Drugs and other physical treatments

Abstract

This chapter is about the use of drugs and electroconvul­sive therapy (ECT). Stimulants for ADHD are covered in Chapter 32, and psychological treatments in Chapter 14. This is a convenient way of dividing the subject matter of a book, but in practice these physical treatments should always be combined with psychological treatment, unless the patient chooses not to undertake this. The account in this chapter is concerned with prac­tical therapeutics rather than basic pharmacology, and it will be assumed that the reader has studied the basic pharmacology of the principal types of drug used in psychiatric disorders (readers who do not have this knowledge should consult a textbook, see, for example, ‘Further reading’). Nevertheless, a few important points about the actions of psychotropic drugs will be con­sidered, before describing the specific groups of drugs (see Science box 13.1). To be effective, psychotropic drugs must reach the brain in adequate amounts. How far they do this depends on their absorption, metabolism, excretion, and passage across the blood– brain barrier. Most psychotropic drugs are absorbed readily from the gut, but absorption can be reduced by intestinal hurry or a malabsorption syndrome. Absorption can be slowed down by use of enteric coatings on capsules, should the clinician wish for a drug to be delivered over a longer period of time. Most psychotropic drugs are metabolized partially in the liver on their way from the intestine via the portal system to the systemic circulation. The amount of this so- called first- pass metabolism differs from one person to another, and it is altered by certain drugs, taken at the same time, which induce liver enzymes (e.g. carbamazepine) or inhibit them (e.g. MAOIs). Although first- pass metabolism reduces the amount of the original drug reaching the brain, the metabolites of some drugs have their own therapeutic effects. As many psychotropic drugs have active metabolites, the measurement of plasma concentrations of the parent drug is generally a poor guide to treatment.