The white pill debossed with H 114 is Methocarbamol 500 mg, a prescription centrally acting skeletal muscle relaxant (brand equivalent to Robaxin). It is used alongside rest, physical therapy, and other measures to relieve acute, painful musculoskeletal conditions such as muscle spasms or strains.
Pill Identification
Attribute – Specification
- Active Ingredient – Methocarbamol (500 mg)
- Imprint – H (on the scored side) / 114 (on the unscored side)
- Color & Shape – White to off-white, capsule-shaped (oblong)
- Size – ~14 mm
- Drug Class – Skeletal muscle relaxants
- Controlled Substance Status – Non-controlled prescription medicine (Rx-only)
- Common Manufacturer – Camber Pharmaceuticals, Inc. / Hetero Drugs Limited
Mechanism of Action
Methocarbamol’s exact biochemical mechanism of action is not fully mapped. It does not directly relax contracted skeletal muscle fibers, nor does it block the motor end-plate or act directly on nerve fibers.
Instead, it works via general central nervous system (CNS) depression. By depressing polysynaptic reflex arcs in the brainstem and spinal cord, it reduces hyperactive reflex transmission and dampens pain-spasm cycles, producing muscle relaxation and mild sedation.
Dosage and Administration
Methocarbamol is designed for short-term, acute use. Doses should be customized by a healthcare provider.
- Initial Dosage (Adults & Teens 16 years): Typically 1,500 mg four times daily (i.e., three 500 mg tablets taken 4 times per day, totaling 6,000 mg/day) during the first 48 to 72 hours.
- Maintenance Dosage: Reduced to 1,000 mg four times daily (two 500 mg tablets, 4 times daily) or 750 mg every 4 hours (3,000–4,000 mg/day total).
- How to Take: Swallowed with water, with or without food. If stomach upset occurs, take with a meal or milk.
- Pediatric Use: Safety and effectiveness have not been established in patients under 16 years of age.
Common and Serious Side Effects
While generally tolerated better than older sedative muscle relaxants, Methocarbamol produces predictable CNS-related side effects.
Common Side Effects:
- Drowsiness, sedation, or lightheadedness
- Dizziness and headache
- Nausea, upset stomach, or metallic taste
- Blurred vision or conjunctivitis
- Harmless darkening of urine (turning green, black, or dark brown on standing)
Serious Adverse Effects (Seek Immediate Medical Attention):
- Severe Allergic Reactions: Anaphylaxis, hives, angioedema (swelling of face, tongue, throat), or severe rash.
- Cardiovascular Symptoms: Marked bradycardia (slow heartbeat), hypotension, or syncope (fainting).
- Neurologic Symptoms: Incoordination (ataxia), confusion, memory problems, or seizures.
- Jaundice: Yellowing of the eyes or skin (rare sign of drug-induced liver injury).
Precautions and Drug Interactions
- CNS Depressants: Concurrent use of alcohol, opioids, benzodiazepines, or sleep aids drastically multiplies sedative and respiratory-depressant risks. Alcohol must be avoided.
- Myasthenia Gravis: Methocarbamol can antagonize anticholinesterase drugs (e.g., pyridostigmine) and exacerbate muscle weakness. It should generally be avoided or used with extreme caution in these patients.
- Driving and Heavy Machinery: Because it impairs cognitive reflexes and coordination, do not drive or operate machinery until its individual effect is known.
- Hepatic or Renal Impairment: Clearance is prolonged in individuals with moderate-to-severe liver disease; lower doses or extended dosing intervals are often required.
- Diagnostic Test Interference: Methocarbamol can cause false-positive readings in screening tests for 5-hydroxyindoleacetic acid (5-HIAA) and vanillylmandelic acid (VMA).
Warnings
- Special Populations
- Pregnancy: Methocarbamol cross-placental safety is not well-established. It should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
- Lactation: It is unknown whether methocarbamol or its metabolites pass into human milk in significant quantities; caution is advised for nursing mothers.
- Elderly: Older adults are more sensitive to anticholinergic and sedative effects, placing them at increased risk for disorientation and fall-related injuries.
- Always consult a prescribing physician or pharmacist to confirm that any medication matches an authorized prescription and to check for interactions with current regimens.