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Raplon

Clinical Pharmacology
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CLINICAL PHARMACOLOGY

Raplon

RAPLONÒ (rapacuronium bromide) for Injection is a nondepolarizing neuromuscular blocking agent with a rapid onset of action (mean onset approximately 90 seconds; range 35-219 seconds) and a dose-dependent duration of action. The recommended dose of 1.5 mg/kg in adults has a short clinical duration of action (mean duration approximately 15 minutes; range 6-30 minutes) (see

CLINICAL PHARMACOLOGY

-Clinical studies). Rapacuronium acts by competing for cholinergic recepotors at the motor end plate. Profound neuromuscular blockade induced by RAPLONÒ can be reversed by neostigmine (see CLINICAL PHRMACOLOGY-Early Reversal).

Pharmacodynamics

The neuromuscular block seen after the intravenous administration of 1.5 mg/kg RAPLONÒ (rapracuronium bromide) for Injection is primarly due to rapacuronium. Plasma levels of the major active metabolite of rapacuronium (the 3-hydroxy metabolite) are relatively low compared to the parent at a dose of 1.5 mg/kg of RAPLONÒ . Pharmacokinetic and pharmacodynamic modeling studies were conducted after the separate administration of rapacurcnium bromide and the 3-hydroxy metabolite. These studies evaluated the effect of plasma drug concentrations on the neuromuscular block achieved as measured by mechanomyography of the adductor pollicies musicle to indirect supramaximal train-of-four stimulation of the ulnar nerve. These results are shown in Tables 1 and 2 Comparison of k° ° (rate constant for the equilibration between effect compartment at 50% drug effect) values of rapacuronium and the 3-hydroxy metabolite shows that the metabolite has slower onset and a higher potency than rapacuronium bromide. However, when comparing the ED90 (dose required to produce 90% suppression of the first [T,] mechanomyographic [MMG] response of the adductor pollicis muscle to indirect supramaximal train-of-four stimulation of the ulnar nerve) of rapacuronium (0.3 mg/kg), vecuronium (0.05 mg/kg) and pancuronium (0.06 mg/kg). Rapacuronium bromide and the3-hydroxy metabolite may be viewed as low potency neuromuscular blocking drugs.

TABLE 1: Pharmacokinetic/pharmacodynamic modeling parameters of rapacuronium bromide after a slow ointravenous infusion of rapacuronium bromide in ten subjects at a median dose of 0.93 mg/kg over a median time of four minutes and forty seconds (mean (%CV)).

Parameter

 

K° ° 1/minute

0.44 (41)

Y

2.97 (23)

EC50. Mcg/mL

4.44 (33)

ED90. Mg/kg

1.03 (33)

TABLE 2: Pharmacokinetic/pharmacodynamic modeling parameters of the 3-hydroxy metabolite after a slow intavenous infusion in seven subjects of a median dose of 0.66 mg/kg over three to five minutes (mean (%CV)).

Parameter

 

K° ° . 1/minute

0.10(40)

y

4.83(44)

Brand Name: Raplon
Generic Name: Rapacuronium

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