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present in certain foods that are rich in protein and can interact with monoamine oxidase inhibitors (MAOIs). As procarbazine has mild MAOI properties, it is possible that taking both together could result in a hypertensive reaction which can cause symptoms of raised blood pressure, headache, pounding heart, neck stiffness, sweating, flushing and vomiting. Patients should therefore be advised to avoid tyramine-rich foods such as mature and aged cheeses, yeast or meat extracts, pickled fish, salami and heavy red wines (Baxter 2008).

Adverse drug reactions

Although we use drugs to diagnose, prevent or treat disease, no drug is administered without risk. However, it is important when choosing a drug treatment that consideration is given to the balance between clinical effect and undesired effects. The World Health Organization definition of adverse drug reactions (ADRs) is ‘harmful, unintended reactions to medicines that occur at doses normally used for treatment’ (WHO 2008). ADRs can be classified as type A or type B reactions. Type A reactions are pharmacologically predictable and usually dose dependent and therefore reversible by reducing or withdrawing the drug in question. An example of a type A reaction would be antidiabetic drugs causing hypoglycaemia. Type B reactions cannot be related to the pharmacological action of the drug, are not dose related and therefore cannot be controlled by dose reduction. An example of a type B reaction would be anaphylaxis due to penicillins. Type A reactions are more common than type B but type B reactions tend to cause a higher rate of serious illness and mortality (Rawlins and Thompson 1977).

The WHO states that ‘ADRs are amongst the leading causes of death in many countries and that in some countries ADR-related costs, such as hospitalization, surgery and lost productivity, exceed the cost of the medications’ (WHO 2008). One study found that the median percentage of preventable drug-related admissions to hospital was 3.7% (the range was between 1.4% and 15.4%). The majority (51%) of preventable drug-related admissions involved either antiplatelets (16%), diuretics (16%), non-steroidal anti-inflammatory drugs (11%) or anticoagulants (8%) (Howard et al. 2007).

Although the effect of a drug cannot always be predicted, it is important that when a drug is given to a patient, the risk of harm is minimized by ensuring that good-quality medicines are used and that they are safe and effective. Consideration should always be given to predisposing factors that drugs or a patient may have which could increase the risk of ADRs, including:

polypharmacy

age of the patient

gender

co-morbidities such as renal disease, race, genetic factors such as G6PD deficiency (some children and adults with G6PD deficiency may develop haemolysis and anaemia if they get a fever or if they take certain medicines (UCL Institute of Child Health 2008))

allergies

drug–drug interactions.

(Koda-Kimble et al. 2005, Walker and Edwards 2003)

Pharmacovigilance is an important aspect for all healthcare professionals to consider in order to identify information about potential new hazards related to medicines and prevent harm to patients (MHRA 2010a).

Although medicines are widely tested within clinical trials before they become commercially available, information on patient populations different from those in the trials cannot be provided. The only way for this information to be collected is through careful patient monitoring and further collection of data through postmarketing surveillance. In the UK this information is collected through the Yellow Card Scheme which is run by the MHRA and the Commission on Human Medicines (CHM). The scheme is used to collect information from both health professionals and patients on suspected ADR with prescribed medicines, OTC medicines and herbal medicines. Yellow Cards can be completed by using the MHRA website or by completing a hard copy found in the British National Formulary (BNF), the ABPI Medicines Compendium or in the MIMS Companion.

Allergic reactions

Allergic reactions