Mechanism of Action
Signals are normally going from the brain to the muscles, causing a contraction of a muscle. The same thing is happening when people are experiencing back spasms. So if you create a drug that’s going to stop this, how would it relax the muscles? We don’t have a drug that could stop the muscular activity of a certain muscle group. Instead, muscle relaxants slow down activity in the brain so there’s less activity in the brain going out to these muscles. This would cause a relaxation and you’d feel better. There is no drug that’s going to work specifically on back muscle pain so there’s going to be a lot of side effects.
Side effects include: mental clouding, drowsiness and weakness.
Muscle Relaxants approved for FDA use
If these drugs went through studies today, the odds are they wouldn’t be approved for lower back muscle spasms or as muscle relaxants. You would sleep well for days, however. What happens to your muscles when you sleep for days? They relax. These drugs relied more on sleep, than actual muscle relaxation. It’s a byproduct of sleeping that caused this. Ironically, the government realized for one of these drugs, after 40 years, that it was mostly just a drug of abuse and not really doing anything in regards to its intended use. If you look at the package inserts, it’s intended for 2 weeks, and if it doesn’t work for 2 weeks, that means there’s something else going on. Unfortunately this is why you find a lot of addiction (medically induced) to relieve the pain.  The muscle relaxant works initially, then stops working, then a narcotic is prescribed, which works until tolerance is built up, and the dosage is increased and so where do we draw the line and say this is addiction? That’s hard to say.
The state law book flat out says you are not to prescribe (nor a pharmacy is to fill) a drug for addiction purposes. How do we know it’s for addiction? What draws the line? 2 months. 2 years? 6 months sounds good, but no where will the law book say that. It’s not defined.
Agents with Questionable Efficacy
- Carisoprodol (Soma) – p.o. – Not a controlled substance but it gets metabolized into a controlled substance. The other 3 below don’t provide the same euphoria and people don’t get hooked on them.
- Chlorzoxazone (Parafon DSC) – p.o.
- Methocarbamol (Robaxin) – p.o.
- Orphenadrine (Norflex) – p.o., inj
Agents with Probable Effectiveness
Diazepam (Valium) – inj., p.o. – Considered a very good muscle relaxant. We could tell you the mechanism of action of this, unlike the others below, and it stimulates the GABA receptors since it’s a benzodiazepine.
Baclofen (Lioresal) – p.o. – FDA approved for patients with spinal cord injury. Even though these people have lost voluntary control, there’s still involuntary spasms occurring and they are put on these drugs indefinitely.
Cyclobenzaprine (Flexeril) – p.o. – Intended for 14 days. No abuse potential. This drug is chemically more closely related to the tricyclic antidepressant drugs and chemically have the same backbone so there might be an interaction with the tricyclic antidepressants. So what side effects will we get? Anticholinergic effects (dry mouth, frequent urination, dry eye, etc.)
Dantrolene (Dantrium) – p.o., inj. – This has a very specific use: Malignant hyperthermia, secondary to general anesthetics.
This is used in very rare emergencies, when a person is having an adverse reaction to a general anesthetic and their body temperature is rising to upwards of 107 degrees which is incompatible with life and they will die if you don’t do something quickly. The reason their temperature is going up is because all the muscles in their body are contracting quickly and giving off heat, causing the body temperature to rise. We need to relax all the muscles in this case. This is a IV drug that every operating room must have even though they will rarely ever use it (maybe a couple times in a persons career).
There is also something called neuroleptic hyperthermia, that is secondary to antipsychotics. Neuroleptic is another word for antipsychotic. The antipsychotics (major tranquilizers) have the potential to cause hyperthermia.
