How does methocarbamol work?

How does methocarbamol work?

Methocarbamol is a type of medication known as a muscle relaxant, and it is indicated for the short-term relief of muscle spasms. Despite being developed in the early 1950, we are still not entirely sure of the exact mechanism in which it alleviates muscles spasms. But several theories have been proposed.

Proposed Mechanisms For Methocarbamol

We do know that methocarbamol does not act directly on the skeletal muscles. It acts centrally, meaning its action takes place within the brain and spinal cord, and one of the ways it does this is through acting as a central nervous system depressant, essentially meaning the activity of the brain and spinal cord is reduced.

This may occur through its modulatory effect on the neurotransmitter – chemical messengers for the nervous system – Gamma Aminobutyric Acid (GABA). This neurotransmitter is involved in modulating muscle tone, which is the continuous contraction of a muscle to maintain posture. Muscle tone is influenced from signals from the central nervous system via the activity of neurotransmitters. Therefore, if there is an enhanced activity, or increased concentration GABA - whose effects include inhibition of motor nerves in the spinal cord which are responsible for initiating muscle contraction– this can lead to reduced muscle spasms.

It is also thought that methocarbamol may influence the functioning – in this case the permeability – of ion channels in nerve cells. With an increased permeability of nerve cells, more sodium ions can flow into the nerve cells. When this occurs, the nerve cell becomes hyperpolarised, which means it cannot transmit nerve signals. This results in less nerve signals reaching skeletal muscles –which would ordinarily ‘telling’ them to contract – and therefore a reduction in the intensity of your muscle spasms.

Methocarbamol may also influence Polysynaptic Reflex Inhibition. These reflex actions are processed in the spinal cord and play an important role in muscle control and co-ordination. More specifically methocarbamol can inhibit reflex arcs. Imagine these as the knee taps with the reflex hammer, where the sensory stimulus detected by the tendon that has been tapped by the reflex hammer fires a nerve impulse into the spinal cord, which then sends back another neve signal telling the muscle to contract. Methocarbamol can interfere with the normal functioning of this reflex arc, possibly through increasing the firing threshold of the sensory neurons, through the aforementioned hyperpolarisation of nerve cells, thereby reducing the intensity and volume of signals sent to the spinal cord and in return reducing the volume of muscle contraction signals sent from the spinal cord to the muscles. The same theory applies to motor neurons, in that if they are hyperpolarised, then the rate at which they fire i.e. ‘tell’ a muscle to contract is reduced. All of this means, that in theory your muscle spasms frequency and severity is reduced. should be reduced.

Conclusion

As documented above, there are several proposed theories on how Methocarbamol works, many of which are complex. Despite this complexity, its clinical effectiveness is well-documented in comparison to other medications such as diazepam, which you can read more about here.

If you're experiencing muscle pain or spasms, and want to consult with me about treatment options, you can do so here.

References

1. ·BNF is only available in the UK. (n.d.). NICE. https://bnf.nice.org.uk/drugs/methocarbamol/

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