Antimicrobial Drugs

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M34_ADAM9811_03_SE_CH34.QXD 12/30/09 1:16 PM Page 483 Chapter 34 <strong>Drugs</strong> for Bacterial Infections 483 which occur when microorganisms normally present in the body are destroyed. These normal microorganisms, or host flora, inhabit the skin and the upper respiratory, genitourinary, and intestinal tracts. Some of these organisms serve a useful purpose by producing antibacterial substances and by competing with pathogenic organisms for space and nutrients. Removal of host flora by an antibiotic gives the remaining microorganisms an opportunity to grow, allowing for overgrowth of pathogenic microbes. Host flora themselves can cause disease if allowed to proliferate without control, or if they establish colonies in abnormal locations. For example E. coli is part of the host flora in the colon but can become a serious pathogen if it enters the urinary tract. Host flora may also become pathogenic if the patient’s immune system becomes suppressed. Microbes that become pathogenic when the immune system is suppressed are called opportunistic organisms.Viruses such as the herpes virus, and fungi are examples of opportunistic organisms that exist on the human body but may become pathogenic if normal flora are suppressed. Superinfection should be suspected if a new infection appears while the patient is receiving anti-infective therapy. Signs and symptoms of a superinfection commonly include diarrhea, bladder pain, painful urination, or abnormal vaginal discharges. Broad-spectrum antibiotics are more likely to cause superinfections because they kill so many different species of microorganisms. 34.7 Host Factors The most important factor in selecting an appropriate antibiotic is to be certain that the microbe is sensitive to the effects of the drug. However, the nurse must also take into account certain host factors that can influence the success of antibacterial chemotherapy. The primary goal of antibiotic therapy is to kill enough bacteria, or to slow the growth of the infection, so that natural body defenses can overcome the invading agent. Unless an infection is highly localized, the antibiotic alone may not be enough: The patient’s immune system and phagocytic cells will be needed to completely rid the body of the infectious agent. Patients with suppressed immune systems may require aggressive antibiotic therapy with bacteriocidal agents. These patients include those with AIDS and those being treated with immunosuppressive or antineoplastic drugs. Because therapy is more successful when the number of microbes is small, antibiotics may be given on a prophylactic basis to patients whose white blood cell (WBC) count is extremely low. Local conditions at the infection site should be considered when selecting an antibiotic because factors that hinder the drug from reaching microbes will limit therapeutic success. Infections of the central nervous system are particularly difficult to treat because many drugs cannot cross the blood–brain barrier. Injury or inflammation can cause tissues to become acidic or anaerobic and to have poor circulation. Excessive pus formation or hematomas can block drugs from reaching their targets. Although most bacteria are extracellular in nature, pathogens such as Mycobacterium tuberculosis, salmonella, toxoplasma, and listeria may reside intracellularly and thus be difficult for anti-infectives to reach in high concentrations. Consideration of these factors may necessitate a change in the route of drug administration or the selection of a more effective antibiotic specific for the local conditions. Severe allergic reactions to antibiotics, while not common, may be fatal. The nurse’s initial patient assessment must include a thorough drug history and a description of any reactions to those drugs. A previous acute allergic incident is highly predictive of future hypersensitivity. If severe allergy to an anti-infective is established, it is best to avoid all drugs in the same chemical class. Because the patient may have been exposed to an antibiotic unknowingly, through food products or molds, allergic reactions can occur without previous incident. Penicillins are the class of antibacterials having the highest incidence of allergic reactions; between 0.7% and 4% of all patients who receive them exhibit some degree of hypersensitivity. Other host factors to be considered are age, pregnancy status, and genetics. The very young and the very old are often unable to readily metabolize or excrete antibiotics; thus, doses are generally decreased. Some antibiotics cross the placenta. For example, tetracyclines taken by the mother can cause teeth discoloration in the newborn; aminoglycosides can affect the infant’s hearing. The benefits of antibiotic use in pregnant or lactating women must be carefully weighed against the potential risks to the fetus and neonate. Lastly, some patients have a genetic absence of certain enzymes used to metabolize antibiotics. For example, patients with a deficiency of the enzyme glucose-6-phosphate dehydrogenase should not receive sulfonamides, chloramphenicol, or nalidixic acid because their erythrocytes may rupture. ANTIBACTERIAL AGENTS Antibacterial agents are derived from a large number of chemical classes. Although drugs within a class have