Benzodiazepines as Centrally Acting Skeletal Muscle Relaxants

Pharmacology 8,366 Views

Centrally acting muscle relaxants

Effects

They produce effects centrally in brain or spinal cord.

Decrease spasm

They are used to decrease the spasm and release spasticity as well as to reduce the pain.

Reasons for spasm

Spasm may be due to:

1. hyperactive stretch reflexes or

2. increased activation of alpha motor neurons or

3. imbalance between excitatory and inhibitory neurotransmitters.

Conditions

Multiple sclerosis
Cerebral palsy
CVA

These drugs do not improve the power or functions of muscles; rather actually decrease the power of muscles.

Skeletal muscle relaxants

In patients of stroke, spasticity is important because it helps in walking, providing support. When skeletal muscle relaxants are given, they expose the weakness of limbs.

Mechanism of Action of centrally acting drugs

Decrease the hyperactivity of stretch reflex arc, as well as decrease the activation of alpha motor neurons.

This is achieved either by increasing the release of inhibitory neurotransmitters or decreasing the release of excitatory neurotransmitters. The pain encountered in these spasms is due to release of subs P, which is decreased by these drugs.

These drugs depress the pulse transmission in polysynaptic pathways.

Benzodiazepines

Benzodiazepines are commonly used for relieving skeletal muscle spasms. They are safe as have fewer adverse effects.

Mechanism of Action

They produce their effects by GABAergic effect meaning that they potentiate the effects of GABA, without directly activating GABA receptors. They bind GABA A component of supramolecular complex.

Pharmacokinetics

They can be given orally or parentally. They can be given I/V for controlling the convulsions in status epilepticus, as well as in tetanus. They are metabolized by the liver.

Adverse effects

Mainly affect CNS, evident in the form of sedation, drowsiness, ataxia, impaired judgment. Only in increased doses can cause depression of CVS and respiratory system.