**Question:** Myasthenics are resistant to following muscle relaxant:

A. Baclofen
B. Cyclobenzaprine
C. Tizanidine
D. Riluzole

**Correct Answer:** D. Riluzole

**Core Concept:**
Muscle relaxants are a class of medications used to alleviate muscle stiffness and spasm. They work by antagonizing the action of excitatory neurotransmitters, such as acetylcholine, at the neuromuscular junction. Myasthenia gravis (MG) is a neuromuscular disorder characterized by muscle weakness due to the obstruction of acetylcholine receptors at the neuromuscular junction. Myasthenics are medications used to treat MG by enhancing acetylcholine release or prolonging its action at the neuromuscular junction.

**Why the Correct Answer is Right:**
Riluzole is a medication primarily used in the treatment of amyotrophic lateral sclerosis (ALS) and is also effective in some patients with MG. It works by inhibiting the release of glutamate, an excitatory neurotransmitter, thereby reducing glutamate-induced excitotoxicity and preventing neuronal damage, which indirectly helps in the management of MG.

**Why Each Wrong Option is Incorrect:**
A. Baclofen and cyclobenzaprine are muscle relaxants primarily used to treat spasticity due to spinal cord or brain injury, multiple sclerosis, or stroke. They work by inhibiting the release of excitatory neurotransmitters, such as glutamate and substance P, thus reducing muscle spasm. However, they are not effective in treating MG and are not the correct answer.

B. Cyclobenzaprine is primarily used to treat muscle spasm and pain due to spinal cord or brain injury, multiple sclerosis, or stroke. It works by inhibiting the release of excitatory neurotransmitters, such as glutamate and substance P, thus reducing muscle spasm. However, it is not specifically used to treat MG and is not the correct answer.

C. Tizanidine is a muscle relaxant used in the management of spasticity due to spinal cord injury, multiple sclerosis, or stroke. It works by inhibiting the release of excitatory neurotransmitters, such as alpha-2 adrenergic receptors, thus reducing muscle spasm. However, it is not effective in treating MG and is not the correct answer.

**Clinical Pearl:**
Riluzole is the only medication used specifically for the treatment of MG, making it the correct answer. Although the other options may be used to manage muscle spasm, they are not specifically indicated for MG and therefore are incorrect choices.