Drugs for MG and side effects

MG Information > Drugs for MG and side effects

Most medicines and drugs have some unwanted side effects. This includes those used to treat MG, where the side effects will vary from patient to patient and with the level and frequency of the dose.

Together with your doctor you must weigh up the benefits of the treatment against the risk of unwanted effects particularly when to cease the treatment could have serious consequences. Generally the benefits of the treatment outweigh the risks.

Let’s look at the possible side effects of three of the main groups of drugs commonly used to treat MG.

Pyridostigmine (Mestinon) and Neostigmine (Prostigmin)
These drugs slow down the elimination of Ach helping to build its concentration on the muscle receptors. Ach plays an important role in many parts of the body in addition to the muscle receptors. The medication is not selective and thus can cause a number of unwanted effects. For instance it may affect the muscle in the wall of the bladder and bowel resulting in frequency of passing urine, even causing incontinence and stomach discomfort and diarrhoea. (may be controlled by reducing the dose or by adding medication to control the bowel) The pupils may be affected making it difficult to focus.

Some patients experience increase in saliva and bronchial mucus. Another side effect may be muscle cramps, muscle twitching (including around the eyes). Generally the effects are minor in relation to the benefits. It should be noted, however, that if the dose is too high it results in actual muscle weakness. In other words more is not always better.

Azathioprine (Imuran)
This drug depresses the immune system causing the reduction of the antibodies responsible for MG. The drug is extremely useful as it allows smaller doses of other drugs, steroids in particular, to be prescribed. Unfortunately, in addition to reducing the antibodies, Imuran also reduces the formation of new blood cells. This effect must be monitored by regular blood tests.

Liver function may also be affected by Imuran but the damage is reversible on stopping the treatment, or reducing the dose.

Imuran is tolerated, by 90% of people, without serious adverse affects however the patient should contact their doctor immediately and stop the medication if any of the following warning signs occur:

Steroids (Corticosteroids)
These are not to be confused with anabolic steroids taken by some athletes and roundly condemned.

Steroids occur naturally in the body and are part of the defence system. Those used in medicine are usually much stronger than those occurring naturally. The most commonly used drug in this group is Prednisilone, but others used are Prednisone, Hydrocortisone and Dexamethasone.

The most common undesirable side effect in the patients view is the increase in fat and fluid on the face and trunk. However this is not considered dangerous to health, and is dose related.

Steroids in chronic use can cause a weakening of the bones in the spine and the pelvis. This is worse for those already at risk, being women past child bearing age and older adults. Calcium supplements are usually suggested.

Steroids also make the body less capable of dealing with glucose and other sugars which may induce mild diabetes or aggravate already present diabetes.

Other possible side effects include:

This list of possible side effects of steroids can be quite scary but the Doctor will be aware of this and alternate day dosing reduces the severity of unwanted effects.

For most of us, the benefits of steroid treatment far outweigh the risks.