Pharm Lecture #7: Skeletal Muscle Relaxants

Front 1

What is the indication and goal for using skeletal muscle relaxants

Back 1

Indication: treat conditions associated with hyperexcitable skeletal muscle

Goal: normalize excitability without decreasing muscle function

Front 2

Discuss the differences between muscle spasms and spasticity

Back 2

Muscle Spasm: increase in muscle tension--usually d/t a peripheral nerve or muscle injury secondary to prolonged increase in tension

Spasticity: increase in muscle excitability--d/t CNS injury--often velocity dependant--occurs secondary to changes in a muscle reflex arc

Front 3

What are agents used to treat muscle spasms called

Back 3

Antispasmotics

Front 4

Describe the 2 types of antispasmotics

Back 4

1. Polysynaptic Inhibitors
-Cyclobenzaprine (Flexeril)
-Oral Administration
-Thought to decrease spinal cord polysynaptic reflex activity--thus decreasing a-motor neuron excitabilit via altering interneuron activity

2. Diazepam (Valium)
-Has muscle relaxant properties but is not as often used bc of side effects at doses needed to relax muscles

Front 5

What are 3 main side effects of antispasmotics

Back 5

1. Sedation--b/c antispasmotics generally decrease CNS activity

2. Physical Dependance

3. Tolerance

Front 6

Are antispasmotics indicated for long-term or short-term use

Back 6

Commonly used for short-term used--PT txt is often used together with these drugs

Front 7

What are 2 names for drugs used to treat spasticity

Back 7

Spasmolytic or Antispasticity Drugs

Front 8

Gives 5 drugs commonly used as spasmolytics

Back 8

1. Baclofen (Lioresal)
2. Diazepam (Valium)
3. Dantrolene Sodium (Dantrium)
4. Tizanidine (Zanaflex)
5. Botulinum Toxin A (Botox)

Front 9

Give administration routes and mechanism of Baclofen

Back 9

Adm: Oral or intrathecal

Mechanism: GABA Agonist (an inhibitory NT)
-Binds to synapses & inhibits AMN's

-Neurontin (GABA-Pentin)--used for SCI or Multiple Sclerosis pts as an anti-convulsant--affects the SC similar to GABA

-Baclofen elicits sedation and similar side effects as other spasticity drugs

Front 10

Give the mechanism of Diazepam

Back 10

Inhibits CNS--thus reducing spasticity--but causes sedation

Long term use is avoided for spasticity control

Front 11

Give the mechanism and Major side effects of Dantrium

Back 11

Mechanism: Blocks Ca+ from being released from the sarcolplasmic reticulum--Ca+ has to be released for the muscle to contract--thus Dantrium is able to stop muscle contraction at the location of contraction

-One problem is Dantrium is not specific so it attacks muscles that aren't spastic

Side Effects: Generalized Muscle Weakness & Liver Toxicity

Front 12

Give the mechanism, indications, & side effects of Tizanidine (Zanaflex)

Back 12

Mechanism: alpha-2 adrenergic agonist--found at interneurons--inhibits the normally excitatory AMN, therefore inhibits the muscle

Indications: Usually after a spinal lesion--occasionally after a cerebral lesion (but not acutely)

Side Effects: overall more mild
-Less generalized muscle weakness

-Mild sedation
-dizziness
-dry mouth

Front 13

Give the indications, administration route, mechanism, and adverse effects of Botox

Back 13

Indications: Control localized muscle dystonias
-Reduce spasticity in specific muscle groups for a variety of functional benefits
-Control muscle hyperexcitability for other purposes

Adm: injection into selected muscles

Mechanism: inhibits Ach release at NMJ by cleaving and inactivating fusion proteins so they cannot bind to the cell membrane & be released from the cell across the NMJ

Only provides a short term effect

Side Effects: Widespread paralysis with systemic use
-Widespread paralysis would be detrimental if affecting the diaphragm

Front 14

Give the main cons of Botox use for spasticity txt

Back 14

1. Does not cure spasticity
2. Limited number of muscle groups affected at a time
3. Too high of a dose can cause an immune response
4. Even drug is potentially lethal--their is a small incidence of side effects

Front 15

Describe normal skeletal muscle relaxant pharmacokinetics

Back 15

Absorption: most skeletal muscle relaxants are absorbed well from GI tract
Metabolism: usually liver via enzymes
Excretion: either intact drug or metabolite excreted through kidneys