NUROMAX binds competitively to cholinergic receptors on the motor end-plate to antagonize the action of acetylcholine, resulting in a block of neuromuscular transmission. This action is antagonized by acetylcholinesterase inhibitors, such as neostigmine.

Pharmacodynamics

NUROMAX is approximately 2.5 to 3 times more potent than pancuronium and 10 to 12 times more potent than metocurine. NUROMAX in doses of 1.5 to 2 x ED₉₅ has a clinical duration of action (range and variability) similar to that of equipotent doses of pancuronium and metocurine (historic data and limited comparison). The average ED₉₅ (dose required to produce 95% suppression of the adductor pollicis muscle twitch response to ulnar nerve stimulation) of NUROMAX is 0.025 mg/ kg (range: 0.020 to 0.033) in adults receiving balanced anesthesia.

The onset and clinically effective duration (time from injection to 25% recovery) of NUROMAX administered alone or after succinylcholine during stable balanced anesthesia are shown in Table 1.

Initial doses of 0.05 mg/ kg (2 x ED₉₅) and 0.08 mg/ kg (3 x ED₉₅) NUROMAX administered during the induction of thiopental-narcotic anesthesia produced good-to-excellent conditions for tracheal intubation in 5 minutes (13 of 15 cases studied) and 4 minutes (eight of nine cases studied) (which are before maximum block), respectively.

As with other long-acting agents, the clinical duration of neuromuscular block associated with NUROMAX shows considerable interpatient variability. An analysis of 390 cases in US clinical trials utilizing a variety of premedications, varying lengths of surgery, and various anesthetic agents, indicates that approximately two thirds of the patients had clinical durations within 30 minutes of the duration predicted by dose (based on mg/ kg actual body weight). Patients ³ 60 years old are approximately twice as likely to experience prolonged clinical duration (30 minutes longer than predicted) than patients <60 years old; thus, care should be used in older patients when prolonged recovery is undesirable (see PRECAUTIONS: Geriatric Use and Individualization of Dosages below). In addition, obese patients (patients weighing ³ 30% more than ideal body weight for height) were almost twice as likely to experience prolonged clinical duration than non- obese patients; therefore, dosing should be based on ideal body weight (IBW) for obese patients (see Individualization of Dosages below).

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