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Flexeril (cyclobenzaprine): How to Safely Use This Muscle Relaxant

Medically reviewed by L. Anderson, PharmD. Last updated on Feb 11, 2019.

Lower Back & Neck Pain: It's All Too Common

Chances are that you've pulled your lower back, strained your neck or twisted some other distant muscle in your body at one time or another - most of us have. If you sit at a desk on a daily basis, you may be all too familiar with this pain. Acute muscle injuries often result in a painful, constant spasm and interrupt work, daily activities, and especially sleep.

Luckily, over time, most of these acute injuries heal on their own and life goes on. But how do we survive until the pain subsides?

  • Here, we'll review Flexeril, one option that might help in the short-term.
  • The generic name for Flexeril is cyclobenzaprine, a frequently prescribed skeletal muscle relaxant used only for a few weeks or less to help quiet the spasm and ease the pain.
  • In fact, using Flexeril for back pain is one of its most common uses.

What is Flexeril (cyclobenzaprine) Used For?

Flexeril (cyclobenzaprine) is a muscle relaxant used in addition to rest and physical therapy for short-term relief of muscle spasm associated with acute, painful musculoskeletal conditions. It is structurally related to the tricyclic antidepressants.

  • Flexeril works by blocking nerve impulses that you recognize as pain.
  • Cyclobenzaprine is often combined with over-the-counter (OTC) pain medications like acetaminophen (Tylenol), or anti-inflammatory NSAIDs like ibuprofen (Advil, Motrin) or naproxen (Aleve).
  • Treatment usually lasts no more than 2 to 3 weeks.

What Strength Does Flexeril Come In?

There are two different forms of cyclobenzaprine: immediate-release tablets and extended-release capsules.

  • The generic immediate-release cyclobenzaprine tablets come in a 5, 7.5, and 10 milligram (mg) strength. You may find that the 7.5 mg tablet is more expensive; it may save you money to split the 5 mg tablet in half to achieve a 7.5 mg dose (a 5 mg tablet + 2.5 mg). Ask your pharmacist about this option.
  • The extended-release form of cyclobenzaprine, which has a brand name of Amrix, comes as a capsule. There is no generic form of Amrix yet, which means it will be much more expensive at the pharmacy. Amrix comes in a 15 and 30 mg strength. Be sure to check with your insurance if you receive a prescription for Amrix to see if it is covered; many insurance companies have stopped paying for this brand. Also check with the manufacturer for any patient assistance if you are unable to pay.

What about price? Most strengths of generic cyclobenzaprine are very affordable, typically costing about $6 to $10 for a bottle of 30 tablets, although some pharmacies have it on their $3 list. Another brand name of cyclobenzaprine is Fexmid, but it only comes in a 7.5 mg strength, and is much more costly.

The brand Flexeril is no longer available in the U.S., but your doctor and many consumers may still use "Flexeril" because this common name of cyclobenzaprine is so well-known.

Flexeril Dosage

Cyclobenzaprine is used in addition to rest and physical therapy, often with NSAIDs, and treatment duration usually does not to exceed 2 to 3 weeks.

Immediate-release tablets: (cyclobenzaprine)

  • Adults and children 15 years of age and older: Initial dose 5 milligrams (mg) orally 3 times a day. If needed, the dose may be increased to 10 mg orally 3 times a day. The maximum dose is 60 mg per day but most people do not use such high doses. Use in children under 15 years must be determined by a doctor. Avoid use in the elderly.
  • Liver disease: In mild hepatic impairment the initial dose is 5 mg and is slowly increased. Immediate-release cyclobenzaprine is not recommended in moderate or severe liver disease.

Extended-release capsules: (Amrix)

  • Adults: Initial dose is 15 milligrams (mg) orally once a day at the same time. If needed, the dose may be increased to 30 mg once a day. May sprinkle capsule content onto applesauce and consume without chewing; rinse mouth after swallowing applesauce. Pediatric use of the extended-release form has not been approved. Do not use this form in the elderly.
  • Liver disease: The extended-release form of cyclobenzaprine is not recommended for use with any level of liver disease.

