• Pharmacology
• Clinical Medicine

Background:

• Mivacurium is a neuromuscular blocking agent used in anesthesia.
• The cis-cis isomer is a metabolite of mivacurium.
• Prolonged infusions may lead to isomer accumulation and prolonged neuromuscular block.

Purpose of the Study:

• To evaluate the pharmacodynamics and pharmacokinetics of the cis-cis isomer of mivacurium.
• To determine if the cis-cis isomer contributes to neuromuscular block during prolonged infusions (>4 hours).
• To compare these effects in young adult and elderly patients.

Main Methods:

• Mechanomyogramic neuromuscular response of the adductor pollicis was recorded in 51 adult patients (18-59 yr and >60 yr).
• Mivacurium infusion rate was adjusted to maintain 95% twitch depression.
• Plasma concentrations of the cis-cis isomer were measured throughout the infusion.

Main Results:

• Elderly patients required lower mivacurium infusion rates (4.3 µg/kg/min) compared to young adults (6.0 µg/kg/min).
• Patients with low cholinesterase activity had the lowest infusion requirement (2.4 µg/kg/min).
• Plasma cis-cis isomer concentrations peaked early and remained stable, with no correlation to infusion duration or recovery indices.

Conclusions:

• The plasma concentration of the cis-cis isomer of mivacurium did not increase during prolonged infusions.
• Neuromuscular transmission recovered satisfactorily in all patients, regardless of infusion duration or isomer concentration.
• Titration to maintain 95% twitch depression prevented accumulation and ensured adequate recovery.