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Pharmacology: Skeletal Muscle Relaxation: Inhibition of experimentally induced muscle rigidity: Eperisone hydrochloride suppresses intercollicular section-induced decerebrate rigidity (γ-rigidity) and ischemic decerebrate rigidity (α-rigidity) in rats dose-dependently.
Suppression of spinal reflexes: In spinal cats, eperisone hydrochloride suppresses mono- and poly-synaptic reflex potentials induced through spinal nerve efferent root stimulation to a similar degree.
Reduction of muscle spindle sensitivity via γ-motor neurons: Eperisone hydrochloride suppresses the activity of afferent nerve fibers (Ia fibers) from human muscle spindles at 20 min after administration. Eperisone hydrochloride suppresses the spontaneous discharge of γ-motor neurons, but does not act directly on muscle spindles in animals. Accordingly, eperisone hydrochloride reduces muscle spindle sensitivity via the γ-motor neurons.
Vasodilatation and Augmentation of blood flow: Vasodilatory Action: Eperisone hydrochloride dilates the blood vessels due to Ca++-antagonistic action (in guinea pigs) on the vascular smooth muscle and muscular sympatholytic actions (in humans).
Augmentation of blood flow: Eperisone hydrochloride increases the volume of blood flow in skin, muscle, external and internal carotid arteries and vertebral arteries in humans, monkeys and dogs.
Analgesic action and inhibition of the pain reflex in the spinal cord: When eperisone hydrochloride is perfused into the spinal cord of rats, a tail pinch-induced pain reflex is suppressed, but the reflex returns with the withdrawal of eperisone hydrochloride. This suggests that eperisone hydrochloride possesses an analgesic action at the spinal cord level.
Facilitation of voluntary movement: When eperisone hydrochloride is used in the treatment of spastic paralysis in patients with cerebral apoplexy, it improves the cybex torque curve and electromyogram and facilitates voluntary movements such as extension and flexion of the extremities, without reducing the muscular force.
Clinical Studies: Cervical syndrome, Periarthritis of the Shoulder, Lumbago: In open labeled clinical trial undertaken to determine the effects of MYONAL on myotonic symptoms associated with these diseases, an efficacy rate of 52.1% (234/449) was achieved. (When fairly effective responses are included, the efficacy rate was as high as 80.4%.)
Spastic Palsy: Patients (>18 years) with moderate to severe spastic palsy were eligible in the double-blind, randomized study; they received eperisone 300 mg/day or baclofen 60 mg/day for 6 weeks. The results suggest that eperisone 300 mg/day is as effective and well-tolerated as oral baclofen. However, eperisone might be associated with some additional clinical benefits when compared with baclofen.
In a randomized, placebo-controlled, double-blind, three-way cross-over study, patients (18-75 years) with spastic palsy received three consecutive treatment cycles: eperisone 150 mg/day, eperisone 300 mg/day or placebo for 8 weeks. Every treatment period lasted for 14 days. The reduction in the intensity of spasticity versus the beginning of each treatment cycle was significant with eperisone 300 mg/day (p=0.004).
The results of these studies could overall suggest that eperisone 300 mg/day is effective and well-tolerated in the treatment of spastic palsy of different etiologies.
Pharmacokinetics: Blood Concentration: Eperisone hydrochloride was administered orally to 8 healthy adult male volunteers at a single dose of 150 mg/day (a single dose of 150 mg is not approved) for 14 consecutive days and the plasma concentration was determined at days 1, 8 and 14. The time to reach the peak plasma concentration (tmax) ranged from 1.6-1.9 hr, the peak plasma concentration (Cmax) was 7.5-7.9 ng/mL, elimination half-life (t½) was 1.6-1.8 hr, and the area under the plasma concentration-time curve (AUC) was 19.7-21.1 ng·hr/mL. The plasma concentration profiles of eperisone hydrochloride determined at days 8 and 14 did not significantly vary from those of the 1st day. (See Figure.)
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