Chapter 21

### Introduction

A custome loathsome to the eye, hateful to the nose, harmeful to the braine, dangerous to the lungs and the blacke stinking fume thereof, neerest resembling the horrible Stigian smoke of the bottomless pit.

James I (1566–1625), On Smoking

Ecstasy: a drug so strong it makes white people think that they can dance.

Lenny Henry (1958–)

If you want to keep a dead man, put him in whisky; if you want to kill a live man put whisky in him.

Thomas Guthrie (1803–73)

Drug-related problems are true masquerades in family practice. This includes prescribed drugs, over-the-counter drugs and social or illegal street drugs. It is important therefore that all prescribing doctors maintain a high index of suspicion that any clinical problem may be associated with their treatment of the patient.

An adverse drug effect is defined as ‘any unwanted effect of treatment from the medical use of drugs that occurs at a usual therapeutic dose’. Almost every drug can cause an adverse reaction, which must be elicited in the history. Any substance that produces beneficial therapeutic effects may also produce unwanted, adverse or toxic effects. The severity of the reaction may range from a mild skin rash or nausea to sudden death from anaphylaxis. A study has shown that the incidence of adverse reactions increases from about 3% in patients 10–20 years of age to about 20% in patients 80–89 years of age.1

Reactions can be classified in several ways—side effects, overdosage, intolerance, hypersensitivity and idiosyncrasy. However, a useful classification of unwanted effects is divided into type A and type B.

Type A reactions are the most common and involve augmented pharmacology; that is, they are caused by unwanted, albeit predictable, effects of the drug. Examples include:

• constipation due to verapamil

• blurred vision and urinary outflow problems due to tricyclic antidepressants

• hyperuricaemia due to thiazide diuretics

Type A reactions are dose-dependent.

Type B reactions are by definition bizarre. The reactions are unpredictable from known properties of the drug. Examples include hepatotoxicity and blood dyscrasias.

#### Golden rules for prevention of adverse effects

Before prescribing any drug the prescriber should consider the following rules:

1. Is the drug really necessary?

2. What will happen if it is not used?

3. What good do I hope to achieve?

4. What harm may result from this treatment?

There is an extensive list of clinical problems caused by drugs as side effects or interactions that are highlighted throughout this book. Common side effects include:

• CNS—malaise, drowsiness, fatigue/tiredness, headache, dizziness

• CVS—palpitations, peripheral oedema, hypotension

• GIT—nausea, vomiting, dyspepsia, change in bowel habit (diarrhoea, constipation)

• skin—rash, pruritus, flushing

• psychiatric/emotional—insomnia, ...

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