McKenna's Pharmacology for Nursing, 2e

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

Contraindications and cautions These drugs are contraindicated with known allergy to any component of the drug. The sulfonamides are also contraindicated with known allergy to antibacterial sulfonamides and thiazide diuretics to avoid hypersen- sitivity reactions. When it is discontinued, zonisamide should be tapered over 2 weeks because of a risk of precip­ itating seizures. People who take this drug should be very well hydrated due to risk of renal calculi development. Caution should be used in people with hepatic or renal impairment, which could alter metabolism and excretion of the drug. These drugs should not be used during pregnancy or breastfeeding unless the benefit clearly outweighs the risk to the fetus or neonate because of the potential for serious adverse effects on the baby. Cross sensitivity between acetazolamide, sulfona­ mides and other sulphonamide derivatives is possible. Acetazolamide is contraindicated in individuals with marked liver disease or impairment of liver function, including cirrhosis, because of the risk of development of hepatic encephalopathy. Adverse effects Sodium valproate is associated with liver toxicity. All of these drugs cause CNS effects related to CNS suppression—weakness, fatigue, drowsiness, dizziness and paraesthesias. Acetazolamide and zonisamide may cause rash and dermatological changes. Zonisamide is associated with bone marrow suppression, renal calculi development and GI upset. Clinically important drug–drug interactions Acetazolamide increases the serum levels of quinidine, tricyclic antidepressants and amphetamines and may increase salicylate toxicity when given with salicylates. Sodium valproate can increase serum levels and potential toxicity of phenobarbitone, ethosuximide, diazepam, primidone and zidovudine. If any of these drugs are used in combination, the person should be monitored carefully and doses adjusted appropriately. Breakthrough seizures have been reported when sodium valproate is combined with phenytoin, and extreme care should be taken if this combination must be used. Zonisamide levels and toxicity are increased if it is combined with carbamazepine, and the person should be monitored and zonisamide dose reduced as needed.

acetazolamide, sodium valproate and zonisamide. See Chapter 20 for care considerations for people receiving barbiturates or benzodiazepines. Assessment: History and examination ■ ■ Assess for contraindications or cautions to the use of hydantoins, including known history of allergy to hydantoins to avoid hypersensitivity reactions ; cardiac arrhythmias, hypotension, diabetes, coma or psychoses, which could be exacerbated by the use of the drug ; history of renal or hepatic dysfunction that might interfere with drug metabolism or excretion ; and current status related to pregnancy and breastfeeding. ■ ■ Assess for contraindications or cautions to the use of succinimides, including any known allergies to these drugs; history of intermittent porphyria, which could be exacerbated by these drugs ; history of renal or hepatic dysfunction that might interfere with drug metabolism or excretion ; and current status related to pregnancy or breastfeeding. ■ ■ Obtain a description of seizures, including onset, aura, duration and recovery, to determine type of seizure and establish a baseline . baseline data for determining the effectiveness of therapy and the occurrence of any potential adverse effect. ■ ■ Inspect the skin for colour and lesions to determine evidence of possible skin effects ; assess pulse and blood pressure and auscultate heart to evaluate for possible cardiac effects ; assess level of orientation, affect, reflexes and bilateral grip strength to evaluate any CNS effects ; monitor bowel sounds and urine output to determine possible gastrointestinal or genitourinary effects ; and evaluate gums and mucous membranes to establish baseline and monitor changes associated with adverse effects. ■ ■ Perform a physical assessment to establish ■ ■ Obtain a baseline electroencephalogram if appropriate to evaluate brain function. ■ ■ Assess the person’s renal and liver function, including renal and liver function tests, to determine appropriateness of therapy and determine the need for possible dose adjustment. Refer to the Critical thinking scenario for a full discussion of care for a person who is being

prescribed antiepileptic drugs. Implementation with rationale

Care considerations for people receiving drugs for treating generalised seizures

■ ■ Discontinue the drug at any sign of hypersensitivity reaction, liver dysfunction or severe skin rash to limit reaction and prevent potentially serious reactions.

The information that follows primarily relates to drug therapy with hydantoins and succinimides,