Drug allergy

Types of drugs that can trigger allergic reactions

These drugs are the main ones to be aware of, although there may be others.

• Vaccines

  Vaccines are used to prevent and treat infectious diseases and for desensitising people who are allergic to allergens including insect venom, pollen and cats.

  If you are allergic to egg , be aware that certain vaccines such as the seasonal flu vaccine and yellow fever vaccine can contain small amounts of egg protein. You can discuss this with your doctor or allergy specialist, plus read more about egg allergies and vaccines.

  The MMR vaccine has been shown to be safe for children with egg allergy even though it’s normally cultured on cells from chick embryos. A 2010 medical paper written by UK experts said:

  “All children with egg allergy should receive their normal childhood immunizations, including the MMR vaccination, as a routine procedure performed by their family doctor/nurse… Studies on large numbers of egg-allergic children show there is no increased risk of severe allergic reactions to the vaccines. Children who have had documented anaphylaxis to the vaccine itself should be assessed by an allergist.”

  If your doctor is concerned that you or your child may react to a vaccine, it can be given in hospital.

• Insulin

  Insulin, which is used for diabetes, has the potential to trigger allergic reactions, but anaphylaxis is rare. This may be because the injections are usually used for life so people develop a degree of tolerance. Insulin-induced anaphylaxis may be more common in people whose treatment is interrupted or intermittent.

• Antibiotics such as penicillin

  Antibiotics are used to treat infections. They are among the drugs most likely to cause allergy. It is also common for people to be wrongly diagnosed with an allergy to antibiotics because the symptoms of an allergy can be similar to symptoms caused by the infection, such as a rash.

  If the rash comes on immediately after taking the antibiotic or is widespread, or you have other symptoms such as facial swelling or breathing problems, these are likely to be caused by an allergy. If this happens, your doctor can refer you to an allergy clinic for a skin prick test and intradermal testing, which are generally more helpful than blood tests.

  If you have been told you are allergic to penicillin, it is useful to try to find out why, and the reason may be included in your medical records. It’s also helpful to know which penicillin was involved. People with penicillin allergy can become non-allergic after many years without exposure to it, but this must always be confirmed by a specialist.

  Occasionally, people who are allergic to one antibiotic may react to another within the same ‘family’ of antibiotics. Talk to your GP or pharmacist about whether you need to avoid antibiotics in the same family. They will refer you to a specialist if needed.

• Pain killers (analgesics) and anti-inflammatories

  There is a large group of drugs with pain-killing and anti-inflammatory properties, known as the ‘aspirin-like drugs’ or as ‘non-steroidal anti-inflammatory drugs’ (NSAIDs). They include aspirin and ibuprofen. If you have any symptoms caused by these drugs, tell your GP.

  If you have had a reaction to aspirin or ibuprofen you should be considered sensitive to the other drugs in this group (such as diclofenac) until it is proven otherwise.

  Paracetamol is not an NSAID and evidence suggests that most people who are sensitive to aspirin are able to take paracetamol. If you become allergic to aspirin or ibuprofen, and you’re not sure whether you may also react to paracetamol because you haven’t taken it for some time, you could ask your GP about being referred to a specialist. They can do a paracetamol challenge under medical supervision to test whether you are sensitive to it. If you do react to paracetamol, your doctor should help you find an alternative painkiller.

• General anaesthetics

  If you have an allergic reaction to a general anaesthetic, you will generally be asleep when the reaction starts. This means the anaesthetist will watch for symptoms such as falling blood pressure and difficulty breathing. Fortunately, sensitivity to these drugs is rare, but because they are injected straight into the bloodstream, symptoms may be severe and progress quickly.

  If you believe you could be allergic to anaesthesia, tell your anaesthetist at the pre-assessment stage before surgery. Mention any food allergies you have in case there are any food derivatives in the drugs being used.

  It’s common for several drugs to be given together or in quick succession when you have a general anaesthetic. These include:
  • induction agents to make you unconscious
  • neuromuscular blockers which have a temporary paralysing effect – these are the most common cause of reactions
  • antibiotics
  • painkillers
  • blood or plasma substitute infusions.

  Any of these could cause anaphylaxis. If you have a reaction, it is important to find out which one caused it and which alternatives are likely to be safe in future.

  If you have a reaction that’s thought to be caused by the general anaesthetic, your anaesthetist should refer you to a hospital department with experience of anaesthetic-related reactions. You may have a skin prick test, intradermal testing and sometimes a drug challenge as part of the diagnosis.

  Sometimes, the anaesthetic drugs may not be responsible for the allergic reaction, for example, it might be due to the latex used in the gloves or medical equipment.

• Local anaesthetics

  Local anaesthetics, for example during dental surgery, are a rare cause of anaphylactic reactions.