McKenna's Pharmacology for Nursing, 2e

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P A R T 2  Chemotherapeutic agents

Praziquantel is taken in a series of three oral doses at 4- to 6-hour intervals. It is rapidly absorbed from the GI tract and reaches peak plasma levels within 1 to 3 hours. It is metabolised in the liver with a half-life of 0.8 to 1.5 hours. Excretion of praziquantel occurs primarily through the urine. Pyrantel is poorly absorbed, and most of the drug is excreted unchanged in the faeces, although a small amount may be found in the urine. Contraindications and cautions Overall contraindications to the use of anthelmintic drugs include the presence of known allergy to any of these drugs; breastfeeding because the drugs can enter breast milk and could be toxic to the infant —women are advised to refrain from breastfeeding when using these drugs; and pregnancy (in most cases) because of reported associated fetal abnormalities or death. Women of childbearing age should be advised to use barrier contraceptives while taking these drugs. Pyrantel has not been established as safe for use in children younger than 2 years. Albendazole should be used only after the causative worm has been identified because it can cause adverse effects on the liver, which could be problematic if the person has liver involvement. Use caution in the presence of renal or hepatic disease that interferes with the metabolism or excretion of drugs that are absorbed systemically and in cases of severe diarrhoea and malnourishment, which could alter the effects of the drug on the intestine and any pre-existing helminths. Adverse effects Adverse effects frequently encountered with the use of these anthelmintic agents are related to their absorp- tion or direct action in the intestine. Mebendazole and pyrantel, which are not absorbed systemically, may cause abdominal discomfort, diarrhoea or pain but have very few other effects and are well tolerated. Anthelmintics that are absorbed systemically may cause the following effects: headache and dizziness; fever, shaking, chills and malaise associated with an immune reaction to the death of the worms; rash; pruritus; and loss of hair. Renal failure and severe bone marrow depression are associated with albendazole, which is toxic to some human tissues. People taking this drug require careful monitoring. Clinically important drug–drug interactions The effects of albendazole, which are already severe, may increase if the drug is combined with dexameth- asone, praziquantel or cimetidine. These combinations should be avoided if at all possible; if they are necessary, people should be monitored closely for the occurrence of adverse effects.

Prototype summary: Mebendazole Indications: Treatment of whipworm, pinworm, roundworm and hookworm infections. Actions: Irreversibly blocks glucose uptake by susceptible helminths, depleting glycogen stores needed for survival and reproduction, causing the death of the helminth. Pharmacokinetics: Route Onset Peak Oral Slow 2–4 hours T 1/2 : 2.5 to 9 hours; metabolised in the liver and excreted in the faeces. Adverse effects: Transient abdominal pain, diarrhoea, fever. ■ ■ Assess for possible contraindications or cautions: history of allergy to any of the anthelmintics to avoid hypersensitivity reactions ; history of hepatic or renal dysfunction that might interfere with drug metabolism and excretion of the drug ; and current status related to pregnancy and breastfeeding, which are contraindications to the use of these drugs . ■ ■ Perform a physical assessment to establish baseline data for determining the effectiveness of the drug and the occurrence of any adverse effects associated with drug therapy . ■ ■ Obtain a culture of stool for ova and parasites to determine the infecting worm and establish appropriate treatment . ■ ■ Examine reflexes and muscle strength to evaluate changes that occur as a result of drug therapy . ■ ■ Evaluate liver function and renal function tests to determine appropriateness of therapy and to monitor for toxicity . ■ ■ Examine skin, including colour, temperature and texture, and note any lesions to assess for possible adverse effects. ■ ■ Assess the abdomen to evaluate for any changes from baseline related to the infection, identify possible adverse effects and monitor for improvement . Implementation with rationale ■ ■ Arrange for appropriate culture and sensitivity tests before beginning therapy to ensure identification Care considerations for people receiving anthelmintics Assessment: History and examination