From the Guidelines
Flexeril (cyclobenzaprine) is a centrally acting 5-HT2 receptor antagonist that acts as a skeletal muscle relaxant.
Key Characteristics
- It is structurally related to amitriptyline and has peripheral and central anticholinergic activity 1.
- Common side effects include hallucinations, confusion, drowsiness, constipation, urinary retention, and dry mouth 1.
- It can cause norepinephrine potentiation and has the potential to interact with sedatives and anesthetic agents 1.
- Long-term use can lead to withdrawal symptoms such as malaise, nausea, and headache, which can be prevented by tapering the medication over 2 to 3 weeks 1.
Clinical Use
- It is used to treat musculoskeletal conditions and has been found to be moderately superior to placebo for short-term pain relief in acute low back pain 1.
- However, there is insufficient evidence to conclude that cyclobenzaprine is superior to other muscle relaxants for benefits or harms 1.
- In patients with fibromyalgia, cyclobenzaprine has been found to have a small, significant improvement in sleep, but not pain, relative to baseline at 12 weeks 1.
From the FDA Drug Label
Cyclobenzaprine HCl relieves skeletal muscle spasm of local origin without interfering with muscle function. Cyclobenzaprine reduced or abolished skeletal muscle hyperactivity in several animal models Cyclobenzaprine Hydrochloride Tablets, USP are supplied as 5 mg and 10 mg tablets for oral administration
Flexeril (cyclobenzaprine) is a skeletal muscle relaxant that relieves skeletal muscle spasm of local origin without interfering with muscle function 2. It is supplied as tablets for oral administration in strengths of 5 mg and 10 mg 2.
From the Research
What is Flexeril (Cyclobenzaprine)?
- Flexeril, also known as cyclobenzaprine, is a muscle relaxant used to treat muscle spasms and pain [ 3 , 4 ]
- It is a tricyclic pharmacologic agent that works by inhibiting tonic somatic motor function, likely through modulation of noradrenergic and serotonergic systems [ 5 ]
- Cyclobenzaprine has a reasonable safety profile, but can cause side effects such as sedation, dry mouth, and somnolence [ 3 , 4 ]
Mechanism of Action
- The exact mechanism of action of cyclobenzaprine is not fully understood, but it is thought to mediate its effects centrally [ 5 ]
- Cyclobenzaprine has been shown to exhibit low nanomolar affinity for the cloned human histamine H1 receptor, and binds to the H1R in a noncompetitive manner [ 5 ]
- This off-target central antagonism of H1R by cyclobenzaprine may contribute to its sedative effects [ 5 ]
Clinical Uses
- Cyclobenzaprine is used to treat acute musculoskeletal pain, including back and neck pain [ 3 , 4 ]
- It has also been used to treat fibromyalgia, although more research is needed to fully understand its effectiveness in this context [ 4 ]
- Cyclobenzaprine should be used with caution in patients taking other medications, as it can interact with certain drugs and increase the risk of adverse effects, such as serotonin syndrome [ 6 ]