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Hemolytic potential of methocarbamol
Abstract:
Methocarbamol, a compound related to mephenesin, has in vitro hemolytic potential. A study was performed to determine whether any hemolysis was detectable after intravenous injection. Methocarbamol and its vehicle (50% polyethylene glycol-300) was compared with vehicle alone and with normal saline controls in high- and low-dose regimens in normal volunteers. Significant increases in plasma hemoglobin were detected 30 min after intravenous injection of methocarbamol or its vehicle alone. Maximum initial plasma hemoglobin levels were approximately 10 mg/dl with vehicle alone, but only 4 mg/dl with the methocarbamol added. Serum haptoglobin levels fell after both high-dose methocarbamol and vehicle during the 3-day period of treatment. Hemolysis, though detectable, did not exceed levels found under physiologic circumstances such as exercise, and represents only a small fraction of the normal daily hemolysis of aged erythrocytes.
Insights
Methocarbamol, a muscle relaxant, showed detectable hemolysis after IV injection. However, the hemolysis was minimal, not exceeding normal physiological levels.
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.