Antimicrobial Drugs

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M34_ADAM9811_03_SE_CH34.QXD 12/30/09 1:16 PM Page 489 Chapter 34 <strong>Drugs</strong> for Bacterial Infections 489 tetracyclines should not be taken with milk or iron supplements. Calcium and iron can decrease the drug’s absorption by as much as 50%. Direct exposure to sunlight can result in severe photosensitivity during therapy. Unless suffering from a life-threatening infection, patients younger than 8 years of age are not given tetracyclines because these drugs may cause permanent yellow-brown discoloration of the permanent teeth in young children. Tetracyclines also affect fetal bone growth and teeth development and are pregnancy category D agents; therefore, they should be avoided during pregnancy. Because of the drugs’ broad spectrum, the risk for superinfection is relatively high and the nurse should be observant for signs of a secondary infection. When administered parenterally or in high doses, certain tetracyclines can cause hepatotoxicity, especially in patients with preexisting liver disease. Because outdated tetracycline may deteriorate and become nephrotoxic, unused prescriptions should be discarded promptly. The newest of the tetracyclines is tigecycline (Tygacil), approved in 2005. Tigecycline is indicated for drug-resistant intra-abdominal infections and complicated skin and skinstructure infections, especially those caused by MRSA. Nausea and vomiting may be severe with this drug. Tigecycline is available by IV infusion. See Nursing Process Focus: Patients Receiving Antibacterial Therapy on page 496 for the Nursing Process applied to all antibacterials. Macrolides Erythromycin (E-mycin, Erythrocin), the first macrolide antibiotic, was isolated from Streptomyces in a soil sample in 1952. Macrolides are considered safe alternatives to penicillin, although they are drugs of choice for relatively few infections. AVOIDING MEDICATION ERRORS Mr. Johnson is admitted for a severe upper respiratory infection and dehydration. During the nurse’s initial assessment, Mr. Johnson is questioned about allergies and reports being allergic to peanuts, aspirin, sulfa, and ragweed. Following a history and physical examination,the primary care physician orders trimethoprim–sulfamethoxazole (Bactrim) DS. When the medication arrives from the pharmacy, it is in a unit-dose package. It is a large tablet containing 160 mg of trimethoprim and 800 mg of sulfamethoxazole.The nurse breaks the tablet in half, for easier swallowing, and gives Mr. Johnson his first dose with a large glass of water.What should the nurse have done differently? See Appendix D for the suggested answer. 34.11 Pharmacotherapy with Macrolides The macrolides inhibit protein synthesis by binding to the bacterial ribosome. At low doses, this inhibition produces a bacteriostatic effect. At higher doses, and in susceptible species, macrolides may be bacteriocidal. Macrolides are effective against most gram-positive bacteria and many gramnegative species. Common indications include the treatment of whooping cough, Legionnaires’ disease, and infections by streptococcus, H. influenza, and Mycoplasma pneumoniae. <strong>Drugs</strong> in this class are used against bacteria residing inside host cells, such as Listeria, Chlamydia, Neisseria, and Legionella. Clarithromycin is one of several antibiotics used to treat peptic ulcer disease, due to its activity against H. pylori (chapter 40 ). The macrolides are listed in Table 34.5. The newer macrolides are synthesized from erythromycin. Although their spectrums of activity are similar, these drugs have longer half-lives and cause less gastric irritation than erythromycin. For example, azithromycin (Zithromax, Z-Pak) has such an extended half-life that it is administered for only 5 days, rather than the 10 days required for most antibiotics. The shorter duration of therapy is thought to increase patient adherence. The macrolides exhibit few serious adverse effects. Mild GI upset, diarrhea, and abdominal pain are the most frequent adverse effects. Because macrolides are broad-spectrum agents, superinfections may occur. Like most of the older antibiotics, macrolide-resistant strains are becoming more common. Other than prior allergic reactions to macrolides, there are no contraindications to therapy. See Nursing Process Focus: Patients Receiving Antibacterial Therapy on page 496 for the Nursing Process applied to all antibacterials. Aminoglycosides The first aminoglycoside, streptomycin, was named after Streptomyces griseus, the soil organism from which it was isolated in 1942. Although more toxic than other antibiotic classes, aminoglycosides have important therapeutic applications for the treatment of aerobic gram-negative bacteria, mycobacteria, and some protozoans. The aminoglycosides are listed in Table 34.6. TABLE 34. 5 Macrolides Drug Route and Adult Dose (max dose where indicated) Adverse Effects azithromycin (Zithromax, Z-Pak) PO; 500 mg for one dose, then 250 mg/day for 4 days Nausea, vomiting, diarrhea, abdominal cramping, dry skin clarithromycin (Biaxin) PO; 250–500 mg bid or burning (topical route) dirithromycin (Dynabac) PO; 500 mg/day Anaphylaxis, ototoxicity, pseudomembranous colitis, hepatotoxicity, superinfections, dysrhythmias erythromycin (E-Mycin, Erythrocin) PO; 250–500 mg bid or 333 mg tid # 102887 Cust: PE/NJ/CHET Au: ADAMS Pg. No. 489 Title: Pharmacology for Nurses Server: Jobs2 C/M/Y/K Short / Normal DESIGN SERVICES OF S4CARLISLE Publishing Services
