Although not often tested in depth, a knowledge of the terminology used to describe adverse drug reactions is useful. True anaphylactic and anaphylactoid reactions clearly require a more detailed knowledge. The official World Health Organization (WHO) definition of an adverse drug reaction is lengthy and unlikely to be tested. A more succinct definition is used in relation to anaesthesia.

Adverse drug reaction

The occurrence of any drug effect that is not of therapeutic, diagnostic or prophylactic benefit to the patient.

Types of adverse reactions

The WHO definition encompasses six groups, which need not be memorized but which are included for completeness.

1. Group 1 Dose-related reactions

2. Group 2 Non-dose-related reactions

3. Group 3 Dose- and time-related reactions

4. Group 4 Time-related reactions

5. Group 5 Withdrawal reactions

6. Group 6 Treatment failure.

The reactions can be more simply defined as one of two types:

Type A

• dose dependent

• common

• extension of known pharmacological effect.

Type B

• dose independent

• uncommon

• symptoms and signs of drug allergy.

The most important type to the anaesthetist is type B, which encompasses both anaphylactic and anaphylactoid reactions.

Anaphylactic reaction

A response to a substance to which an individual has been previously sensitized via the formation of a specific IgE antibody. It is characterized by the release of vasoactive substances and the presence of systemic symptoms.

Anaphylactoid reactions

A response to a substance that is not mediated by a specific IgE antibody but is characterized by the same release of vasoactive substances and presence of systemic symptoms as an anaphylactic reaction.