Allergic Drug Reaction (ADR) and Allergy Testing

Allergic drug reaction is an unintended side effect of a drug and it ranges from minor rash to life threatening reaction.

Allergic Drug Reaction (ADR) and Allergy Testing

Allergic drug reaction is an unintended side effect of a drug and it ranges from minor rash to life threatening reaction.

However, an allergy reaction to a drug is often misdiagnosed, over-diagnosed, or not reliably documented e.g. penicillin allergy. This becomes a problem when penicillin or related drugs e.g. Amoxycillin is essential and required by doctors to treat certain diseases and there is no better alternative. In such scenarios, a controlled allergy testing is required to see if the documented allergy is really true or not. If the testing shows that there is no allergy, then the drug can be safely used again.

There are various ways to do Drug Allergy tests

Skin Test

Skin testing plays an important role in the diagnosis of allergy. Prick and intradermal test reactions are read and interpreted after 15 min. In the case of rash eruptions, late readings after 24, 48 or 72 hour may be necessary (e.g., when investigating amoxicillin eruptions). Sometimes, skin test reactions can even occur after more than 1 week.

    Blood Tests

    Blood tests to measure specific IgE antibodies to a limited range of drugs (e.g. penicillin, amoxicillin) are available. However, it is not possible to conclusively detect or exclude drug allergy solely on the basis of blood tests.
    Blood test results can only be interpreted together with patient history/clinical findings and possibly skin testing.

      Provocation Tests

      Provocation tests are necessary when the drug allergy cannot be identified with sufficient reliability on the basis of history, skin testing, and blood test investigations; and when the benefit of result obtained from provocation testing outweighs the risks. In cases of suspected and low likelihood of reactions to drugs that are essential (e. g., pain killers, antibiotics, local anesthetics), provocation tests are necessary and useful. In-patient medical supervision is required when provocation tests have the potential to trigger systemic reactions.

        Skin Reaction & Time Interval

        There are 2 broad groups of drug allergy reaction and it is co-related to the time lapse of drug intake:

        • Immediate reaction – rash erupt immediately or within 1–6 hours following drug intake
        • Delayed reaction – several hours to days or weeks later

        Allergy test will not be done in the following situations:

        • Pregnancy and breastfeeding
        • Potential allergic reactions that may be beyond medical control (e.g. uncontrolled asthma, serious life threatening allergy)
        • Severe pre-existing diseases that carry an increased risk despite essentially controllable reactions (e. g., severe heart disease, severe asthma).
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          Dr. Wong Soon Tee

          Consultant Dermatologist

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          • MBBS, Yong Loo Lin School of Medicine, Singapore
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          • Adjunct Assistant Professor, National University of Singapore
          • Visiting Consultant, University Dermatology Division, National University Hospital
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