CARISOPRODOL COMPOUND
Clinical safety rating
safeCNS depressants including alcohol can cause additive sedation Metabolism produces meprobamate a controlled substance with abuse potential.
Carisoprodol is a centrally acting muscle relaxant that acts as a prodrug for meprobamate, a barbiturate-like compound with sedative and anxiolytic properties. Its mechanism is thought to involve GABA-A receptor modulation and depression of polysynaptic reflexes in the spinal cord and reticular formation. Aspirin provides analgesic and anti-inflammatory effects via irreversible inhibition of cyclooxygenase (COX-1 and COX-2), reducing prostaglandin synthesis. Codeine is an opioid agonist at mu-opioid receptors, producing analgesia by mimicking endogenous endorphins.
| Metabolism | Carisoprodol is metabolized by CYP2C19 to meprobamate (active metabolite). Aspirin is hydrolyzed by esterases in the liver and plasma to salicylic acid, which is further conjugated. Codeine is metabolized by CYP2D6 to morphine (active) and by CYP3A4 to norcodeine. |
| Excretion | Carisoprodol is primarily metabolized in the liver, with about 50% excreted renally as unchanged drug and metabolites; the major metabolite meprobamate is also renally excreted. Fecal excretion is negligible (<2%). |
| Half-life | Carisoprodol has a terminal elimination half-life of approximately 1.5–2 hours; its active metabolite meprobamate has a half-life of 9–12 hours, which may lead to prolonged effects with chronic use. |
| Protein binding | Carisoprodol is approximately 60% bound to plasma proteins, mainly albumin. |
| Volume of Distribution | Volume of distribution is approximately 0.6–0.8 L/kg, indicating distribution into total body water. |
| Bioavailability | Oral bioavailability is nearly complete (close to 100%) due to rapid and extensive absorption. |
| Onset of Action | Oral: Onset of muscle relaxation occurs within 30 minutes, with peak effects at 1–2 hours. |
| Duration of Action | Duration of action is 4–6 hours for single doses due to carisoprodol's short half-life; however, accumulation of meprobamate can extend effects with repeated dosing. |
| Molecular Weight | 260.33 |
1-2 tablets (carisoprodol 200 mg/aspirin 325 mg) orally 4 times daily.
| Dosage form | TABLET |
| Renal impairment | Contraindicated in severe renal impairment (CrCl <30 mL/min). No specific dose adjustment for mild-moderate impairment; use caution. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh class C). For moderate impairment, reduce dose or increase interval; specific guidelines not established. |
| Pediatric use | Not recommended for pediatric patients due to aspirin content and risk of Reye syndrome. |
| Geriatric use | Initiate at lowest effective dose; monitor for CNS depression, falls, and aspirin-related bleeding. Avoid in patients ≥65 years due to risks of dizziness, sedation, and GI bleeding. |
| 1st trimester | Contraindicated due to risk of congenital malformations; carisoprodol is metabolized to meprobamate, a known teratogen. Avoid use. |
| 2nd trimester | Contraindicated; potential fetal harm from meprobamate exposure. Use only if clearly needed and no safer alternative. |
| 3rd trimester | Contraindicated; neonatal withdrawal syndrome possible from meprobamate. Avoid use near term. |
Clinical note
CNS depressants including alcohol can cause additive sedation Metabolism produces meprobamate a controlled substance with abuse potential.
| FDA category | Animal |
| Placental transfer | Carisoprodol and its active metabolite meprobamate cross the placenta. Meprobamate is a known teratogen and can cause neonatal withdrawal. Significant transfer confirmed. |
| Breastfeeding | Carisoprodol and its active metabolite meprobamate are excreted into breast milk. Meprobamate reaches concentrations 2-4 times maternal plasma levels. Potential for infant sedation, poor feeding, and withdrawal. The American Academy of Pediatrics considers meprobamate contraindicated during breastfeeding. Avoid use. |
| Lactation Rating | L5 - Contraindicated |
| Teratogenic Risk | Carisoprodol is a pregnancy category C drug. Data from animal studies are insufficient or show adverse effects, but no adequate human studies exist. There is a potential risk of fetal harm if used during the first trimester due to possible neural tube defects based on limited reports. In the second and third trimesters, maternal use may cause neonatal withdrawal symptoms (e.g., irritability, feeding difficulties) and respiratory depression if used near term. Carisoprodol is not recommended during pregnancy unless benefit outweighs risk. |
| Fetal Monitoring | Monitor maternal liver and renal function periodically due to hepatic metabolism and renal excretion. Assess maternal blood pressure and heart rate for potential tachycardia or hypotension. Fetal monitoring: ultrasound for growth and morphology in the first trimester if exposed; near-term, monitor fetal heart rate and movement. After delivery, observe neonate for signs of withdrawal (jitteriness, high-pitched cry, poor feeding) or respiratory depression. |
| Fertility Effects | Carisoprodol may have minor effects on fertility based on animal studies, but human data are lacking. No specific impairment of spermatogenesis or ovulation has been reported. It may cause hormonal imbalances in males (decreased testosterone) at high doses, but clinical significance is unknown. |
■ FDA Black Box Warning
None
| Common Effects | spasms |
| Serious Effects |
Known hypersensitivity to carisoprodol, meprobamate, or any componentAcute intermittent porphyriaConcomitant use with other CNS depressants (relative, but considered absolute in pregnancy)History of drug abuse or dependence
| Precautions | Risk of dependence, abuse, and withdrawal with carisoprodol and codeine, CYP2D6 ultrarapid metabolizers may have morphine toxicity from codeine, Reye's syndrome risk in children with viral illness (aspirin), GI bleeding risk with aspirin, Respiratory depression with codeine, Sedation and impaired motor function, Hepatic impairment, Renal impairment |
| Food/Dietary | Avoid alcohol and grapefruit juice. Alcohol increases CNS depression and risk of hepatotoxicity. Grapefruit juice may inhibit metabolism, leading to increased levels and toxicity. |
| Clinical Pearls | Carisoprodol is metabolized to meprobamate, a controlled substance with abuse potential; use cautiously in patients with history of substance abuse. Combination with other CNS depressants (e.g., alcohol, benzodiazepines) increases sedation risk. Limit use to 2-3 weeks due to lack of efficacy beyond that and risk of dependence. Avoid in patients with porphyria because carisoprodol may be porphyrinogenic. |
| Patient Advice | This medication may cause drowsiness, dizziness, or blurred vision; avoid driving or operating machinery until you know how it affects you. · Do not consume alcohol or other CNS depressants while taking this drug. · Take only as prescribed; do not increase dose or frequency. This drug has abuse potential. · Inform your doctor if you have a history of drug or alcohol abuse, seizures, or liver/kidney disease. · Do not use for longer than 2-3 weeks unless directed by your doctor. |
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