Pharmacology, part 28: Musculoskeletal Medications - Neuromuscular Blocking Agents & Muscle Relaxants
by Cathy Parkes March 23, 2021 Updated: April 14, 2022 5 min read
In this article, we cover neuromuscular blocking agents and two types of muscle relaxants: direct-acting and centrally-acting. The Nursing Pharmacology video series follows along with our Pharmacology Flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.
When you see this Cool Chicken, that indicates one of Cathy's silly mnemonics to help you remember. The Cool Chicken hints in these articles are just a taste of what's available across our Level Up RN Flashcards for nursing students!
This video marks the beginning of our musculoskeletal medication coverage within our Pharmacology Series. Video articles in the Musculoskeletal section include:
- (this video) Part 28: Neuromuscular Blocking Agents & Muscle Relaxants
- Part 29: Osteoporosis Medications
- Part 30: Medications for Gout
What is muscle spasticity?
Spasticity is when muscles abnormally stiffen, tighten, or contract, which can interfere with movement, speech, or cause discomfort or pain. This often occurs in the legs or arms and can result in involuntary movements. This symptom is often found in cerebral palsy, spinal cord injury, or multiple sclerosis (MS). These disorders are covered in our Medical-Surgical Flashcards for nursing students.
Neuromuscular blocking agents - Succinylcholine (Anectine) and pancuronium (Pavulon)
Neuromuscular blocking agents include medications like succinylcholine and pancuronium, which are used as an adjunct to anesthesia during surgery or intubation procedures. An adjunct is a medication used together with a primary medication that helps to assist the effects of the primary medication. These medications can also help with side effects from the main treatment.
Mode of action
Neuromuscular blocking agents like succinylcholine and pancuronium work by blocking acetylcholine at the neuromuscular junction which results in skeletal muscle paralysis.
“Suck it! You can’t get to the ACh receptors. I put pans on all of them!”
Side effects seen with neuromuscular blocking agents like succinylcholine and pancuronium can be serious, including respiratory arrest, apnea, muscle pain, as well as malignant hyperthermia.
Malignant hyperthermia is a drug reaction that can happen to susceptible individuals, in response to succinylcholine or other "volatile" anesthetic agents. Symptoms of malignant hyperthermia include muscle rigidity and fever.
Black box warning
Neuromuscular blocking agents like succinylcholine carry a black box warning due to the risk of cardiac arrest associated with hyperkalemic rhabdomyolysis, which is skeletal muscle injury that leads to the leakage of myoglobin and electrolytes into the circulatory system and urine.
Administration & Interventions
There are some key points to keep in mind for the administration of neuromuscular blocking agents like succinylcholine and pancuronium. If you had a patient on succinylcholine who got malignant hyperthermia (marked by muscle rigidity and fever) then you would want to remember the following interventions: Administer oxygen, administer dantrolene (a key skeletal muscle relaxant and a known antidote for succinylcholine) and provide cooling measures.
Direct-acting skeletal muscle relaxants - Dantrolene (Dantrium)
Dantrolene is a direct-acting skeletal muscle relaxant that is used to reduce muscle spasticity in conditions like spinal cord injuries, cerebral palsy, and multiple sclerosis (MS). As we just mentioned in the previous section, Dantrolene can be used to treat and prevent malignant hyperthermia.
Mode of action
Dantrolene's mode of action is to prevent the release of calcium in the muscles, which inhibits muscle contractions and decreases muscle spasticity.
Dan got run over by a trolley, and sadly became a paraplegic. He needs dantrolene for muscle spasms.
Dantrolene's side effects can include drowsiness, muscle weakness, GI upset, and hepatotoxicity.
Black box warning
Dantrolene carries a black box warning due to its risk of hepatotoxicity (liver damage).
If you have a patient taking dantrolene, it is important to monitor their liver enzymes and monitor them for signs and symptoms of liver damage, due to the risk for hepatotoxicity.
Centrally-acting muscle relaxant - Baclofen (Gablofen, Lioresal)
Baclofen is a centrally-acting muscle relaxant that can be used to treat muscle spasticity related to a spinal cord injury, cerebral palsy, or MS.
Mode of action
Baclofen works by enhancing the effect of GABA in the central nervous system, which reduces muscle spasticity.
If you pull out your back, you might need baclofen.
Side effects of baclofen can include drowsiness, nausea, and constipation.
Because baclofen can cause constipation, some important patient teaching to remember is to advise your patient to increase their fluid and fiber intake.
Okay. In this video, we are going to start in on our musculoskeletal medications. If you are following along with cards, I am on card 90. And in this video, we are going to talk about neuromuscular blocking agents as well as muscle relaxants.
Alright. So let's first cover those neuromuscular blocking agents which include medications such as succinylcholine and pancuronium.
These medications are used as an adjunct to anesthesia during surgery or during intubation procedures.
They work by blocking acetylcholine at the neuromuscular junction which results in skeletal muscle paralysis.
So my weirdo way of remembering these medications, if you look at the names, we have succinylcholine and pancuronium. I think of, "Suck it. You can't get to these acetylcholine receptors. I put pans on all of them." And that just helps me remember that these medications really block that acetylcholine.
In terms of side effects, they are serious. They include respiratory arrest, apnea, as well as malignant hyperthermia.
I would definitely be familiar with the signs and symptoms of malignant hyperthermia which include muscle rigidity and fever. Also, following surgery, patients sometimes have muscle pain due to the use of these medications.
This class of medication also carries a black box warning due to the risk of cardiac arrest associated with hyperkalemic rhabdomyolysis.
In terms of key points that you definitely need to keep in mind when administering these medications, if your patient was to end up with malignant hyperthermia, which again, those symptoms are muscle rigidity and fever, then you would want to take the following interventions. You would want to administer oxygen, give the patient dantrolene, which is a key skeletal muscle relaxant, and then provide cooling measures as well.
Alright. Now let's talk about direct-acting skeletal muscle relaxants. The key medication to know within this class is dantrolene, which we actually just mentioned when we were covering neuromuscular blocking agents because dantrolene can be used to treat malignant hyperthermia, and can actually be used to prevent it as well.
And it is also used to reduce muscle spasticity in conditions such as spinal cord injuries, cerebral palsy, and MS.
So the mode of action of dantrolene is that it prevents the release of calcium in the muscles. So this inhibits muscle contractions and decreases muscle spasticity.
Side effects can include drowsiness, muscle weakness, GI upset as well as hepatotoxicity.
So this medication actually carries a black box warning as well due to that risk for hepatotoxicity.
The way I remember this medication, if you look at the word dantrolene, you have Dan and then Trol. So I think, "Dan got run over by a trolley and became a paraplegic, and now he needs dantrolene to treat his muscle spasms." So while your patient is on this medication, because of that risk of hepatotoxicity, definitely monitor their liver enzymes and monitor the patient for signs and symptoms of liver damage.
Okay. Finally, let's talk about a centrally-acting muscle relaxant. The key medication that falls within this class is baclofen.
Baclofen can be used to treat muscle spasticity related to a spinal cord injury to cerebral palsy as well as MS.
It works by enhancing the effect of GABA in the central nervous system which reduces muscle spasticity.
The way I remember this medication is that if you pull out your back, you might need baclofen.
So side effects can include drowsiness, nausea, as well as constipation.
Because it can cause constipation, you definitely want to advise your patient to increase their fluid and fiber intake to help counteract this side effect.
So that is it for this video. When I come back, we will talk about medications that are used for osteoporosis. Thank you so much for watching!
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