What are corticosteroids? - Allergy treatments

Corticosteroids are naturally occurring steroid-based hormones which are made in the adrenal cortex (part of the adrenal glands, which are small organs that sit on top of the kidneys). There are two types – glucocorticoids and mineralocorticoids, which differ in their chemical structure.

Corticosteroid drugs are widely used to counteract the immune system. They are based mainly around glucocorticoids, but some (for example, prednisolone) have a small amount of mineralocorticoid action as well. It is the glucocorticoid part of the corticosteroid drug that works to suppress the immune system, however, for best and long-lasting treatment, a very small amount of mineralocorticoid function or no mineralocorticoid is also beneficial.

These drugs work by inhibiting phospholipase A2, which is an enzyme in an important chemical pathway. The products of this chemical pathway are a variety of chemicals involved in inflammation – leukotrienes and prostaglandins. The effects of prostaglandins and leukotrienes involve making blood vessels wider and more leaky in the area they are released in, narrowing the airways, making more mucus in the respiratory tract, and causing more inflammatory white blood cells to arrive in the area. Corticosteroid drugs which inhibit this pathway can stop prostaglandins and leukotrienes being formed, and the changes in blood vessels, airways, and mucus production will not happen.

Corticosteroid drugs which have a high mineralocorticoid effect, such as cortisone and hydrocortisone, can also cause fluid retention, meaning we do not excrete water (in the urine) as much as we should. Problems associated with fluid retention include heart and lung problems (pericardial effusions in the heart, and pleural effusions and oedema in the lungs), high blood pressure (which can lead to blood vessel and kidney damage), and swelling (oedema). These drugs are useful for a short-term basis, but problems with fluid retention means that we can't use these drugs for a long term solution. Hydrocortisone is useful as a cream, as it will work on the skin and here its side effects are less marked.

Drugs which have a very high amount of glucocorticoid function and an insignificant amount of mineralocorticoid function, such as dexamethasone and betamethasone, can be used in high doses for long periods of time. Fluid retention is not a problem with drugs with low mineralocorticoid function. The effects of betamethasone and dexamethasone also last a long time. Drugs derived from beclometasone and betamethasone can be used as potent corticosteroid creams and inhalers.

Prednisolone has mainly glucocorticoid activity but a small amount of mineralocorticoid function too. It is the most widely used corticosteroid drug.

An important side effect of corticosteroid drugs is a lowered immunity. This can be local (restricted to one place), such as with inhalers or creams. You might notice opportunistic infections, such as candidiasis, in the back of your throat with inhalers. In addition, serious infections such as tuberculosis might reach dangerous stages without being noticed. You should take care to avoid chickenpox and measles. If you are on corticosteroids for a very long time, your body may also realise that it doesn't have to spend energy making any of its own corticosteroids as it is getting some from your drug regimen. Your adrenal glands might get smaller and lose their function (atrophy), which can cause problems when you stop your corticosteroid therapy.

High doses of corticosteroid therapy can cause mood and psychological changes too, including anxiety, an inability to sleep (insomnia), nightmares, suicidal thoughts, irritability, or euphoria. There are higher risks of such side effects developing in people who already have or have had any psychological problems. You should see your doctor if you have mental changes during your treatment with corticosteroids.

Mineralocorticoids can cause you to retain water and to fail to excrete it adequately in the urine. This is called fluid retention or water retention and can cause hypertension, as well as problems in your kidneys, heart, or lungs. Glucocorticoids can cause your bones to become weaker and increase the chance of osteoporosis (a bone disease where bones fracture easily because they are abnormally weak).

Caution may be needed during breastfeeding and pregnancy. Not all corticosteroid drugs can cross the placenta and enter your baby while you are still carrying it. Betamethasone and dexamethasone can easily cross the placenta into your baby, whereas a lot of prednisolone will be deactivated when it enters your baby. However, there is no evidence that corticosteroids will cause any harm to your unborn baby. Caution may also be needed if you are giving corticosteroid drugs to your child (as it can slow growth), or if you have kidney, liver, bone, or heart problems or high blood pressure.

Like antihistamines, corticosteroid drugs may be given to you in a variety of ways. Injections and tablets both exist, and these can deliver the drug to all parts of your body. Corticosteroid drugs are also found in inhalers (for the management of asthma) and creams (for eczema and skin conditions). Beclometasone is a corticosteroid commonly found in nasal sprays (for the management of allergic rhinitis).

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