Flexeril Side Effects

Side effects with cyclobenzaprine can be frequent, bothersome, and sometimes dangerous. Flexeril can impair your thinking or how quickly you can react.

Don't drive or do any dangerous activity. Also, avoid combining Flexeril and alcohol which can worsen these side effects.

  • Drowsiness, fatigue and sedation (up to 40% of patients) is the most common side effect; do not drive or drink alcohol while taking this medication and always check for drug interactions.
  • Dizziness (11%) and confusion (1 to 3%) might increase the risk for a fall, especially in the elderly.
  • Dry mouth (30%) and blurred vision (1 to 3%)
  • Headache (1 to 5%)
  • Constipation (1 to 3%)

Be sure to review the information that comes with your prescription to understand all of the side effects.

How Does Flexeril Work?

Acute muscle spasms in the neck or back can be very painful. However, over time the pain should lessen. It is thought cyclobenzaprine, which acts in the brain, boosts levels of norepinephrine and binds to serotonin receptors to reduce spasm and lessen pain.

You can determine how well your therapy is working based on your relief of muscle spasm and pain, decreasing tenderness, and increased ability to move around more easily.

Muscle relaxants like cyclobenzaprine are usually used with a combination of rest, ice and/or heat, physical therapy, OTC pain relievers -- and time. You might like to join the Muscle Spasm support group to learn about experiences of others.

There's a catch with use of this drug: laying in bed and lack of activity may actually be worse for low back pain or other types of muscle pain and may increase your time to full recovery. Using cyclobenzaprine may make you very drowsy and you may not feel like moving at all. But eventually you should get back to movement.

  • Ask your doctor how you should approach your exercise and movement as you heal from your muscle strain.
  • Two or three sessions of physical therapy, and at-home exercises may speed recovery.
  • Yoga and meditation have been shown to be helpful for some patients, too.
  • If you don't start to feel relief in a week or two, contact your doctor.

Flexeril Contraindications & Warnings

There may be reasons why you shouldn't use cyclobenzaprine at all.

Many skeletal muscle relaxants like cyclobenzaprine can cause "anticholinergic" side effects.

  • Anticholinergic activity blocks the action of the neurotransmitter acetylcholine and can lead to wide range of side effects.
  • Because of this, cyclobenzaprine should be used cautiously if you have certain forms of glaucoma and high blood pressure in the eye, urinary frequency/hesitancy, or if you take other medications that also have anticholinergic effects.
  • If you aren't sure if your medicines have anticholinergic effects, be sure to ask your pharmacist.

You should NOT use cyclobenzaprine during or within 14 days of taking a monoamine oxidase inhibitor (MAOI). MAOIs are used for depression or Parkinson's disease, and include agents such as:

  • isocarboxazid
  • tranylcypromine
  • phenelzine
  • selegeline

Also tell your doctor if you have any thyroid gland or heart problems.

Effects of Flexeril in the Elderly

Cyclobenzaprine use in individuals older than 65 should be avoided in most circumstances as there is a higher risk for dangerous side effects.

Experts have developed the Beers Criteria, a set of guidelines that lists medications to avoid in the elderly. Cyclobenzaprine, an anticholinergic agent, is listed in the Beers 2019 Criteria as a potentially inappropriate medication for the elderly 65 years and older.

In general, muscle relaxants like cyclobenzaprine are poorly tolerated in older patients due to anticholinergic effects which can lead to a high risk of:

  • drowsiness, sedation
  • confusion
  • dizziness
  • problems with urination
  • constipation
  • an elevated risk for falls, possibly leading to bone fractures.

Serotonin Syndrome & Cyclobenzaprine Drug Interactions

A potentially serious and life-threatening, but uncommon, side effect with cyclobenzaprine is known as serotonin syndrome.

