The yellow, five-sided pill imprinted with D and 32 is Cyclobenzaprine Hydrochloride 10 mg, a centrally acting skeletal muscle relaxant.
Pill Identification
Attribute – Details
- Imprint – D above 32 on one side, plain on the reverse
- Active Ingredient – Cyclobenzaprine Hydrochloride (10 mg)
- Appearance – Butterscotch yellow, five-sided / D-shaped, film-coated tablet
- Size – ~7 mm
- Manufacturer / Labeler – Aurobindo Pharma USA, Inc.
- Drug Class – Skeletal muscle relaxant (centrally acting)
- Controlled Status – Non-controlled prescription medication
Mechanism of Action
Cyclobenzaprine is structurally and pharmacologically related to first-generation tricyclic antidepressants (TCAs) such as amitriptyline. It relieves muscle spasms through central actions rather than acting directly on skeletal muscle fibers or the neuromuscular junction:
- Brainstem Modulation: Cyclobenzaprine primarily acts within the brainstem, specifically reducing tonic somatic motor activity by dampening motor neuron output.
- Inhibition of Motor Systems: It exerts inhibitory control over both gamma and alpha motor systems, decreasing excessive spinal cord reflex arcs that drive involuntary muscle spasms.
- Serotonergic & Anticholinergic Activity: It exhibits high-affinity antagonism at serotonin receptors and strong competitive antagonism at muscarinic acetylcholine receptors, which accounts for both its sedative and anticholinergic clinical effects.
Indications & Clinical Dosage
Primary Indications
- Short-term adjunctive therapy (alongside rest, physical therapy, and conservative measures) for the acute relief of muscle spasms associated with acute, painful musculoskeletal conditions (e.g., strains, sprains, acute lower back spasms).
- Note: Not effective in the treatment of spasticity caused by cerebral or spinal cord disease (e.g., cerebral palsy, multiple sclerosis).
Standard Dosage Regimens
- Standard Adult Dosing: 5 mg to 10 mg orally three times daily (TID) as needed.
- Maximum Daily Dose: 30 mg per day.
- Duration of Therapy: Limited strictly to 2 to 3 weeks. Long-term use is not supported by clinical trials due to lack of demonstrated efficacy beyond short-term injury repair cycles.
- Hepatic Impairment / Elderly: Initiated at 5 mg once daily or BID, with careful upward titration due to reduced metabolic clearance and heightened risk of cognitive impairment.
Side Effects
Common Adverse Reactions
- Central Nervous System: Drowsiness and marked somnolence (affecting up to 38% of patients), dizziness, fatigue, headache.
- Anticholinergic Symptoms: Dry mouth (xerostomia), blurred vision, constipation, altered taste.
- Gastrointestinal: Dyspepsia, nausea, abdominal discomfort.
Serious / Rare Adverse Reactions
- Cardiovascular Complications: Tachycardia, palpitations, conduction disturbances, arrhythmias, or orthostatic hypotension.
- Serotonin Syndrome: In patients combining cyclobenzaprine with serotonergic agents.
- Allergic Reactions: Anaphylaxis, angioedema, facial swelling, urticaria, or severe pruritus.
- Psychiatric Changes: Confusion, hallucinations, or agitation (especially in elderly patients).
Precautions & Drug Interactions
- CNS Depressants & Alcohol: Concurrent use with alcohol, benzodiazepines, barbiturates, or opioids creates potent additive sedative and respiratory depressive effects.
- Serotonergic Drugs: Co-administration with SSRIs, SNRIs, TCAs, tramadol, or buspirone increases the risk of serotonin syndrome (hyperthermia, rigidity, hyperreflexia, autonomic instability).
- Anticholinergic Agents: Additive risk of urinary retention, constipation, severe dry mouth, and confusion when taken with other anticholinergics or bladder antispasmodics.
- Hepatic Function: Metabolized extensively by hepatic CYP1A2, CYP3A4, and CYP2D6; patients with moderate-to-severe hepatic impairment require extreme caution or avoidance
Critical Warnings & Contraindications
- MAO Inhibitor Contraindication: Strictly contraindicated during or within 14 days of discontinuing Monoamine Oxidase Inhibitors (MAOIs). Hyperpyretic crises, severe convulsions, and death can occur.
- Cardiac Contraindications: Contraindicated during the acute recovery phase after myocardial infarction, in patients with heart block or other cardiac conduction abnormalities, congestive heart failure (CHF), or cardiac arrhythmias.
- Hyperthyroidism: Contraindicated due to the heightened vulnerability to dangerous arrhythmias and adrenergic sensitivity.
- Glaucoma & Urinary Retention: Contraindicated in patients with angle-closure glaucoma or active urinary retention due to significant atropine-like anticholinergic activity.
- Impairment of Alertness: Causes profound sedation; patients should not drive, operate heavy machinery, or engage in hazardous activities while taking this medication.