M34_ADAM9811_03_SE_CH34.QXD 12/30/09 1:16 PM Page 490 490 Unit 5 The Immune System Prototype Drug Therapeutic Class: Antibacterial ❘ Erythromycin (E-Mycin, Erythrocin) Pharmacologic Class: Macrolide; protein synthesis inhibitor ACTIONS AND USES ADVERSE EFFECTS Erythromycin is inactivated by stomach acid and is thus formulated as coated, acid-resistant tablets or capsules that dissolve in the small intestine.Its main application is for patients who are unable to tolerate penicillins or who may have a penicillin-resistant infection.It has a spectrum similar to that of the penicillins and is effective against most gram-positive bacteria. It is often a preferred drug for infections by Bordetella pertussis (whooping cough) and Corynebacterium diphtheriae. ADMINISTRATION ALERTS ■ Administer oral drug on an empty stomach with a full glass of water. ■ For suspensions,shake the bottle thoroughly to ensure the drug is well mixed. ■ Do not give with or immediately before or after fruit juices. ■ Pregnancy category B PHARMACOKINETICS Onset: 1 h Peak: 1–4 h Half-life: 1.5–2 h Duration: Unknown The most frequent adverse effects from erythromycin are nausea, abdominal cramping, and vomiting, although these are rarely serious enough to cause discontinuation of therapy. Concurrent administration with food reduces these symptoms.The most severe adverse effect is hepatotoxicity caused by the estolate salt (Ilosone) of the drug. Hearing loss, vertigo, and dizziness may be experienced when using high doses, particularly in older adults and in those with impaired hepatic or renal excretion. Contraindications: Erythromycin is contraindicated in patients with hypersensitivity to drugs in the macrolide class, and for those taking terfenadine, astemizole, or cisapride. INTERACTIONS Drug–Drug: Anesthetics, azole antifungals and anticonvulsants may interact to cause serum drug levels of erythromycin to rise and result in toxicity.This drug interacts with cyclosporine, increasing the risk for nephrotoxicity. It may increase the effects of warfarin.The concurrent use of erythromycin with lovastatin or simvastatin is not recommended because it may increase the risk of muscle toxicity. Ethanol use may decrease the absorption of erythromycin. Lab Tests: Erythromycin may interfere with AST and give false urinary catecholamine values. Herbal/Food: St. John’s wort may decrease the effectiveness of erythromycin. Treatment of Overdose: There is no specific treatment for overdose. Refer to MyNursingKit for a Nursing Process Focus specific to this drug. TABLE 34. 6 Aminoglycosides Drug Route and Adult Dose (max dose where indicated) Adverse Effects amikacin (Amikin) IM; 5.0–7.5 mg/kg as a loading dose, then 7.5 mg/kg bid Pain or inflammation at injection site, rash, fever, nausea, gentamicin (Garamycin, others) IM; 1.5–2.0 mg/kg as a loading dose, then 1–2 mg/kg bid–tid diarrhea, dizziness, tinnitus kanamycin (Kantrex) IM; 5.0–7.5 mg/kg bid–tid Anaphylaxis, nephrotoxicity, irreversible ototoxicity, superinfections neomycin PO; 4–12 g/day in divided doses paromomycin (Humatin) PO; 7.5–12.5 mg/kg in three doses streptomycin IM; 15 mg/kg up to 1 g as a single dose tobramycin (Nebcin) IM/IM; 1 mg/kg tid (max: 5 mg/kg/day) Italics indicate common adverse effects; underlining indicates serious adverse effects. 34.12 Pharmacotherapy with Aminoglycosides Aminoglycosides are bacteriocidal and act by inhibiting bacterial protein synthesis. They are normally reserved for serious systemic infections caused by aerobic gram-negative organisms, including those caused by E. coli, Serratia, Proteus, Klebsiella, and Pseudomonas. They are sometimes administered concurrently with a penicillin, cephalosporin, or vancomycin for treatment of enterococcal infections. When used for systemic bacterial infections, aminoglycosides are given parenterally because they are poorly absorbed from the GI tract. They are occasionally given orally for their local effect on the GI tract to sterilize the bowel prior to intestinal surgery. Neomycin is available for topical infections of the skin, eyes, and ears. Paromomycin (Humatin) is given orally for the treatment of parasitic infections. Once widely used, streptomycin is now usually restricted to the treatment of tuberculosis because of the emergence of a large number of strains resistant to the antibiotic. The nurse should note the differences in spelling of some drugs—such as -mycin versus -micin—which reflect the different organisms from which the drugs were originally isolated. # 102887 Cust: PE/NJ/CHET Au: ADAMS Pg. No. 490 Title: Pharmacology for Nurses Server: Jobs2 C/M/Y/K Short / Normal DESIGN SERVICES OF S4CARLISLE Publishing Services
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Antimicrobial Drugs

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