Muscle relaxants

Muscle relaxants are the drugs that cause the effect of relaxing the muscle tissue. The use of these drugs can reduce pain caused by muscle spasms. An important property of muscle relaxants is their ability to block the reflex activity of the voluntary muscles, which is very useful in anesthesiology and surgery, as the muscle tone is often a hindrance during surgery and intubation.

Classification of muscle relaxants: relaxants involve the peripheral and central actions.

Muscle relaxants peripherally acting drugs include curariform directly effect on cholinergic receptors of skeletal muscles and disrupt neuromuscular transmission.

The second group (central action) muscle relaxants include drugs from various groups that have a depressant effect on the central structure of the regulation of muscle tone, along with other effects. Similar property is possessed by, for example, tranquilizers. Among tranquilizers, the most pronounced effect is the ability to cause muscle relaxation due to the presence of substance – benzodiazepines (such as hlozepid, diazepam, phenazepam). Tranquilizers of certain other chemical structure can cause muscle relaxation too – meprotan izoprotan and midokalm and baclofen.

Unlike curariform muscle relaxants, centrally acting muscle relaxants do not affect the transmission of impulses in the nerve-muscle synapses. They inhibit the activity of neurons of the spinal cord reflex paths and locate above the nervous system.

Curariform substances are used in surgical interventions, correcting dislocations, repositioning of bone fragments etc.

The side effects of muscle relaxants include drowsiness, dizziness, and lethargy. Prolonged use can develop addiction and drug dependence. Not recommended for use amongst those occupations that require considerable mental reaction and high coordination.

Muscle relaxants have become an important component of modern balanced anesthesia. Most modern muscle relaxants do not cause significant side effects (especially Vecuronium and Cisatracurium). The use of muscle relaxants involves some difficulties, including fluctuations in duration, accumulation of certain diseases, and inadequate termination. Some muscle relaxants cause side effects (histamine release). Their severity, however, is less than of most new drugs. Muscle relaxants are unique in the sense that direct and accurate monitoring of their action is possible. In conclusion, it should be recalled that the use of muscle relaxants masks important symptoms of inadequate anesthesia and increases the frequency of intraoperative recovery of consciousness. Therefore, muscle relaxants should be used only when it is absolutely necessary, and be limited to the minimum of effective dose.

A specific opioid antagonist naloxone has both therapeutic and adverse affect. It works within 1-2 min, but has a short duration of action. The duration of action of naloxone is usually shorter than the above introduced opioid. Consequently, after a while, the opioid’s action can finish, and then naloxone should be introduced again. Since naloxone eliminates the effects of opioids, it should be administered very slowly. With this approach, naloxone received a degree of analgesia. An alternative tactic involves the use of respiratory stimulants (eg, Doxapram), which are rapidly eliminated due to respiratory depression of opioids without compromising analgesia. Careful fractional administration of opioids to achieve the desired analgesia reduces the risk of overdose and the need for antagonists.

Cyclobenzaprine Hydrochloride

Cyclobenzaprine is primarily prescribed to relieve muscle spasms and tightness associated with acute musculoskeletal conditions. It is often used in combination with rest and physical therapy. Cyclobenzaprine is usually taken orally in the form of tablets or extended-release capsules.

Tizanidine Hydrochloride

Tizanidine hydrochloride may cause drowsiness; patients affected should not drive or operate machinery. Other adverse effects include dry mouth, fatigue, dizziness or vertigo, muscle pain and weakness, insomnia, anxiety, headache, bradycardia, nausea, and gastrointestinal disturbances.


Slightly soluble in water; very slightly soluble in alcohol; practically insoluble in acetone; dissolves in dilute mineral acids and in dilute solutions of alkali hydroxides. A white to off-white, odourless or practically odourless, crystalline powder.

Botulinum Toxins

Botulinum toxins A and B are neurotoxins produced by Clostridium botulinum. They are proteins comprising a heavy chain thought to be responsible for binding to the target cells and translocation of the toxin across the cell membrane, linked by a disulfide bond to a light chain responsible for the toxic activity.

Muscle Relaxants

The muscle relaxants included in this chapter are used in the management of musculoskeletal and neuromuscular disorders. Their mechanism of action may be due to their CNS-depressant activity.


Chlorzoxazone is a muscle relaxant medication that relieves muscle spasms and discomfort caused by strains, sprains, or other muscle injuries. It is typically prescribed as part of a comprehensive treatment plan, including rest, physical therapy, and other measures to alleviate musculoskeletal pain.


Carisoprodol is a muscle relaxant that alters communication between nerves in the central nervous system. It is used in the short-term treatment of muscle pain and discomfort. Carisoprodol is typically prescribed with rest, physical therapy, and other measures to relieve musculoskeletal conditions.


A white powder, odourless or having a slight characteristic odour. M.p. about 94° or, if previously ground to a fine powder, about 90°. Soluble 1 in 40 of water at 20°; sparingly soluble in chloroform; soluble in alcohol only with heating; insoluble in n-hexane and in benzene.

Few Muscle Relaxants

Afloqualone is a centrally acting skeletal muscle relaxant that has been given orally for the treatment of muscle spasm associated with musculoskeletal conditions. Photosensitivity reactions have been reported.

Dantrolene Sodium

Dantrolene Sodium treats muscle stiffness, spasms, and spasticity. It belongs to a class of drugs known as muscle relaxants. Dantrolene is used to manage muscle spasticity associated with neurological disorders, including cerebral palsy, multiple sclerosis, and spinal cord injuries as well as preventing and treating malignant hyperthermia.

Chlorphenesin Carbamate

Chlorphenesin carbamate produces drowsiness and dizziness. There may also be nausea, headache, weakness, confusion, agitation, and insomnia.