McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 5 1 Diuretic agents

Drug therapy across the lifespan (continued)

BOX 51.1

People taking potassium-losing diuretics should be encouraged to eat foods that are high in potassium and to have their serum potassium levels checked periodically. People taking potassium-sparing diuretics should be

and thiazide-like diuretics are among the most fre- quently used diuretics. Therapeutic actions and indications Thiazide and thiazide-like diuretics act to block the chloride pump. Chloride is actively pumped out of the tubule by cells lining the ascending limb of the loop of Henle and the distal tubule. Sodium passively moves with the chloride to maintain electrical neutrality. (Chloride is a negative ion, and sodium is a positive ion.) Blocking of the chloride pump keeps the chloride and the sodium in the tubule to be excreted in the urine, thus preventing the reabsorption of both chloride and sodium in the vascular system (see Figure 51.1). Because OLDER ADULTS Older adults often have conditions that are treated with diuretics.They are also more likely to have renal or hepatic impairment, which requires cautious use of these drugs. Older adults should be started on the lowest possible dose of the drug and the dose should be titrated slowly based on individual response. Frequent serum electrolyte measurements should be done to monitor for adverse reactions. The intake and activity level of the person can alter the effectiveness and need for the diuretic. High-salt diets and inactivity can aggravate conditions that lead to oedema, and people should be encouraged to follow activity and dietary guidelines if possible. Prototype summary: Hydrochlorothiazide Indications: Adjunctive therapy for oedema associated with HF, cirrhosis, corticosteroid or oestrogen therapy, and renal dysfunction; treatment of hypertension as monotherapy or in combination with other antihypertensives. Actions: Inhibits reabsorption of sodium and chloride in distal renal tubules, increasing the excretion of sodium, chloride and water by the kidneys. Pharmacokinetics: Route Onset Peak Duration Oral 2 hours 4–6 hours 6–12 hours T 1/2 : 5.6–14 hours; metabolised in the liver and excreted in urine. Adverse effects: Dizziness, vertigo, orthostatic hypotension, nausea, anorexia, vomiting, dry mouth, diarrhoea, polyuria, nocturia, muscle cramps or spasms.

cautioned to avoid those same foods. PREGNANCY AND BREASTFEEDING

The use of diuretics to change the fluid shifts associated with pregnancy is not appropriate. Women maintained on these drugs for underlying medical reasons should not stop taking them, but they need to be aware of the potential for adverse effects on the fetus. Breastfeeding women who need a diuretic should find another method of feeding the baby because of the potential for adverse effects on the baby as well as the breastfeeding mother.

Safe medication administration

T hiazide and thiazide - like diuretics The thiazide diuretics belong to a chemical class of drugs called the sulfonamides. Thiazide-like diuretics have a slightly different chemical structure but work in the same way as thiazide diuretics. Thiazide diuretics include hydrochlorothiazide ( Dithiazide ). Thiazide-like diuretics include chlorthali- done ( Hygroton ) and indapamide ( Dapa-Tabs ). Thiazide Explaining fluid rebound Care must be taken when using diuretics to avoid fluid rebound , which is associated with fluid loss. If a person stops taking in water and takes the diuretic, the result will be concentrated plasma of smaller volume. The decreased volume is sensed by the nephrons, which activate the renin– angiotensin cycle. When the concentrated blood is sensed by the osmotic centre in the brain, antidiuretic hormone (ADH) is released to hold water and dilute the blood. The result can be a “rebound” oedema as fluid is retained. Many people who are taking a diuretic markedly decrease their fluid intake so as to decrease the number of trips to the bathroom. The result is a rebound of water retention after the diuretic effect. This effect can also be seen in many diets that promise “immediate results”; they frequently contain a key provision to increase fluid intake to 8 to 10 full glasses of water daily. The reflex result of diluting the system with so much water is a drop in ADH release and fluid loss. Some people can lose 2–3 kg in a few days by doing this. However, the body’s reflexes are quickly activated, causing rebound retention of fluid to re-establish fluid and electrolyte balance. People can become frustrated at this point and give up the fad diet. It is important to be able to explain this effect. Teaching people about balancing the desired diuretic effect with the actions of the normal reflexes is a clinical skill.