Muscle relaxants are drugs, as their very name says, that are able to relax both the skeletal (voluntary muscles, ie those muscles of the human body whose contraction is regulated by voluntary brain activity) and the smooth (ie the muscles in the human body whose contraction is regulated by the autonomic nervous system and therefore does not depend on the will of the subject) muscles of the body.
There are several mechanisms of action by which the muscle relaxant drugs induce muscle relaxation:
- Some muscle relaxants, known as "central muscle relaxants", act mostly at the level of the central nervous system by inhibiting muscle contraction. They are used as antispasmodics and neuromuscular blocking agents in the field of surgical anesthesia (baclofen, carisoprodol, chlorzoxazone, cyclobenzaprine, mephenesin, meprobamate, methocarbamol);
- The second group of muscle relaxants acts at the level of the peripheral nervous system. They are referred to as "competitive muscle relaxants" or "non-depolarizing muscle relaxants": competitive muscle relaxants interrupt the neuromuscular transmission by competing with the activity of the neurotransmitter acetylcholine by reducing the response of acetylcholine receptors later released from the nervous impulse. Part of this group includes the alcuronium, atracurium, the gallamine triethiodide, the metocurina, pancuronium, tubocurarine and vecuronium. Generally, these types of muscle relaxants have a rather prolonged action and are used during the longer operations;
- The third group of muscle relaxants acts at the level of the peripheral nervous system. They are known as "depolarizing muscle relaxants": the depolarizing compounds block neuromuscular transmission producing a sustained partial depolarization of the endplate, which makes the tissues unable to respond to the neurotransmitter. Generally, they last less than competitive muscle relaxants, and are therefore used in the smaller operations and interventions. The decamethonium and succinylcholine are also part of this group.
How should muscle relaxants be taken?
The muscle relaxant drugs are commercially available in the form of tablets, capsules or suspensions to be taken orally, or in the form of solutions for injection, which may be administered by subcutaneous, intramuscular or intravenous approach.
Muscle relaxants should always be used on prescription with strictly following your doctor's instructions regarding the dosage and mode of application. Not doing so can reduce the absorption of the drug or render the treatment useless.
Contraindications and warnings associated with the use of muscle relaxants
Contraindications due to the consumption of this type of drugs will vary depending on the dosage taken and the type of medication. The main reported side effects include:
- Hypotonia
- Fatigue
- Dizziness
- Disorders of the gastrointestinal tract
- Difficulty sleeping
Drowsiness may be induced to a greater extent by drugs that act on the central nervous system. However, these drugs are usually well tolerated for prolonged treatment.
The use of muscle relaxants during lactation is not recommended because the drug taken by the mother passes into breast milk. In terms of using muscle relaxants during pregnancy, they should be used only if the potential benefit to the mother outweighs the potential risk to the fetus; however, their use is not recommended during the first three months of pregnancy.
