CARISOPRODOL AND ASPIRIN
Clinical safety rating: safe
CNS depressants including alcohol can cause additive sedation Metabolism produces meprobamate a controlled substance with abuse potential.
Carisoprodol is a centrally acting muscle relaxant that modulates GABA-A receptor activity and may act as a weak partial agonist at the central nervous system. Aspirin irreversibly inhibits cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), reducing prostaglandin synthesis, which results in analgesic, antipyretic, and anti-inflammatory effects.
| Metabolism | Carisoprodol is N-deacetylated via CYP2C19 to meprobamate, a schedule IV controlled substance. Aspirin is hydrolyzed to salicylic acid in the liver and gastrointestinal tract. |
| Excretion | Carisoprodol: Renal excretion of metabolites (hydroxycarisoprodol, meprobamate) and <1% unchanged. Aspirin: Renal excretion of salicylate and metabolites (salicyluric acid, gentisic acid); ~80% renal, with dose-dependent elimination via first-order and Michaelis-Menten kinetics. |
| Half-life | Carisoprodol: 1.5-2 hours (terminal half-life), but active metabolite meprobamate has half-life of 9-12 hours, contributing to prolonged sedation. Aspirin: 15-20 minutes (parent drug); salicylate: 2-3 hours at low doses, 15-30 hours at high doses due to saturable hepatic metabolism. |
| Protein binding | Carisoprodol: ~60% bound to albumin. Aspirin: 80-90% bound to albumin (salicylate); highly protein-bound at therapeutic concentrations. |
| Volume of Distribution | Carisoprodol: ~0.7 L/kg (large Vd, extensive tissue distribution). Aspirin: ~0.15 L/kg (salicylate; low Vd, primarily in extracellular fluid). Clinical meaning: Carisoprodol distributes into CNS and muscle; aspirin remains largely in plasma and interstitial space. |
| Bioavailability | Oral: Carisoprodol: ~90% (well absorbed). Aspirin: ~40-50% (presystemic hydrolysis in GI mucosa and liver; rectal: 100% absorbed, but avoids first-pass). |
| Onset of Action | Oral: Carisoprodol: ~30 minutes; Aspirin: ~15-30 minutes (analgesic), 25-40 minutes (antiplatelet). Onset of muscle relaxant effect typically within 30 minutes. |
| Duration of Action | Carisoprodol: 4-6 hours (single dose); meprobamate accumulation may extend effects. Aspirin: 4-6 hours (analgesic), ~7-10 days (antiplatelet effect due to irreversible COX-1 inhibition). Clinical note: Duration of combination product is limited by carisoprodol's shorter action. |
1-2 tablets (carisoprodol 200 mg / aspirin 325 mg) orally 4 times daily.
| Dosage form | TABLET |
| Renal impairment | eGFR 30-59 mL/min: avoid or reduce dose; eGFR <30 mL/min: contraindicated. |
| Liver impairment | Child-Pugh Class A: caution; Class B or C: contraindicated. |
| Pediatric use | Not recommended for pediatric patients under 12 years of age. For older adolescents, weight-based dosing of aspirin 10-15 mg/kg/dose every 4-6 hours (max 80 mg/kg/day) and carisoprodol 5-10 mg/kg/dose three times daily; avoid routine use due to risk of Reye's syndrome. |
| Geriatric use | Initiate at lowest effective dose; monitor for CNS depression, renal function, and bleeding risk. Avoid in patients with significant renal impairment or peptic ulcer disease. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
CNS depressants including alcohol can cause additive sedation Metabolism produces meprobamate a controlled substance with abuse potential.
| FDA category | Animal |
| Breastfeeding | Aspirin and carisoprodol are excreted into breast milk. M/P ratio for aspirin is approximately 0.6-0.9; carisoprodol M/P ratio not established. Risk of Reye syndrome with aspirin, neonatal salicylate accumulation, and sedation from carisoprodol. Use not recommended during breastfeeding. |
| Teratogenic Risk |
■ FDA Black Box Warning
None.
| Common Effects | spasms |
| Serious Effects |
["Hypersensitivity to carisoprodol or aspirin.","Children and teenagers with viral infections (Reye's syndrome risk).","Active peptic ulcer disease or GI bleeding.","Severe hepatic impairment.","History of asthma induced by aspirin or NSAIDs.","Concomitant use with meprobamate-containing products."]
| Precautions | ["Dependence and withdrawal: Carisoprodol may cause dependence and withdrawal symptoms.","Sedation and CNS depression: Additive effects with alcohol and other CNS depressants.","Reye's syndrome: Aspirin use in children and teenagers with viral illness.","Gastrointestinal bleeding: Aspirin increases risk of GI bleeding.","Hypersensitivity reactions: Anaphylaxis, angioedema."] |
| Food/Dietary |
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| First trimester: Aspirin associated with increased risk of neural tube defects and gastroschisis; carisoprodol limited data. Second and third trimesters: Aspirin use increases risk of premature closure of ductus arteriosus and oligohydramnios; carisoprodol not well studied but may cause neonatal withdrawal. Avoid in third trimester due to aspirin's antiprostaglandin effects. |
| Fetal Monitoring | Monitor fetal ultrasound for ductus arteriosus patency and amniotic fluid volume in third trimester if exposed. Assess neonatal outcomes for signs of withdrawal or bleeding. Maternal monitoring of coagulation parameters, blood pressure, and renal function due to aspirin. |
| Fertility Effects | Aspirin may interfere with ovulation by inhibiting prostaglandin synthesis; carisoprodol no known fertility impact. Both drugs not indicated for chronic use affecting fertility. |
| Avoid alcohol. Take with food or milk to reduce gastrointestinal irritation. Avoid high-tyramine foods (e.g., aged cheese, cured meats) as aspirin may potentiate tyramine effects. |
| Clinical Pearls | Carisoprodol is metabolized to meprobamate, a controlled substance; monitor for abuse potential. Aspirin increases bleeding risk; avoid in children with viral illness due to Reye's syndrome. Combination may cause CNS depression and impaired motor function. Use with caution in renal impairment. |
| Patient Advice | Do not drive or operate machinery until you know how this medication affects you. · Avoid alcohol and other CNS depressants while taking this medication. · Take with food or milk to reduce stomach upset. · Do not use in children or teenagers with flu-like symptoms or chickenpox due to risk of Reye's syndrome. · Report signs of bleeding (easy bruising, black stools, vomiting blood) or allergic reactions (rash, swelling, difficulty breathing). · Rapid discontinuation may cause withdrawal symptoms (anxiety, insomnia, muscle twitching). |