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.