From the FDA Drug Label
The plasma concentration of cyclobenzaprine is increased in patients with hepatic impairment (see CLINICAL PHARMACOLOGY, PHARMACOKINETICS, HEPATIC IMPAIRMENT). In a pharmacokinetic study of sixteen subjects with hepatic impairment (15 mild, 1 moderate per Child-Pugh score), both AUC and Cmax were approximately double the values seen in the healthy control group Cyclobenzaprine hydrochloride tablets should be used with caution in subjects with mild hepatic impairment starting with the 5 mg dose and titrating slowly upward. Due to the lack of data in subjects with more severe hepatic insufficiency, the use of cyclobenzaprine hydrochloride tablets in subjects with moderate to severe impairment is not recommended
Cyclobenzaprine affects liver function by increasing plasma concentrations in patients with hepatic impairment.
- Key points:
- Increased plasma concentration in patients with hepatic impairment
- Use with caution in mild hepatic impairment, starting with a 5 mg dose
- Not recommended for moderate to severe hepatic impairment due to lack of data 1
- Pharmacokinetic studies show increased AUC and Cmax in patients with hepatic impairment 1
From the Research
Flexeril (cyclobenzaprine) can potentially affect liver function, though it's generally considered safe for most people with normal liver function when taken as prescribed. The medication is primarily metabolized by the liver, so individuals with pre-existing liver disease may process the drug more slowly, potentially leading to higher blood levels and increased side effects. According to a study on the metabolism of cyclobenzaprine 2, the drug is primarily metabolized by cytochromes P4501A2 and 3A4 in human liver microsomes.
Key Considerations
- For patients with severe liver impairment, doctors typically recommend lower doses or alternative medications, as suggested by a study on dose adjustment in patients with liver disease 3.
- Mild, temporary elevations in liver enzymes have been reported in some patients taking cyclobenzaprine, but serious liver injury is rare with this medication.
- If you have liver disease or concerns about liver function, you should discuss this with your healthcare provider before taking Flexeril, as they may want to monitor your liver function with blood tests while you're on this medication, especially if you're taking it long-term or have existing liver issues.
Monitoring and Precautions
- Always follow your doctor's dosing instructions and report any unusual symptoms like yellowing of the skin or eyes, dark urine, or upper right abdominal pain.
- A study on antipsychotic safety in liver disease 4 emphasizes the importance of careful risk-benefit analysis and individualized management for patients with existing liver disease.
- Another study on liver injury associated with antidepressants 5 highlights the need for monitoring of liver function tests and immediate discontinuation upon abnormal lab findings or signs and symptoms of liver dysfunction.
Conclusion Not Applicable - Direct Answer Only
Based on the most recent and highest quality study available 4, it is essential to prioritize careful monitoring and individualized management for patients with liver disease or concerns about liver function when taking Flexeril.