McKenna's Pharmacology, 2e

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C H A P T E R 3  Toxic effects of drugs

numbness and tingling, slow heart rate, low blood pressure, decreased urine output and difficulty breathing. Interventions Institute measures to decrease the serum potassium concentration, including use of sodium polystyrene sul­ fonate. When trying to stabilise the potassium level, it is possible that the person may experience low potassium levels. Careful monitoring is important until the person’s potassium levels are stable. Offer supportive measures to cope with discomfort. Institute safety measures to prevent injury or falls. Monitor for cardiac irregulari­ ties because potassium is an important electrolyte in the action potential, which is needed for cell membrane sta­ bility. When potassium levels are too high, the cells of the heart become very irritable and rhythm disturbances can occur. Be prepared for a possible cardiac emergency. In severe cases, be aware that dialysis may be needed. Sensory effects Drugs can affect the senses, including the eyes and ears. Alterations in seeing and hearing can pose safety problems for people. Ocular damage The blood vessels in the retina are very tiny and are called “end arteries”, that is, they stop and do not inter­ connect with other arteries feeding the same cells. Some drugs are deposited into these tiny arteries, causing inflammation and tissue damage. Hydroxychloroquine ( Plaquenil ), a drug used to treat some rheumatoid diseases, can cause retinal damage and even blindness. Assessment Blurring of vision, vision changes, corneal damage and blindness may be noted. Interventions Monitor the person’s vision carefully when they are receiving known oculotoxic drugs. Consult with the prescriber and/or primary caregiver and discontinue the drug as appropriate. Provide supportive measures, espe­ cially if vision loss is not reversible. Monitor lighting and exposure to sunlight. Auditory damage (ototoxicity) Tiny vessels and nerves in the eighth cranial nerve are easily affected and damaged by certain drugs. The macrolide antibiotics can cause severe auditory nerve damage. Aspirin, one of the most commonly used drugs, is often linked to auditory ringing and eighth cranial nerve effects. Assessment Dizziness, ringing in the ears (tinnitus), loss of balance and loss of hearing may be assessed.

Provide support to help the person deal with signs and symptoms (e.g. provide access to bathroom facilities, control the temperature of the room, decrease stimu­ lation while the person is in crisis, offer reassurance, provide mouth care—the person will experience dry mouth and bad breath with the ensuing acidosis and mouth care will help to make this more tolerable). Electrolyte imbalances Drugs can have an effect on various electrolyte levels in the body. These effects can have serious consequences as many physiological functions are intricately depend­ ent on certain electrolyte levels. The electrolyte that can cause the most serious effects when it is altered, even a little, is potassium. Hypokalaemia Some drugs affecting the kidney can cause low serum potassium levels (hypokalaemia) by altering the renal exchange system. For example, loop diuretics function by causing the loss of potassium, as well as of sodium and water. Potassium is essential for the normal func­ tioning of nerves and muscles. Assessment Symptoms include a serum potassium concentration ([K + ]) lower than 3.5 mmol/L, weakness, numbness and tingling in the extremities, muscle cramps, nausea, vomiting, diarrhoea, decreased bowel sounds, irregular pulse, weak pulse, orthostatic hypotension and dis­ orientation. In severe cases, paralytic ileus (absent bowel sounds, abdominal distension and acute abdomen) may occur. Interventions Replace serum potassium and carefully monitor serum levels and the person’s response; achieving the desired level can take time and the person may experience high potassium levels in the process. Provide supportive therapy (e.g. safety precautions to prevent injury or falls, reorientation of the person, comfort measures for pain and discomfort). Cardiac monitoring may be needed to evaluate the effect of the fluctuating potassium levels on Some drugs that affect the kidney, such as the potassium-sparing diuretics, can lead to potassium retention and a resultant increase in serum potassium levels (hyperkalaemia). Other drugs that cause cell death or injury, such as many antineoplastic agents, can also cause the cells to release potassium, leading to hyperkalaemia. Assessment Symptoms include a serum potassium level higher than 5.0 mEq/L, weakness, muscle cramps, diarrhoea, heart rhythm. Hyperkalaemia