Relajantes musculares

What are muscle relaxants?

Muscle relaxants are medicines that are used to prevent and reduce muscle spasms and tightness (spasticity). Muscle spasms occur when there is an uncontrolled (involuntary) contraction of a group of muscles.

The muscles usually shorten (contract) suddenly; this is often painful. Spasticity occurs when some muscles contract tightly and can then become stiff and harder to use.

What muscle relaxants are available?

Several muscle relaxants are available to prescribe in the UK. They include:

• Baclofeno.

• Dantrolene.

• Diazepam.

• Clonazepam.

• Tizanidine.

• Gabapentina.

• Methocarbamol.

• A cannabis extract containing dronabinol and cannabidiol (trade name Sativex®).

Most muscle relaxant preparations are available as tablets, capsules, or liquids. Baclofen is also available as an injection into the back (an intrathecal injection).

Diazepam is also available as a liquid that can be inserted into the back passage (rectum) and there is a diazepam preparation that can be injected into muscle.

Cannabis extract is only available as a spray for the mouth. Other treatments sometimes used for muscle spasticity are injections into the affected areas with Botox® (toxina botulínica) and other chemicals.

Can I buy muscle relaxants?

No - you cannot buy muscle relaxants. They are only available from your pharmacy, on prescription.

How do muscle relaxants work?

Muscle relaxants work by causing the muscles to become less tense or stiff, which in turn reduces pain and discomfort. They do this in different ways. Baclofen, diazepam, methocarbamol and tizanidine act on the central nervous system (brain and spinal cord). Dantrolene works directly on the muscle.

Cannabis extract works on the brain and spinal cord as well as the muscles. Because dantrolene only works on the muscles, it is thought to have fewer side-effects compared with other muscle relaxants. For this reason, dantrolene is often the first muscle relaxant to be prescribed for people with long-term muscle spasms.

When are muscle relaxants prescribed?

Muscle relaxants are used to relieve muscle spasms which may result from some conditions which affect the nervous system, such as:

• Esclerosis múltiple.

• Enfermedad de la neurona motora.

• Cerebral palsy.

• Sometimes, injuries to the head or back.

Generally, physiotherapy and exercises are better first-line treatments, but medications are sometimes used if these are not working.

Esclerosis múltiple

Muscle relaxants used in MS include baclofen, tizanidine, gabapentin, diazepam, clonazepam, and dantrolene.

Cannabis extract (Sativex®) is always started by a consultant in a hospital and is only available on the NHS for a very limited range of uses. The muscle relaxant indication is for people with multiple sclerosis who have tried other muscle relaxants which are not working.

In most cases it is given as a four-week trial to see if it helps with symptoms, and can be continued if the symptoms have improved by at least 20%, using a numerical rating scale.

Enfermedad de la neurona motora

Baclofen, tizanidine, dantrolene, and gabapentin are sometimes used for muscle stiffness or spasticity in people with motor neurone disease.

Benzodiazepines such as diazepam, and botulinum toxin (Botox®) injections might be offered by specialists, if other options haven't worked.

- el daño cerebral causa problemas con las funciones musculares.

Muscle relaxants used in cerebral palsy include baclofen, diazepam, tizanidine, and botulinum toxin (Botox®) injections.

Head and back injuries

Muscle relaxants are sometimes prescribed to help spasm in acute (recent-onset) injuries, such as lower back pain or neck pain in conditions such as whiplash.

This is controversial, though, because there is not much scientific evidence that they actually work, and they have risks. For example, diazepam and other benzodiazepines can be highly addictive.

A recent study looked at the evidence for muscle relaxants in acute lower back pain, and concluded that benzodiazepines did not seem to have a beneficial effect on back pain. It also found that non-benzodiazepine muscle relaxants might reduce pain slightly, but that this effect was very small.

Guidelines on the use of muscle relaxants for back and neck pain differ across the world. In the UK, the National Institute for Health and Care Excellence (NICE) recommends that benzodiazepines such as diazepam should not be used for acute low back pain or sciatica, because the potential harms are thought to outweigh the benefits for most people.

How should muscle relaxants be taken?

These medicines are usually taken by mouth (tablets, capsules or liquids). In general, your doctor will start off with a low dose and increase this gradually over a number of weeks. This is in order to help your body get used to these medicines. Injections into the back are always started in the hospital.

