Common side effects include headache, feeling tired, dizziness, and dry mouth.[5] Serious side effects may include an irregular heartbeat.[5] There is no evidence of harm in pregnancy, but it has not been well studied in this population.[5] It must not be used with an MAO inhibitor.[5] How it works is unclear.[5]
Cyclobenzaprine was approved for medical use in the United States in 1977.[5] It is available by prescription as a generic medication.[5] In 2021, it was the 45th most commonly prescribed medication in the United States, with more than 15million prescriptions.[6][7] It was not available in the United Kingdom as of 2012.[8]
Medical use
Cyclobenzaprine is used, in conjunction with physical therapy, to treat muscle spasms that occur because of acute musculoskeletal conditions.[9] After sustaining an injury, muscle spasms occur to stabilize the affected body part, which may increase pain to prevent further damage. Cyclobenzaprine is used to treat such muscle spasms associated with acute, painful musculoskeletal conditions.[10] It decreases pain in the first two weeks,[11][12] peaking in the first few days, but has no proven benefit after two weeks.[11][13] Since no benefit is proven beyond that, therapy should not be continued long-term.[10] It is the best-studied muscle relaxer.[11] It is not useful for spasticity due to neurologic conditions such as cerebral palsy.[10][14]
A 2004 review found benefit for fibromyalgia symptoms, with a reported number needed to treat of 4.8 (meaning that 1 person out of every 4.8 benefits from treatment) for pain reduction, but no change in fatigue or tender points.[15] A 2009 Cochrane review found insufficient evidence to justify its use in myofascial pain syndrome.[16] It may also be used along with other treatments for tetanus.[17]
Agitation is a common side effect observed, especially in the elderly. Some experts[who?] believe that cyclobenzaprine should be avoided in elderly patients because it can cause confusion, delirium, and cognitive impairment.[19][20] In general, the National Committee for Quality Assurance recommends avoiding the use of cyclobenzaprine in the elderly because of the potential for more severe side effects.[21]
Monoamine oxidase inhibitors taken within two weeks of cyclobenzaprine may result in serious, life-threatening side effects.[10]
Cyclobenzaprine may affect the medications used in surgical sedation and some surgeons request that patients temporarily discontinue its use prior to surgery.[25]
Pharmacology
Cyclobenzaprine is a centrally acting muscle relaxant.[26] Cyclobenzaprine is a 5-HT2 receptor antagonist; it relieves muscle spasm through action on the central nervous system at the brain stem, rather than targeting the peripheral nervous system or muscles themselves.[27]
Values are Ki (nM), unless otherwise noted. The smaller the value, the more strongly the drug binds to the site.
Pharmacokinetics
Cyclobenzaprine has an oral bioavailability of about 55% and approximately 93% is bound to proteins in plasma. The half-life of the drug is 18 hours and it has a plasma clearance of 0.7 litres per minute.[26][29][30]
Comparison to other medications
Cyclobenzaprine has been found to be not inferior to tizanidine, orphenadrine, and carisoprodol in the treatment of acute lower back pain, although none have been proven to be effective for long-term use (beyond two weeks of treatment). No differences in pain or spasm scores were noted among these agents, nor when compared to benzodiazepines.[31] However, nonbenzodiazepine (including cyclobenzaprine) treatment was found to have a lower risk of medication abuse and continuation of use against medical advice.[medical citation needed] Side effects such as sedation and ataxia are also less pronounced with nonbenzodiazepine antispasmodics.[medical citation needed]
In a study on the treatment of musculoskeletal pain treatment with cyclobenzaprine alone or in combination with ibuprofen, no significant differences in pain scores were noted among the three treatment groups. Peak benefit was found to occur on day seven of the treatment for all groups.[32]
Formulations
Cyclobenzaprine 10mg tablets
By mouth, cyclobenzaprine is marketed as Apo-Cyclobenzaprin, Fexmid, Flexeril and Novo-Cycloprine. It is available in generic form. A once-a-day, extended-release formulation, Amrix, is available.[33] Cyclobenzaprine is also used by compounding pharmacies in topical creams.[citation needed]
Related Research Articles
Tricyclic antidepressants (TCAs) are a class of medications that are used primarily as antidepressants. TCAs were discovered in the early 1950s and were marketed later in the decade. They are named after their chemical structure, which contains three rings of atoms. Tetracyclic antidepressants (TeCAs), which contain four rings of atoms, are a closely related group of antidepressant compounds.
