How long does Robaxin stay in your system? (+1 factors)

In this article, we will discuss the stay time of Robaxin in your system. We will also discuss some factors which may affect the stay time of Robaxin in your body and how to ensure proper use of Robaxin.

How long does Robaxin stay in your system?

Robaxin can stay in your system for about 4-5 hours. Robaxin (methocarbamol) has an elimination half-life of about 1-2 hours in a healthy individual. After 1-2 hours, the drug concentration in the system is reduced to half.

The remaining concentration is further reduced in the next 1-2 hours. This process continues until all of Robaxin is excreted out of your system. If you take another dose of Robaxin during this time, the process will start from the beginning (1).

Biological sample Duration of Robaxin detectability
Blood 5-10 hours
Urine 5-10 hours
Hair Up to 90 days

What is the half-life of Robaxin?

The half-life of Robaxin is around 1-2 hours (average 1.14 hours). However, in patients with liver dysfunction, the half-life increases to 3.8 hours. In kidney disease, the average elimination half-life increases to 1.24 (1).

Therefore, the dose should be adjusted in patients with liver and kidney dysfunction. It is important to monitor such patients for possible side effects due to prolonged stay of the drug in the system.

Factors affecting the stay time of Robaxin in your system

Several factors can affect the stay time of Robaxin in your system, including:

Dosage strength

Robaxin is available in 500 mg and 750 mg tablets. The dosage strength may affect the stay of Robaxin in your body. A higher dose generally requires more time to get metabolized and eliminated from your body. However, if you are taking 500 mg of Robaxin, it might be eliminated more rapidly.

Liver problem

If you have liver disease, Robaxin may build up in your body because of the slower removal of Robaxin from the body. In some rare cases,  Robaxin may cause liver injury at a normal dose (2).

Renal disease

Intravenous (IV) dose of Robaxin is contradicted in patients with renal disorder due to the presence of polyethylene glycol (PEG) in injection as an excipient. It should also be used with caution in patients on dialysis. Kidney impairment slightly increases the elimination half-life of Robaxin.


The stay of Robaxin in elderly patients may be longer than the healthy individuals due to liver and kidney dysfunction. The half-life of Robaxin is slightly longer than that of a healthy individual (3).

How to ensure the proper use of Robaxin?

The following are important ways of ensuring the safe, proper and effective use of Robaxin:

  • Avoid alcohol: The combined use of alcohol and Robaxin may cause increased dizziness, confusion, and a depressed central nervous system (4). Sometimes it may be fatal.
  • Dosage regimen: Always follow the dosage regimen prescribed by your doctor. Do not take less or more than the prescribed dose of Robaxin.
  • Missed dose: In case you miss a dose, take Robaxin as soon as possible. However, it is almost time for your next dose, skip the missed dose and follow the regular pattern.
  • Report side effects: The common side effects associated with Robaxin include blurred vision, palpitations, dizziness, memory problems, and nausea.
  • Other medicines: Always inform your doctor about the use of other prescription and nonprescription medications which you are using to avoid possible side effects.
  • Follow-up: Make sure you do regular follow-ups with your doctor to see the progress of Robaxin and for the proper identification of possible harmful effects.
  • Myasthenia gravis: Robaxin should not be given to patients suffering from myasthenia gravis as it may exacerbate muscle weakness and fatigue (5).

In my opinion as a pharmacist, safe and effective use of Robaxin is possible only if you strictly adhere to the dosage regimen. If you feel your condition is not improving or the side effects are reducing your quality of life then inform your doctor.

Your doctor may prescribe you another muscle relaxant or reduce the dose of Robaxin. If you are not comfortable with IV injection because of pain or needle phobia, you may take Robaxin tablets after consulting with your doctor.

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