McKenna's Pharmacology for Nursing, 2e

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

Therapeutic actions and indications The CNS stimulants act as cortical and RAS stimulants, possibly by increasing the release of catecholamines from presynaptic neurons, leading to an increase in stim- ulation of the postsynaptic neurons. The paradoxical effect of calming hyperexcitability through CNS stimu­ lation seen in attention-deficit syndrome is believed to be related to increased stimulation of an immature RAS, which leads to the ability to be more selective in response to incoming stimuli. The CNS stimulants are indicated, as part of a com- prehensive treatment program, for the treatment of attention-deficit syndromes, including behavioural syn- dromes characterised by hyperactivity and distractibility, as well as for narcolepsy and improvement of wakeful- ness in people with various sleep disorders. Pharmacokinetics These drugs are rapidly absorbed from the GI tract, reaching peak levels in 2 to 4 hours. They are metabo- lised in the liver and excreted in the urine, with half-lives ranging from 2 to 15 hours, depending on the drug. Safety for use during pregnancy and breastfeeding has not been established; during those periods, these drugs should be used only if the benefit to the mother clearly outweighs the potential risk to the fetus or neonate. Contraindications and cautions The CNS stimulants are contraindicated in the presence of known allergy to the drug, which could lead to hypersensitivity reactions . Other contraindications include the following conditions: marked anxiety, agi- tation or tension and severe fatigue or glaucoma, which could be exacerbated by the CNS stimulation caused by these drugs ; cardiac disease, which could be aggra- vated by the stimulatory effects of these drugs, making it important to rule out congenital heart problems ; and pregnancy and breastfeeding because of the potential for adverse effects on the fetus or neonate. Caution should be used in people with a history of seizures, which could be potentiated by the CNS stim- ulation ; in people with a history of drug dependence, including alcoholism, because these drugs may result in physical and psychological dependence ; and in people with hypertension, which could be exacerbated by the stimulatory effects of these drugs. Adverse effects The adverse effects associated with these drugs are related to the CNS stimulation they cause. CNS effects can include nervousness, insomnia, dizziness, headache, blurred vision and difficulty with accommodation. GI effects such as anorexia, nausea and weight loss may occur. CV effects can include hypertension, arrhythmias

and angina. Skin rashes are a common reaction to some of these drugs. Physical and psychological dependence may also develop. Because CNS stimulants have this effect, the drugs are controlled substances. Atomoxe- tine, which does not show dependence development, is not a controlled substance. The adverse effects asso- ciated with this drug are mainly anticholinergic (dry mouth, constipation, nausea, urinary hesitancy). Clinically important drug–drug interactions The combination of a CNS stimulant with a monoamine oxidase (MAO) inhibitor leads to an increased risk of adverse effects and increased toxicity and should be avoided if possible. In addition, the combination of CNS stimulants with tricyclic antidepressants or phenytoin leads to a risk of increased drug levels. People who receive such a combi- nation should be monitored for toxicity. Prototype summary: Methylphenidate Indications: Narcolepsy and attention-deficit disorder. Actions: Mild cortical stimulant with CNS actions similar to those of amphetamines. Pharmacokinetics: Route Onset Peak Duration Oral Varies 1–3 hours 4–6 hours T 1/2 : 1–3 hours; metabolised in the liver; excreted in the urine. Adverse effects: Nervousness, insomnia, increased or decreased pulse rate and blood pressure, tachycardia, loss of appetite, nausea, abdominal pain.

Care considerations for people receiving central nervous system stimulants

Assessment: History and examination

■ ■ Assess for contraindications or cautions for the use of the drug , including any known allergies to the drug; glaucoma, anxiety, tension, fatigue or seizure disorder; cardiac disease and hypertension; pregnancy or breastfeeding; a history of leukaemia; and a history of drug dependency, including alcoholism. ■ ■ Assess temperature; skin colour and lesions; CNS orientation, affect and reflexes; ophthalmic examination; bowel sounds and reported output; pulse, auscultation and blood pressure, including orthostatic blood pressure; respiration rate and adventitious sounds; and urinary output