Introduction

Methocarbamol is a commonly used, centrally acting muscle relaxant and has not been linked to instances of liver injury.

Background

Methocarbamol (meth" oh kar' ba mol) is a guaifenesin derivative and acts centrally as a muscle relaxant by an unknown mechanism. Methocarbamol was approved for use in the United States in 1957, and currently more than 3 million prescriptions are filled yearly. Methocarbamol is indicated for the relief of acute, painful musculoskeletal conditions. Methocarbamol is available in 500 and 750 mg tablets in several generic formulations, both alone and in combination with other drugs and under the brand names of Robaxin and Marbaxin. The recommended dosage is 1500 mg orally three to four times daily. The most common side effects of methocarbamol are drowsiness blurred vision, headache, nausea and skin rash.

Hepatotoxicity

While the product label for methocarbamol states that it can cause jaundice (including cholestatic jaundice), there is little published evidence to suggest that methocarbamol is a cause of hepatic injury or clinically apparent drug induced liver disease. During clinical trials of methocarbamol, some patients had to stop treatment because of nausea, dizziness, or other nonspecific complaints, but no serum aminotransferase levels or other laboratory results were reported. Methocarbamol appears to be well tolerated, but the lack of monitoring of serum aminotransferase levels during clinical trials with methocarbamol makes it impossible to rule out the possibility of mild liver injury occurring with treatment.

Likelihood score: E (Unlikely cause of clinically apparent liver injury).

Drug Class: Muscle Relaxants