Muscle relaxant
A muscle relaxant is a drug that affects skeletal muscle function and decreases the muscle tone. It may be used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. The term "muscle relaxant" is used to refer to two major therapeutic groups: neuromuscular blockers and spasmolytics. Neuromuscular blockers act by interfering with transmission at the neuromuscular end plate and have no central nervous system (CNS) activity. They are often used during surgical procedures and in intensive care and emergency medicine to cause temporary paralysis. Spasmolytics, also known as "centrally acting" muscle relaxant, are used to alleviate musculoskeletal pain and spasms and to reduce spasticity in a variety of neurological conditions. While both neuromuscular blockers and spasmolytics are often grouped together as muscle relaxant,[1][2] the term is commonly used to refer to spasmolytics only.[3][4]
This article is about skeletal muscle relaxants. For smooth muscle relaxants, see Antispasmodic.History[edit]
The earliest known use of muscle relaxant drugs was by natives of the Amazon Basin in South America who used poison-tipped arrows that produced death by skeletal muscle paralysis. This was first documented in the 16th century, when European explorers encountered it. This poison, known today as curare, led to some of the earliest scientific studies in pharmacology. Its active ingredient, tubocurarine, as well as many synthetic derivatives, played a significant role in scientific experiments to determine the function of acetylcholine in neuromuscular transmission.[5] By 1943, neuromuscular blocking drugs became established as muscle relaxants in the practice of anesthesia and surgery.[6]
The U.S. Food and Drug Administration (FDA) approved the use of carisoprodol in 1959, metaxalone in August 1962, and cyclobenzaprine in August 1977.[7]
Other skeletal muscle relaxants of that type used around the world come from a number of drug categories and other drugs used primarily for this indication include orphenadrine (anticholinergic), chlorzoxazone, tizanidine (clonidine relative), diazepam, tetrazepam and other benzodiazepines, mephenoxalone, methocarbamol, dantrolene, baclofen.[7] Drugs once but no longer or very rarely used to relax skeletal muscles include meprobamate, barbiturates, methaqualone, glutethimide and the like; some subcategories of opioids have muscle relaxant properties, and some are marketed in combination drugs with skeletal and/or smooth muscle relaxants such as whole opium products, some ketobemidone, piritramide and fentanyl preparations and Equagesic.
Side effects[edit]
Patients most commonly report sedation as the main adverse effect of muscle relaxants. Usually, people become less alert when they are under the effects of these drugs. People are normally advised not to drive vehicles or operate heavy machinery while under muscle relaxants' effects.
Cyclobenzaprine produces confusion and lethargy, as well as anticholinergic side effects. When taken in excess or in combination with other substances, it may also be toxic. While the body adjusts to this medication, it is possible for patients to experience dry mouth, fatigue, lightheadedness, constipation or blurred vision. Some serious but unlikely side effects may be experienced, including mental or mood changes, possible confusion and hallucinations, and difficulty urinating. In a very few cases, very serious but rare side effects may be experienced: irregular heartbeat, yellowing of eyes or skin, fainting, abdominal pain including stomach ache, nausea or vomiting, lack of appetite, seizures, dark urine or loss of coordination.[39]
Patients taking carisoprodol for a prolonged time have reported dependence, withdrawal and abuse, although most of these cases were reported by patients with addiction history. These effects were also reported by patients who took it in combination with other drugs with abuse potential, and in fewer cases, reports of carisoprodol-associated abuse appeared when used without other drugs with abuse potential.[40]
Common side effects eventually caused by metaxalone include dizziness, headache, drowsiness, nausea, irritability, nervousness, upset stomach and vomiting. Severe side effects may be experienced when consuming metaxalone, such as severe allergic reactions (rash, hives, itching, difficulty breathing, tightness in the chest, swelling of the mouth, face, lips, or tongue), chills, fever, and sore throat, may require medical attention. Other severe side effects include unusual or severe tiredness or weakness, as well as yellowing of the skin or the eyes.[41] When baclofen is administered intrathecally, it may cause CNS depression accompanied with cardiovascular collapse and respiratory failure. Tizanidine may lower blood pressure. This effect can be controlled by administering a low dose at the beginning and increasing it gradually.[42]