DELAXIN
Clinical safety rating: caution
Comprehensive 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. |
| 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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DELAXIN (DELAXIN).
| Breastfeeding | It is not known whether methocarbamol is excreted in human breast milk. The M/P ratio has not been determined. Due to potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother. |
| 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. |
■ FDA Black Box Warning
None
| Serious Effects |
Concomitant use with MAOIs or within 14 days of MAOI therapy, acute recovery phase of myocardial infarction, heart block, congestive heart failure, hyperthyroidism, and hypersensitivity to cyclobenzaprine.
| 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. |
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| 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. |