Medicines can give rise to various side effects, including allergies.

EVERYONE falls ill at some time or other. Many illnesses are self limiting and do not require anything more than rest. Other illnesses require medicines for a limited period of time.

Some people have chronic conditions which require medicines for a longer period or throughout their lives.

Medicines have benefits and risks. The majority of medicines do not have significant adverse reactions. However, there are occasions when there are adverse reactions to medicines. They include interactions between two or more medicines; the inability to break down (metabolise) the medicine, e.g. when there is liver or kidney damage; and allergic reactions to the medicine.

Allergic reactions comprise less than 10% of all adverse reactions to medicines. It does not occur on the first occasion that the medicine is consumed but occurs on the second or subsequent time the medicine is taken.

If an allergic reaction appears on the first occasion the medicine is consumed, it is very likely that the affected person had taken the medicine on a previous occasion without having known it. This is not uncommon as many patients do not know the names of the medicines they are taking.


When the body is exposed to a substance for the first time, the immune system recognises it as foreign and reacts to it by producing antibodies.

In the case of allergic reactions to medicines, antibodies called immunoglobulin E (IgE) are produced and stored. When the body is exposed to the medicine again, the IgE reacts to it and stimulates the body’s cells to produce chemicals called mediators, e.g. histamine, which act on organs, leading to the features of an allergic reaction.

The commonly used medicines which are the causes of allergic reactions are antibiotics like penicillin, sulpha compounds; painkillers (analgesics) like aspirin; non-steroidal anti-inflammatory drugs (NSAIDs), e.g. indomethacin, ibuprofen; and anti-epilepsy medicines like phenytoin.

Certain risk factors increase the likelihood of an allergic reaction to medicine. They include a family history of allergies or asthma; allergies to certain foods, e.g. eggs, seafood; large doses of medicines; and administration of medicines by injections.


The features of an allergic reaction to medicine vary considerably. They range from a mild skin rash to severe reactions from the body’s vital organ systems.

The reaction occur days or weeks after exposure to the medicines. This is unlike that of most other allergic reactions, which usually occur soon after exposure to the allergen.

The skin is commonly involved. The usual features are that of a rash or irregularly shaped swellings which are itchy, elevated, and slightly reddish.

People who are sensitive to sunlight can have a scaly and itchy rash on the exposed areas of the body.

The other common features include fever, joint aches, muscle aches, and swelling of the lymph nodes. The kidneys are also commonly involved.

Anaphylaxis is a life-threatening allergic reaction which is, thankfully, rare. Most anaphylactic reactions occur shortly after taking the medicines. The features include difficulty breathing, fainting, and swelling of the throat.


The management of allergic reactions to medicines is dependent on their severity.

It is important that the doctor or pharmacist who prescribed or dispensed the medicine, be contacted immediately for advice.

Attention should be sought at the Accident and Emergency department of a hospital without delay if:

> The doctor or pharmacist cannot be contacted.

> There is difficulty breathing, fainting, or swelling of the throat.

Doctors are conversant with the management of allergic reactions to medicines. Laboratory tests are carried out only in unusual situations.

The treatment of mild (localised reactions) involves stopping the medicine that caused the allergic reaction and taking antihistamine medicines, which may be consumed orally or applied topically. Alternatives to the medicine that caused the allergic reaction may be prescribed.

If the allergic reaction is moderate (involves larger areas of the body), oral corticosteroids or histamine blockers will be prescribed in addition to that of the measures for mild reactions.

Severe allergic reactions require hospitalisation whilst mild reactions can be managed at home after the doctor is satisfied that it can be managed so.

The management of severe reactions or anaphylaxis will be discussed in the next article in a fortnight’s time.

The reduction of physical activity and the wearing of light clothing that does not irritate the skin would be helpful. It is essential to keep the follow-up appointment after an allergic reaction to medicines has been treated. An assessment of the recovery can be carried out at this visit. At the same time, medicines may have to be adjusted and preventive advice given.

It is essential that the doctor be consulted if the response to the treatment prescribed is absent or unsatisfactory.

If there are features of anaphylaxis, there are some important tips to adhere to while awaiting the arrival of the ambulance:

> Stay calm.

> If it is available, take an antihistamine tablet and inhale a bronchodilator, if there is difficulty in breathing or if there is wheezing.

> If you are feeling faint, raise the legs to a level higher than the head.

> If there is collapse, administration of cardio-pulmonary resuscitation by someone who is able to do so.


It is very difficult to prevent allergic reactions to medicines. This is compounded by the fact that many patients do not know what medicines they are taking. In addition, many people take traditional and complementary medicines, the composition of which are not known.

The more medicines a person takes, the higher the likelihood of an allergic reaction to medicines. However, there is much that everyone can do to reduce the likelihood. They include:

> Knowing the names of medicines that one is taking and its common adverse reactions.

> Not taking any medicine that one has had an allergic reaction to in the past.

> Informing the doctor and pharmacist of one’s allergies, particularly to medicines, and the nature of the reactions. This is vital if one is consulting a doctor who is not his regular doctor.

> Informing the doctor and pharmacist about prescriptions or over-the-counter medicines that one is currently taking.

> Informing the doctor and pharmacist about the traditional and complementary medicine that one is currently taking.

> Practising self medication with the knowledge and advice of one’s doctor;

> Carrying a card containing one’s relevant medical information in the handbag or wallet, particularly the names of medicines that one is taking and those that one has had an allergic reaction to previously.

Source: Dr Milton Lum