Cannabis extract is a spray for the mouth. It should be sprayed under the tongue or on to the inside of the cheek once or twice a day. Always change the area in your mouth where you spray, to prevent irritation of the mouth. Like other muscle relaxants you will normally start off with a low dose. The number of sprays used is normally increased over a number of days.

Muscle relaxant side-effects

Muscle relaxants have a number of possible side-effects. However, not everyone experiences them and they usually improve as your body adjusts to the new medicine.

Most muscle relaxants cause muscle weakness as a side-effect. Other common side-effects include:

• Baclofeno - feeling sick, tiredness, drowsiness, problems with eyesight, weakness, dizziness, light-headedness, headache, boca seca, breathing difficulties, aching muscles, sleeplessness or nightmares, feeling anxious or agitated, confusion, unsteadiness, increased need to pass urine, shakiness, increased sweating, and skin rash.

• Dantrolene - feeling dizzy, sleepy, tired, or generally unwell, diarrea, feeling or being sick, tummy (abdominal) pain, headache, loss of appetite, rash, speech or sight difficulties, temperatura alta (fiebre), chills, difficulty in breathing, seizures. It may also cause inflammation of the lining around the heart (sometimes with fluid in the lungs). Liver toxicity is also a possible side-effect of dantrolene.

• Diazepam - feeling sleepy, weak, or light-headed, forgetfulness, feeling confused or unsteady, feeling (or being) aggressive. Diazepam can also be addictive and lead to dependence, and should be used cautiously, ideally for a short time only.

• Methocarbamol - forgetfulness, allergic reactions, being anxious, blurred vision, a slow heart rate, being confused or dizzy, headache, acidez, feeling or being sick, itching, rash, and low blood pressure.

• Cannabis extract - feeling dizzy, depressed mood, diarrhoea or estreñimiento, úlceras bucales or pain, feeling tired or sick, appetite changes. Hallucinations have also been reported.

It is not possible in this leaflet to list all the possible side-effects for these medicines. For more detailed information, see the leaflet that comes with the medicine packet.

Who cannot take muscle relaxants?

For a full list of people who should not take each type of muscle relaxant, refer to the specific leaflet for that medication.

• Baclofen should not usually be given to people who have a úlcera de estómago, epilepsia, mental health problems, Parkinson's disease, a history of substance abuse or diabetes, and caution should be advised before prescribing for people who are very elderly.

• Dantrolene should not be given to people with liver, heart or breathing problems, or reduced lung function.

• Diazepam should be avoided in people who have severe breathing difficulties - for example, people who have myasthenia gravis and people with lung problems.

• Tizanidine should not usually be given to elderly people, or people who have severe problems with their liver.

• Methocarbamol should not be used for people who have myasthenia gravis, epilepsy or brain damage.

• Cannabis extract can only be prescribed by specialists for people with multiple sclerosis. People who have a personal or family history of hallucinations or delusions or any other severe psychiatric disorder should not take cannabis extract, and caution should be used if considering it for people who have epilepsy or significant cardiovascular disease.

Other uses of muscle relaxants

Muscle relaxants are sometimes used to treat other conditions - for example, diazepam is sometimes used to treat ansiedad o difficulty with sleeping (insomnia). It is given as a pre-medication (often called a 'pre-med') before an operation, particularly during procedures that may cause anxiety or discomfort.

It can also be used to treat convulsiones. Rectal diazepam tubes may be prescribed for this, as they are useful if a quick effect is needed or if it is not possible to give the medicine by mouth.

Some medicines that are given by injection into the vein during surgery are also known as muscle relaxants. They are sometimes called 'neuromuscular blocking drugs' and are used to relax the muscles when someone is under anaesthetic. They work in a completely different way to baclofen, dantrolene, diazepam, tizanidine, and cannabis extract and are not discussed here.

Things to consider when taking muscle relaxants

• These medicines can cause drowsiness. If you feel drowsy when taking these medicines, do not operate machinery, do not drive, and do not drink alcohol.

• Baclofen should not be stopped suddenly. The dose should be lowered slowly over a few weeks and then stopped.

• Diazepam - people who take this medicine continuously for too long can become dependent on it. This means that withdrawal symptoms occur if the tablets are stopped suddenly. See the separate leaflet called Benzodiazepines and Z drugs for more details.