safety medical

Flexeril (Cyclobenzaprine Hydrochloride)

Flexeril, also called cyclobenzaprine hydrochloride, is a pharmacological agent that is used as a muscle relaxant. In this article, we shall briefly review what Flexeril is and a little bit about its pharmacokinetics and breakdown within the body.

What is cyclobenzaprine (Flexeril)?

Flexeril is cyclobenzaprine hydrochloride. It is a water-soluble and alcohol soluble agent that is used in treating spasmodic muscle disorders. In other words, it is a powerful muscle relaxant.

One of the primary advantages of using Flexeril is that it acts locally without affecting the function of the muscles. This means that if there is a spasm of muscle in a localised part of the body, Flexeril is an excellent agent in treating this. This has been shown through numerous clinical trials and animal studies.

However, Flexeril is not useful in treating muscle spasms that occurred due to disease within the central nervous system. Furthermore, it is not active at the neuromuscular junctions or when used directly on skeletal muscles.

Mode of action

Flexeril acts on the brain stem which is located at the lower part of the brain just above its junction with the spinal-cord. Clinical studies have shown that it works by acting upon certain specialised systems known as alpha and gamma motor systems and results in a reduction in overall motor activity of the muscles.

Flexeril is available in 5 and 10 mg doses and should be taken as prescribed by a registered health care practitioner. When managing skeletal muscle spasm, it is often prescribed three times a day for a period of 2 to 3 weeks in total.

Half life and breakdown

Once ingested, around 33 to 50% of the Flexeril is absorbed and available for action within the body. Flexeril has a relatively long half life ranging between 1 to 3 days. This means that once it is absorbed, the levels drop a half within the blood stream after around three days. For it to be completely eliminated from the body, it can take up to 5 ½ half lives in total. This means that it can take around two weeks or just more than that to be completely expelled from the body.


Unfortunately, Flexeril (cyclobenzaprine hcl) also has certain side-effects that every patient and doctor prescribing the drug needs to be aware of. A full description of side-effects has been made elsewhere but in brief, patients can experience dry mouth, headaches, fatigue, nausea, constipation and dizziness. Stopping the drug suddenly can result in withdrawal symptoms which every patient must be aware of. Withdrawal of the drug can cause nausea, headaches and weakness.

Flexeril is a powerful muscle relaxant that is used in treating painful muscle conditions. It has a long half life and has a potential of causing side-effects and withdrawal effects.

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