McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 5 1 Diuretic agents

■■ TABLE 51.2 Comparison of diuretics Diuretic class

Major site of action Usual indications

Major adverse effects

Thiazide,

Distal

Oedema of HF, liver and renal disease Adjunct for hypertension Acute HF Acute pulmonary oedema Hypertension Oedema of HF, renal and liver disease

GI upset, CNS complications, hypovolaemia

thiazide-like

convoluted tubule

Loop

Loop of Henle

Hypokalaemia, volume depletion, hypotension, CNS effects, GI upset, hyperglycaemia

Carbonic

Proximal tubule Glaucoma

GI upset, urinary frequency

anhydrase inhibitors

Diuresis in HF Mountain sickness Epilepsy

Potassium- sparing

Distal tubule and collecting duct

Adjunct for oedema of HF, liver and renal disease Treatment of hypokalaemia Adjunct for hypertension Hyperaldosteronism Reduction of intracranial pressure Prevention of oliguric phase of renal failure Reduction of intraocular pressure Renal clearance of toxic substances

Hyperkalaemia, CNS effects, diarrhoea

Osmotic

Glomerulus, tubule

Hypotension, GI upset, fluid and electrolyte imbalances

combination is used, the drugs should be taken sepa- rated by at least 2 hours. The risk of digoxin toxicity increases due to potential changes in potassium levels; serum potassium should be monitored if this combination is used. Risk of quinidine toxicity increases due to decreased quinidine excretion with an alkaline urine, leading to increased serum levels of quinidine. If this combination is used, the person must be monitored closely and quinidine dose decreased as appropriate. Decreased effectiveness of agents to control elevated blood glucose levels may occur related to the changes in glucose metabolism; dose adjustment of those agents may be needed. The risk of lithium toxicity may increase if these drugs are combined. Serum lithium levels should be monitored and appropriate dose adjustment made as needed. L oop diuretics Loop diuretics are so named because they work in the loop of Henle. Loop diuretics are also referred to as high-ceiling diuretics because they cause a greater degree of diuresis than other diuretics do. Three loop diuretics are available: ethacrynic acid ( Edecrin [not available in New Zealand]) the first loop diuretic intro- duced; bumetanide ( Burinex ); and frusemide ( Lasix ), the most commonly used loop diuretic. Therapeutic actions and indications Loop diuretics block the chloride pump in the ascend- ing loop of Henle, where normally 30% of all filtered

the potential for adverse effects on fluid and electrolyte changes in the baby . Adverse effects The most common adverse effects associated with diuretic agents include GI upset, fluid and electrolyte imbalances, hypotension and electrolyte disturbances. Adverse effects associated with the use of thiazide and thiazide-like diuretics are related to interference with the normal regulatory mechanisms of the nephron. Potas- sium is lost at the distal tubule because of the actions on the pumping mechanism, and hypokalaemia (low blood levels of potassium) may result. Signs and symptoms of hypokalaemia include weakness, muscle cramps and arrhythmias. Another adverse effect is decreased calcium excretion, which leads to increased calcium levels in the blood. Uric acid excretion is also decreased because the thiazides interfere with its secretory mechanism. High levels of uric acid can result in gout. If these drugs are used over a prolonged period, blood glucose levels may increase. This may result from the change in potassium levels (which keeps glucose out of the cells), or it may relate to some other mechanism of glucose control. Urine is slightly alkalinised when the thiazides or thiazide-like diuretics are used because they block the reabsorption of bicarbonate. This effect can cause problems for individuals who are susceptible to bladder infections. Clinically important drug–drug interactions Decreased absorption of these drugs may occur if they are combined with cholestyramine or colestipol. If this