Drug Allergy

Prescription drugs have been through a rigorous process of testing to ensure safety, despite this, a minority of individuals will develop side-effects. These are called “adverse drug reactions” and, while most are mild and may not require stopping the drug, more serious reactions can occasionally occur.

The majority of adverse drug reactions are predictable and affect susceptible patients, for example, aspirin causing stomach upset, or warfarin leading to bleeding when taken with some antibiotics. These reactions account for approximately 6.5% of hospital admissions and in up to 15% of patients prolong their hospital stay.

A smaller proportion of adverse drug reactions are due to drug allergy. In these cases, the drug causes an unexpected reaction, which is not predictable in a particular individual. Typical symptoms include swelling of the face, throat and tongue (angioedema), which may lead to difficulty in breathing, widespread itchy rash (urticaria), tight chest with wheeze and, in very severe cases, a drop in blood pressure leading to collapse or loss of consciousness. Suspected allergic reactions are investigated and managed in an NHS allergy department.

If you experience such a reaction to a drug, try to keep the drug packaging, note how much was taken, and document the reaction (photos may help).

Typical cases referred to an allergy department include:

• Patients allergic to multiple antibiotics, making treatment of infections difficult.
• Severe reactions such as difficulty breathing or swelling after taking anti-inflammatories like aspirin, ibuprofen, or diclofenac, especially if these medications are now needed for conditions like arthritis.
• Patients who have had an allergic reaction during general anaesthesia.
  Note: Referrals are only accepted with a fully completed NHS peri-operative anaphylaxis Proforma – ideally completed by the anaesthetist involved. Incomplete forms cannot be processed.
• Suspected allergy to local anaesthetic (e.g. at the dentist), especially if this affects future treatment.
• Patients who have experienced a suspected allergic reactions after vaccination.

Patients on ACE inhibitors who develop angioedema.
This reaction is not a true allergy but can still be serious. It may occur even after long-term use. The first step is to stop the medication. Referral to an allergy department is only needed if swelling episodes continue after stopping the drug.

If the allergic reaction involves topically applied creams or ointments, or widespread peeling of the skin, referral to a dermatology clinic is more appropriate.

Finally, all referrals for drug allergy assessment must be made through your GP or the hospital doctor involved at the time of the reaction. The referring doctor should provide details of the suspected allergic reactions, which are essential before investigation can commence.   Your GP will also know of a suitable allergy clinic to which referral can be made.