McKenna's Pharmacology for Nursing, 2e

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

TABLE 21.1

DRUGS IN FOCUS Tricyclic antidepressants (continued)

Common side effects

Sedation

Anticholinergic Hypotension Cardiovascular

Drug name

Usual dosage

Amines (continued) doxepin (Deptran, Sinequan)

+++

+++

++

++

10–100 mg PO b.d. Adult: 50–200 mg/day PO Paediatric (5–8 years): 20–30 mg/day Paediatric (>12 years): 25–75 mg/day Maximum 2.5 mg/kg/day

++

++

+++

++

imipramine (Tofranil)

trimipramine (Surmontil)

+++

++

++

++

Adult:

75–150 mg/day PO

Paediatric:

50 mg/day PO

Geriatric:

50–100 mg/day PO

Secondary amines nortriptyline (Allegron)

+

+

+

+

Adult: 25–50 mg PO t.d.s. (Allegron) to q.i.d. Geriatric: 30–50 mg/day PO in divided doses

+ + + +, marked effects; + + +, moderate effects; + +, mild effects; +, negligible effects.

accumulation of these neurotransmitters in the synaptic cleft and increased stimulation of the postsynaptic receptors. The exact mechanism of action in decreasing depression is not known but is thought to be related to the accumulation of noradrenaline and 5HT in certain areas of the brain. TCAs are indicated for the relief of symptoms of depression. The sedative effects of these drugs may make them more effective in people whose depression is characterised by anxiety and sleep disturbances. They are effective for treating enuresis in children older than 6 years (see Box 21.1). Some of these drugs are being investigated for the treatment of chronic, intractable pain. In addition, the TCAs are anticholinergic. Clomi­ pramine is now also approved for use in the treatment of obsessive–compulsive disorders (OCDs). Pharmacokinetics The TCAs are well absorbed from the gastrointestinal (GI) tract, reaching peak levels in 2 to 4 hours. They are highly bound to plasma proteins and are lipid soluble; this allows them to be distributed widely in the tissues,

including the brain. TCAs are metabolised in the liver and excreted in the urine, with relatively long half- lives, ranging from 8 to 46 hours. The TCAs cross the placenta and enter breast milk (see Contraindications and cautions). Contraindications and cautions One contraindication to the use of TCAs is the presence of allergy to any of the drugs in this class because of the risk of hypersensitivity reactions . Other contrain­ dications include recent myocardial infarction because of the potential occurrence of reinfarction or extension of the infarct with the cardiac effects of the drug ; mye­ lography within the previous 24 hours or in the next 48 hours because of a possible drug–drug interaction with the dyes used in these studies ; and concurrent use of an MAO inhibitor because of the potential for serious adverse effects or toxic reactions. In addition, pregnancy and breastfeeding are contraindications because of the potential for adverse effects in the fetus and neonate ; TCAs should not be used unless the benefit to the mother clearly outweighs the potential risk to the neonate.