McKenna's Pharmacology for Nursing, 2e

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P A R T 4  Drugs acting on the central and peripheral nervous systems

Presynaptic cell

Building blocks (from diet) become neurotransmitters

MAO inhibitors work here to prevent the breakdown of dopamine, noradrenaline and serotonin

TCAs work here to block the reuptake of serotonin and noradrenaline

Neurotransmitter

SSRIs work here to specifically block the reuptake of serotonin

Neurotransmitter release: may be noradrenaline, dopamine or serotonin

Varying block of reuptake of noradrenaline and/or serotonin

Ca+

Return to presynaptic cell

Ca+

Inactive product to blood vessel

COMT

bupropion desvenlafaxine mirtazapine reboxetine venlafaxine

Into blood vessel

Postsynaptic receptor

cAMP

FIGURE 21.1  Sites of action for the antidepressants: monoamine oxidase (MAO) inhibitors, tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and other agents, cAMP, cyclic adenosine monophosphate; COMT, catecholamine- O -methyltransferase.

Postsynaptic cell

Drug therapy across the lifespan

BOX 21.1

Antidepressant agents CHILDREN Use of antidepressant drugs with children poses a challenge.The response of the child to the drug may be unpredictable, and the long-term effects of many of these agents are not clearly understood. Studies have not shown efficacy in using these drugs to treat depression in children and also indicate that there may be an increase in suicidal ideation and suicidal behaviour when antidepressants are used to treat depression in children. Of the tricyclic drugs (TCAs), clomipramine, imipramine, nortriptyline and trimipramine have established paediatric doses in children older than 6 years. Children should be monitored closely for adverse effects, and dose changes should be made as needed. Monoamine oxidase (MAO) inhibitors should be avoided in children if at all possible because of the potential for drug–food interactions and the serious adverse effects. The selective serotonin reuptake inhibitors (SSRIs) can cause serious adverse effects in children. Fluvoxamine and sertraline have established paediatric dose guidelines for the treatment of obsessive–compulsive

disorders. Fluoxetine is widely used to treat depression in adolescents, and a 2000 survey of off-label uses of drugs showed that it was being used in children as young as 6 months. Dosage regimens must be established according to the child’s age and weight, and a child receiving an antidepressant should be monitored very carefully. Underlying medical reasons for the depression should be ruled out before antidepressant therapy is begun. Again, these children should be monitored for any suicidal ideation. ADULTS Adults using these drugs should have medical causes for their depression ruled out before therapy is begun. Thyroid disease, hormonal imbalance and cardiovascular disorders can all lead to the signs and symptoms of depression. The person needs to understand that the effects of drug therapy may not be seen for 4 weeks and that it is important to continue the therapy for at least that long. PREGNANCY AND BREASTFEEDING These drugs should be used very cautiously during pregnancy and breastfeeding because of the potential