Serotonin syndrome may result in behavioral changes like agitation, confusion, seizures or hallucinations, high blood pressure, excessive sweating, muscle tremors or stiffness, and stomach problems like nausea, vomiting, or diarrhea.

Drug interactions with cyclobenzaprine can boost this risk, too, so always have a pharmacist run a drug interaction screen.

Common drugs that could increase this risk include:

Lower Back Pain Treatment

Lower back pain is one of the most common ailments that doctors see in the U.S. However, studies have shown that short-term use of opioid pain killers like hydrocodone or oxycodone is no more effective than using an NSAID like ibuprofen or naproxen alone. Therefore, many doctors are reluctant to prescribe opioids for back pain due to addiction risk and lack of any real added effectiveness over an NSAID. Muscle relaxants have not been shown to add any real benefit over NSAIDs alone.

However, for some patients, short-term use of a muscle relaxant plus an NSAID may help to take the edge off of the pain in the short-run and allow for some much needed sleep. Since drowsiness is a common side effect with muscle relaxants, some patients may prefer to use the anti-inflammatory NSAIDs like ibuprofen or naproxen in the daytime, and add the muscle relaxant just at bedtime.

Flexeril for Fibromyalgia

Cyclobenzaprine may be used "off-label" for fibromyalgia, meaning it may be prescribed by your doctor for a generally accepted use not specifically approved by the FDA or listed in package labeling.

For fibromyalgia, cyclobenzaprine has been shown to help with sleep and pain for some patients, but not provide relief for fatigue or tender points.

"Off-label" uses for cyclobenzaprine include:

Your doctor can help guide you to determine if these "off-label" uses are right for you.

Cyclobenzaprine Research for PTSD

A sublingual (under the tongue) form of cyclobenzaprine known as TNX-102 SL (cyclobenzaprine HCl sublingual tablets) is under investigation for the treatment of Post Traumatic Stress Disorder (PTSD), including those with military-related PTSD.

In December 2016, the FDA granted Breakthrough Therapy designation to Tonmya (cyclobenzaprine SL) as a possible treatment for PTSD.

  • Tonmya is being developed by Tonix Pharmaceuticals. In studies, Tonmya has been given at a sublingual dose of 5.6 mg (2 x 2.8 mg tablets) at bedtime.
  • Tonmya targets mechanisms which are associated with disturbed sleep and nightmares linked with PTSD. Restoring deeper stages of sleep in PTSD may allow the body's natural recovery processes from severe trauma.
  • In the Phase 3 HONOR study of Tonmya in military-related PTSD was a 12-week randomized, double-blind, placebo-controlled trial evaluating the efficacy of Tonmya 5.6 mg in up to 550 participants with military-related PTSD. The HONOR study was halted early when the primary endpoint did not cross a predefined study continuation threshold. There were no serious and/or unexpected adverse events revealed.
  • The Phase 3 RECOVERY trial for the treatment of posttraumatic stress disorder (PTSD) begins the first quarter of 2019. RECOVERY is a 12-week, double-blind, randomized, placebo-controlled study of Tonmya 5.6 mg for treatment for civilian and military-related PTSD in about 250 participants. The primary endpoint will be the Week 4 mean change from baseline in the severity of PTSD symptoms as measured by CAPS-5 between the Tonmya group and those receiving placebo. CAPS-5 is a standardized structured clinical interview used for measuring the symptom severity of PTSD.

List of Muscle Relaxers

In addition to cyclobenzaprine, many other muscle relaxant-type drugs are available:

In the US, diazepam (classified as a benzodiazepine but also used as a muscle relaxant), and carisoprodol are both scheduled as controlled substances and can become habit-forming.

Most skeletal muscle relaxants are available as cost-saving generics in the US.

Finished: Flexeril (cyclobenzaprine): How to Safely Use This Muscle Relaxant

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Further information

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