Methoflex

Approved Indications:

• Adjunctive therapy for musculoskeletal conditions:
• Relief of discomfort associated with acute, painful musculoskeletal disorders, such as muscle spasm, strains, sprains, and low back pain.
• Adjunct in supportive care for tetanus:
• Used to manage muscle spasm and rigidity when combined with standard tetanus management.

Clinically Accepted Off‑label Uses:

• Symptomatic relief in fibromyalgia (short-term)
• Adjunct for chronic low back pain in combination with physical therapy
• Muscle spasm relief in sports injuries or postoperative muscle spasm management

Route: Oral, Intramuscular (IM), Intravenous (IV)

Oral (Adults):

• Initial: 1,500 mg four times daily (6,000 mg/day)
• Maintenance: 4,000–6,000 mg/day divided every 4–6 hours
• Maximum: 8,000 mg/day

Pediatrics: (7–17 years)

• Oral: 15 mg/kg every 6 hours (up to max 4,000 mg/day)
• <7 years: Not generally recommended

IM/IV (Adults):

• 1 gram every 8 hours or 3 grams every 8 hours for more severe spasm
• Use IM if oral intake not possible
• IV administration should occur over at least 15 minutes and use a non-PVC container

Special Populations:

• Elderly:
• Start at lower doses; monitor for sedation, dizziness, or confusion
• Renal Impairment:
• Use with caution; dose adjustment may be needed in severe impairment
• Hepatic Impairment:
• Limited data; use caution due to metabolism in the liver

Methocarbamol is a centrally acting muscle relaxant that depresses the central nervous system, likely at the level of the brainstem. It interferes with reflex arcs responsible for muscle spasm without directly affecting skeletal neuromuscular transmission or muscle contractility. The exact mechanism remains unclear, but the result is decreased muscle tone and relief from local musculoskeletal discomfort.

• Absorption: Well absorbed orally; peak plasma levels in ~1 hour
• Distribution: Widely distributed; crosses blood-brain barrier; protein binding ~46%
• Metabolism: Extensively metabolized in the liver via dehydrogenation, hydroxylation, and conjugation
• Active Metabolites: No known active metabolites
• Half-life: Approximately 1–2 hours
• Excretion: Primarily renal (65–70%) with remainder in feces as metabolites

• Pregnancy:
• FDA Category C. Animal studies show potential for fetal effects at high doses; insufficient human data. Use only if benefits outweigh risks.
• Lactation:
• Excreted in breast milk in low concentrations. Use with caution in breastfeeding women; monitor the infant for sedation or feeding difficulties.

• Primary Class: Muscle Relaxant
• Subclass: Centrally Acting Muscle Relaxant

• Hypersensitivity to methocarbamol or excipients
• Use of IV form in patients with intramuscular injection allergy to guaifenesin
• Not recommended for pediatrics under 7 years

• CNS depression: Drowsiness, dizziness, and confusion; avoid use with alcohol or sedatives
• Orthostatic hypotension: Exercise caution upon standing
• Renal or hepatic impairment: Close monitoring required
• Caution in elderly: Greater sensitivity to sedative effects and fall risk
• Excessive use or combining with opioids/barbiturates: Increases respiratory and CNS depression

Common:

• CNS: Drowsiness, dizziness
• GI: Nausea, vomiting
• Musculoskeletal: Headache, blurred vision
• General: Flushing, malaise

Less Common/Rare:

• GI: Constipation
• Allergic: Rash, itching
• Cardiovascular: Bradycardia, hypotension
• Others: Urinary retention, jaundice (cholestatic), seizure (rare)

Onset: CNS and GI effects may appear shortly after dosing; most side effects resolve with short-term use.

• Alcohol, opioids, benzodiazepines: Additive CNS and respiratory depression
• CNS depressants (e.g., antihistamines): Enhanced sedation
• Anticholinergics: Increased risk of urinary retention and dry mouth
• No significant CYP450 interactions: Does not induce or inhibit major CYP enzymes

• Clinical guidelines (2024): Advise cautious short-term use (<2 weeks); functional and physical therapy prioritized
• FDA review: Safety reaffirmed; no new warnings added
• Increased recommendations against use in elderly due to fall risk; monitoring emphasized

• Tablets (oral): Store at 20–25 °C (68–77 °F); protect from moisture; keep in original tight container
• Injection (IM/IV): Store at 20–25 °C; protect from light; do not freeze
• Handling: Discard if discoloration or particulate matter is present; ensure sterility with injections