DELAXIN
Clinical safety rating
cautionComprehensive clinical and safety monograph for DELAXIN (DELAXIN).
DELAXIN (cyclobenzaprine) is a centrally acting muscle relaxant that is thought to relieve muscle spasms by inhibiting the descending serotonergic pathways in the spinal cord, specifically at the level of the brainstem. It acts as a serotonin 5-HT2 receptor antagonist, reducing excessive motor neuron activity.
| Metabolism | Primarily hepatic via cytochrome P450 enzymes, mainly CYP3A4, CYP1A2, and CYP2D6. Also undergoes N-demethylation and glucuronidation. |
| Excretion | Renal: 60-70% as unchanged drug; biliary/fecal: 20-30% as metabolites. |
| Half-life | Terminal elimination half-life: 12-18 hours (prolonged in renal impairment; up to 30 hours in severe renal failure). |
| Protein binding | 92-95% bound to albumin. |
| Volume of Distribution | Vd: 0.8-1.2 L/kg (indicates extensive tissue distribution). |
| Bioavailability | Oral: 70-80% (first-pass metabolism); intramuscular: 100%. |
| Onset of Action | Oral: 30-60 minutes; intramuscular: 15-30 minutes; intravenous: 5-15 minutes. |
| Duration of Action | Oral: 6-8 hours; intramuscular: 4-6 hours; intravenous: 3-6 hours; longer in hepatic impairment. |
| Molecular Weight | 284.32 |
| Brand Substitutes | Bludec-SP Tablet, Alser D 50mg/10mg Tablet, Diser Tablet, Lupisera D Tablet, Diclomol SP 10 Tablet |
10 mg orally once daily, preferably at bedtime.
| Dosage form | TABLET |
| Renal impairment | GFR 30-50 mL/min: 5 mg once daily; GFR <30 mL/min: not recommended. |
| Liver impairment | Child-Pugh A: 5 mg once daily; Child-Pugh B: 2.5 mg once daily; Child-Pugh C: not recommended. |
| Pediatric use | Not established in pediatric patients under 18 years. |
| Geriatric use | Initiate at 5 mg once daily; may increase to 10 mg based on response and tolerability. |
| 1st trimester | Avoid due to lack of data: no adequate studies in pregnant women; animal studies have shown teratogenicity at high doses. |
| 2nd trimester | Use only if potential benefit outweighs risk; limited human data suggest low risk of major malformations. |
| 3rd trimester | Avoid near term; may cause neonatal withdrawal syndrome (hypotonia, respiratory depression) due to long half-life. |
Clinical note
Comprehensive clinical and safety monograph for DELAXIN (DELAXIN).
| Placental transfer | Crosses placenta; detectable in fetal plasma at levels 50-100% of maternal concentration at steady state. |
| Breastfeeding | Excreted into human milk in low concentrations; however, long half-life may lead to accumulation in infants. Monitor for sedation, poor feeding, and weight gain. Consider alternative agents with shorter half-lives. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | DELAXIN (methocarbamol) is classified as FDA Pregnancy Category C. There are no adequate and well-controlled studies in pregnant women. In animal studies, methocarbamol has demonstrated embryotoxic and fetotoxic effects at doses similar to or greater than human therapeutic doses. Risk to the fetus cannot be ruled out, especially during the first trimester. Use only if potential benefit justifies potential risk. |
| Fetal Monitoring | Monitor for maternal adverse effects: drowsiness, dizziness, hypotension, and gastrointestinal disturbances. Fetal monitoring includes standard prenatal assessments; no specific fetal monitoring is required but consider ultrasound if concerns arise. |
| Fertility Effects | In animal studies, methocarbamol did not impair fertility at doses up to 3 times the maximum human dose. No human data are available regarding effects on fertility. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to DELAXIN or any componentHistory of angioedema with previous therapyAcute narrow-angle glaucomaUntreated open-angle glaucomaMyasthenia gravis
| Precautions | Serotonin syndrome (especially when used with other serotonergic drugs), sedation and impairment of mental/physical abilities, anticholinergic effects, cardiac arrhythmias (in patients with hyperthyroidism or cardiovascular disease), withdrawal symptoms after abrupt discontinuation, and hepatic impairment. |
| Food/Dietary | No significant food interactions. Delaxin (methocarbamol) may be taken with or without food. Grapefruit juice does not interact. Avoid alcohol due to additive CNS depression. |
| Clinical Pearls | DELAXIN is a skeletal muscle relaxant containing methocarbamol. Administer intravenously at a rate not exceeding 3 mL/min to avoid hypotension, bradycardia, and syncope. Extravasation can cause thrombophlebitis. Contraindicated in myasthenia gravis. Onset of action is rapid (30 minutes) for IV route; peak effects at 2 hours. Monitor for CNS depression, especially with concurrent alcohol or sedatives. |
| Patient Advice | May cause drowsiness, dizziness, or blurred vision; avoid driving or operating heavy machinery until effects are known. · Do not consume alcohol or take other CNS depressants while using DELAXIN. · Report any signs of allergic reaction, including hives, difficulty breathing, or swelling of the face, lips, or tongue. · If using the oral tablet, take with food to reduce stomach upset. · Do not stop suddenly; taper under medical supervision if used long-term. |
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