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Eperisone

Eperisone: A Comprehensive Look at the Centrally Acting Muscle Relaxant

Introduction

Eperisone hydrochloride is a centrally acting muscle relaxant with vasodilatory properties, widely used in several Asian countries, including Japan, India, and the Philippines. Although not globally recognized like some Western alternatives, Eperisone plays a critical role in the management of muscle spasticity and musculoskeletal pain.

Chemical and Pharmacological Profile

  • Chemical Name: 4'-ethyl-2-methyl-3-piperidinopropiophenone hydrochloride

  • Molecular Formula: C17H27NO·HCl

  • Molecular Weight: 297.87 g/mol

  • Drug Class: Centrally acting skeletal muscle relaxant

  • ATC Code: M03BX09

Eperisone is structurally similar to tolperisone and belongs to a class of drugs that suppress spinal reflexes and enhance peripheral blood flow. It is available as oral tablets, typically in 50 mg and 100 mg doses.

Mechanism of Action

Eperisone works through central and peripheral mechanisms:

1. Central Action

  • Acts at the spinal cord level to inhibit reflex transmission, likely by reducing the activity of gamma-efferent motor neurons.

  • Reduces tonic muscle contraction by interfering with mono- and polysynaptic reflex arcs.

2. Peripheral Action

  • Exhibits vasodilatory effects by acting on smooth muscle of the blood vessels.

  • May modulate afferent input from muscles to the central nervous system, reducing the perception of pain.

3. Neuromodulatory Effects

  • Thought to enhance microcirculation in muscles by improving blood flow.

  • Influences neurotransmitter balance, particularly by reducing acetylcholine release in motor neurons.

Pharmacokinetics

  • Absorption: Rapidly absorbed after oral administration.

  • Time to peak plasma concentration: ~1.6–2.1 hours

  • Half-life: 1.6–2.4 hours

  • Metabolism: Hepatic metabolism via cytochrome P450 enzymes.

  • Excretion: Primarily renal

Though quickly metabolized, the therapeutic effect may last longer due to sustained action on spinal reflexes and peripheral vessels.

Therapeutic Indications

Eperisone is primarily used for muscle spasticity and related conditions. Its indications include:

1. Spastic Disorders

  • Cerebrovascular disorders (e.g., stroke-related spasticity)

  • Spinal cord lesions

  • Multiple sclerosis

  • Cerebral palsy

2. Musculoskeletal Disorders

  • Cervical spondylosis

  • Lumbago

  • Fibromyalgia

  • Frozen shoulder

  • Myositis

3. Vascular and Peripheral Circulation Conditions

  • Raynaud’s phenomenon

  • Intermittent claudication

In these conditions, Eperisone not only reduces muscle tone but also helps relieve pain through improved blood flow.

Clinical Efficacy

Several clinical studies, particularly from Asia, support Eperisone’s efficacy in reducing muscle stiffness and improving functional mobility.

1. Post-stroke Spasticity

  • Patients demonstrated a significant reduction in muscle tone as measured by the Modified Ashworth Scale.

  • Improvement in range of motion and motor coordination observed within weeks of therapy.

2. Lumbago and Cervical Spondylosis

  • Eperisone combined with NSAIDs significantly improved pain scores and functional disability indexes.

  • Its muscle relaxant effect contributed to early mobilization.

3. Fibromyalgia

  • Although data is limited, anecdotal evidence and small-scale trials suggest Eperisone may benefit diffuse musculoskeletal pain due to central sensitization.

Dosage and Administration

  • Standard Dose: 50–150 mg/day in divided doses (e.g., 50 mg 3 times a day)

  • Duration: Typically prescribed for 7–14 days in acute musculoskeletal conditions; may be used long-term in chronic spastic disorders.

  • With or Without Food: Best taken after meals to minimize gastrointestinal irritation.

Dose adjustments may be necessary in elderly patients or those with hepatic or renal impairment.

Adverse Effects

Eperisone is generally well tolerated, but some adverse effects have been reported:

Common Side Effects

  • Dizziness

  • Fatigue

  • Gastrointestinal discomfort

  • Headache

Less Common but Serious Effects

  • Hypotension (due to vasodilation)

  • Skin rashes or allergic reactions

  • Hepatic dysfunction (rare)

  • Anaphylactic reactions (very rare)

Discontinuation is usually sufficient to reverse adverse effects. Monitoring liver enzymes may be advisable in long-term use.

Contraindications

  • Known hypersensitivity to Eperisone

  • Pregnancy and lactation: Safety not well-established

  • Children: Safety and efficacy not established

  • Myasthenia gravis or other neuromuscular diseases

Due to its action on neuromuscular transmission, caution is warranted in individuals with underlying muscle weakness.

Drug Interactions

Eperisone has minimal drug interactions, but caution is recommended with:

  • Other CNS depressants (e.g., benzodiazepines, opioids): Additive sedation

  • Antihypertensives: Enhanced hypotensive effect

  • Alcohol: May potentiate sedative properties

Because Eperisone is metabolized by the liver, enzyme inducers like rifampin or inhibitors like ketoconazole may affect plasma levels.

Use in Special Populations

Elderly

  • Increased sensitivity to hypotensive and sedative effects

  • Dose reduction may be necessary

Pregnancy and Lactation

  • Category C (based on animal data)

  • Should be used only if benefits outweigh risks

Pediatrics

  • Not recommended due to lack of safety data

Comparison with Other Muscle Relaxants

Drug Mechanism Sedation Vasodilation Common Use
Eperisone Central + Peripheral Mild Yes Spasticity, myalgia
Tolperisone Central Mild Yes Similar to Eperisone
Tizanidine α2-adrenergic agonist Moderate No Spasticity (neurologic origin)
Baclofen GABA-B agonist High No Neurological spasticity
Cyclobenzaprine TCA derivative (central) High No Acute musculoskeletal pain

Eperisone's unique profile makes it suitable for daytime use without significant sedation—an advantage over other muscle relaxants.

Formulations and Brand Names

Eperisone is available in several formulations:

  • Eperisone hydrochloride tablets (50 mg, 100 mg)

  • Combination products with NSAIDs (e.g., Eperisone + Diclofenac)

Brand names include:

  • Myonal®

  • Epry®

  • Muslin®

  • Epsilone®

Availability varies by region, with widespread use in Japan, India, Vietnam, and parts of Southeast Asia.

Clinical Guidelines and Recommendations

While not commonly referenced in Western guidelines, Eperisone features prominently in regional pain management protocols, especially in:

  • Orthopedic clinics

  • Neurology and rehabilitation centers

  • Primary care for back and neck pain

Its favorable tolerability profile makes it a preferred agent in elderly patients or those with high sensitivity to sedation.

Research and Future Directions

Ongoing research is exploring:

  • Neuroprotective potential in stroke and spinal cord injury

  • Role in neuropathic pain and central sensitization disorders

  • Combination therapy with physiotherapy in post-stroke rehabilitation

There is growing interest in repurposing Eperisone for conditions like fibromyalgia and chronic fatigue syndrome due to its dual effect on muscle tone and microcirculation.

Conclusion

Eperisone hydrochloride stands out as a well-tolerated, effective muscle relaxant with a distinct mechanism that bridges central neuromodulation and peripheral vasodilation. Though its use is geographically limited, its efficacy in treating spastic and musculoskeletal conditions is well supported by clinical experience and emerging research. In an era increasingly focused on individualized, multimodal pain management, Eperisone offers a promising, non-sedating option for patients seeking relief from muscle stiffness, pain, and vascular insufficiency.