Myalgia is the medical term for muscle pain. Myalgia is a symptom of many diseases. The most common cause of acute myalgia is the overuse of a muscle or group of muscles; another likely cause is viral infection, especially when there has been no trauma.
An antispasmodic is a pharmaceutical drug or other agent that suppresses muscle spasms.
Tramadol, sold under the brand name Ultram among others, is an opioid pain medication and a serotonin–norepinephrine reuptake inhibitor (SNRI) used to treat moderately severe pain. When taken by mouth in an immediate-release formulation, the onset of pain relief usually begins within an hour. It is also available by injection. It is available in combination with paracetamol (acetaminophen).
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, the term is commonly used to refer to spasmolytics only.
Fibromyalgia is a medical condition defined by the presence of chronic widespread pain, fatigue, waking unrefreshed, cognitive symptoms, lower abdominal pain or cramps, and depression. Other symptoms include insomnia and a general hypersensitivity.
Colloquially known as "downers", depressants or central depressants are drugs that lower neurotransmission levels, or depress or reduce arousal or stimulation in various areas of the brain. Depressants do not change the mood or mental state of others. Stimulants, or "uppers", increase mental or physical function, hence the opposite drug class from depressants are stimulants, not antidepressants.
Duloxetine, sold under the brand name Cymbalta among others, is a medication used to treat major depressive disorder, generalized anxiety disorder, fibromyalgia, neuropathic pain and central sensitization. It is taken by mouth.
Pethidine, also known as meperidine and sold under the brand name Demerol among others, is a fully synthetic opioid pain medication of the phenylpiperidine class. Synthesized in 1938 as a potential anticholinergic agent by the German chemist Otto Eisleb, its analgesic properties were first recognized by Otto Schaumann while working for IG Farben, in Germany. Pethidine is the prototype of a large family of analgesics including the pethidine 4-phenylpiperidines, the prodines, bemidones and others more distant, including diphenoxylate and analogues.
Serotonin–norepinephrine reuptake inhibitors (SNRIs) are a class of antidepressant medications used to treat major depressive disorder (MDD), anxiety disorders, social phobia, chronic neuropathic pain, fibromyalgia syndrome (FMS), and menopausal symptoms. Off-label uses include treatments for attention-deficit hyperactivity disorder (ADHD), obsessive–compulsive disorder (OCD), and migraine prevention. SNRIs are monoamine reuptake inhibitors; specifically, they inhibit the reuptake of serotonin and norepinephrine. These neurotransmitters are thought to play an important role in mood regulation. SNRIs can be contrasted with the selective serotonin reuptake inhibitors (SSRIs) and norepinephrine reuptake inhibitors (NRIs), which act upon single neurotransmitters.
Dantrolene sodium, sold under the brand name Dantrium among others, is a postsynaptic muscle relaxant that lessens excitation-contraction coupling in muscle cells. It achieves this by inhibiting Ca2+ ions release from sarcoplasmic reticulum stores by antagonizing ryanodine receptors. It is the primary drug used for the treatment and prevention of malignant hyperthermia, a rare, life-threatening disorder triggered by general anesthesia or drugs. It is also used in the management of neuroleptic malignant syndrome, muscle spasticity (e.g. after strokes, in paraplegia, cerebral palsy, or patients with multiple sclerosis), and poisoning by 2,4-dinitrophenol or by the related compounds dinoseb and dinoterb.
Baclofen, sold under the brand name Lioresal among others, is a medication used to treat muscle spasticity such as from a spinal cord injury or multiple sclerosis. It may also be used for hiccups and muscle spasms near the end of life, and off-label to treat alcohol use disorder or opioid withdrawal symptoms. It is taken orally or by intrathecal pump. It is also sometimes used transdermally in combination with gabapentin and clonidine prepared at a compounding pharmacy.
