Hemolytic potential of methocarbamol

Area of Science:

• Pharmacology
• Hematology

Background:

• Methocarbamol, a muscle relaxant, is structurally related to mephenesin.
• In vitro studies indicated methocarbamol possesses hemolytic potential.

Purpose of the Study:

• To investigate the in vivo hemolytic potential of methocarbamol following intravenous administration.
• To compare the hemolytic effects of methocarbamol with its vehicle and saline controls.

Main Methods:

• A randomized controlled study in normal volunteers.
• Intravenous administration of methocarbamol, its vehicle (50% polyethylene glycol-300), or saline.
• High- and low-dose regimens were employed.
• Plasma hemoglobin and serum haptoglobin levels were monitored.

Main Results:

• Significant increases in plasma hemoglobin were observed 30 minutes post-injection for both methocarbamol and its vehicle.
• The vehicle alone resulted in higher initial plasma hemoglobin levels (approx. 10 mg/dl) compared to methocarbamol (approx. 4 mg/dl).
• Serum haptoglobin levels decreased in both high-dose methocarbamol and vehicle groups over a 3-day treatment period.

Conclusions:

• Intravenous administration of methocarbamol and its vehicle can cause detectable hemolysis.
• The observed hemolysis is minimal and does not exceed physiological levels seen in circumstances like exercise.
• The hemolytic effect is a small fraction of normal daily erythrocyte turnover.