similarities in their mechanisms and spectrum of activity, each is slightly different, and learning the differences and therapeutic applications among antibacterial agents can be challenging. Basic nursing assessments and interventions TREATING THE DIVERSE PATIENT Hispanic Cultural Beliefs and Antibacterials Certain ethnic groups,such as Hispanics,believe that illness is caused by an imbalance in hot and cold.In a healthy individual, hot and cold are in balance; when an imbalance occurs,disease results. Illnesses are classified as either hot or cold as well.For example,sore throat and diarrhea are considered hot diseases; colds, upper respiratory infections, arthritis, and rheumatism are considered cold diseases. Traditional treatment in such cultures is to restore the body’s balance through the addition or subtraction of herbs, foods,or medications that are classified as either hot or cold.To treat a hot disease, medications or herbs considered cold are used.For example,penicillin is considered a hot medicine, but amoxicillin is less hot. Using acetaminophen with amoxicillin makes it cooler. # 102887 Cust: PE/NJ/CHET Au: ADAMS Pg. No. 483 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 484 484 Unit 5 The Immune System apply to all antibiotic therapies; however, the nurse should individualize the plan of care based on the patient’s condition, the infection, and the antibacterial agent prescribed. Penicillins Although not the first anti-infective discovered, penicillin was the first mass-produced antibiotic. Isolated from the fungus Penicillium in 1941, the drug quickly became a miracle product by preventing thousands of deaths from infections. The penicillins are listed in Table 34.2. 34.8 Pharmacotherapy with Penicillins Penicillins kill bacteria by disrupting their cell walls. Many bacterial cell walls contain a substance called penicillin-binding protein that serves as a receptor for penicillin. Upon binding, penicillin weakens the cell wall and allows water to enter, thus killing the organism. Human cells do not contain cell walls; therefore, the actions of the penicillins are specific to bacterial cells. Gram-positive bacteria are the most commonly affected by the penicillins, including streptococci and staphylococci. Penicillins are indicated for the treatment of pneumonia; meningitis; skin, bone, and joint infections; stomach infections; blood and valve infections; gas gangrene; tetanus; anthrax; and sickle-cell anemia in infants. The portion of the chemical structure of penicillin that is responsible for its antibacterial activity is called the betalactam ring. Some bacteria secrete an enzyme, called beta-lactamase or penicillinase, which splits the beta-lactam ring. This structural change allows these bacteria to become resistant to the effects of most penicillins. Since their discovery, large numbers of resistant bacterial strains have emerged that limit the therapeutic usefulness of the penicillins. The action of penicillinase is illustrated in ➤ Figure 34.3. Other classes of antibiotics also contain the beta-lactam ring, including the cephalosporins, carbapenems, and monobactams. Chemical modifications to the natural penicillin molecule produced drugs offering several advantages. They include the following: ● Penicillinase-resistant penicillins: Oxacillin and cloxacillin (Cloxapen) are examples of drugs that are effective against penicillinase-producing bacteria. These are sometimes called antistaphylococcal penicillins. ● Broad-spectrum penicillins: Ampicillin (Principen) and amoxicillin (Amoxil, Trimox) are effective against a wide range of microorganisms and are called broad-spectrum TABLE 34. 2 Penicillins Drug Route and Adult Dose (max dose where indicated) Adverse Effects NATURAL PENICILLINS penicillin G benzathine (Bicillin) IM; 1.2 million units as a single dose (max: 2.4 million units/day) Rash, pruritus, diarrhea, nausea, fever, penicillin G procaine (Wycillin) IM; 600,000–1.2 million units/day (max: 4.8 million units/day) drowsiness penicillin G sodium/potassium IM/IV; 2–24 million units divided every 4–6 h (max: 80 million units/day) Anaphylaxis symptoms, including angioedema, circulatory collapse and penicillin V (Pen-Vee K,Veetids,Vee-Cillin-K) PO; 125–250 mg qid (max: 7.2 g/day) cardiac arrest; nephrotoxicity PENICILLINASE-RESISTANT cloxacillin (Cloxapen) dicloxacillin nafcillin oxacillin BROAD-SPECTRUM (AMINOPENICILLINS) amoxicillin (Amoxil,Trimox) amoxicillin–clavulanate (Augmentin) ampicillin (Principen) bacampicillin (Spectrobid) EXTENDED-SPECTRUM (ANTIPSEUDOMONAL) carbenicillin (Geocillin) piperacillin sodium piperacillin tazobactam (Zosyn) ticarcillin (Ticar) PO; 250–500 mg bid PO; 125–500 mg qid (max: 4 g/day) PO; 250 mg–1 g qid (max: 12 g/day) PO; 250 mg–1 g qid (max: 12 g/day) PO; 250–500 mg every 6 h (max: 1,750 mg/day) PO; 250 or 500 mg tablet (each with 125 mg clavulanic acid) every 8–12 h PO/IV/IM; 250–500 mg every 6 h (max: 4 g/day PO or 14 g/day IV/IM) PO; 400–800 mg bid PO; 382–764 mg qid IM; 2–4 g tid–qid (max: 24 g/day) IV; 3.375 g qid over 30 min IM; 1–2 g qid (max: 24 g/day) Italics indicate common adverse effects; underlining indicates serious adverse effects. # 102887 Cust: PE/NJ/CHET Au: ADAMS Pg. No. 484 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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