Clinical Pharmacology and Therapeutics

68 ADVERSE DRUG REACTIONS
EXAMPLES OF ALLERGIC AND OTHER
ADVERSE DRUG REACTIONS
Adverse drug reactions can be manifested in any one or multiple
organ systems, and in extraordinarily diverse forms.
Specific instances are dealt with throughout this book. Some
examples to illustrate the diversity of adverse drug reactions
are given here.
RASHES
These are one of the most common manifestations of drug
reactions. A number of immune and non-immune mechanisms
may be involved which produce many different types
of rash ranging from a mild maculopapular rash to a severe
erythema multiforme major (Stevens Johnson syndrome;
Figures 12.2 and 12.3). Commonly implicated drugs/drug
classes include beta-lactams, sulphonamides and other antimicrobial
agents; anti-seizure medications (e.g. phenytoin,
carbamazepine); NSAIDs. Some drugs may give rise to direct
tissue toxicity (e.g. DMPS, used as chelating therapy in patients
with heavy metal poisoning; Figure 12.4, see Chapter 54).
may be involved. The reaction may be confused with a lymphoma,
and the drug history is important in patients with lymphadenopathy
of unknown cause.
BLOOD DYSCRASIAS
Thrombocytopenia, anaemia (aplastic, iron deficiency, macrocytic,
haemolytic) and agranulocytosis can all be caused by
drugs.
Thrombocytopenia can occur with many drugs, and in
many but not all instances the mechanism is direct suppression
of the megakaryocytes rather than immune processes.
Drugs that cause thrombocytopenia include:
• heparin;
• gold salts;
• cytotoxic agents (e.g. azathioprine/6-mercaptopurine);
• quinidine;
• sulphonamides;
• thiazides.
Haemolytic anaemia can be caused by a number of
drugs, and sometimes immune mechanisms are responsible.
Glucose-6-phosphate dehydrogenase deficiency (Chapter 14)
LYMPHADENOPATHY
Lymph-node enlargement can result from taking drugs (e.g.
phenytoin). The mechanism is unknown, but allergic factors
Figure 12.3: Stevens Johnson syndrome following
commencement of penicillin therapy (see Chapter 43).
Figure 12.2: Mouth ulcer as part of Stevens Johnson syndrome as
a reaction to phenytoin therapy (see Chapter 22).
Figure 12.4: Mouth ulcer following DMPS treatment (see
Chapter 54).