McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 9  Antibiotics

MACROLIDES The macrolides (Table 9.9) are antibiotics that inter- fere with protein synthesis in susceptible bacteria. Macrolides include erythromycin ( Erythrocin , Eryc and others), azithromycin ( Zithromax ), clarithromycin ( Clarac, Kalixocin, Klacid ) and roxithromycin ( Rulide ). Therapeutic actions and indications The macrolides, which may be bactericidal or bacteriostatic, exert their effect by binding to the bac- terial cell membrane and changing protein function (see Figure 9.1). This action can prevent the cell from dividing or cause cell death, depending on the sensitivity of the bacteria and the concentration of the drug. Macrolides are indicated for treatment of the following conditions: acute infections caused by suscep- tible strains of S. pneumoniae , M. pneumoniae , Listeria monocytogenes and Legionella pneumophila ; infections caused by group A betahaemolytic streptococci; pelvic inflammatory disease caused by N. gonorrhoeae ; upper respiratory tract infections caused by H. influenzae (with sulfonamides); infections caused by Corynebacte- rium diphtheriae and Corynebacterium minutissimum (with antitoxin); intestinal amoebiasis; and infections caused by C. trachomatis. See Table 9.9 for usual indi- cations for each of these agents. In addition, macrolides may be used as prophylaxis for endocarditis before dental procedures in people with valvular heart disease who are allergic to penicil- lin. Topical macrolides are indicated for the treatment of ocular infections caused by susceptible organisms and for acne vulgaris, and they may also be used prophylactically against infection in minor skin abrasions and for the treat- ment of skin infections caused by sensitive organisms. Pharmacokinetics The macrolides are widely distributed throughout the body; they cross the placenta and enter the breast milk (see contraindications and cautions). These drugs are absorbed in the GI tract. Erythromycin is metabolised in the liver, with excretion mainly in the bile to faeces. The half-life of erythromycin is 1.6 hours. Azithromycin and clarithromycin are mainly excreted unchanged in the urine, making it necessary to monitor renal function when people are taking these drugs. The half-life of azithromycin is 68 hours, making it useful for people who have trouble remembering to take pills because it can be given once a day. The half- life of clarithromycin is 3 to 7 hours. Contraindications and cautions Macrolides are contraindicated in people with known allergy to any macrolide because cross-sensitivity

■ ■ Monitor injection sites regularly to provide warm compresses and gentle massage to injection sites if they are painful or swollen. If signs of phlebitis occur, remove the IV line and reinsert in a different vein. ■ ■ Initiate safety measures, including adequate lighting, side rails on the bed and assistance with ambulation to protect the person from injury if CNS effects occur. ■ ■ Instruct the person about the appropriate dosage schedule and about possible side effects to enhance knowledge about drug therapy and to promote compliance. –– Take safety precautions, including changing position slowly and avoiding driving and hazardous tasks, if CNS effects occur. –– Try to drink a lot of fluids and to maintain nutrition (very important) even though nausea, vomiting and diarrhoea may occur. –– Report difficulty breathing, severe headache, receiving cephalosporins and for at least 72 hours after completing the drug course because serious side effects could occur. Evaluation ■ ■ Monitor person’s response to the drug (resolution of bacterial infection). ■ ■ Monitor for adverse effects (orientation and affect; renal toxicity; hepatic dysfunction; GI effects; and local irritation, including phlebitis at injection and IV sites). ■ ■ Evaluate effectiveness of the teaching plan (person can name drug, dosage, possible adverse effects to expect and specific measures to help avoid adverse effects). ■ ■ Monitor effectiveness of comfort and safety measures and the person’s compliance with the regimen. ■ ■ Provide the following teaching: severe diarrhoea, dizziness or weakness. –– Avoid consuming alcoholic beverages while

KEY POINTS

KEY POINTS

■■ Cephalosporins are a large group of antibiotics, similar to penicillin, that are effective against a wide range of bacteria. ■■ Monitor for GI upsets and diarrhoea, pseudomembranous colitis, headache, dizziness and superinfections.