Nortriptyline, sold under the brand name Pamelor, among others, is a medication used to treat depression. This medicine is also sometimes used for neuropathic pain, attention deficit hyperactivity disorder (ADHD), smoking cessation and anxiety. As with many antidepressants, its use for young people with depression and other psychiatric disorders may be limited due to increased suicidality in the 18–24 population initiating treatment. Nortriptyline is a less preferred treatment for ADHD and stopping smoking. It is taken by mouth.
Orphenadrine is an anticholinergic drug of the ethanolamine antihistamine class; it is closely related to diphenhydramine. It is a muscle relaxant that is used to treat muscle pain and to help with motor control in Parkinson's disease, but has largely been superseded by newer drugs. It is considered a dirty drug due to its multiple mechanisms of action in different pathways. It was discovered and developed in the 1940s.
Methocarbamol, sold under the brand name Robaxin among others, is a medication used for short-term musculoskeletal pain. It may be used together with rest, physical therapy, and pain medication. It is less preferred in low back pain. It has limited use for rheumatoid arthritis and cerebral palsy. Effects generally begin within half an hour. It is taken by mouth or injection into a vein.
Tizanidine, sold under the brand name Zanaflex among others, is an alpha-2 (α2) adrenergic receptor agonist, similar to clonidine, that is used to treat muscle spasticity due to spinal cord injury, multiple sclerosis, and spastic cerebral palsy. Effectiveness appears similar to baclofen or diazepam. It is taken by mouth.
Chlorzoxazone (INN) is a centrally acting muscle relaxant used to treat muscle spasm and the resulting pain or discomfort. It can also be administered for acute pain in general and for tension headache. It acts on the spinal cord by depressing reflexes. It is sold under the brand names Lorzone, Paraflex and Muscol and in combination form as Parafon Forte, a combination of chlorzoxazone and acetaminophen (paracetamol). Possible side effects include dizziness, lightheadedness, malaise, nausea, vomiting, and liver dysfunction. When used with acetaminophen it has added risk of hepatotoxicity.
Eperisone is an antispasmodic drug.
Thiocolchicoside is a muscle relaxant with anti-inflammatory and analgesic effects. Its mechanism of action is unknown, but it is believed to be act via antagonism of nicotinic acetylcholine receptors (nAchRs). However, it also appears to be a competitive antagonist of GABAA and glycine receptors. As such, it has powerful convulsant activity and should not be used in seizure-prone individuals.
An analgesic adjuvant is a medication that is typically used for indications other than pain control but provides control of pain (analgesia) in some painful diseases. This is often part of multimodal analgesia, where one of the intentions is to minimize the need for opioids.
↑ Yang YW, Macdonald JB, Nelson SA, Sekulic A (December 2017). "Treatment of vismodegib-associated muscle cramps with cyclobenzaprine: A retrospective review". Journal of the American Academy of Dermatology. 77 (6): 1170–1172. doi:10.1016/j.jaad.2016.12.017. PMID29132849. S2CID8265576.
↑ "Long-term Use of Cyclobenzaprine for Pain: A Review of the Clinical Effectiveness". CADTH Rapid Response Reports. Ottawa, Ontario: Canadian Agency for Drugs and Technologies in Health. 23 February 2015. PMID25763449.
↑ Kobayashi H, Hasegawa Y, Ono H (September 1996). "Cyclobenzaprine, a centrally acting muscle relaxant, acts on descending serotonergic systems". European Journal of Pharmacology. 311 (1): 29–35. doi:10.1016/0014-2999(96)00402-5. PMID8884233.
↑ Winchell GA, King JD, Chavez-Eng CM, Constanzer ML, Korn SH (January 2002). "Cyclobenzaprine pharmacokinetics, including the effects of age, gender, and hepatic insufficiency". Journal of Clinical Pharmacology. 42 (1): 61–9. doi:10.1177/0091270002042001007. PMID11808825. S2CID7749001.
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