McKenna's Pharmacology for Nursing, 2e

91

C H A P T E R 9  Antibiotics

SULFONAMIDES sulfadiazine sulfamethoxazole sulfasalazine

Penicillins continued dicloxacillin flucloxacillin phenoxymethylpenicillin benzathine phenoxymethylpenicillin potassium procaine penicillin Broad-spectrum penicillins amoxycillin ampicillin piperacillin ticarcillin

isoniazid rifampicin Leprostatic drugs clofazimine dapsone OTHER ANTIBIOTICS Lincosamides clindamycin lincomycin Macrolides azithromycin clarithromycin

erythromycin roxithromycin Monobactams aztreonam

TETRACYCLINES doxycycline minocycline tetracycline tigecycline

NEW CLASSES OF ANTIBIOTICS AND ADJUNCTS New classes of antibiotics daptomycin linezolid Adjuncts to antibiotic therapy clavulanic acid thalidomide

ANTIMYCOBACTERIALS Antituberculosis drugs ethambutol

M any new bacteria appear each year, and researchers are challenged to develop new antibiotics —chemicals that inhibit specific bacteria—to deal with each new threat. Antibiotics are made in three ways: by living microorganisms, by synthetic manufacture, and, in some cases, through genetic engineering. Antibiotics may either be bacteriostatic (preventing the growth of bacteria) or bactericidal (killing bacteria directly), although several antibiotics are both bactericidal and bacteriostatic, depending on the concentration of the particular drug. This chapter discusses the major classes of antibiotics: aminoglycosides, carbapenems, cephalosporins, fluoro- quinolones, penicillins and penicillinase-resistant drugs, sulfonamides, tetracyclines and the disease-specific antimycobacterials, including the antitubercular and lep- rostatic drugs. Antibiotics that do not fit into the large antibiotic classes include lincosamides, macrolides and monobactams. Figures 9.1 and 9.2 show sites of cellular action of these classes of antibiotics. Many antibiotics used to treat childhood infections, such as otitis media and other upper respiratory tract infections (URTIs), come in an oral suspension, suitable for children. The order for these solutions is usually written in mLs for the convenience of the parent who will be dispensing the medication. It is very important to make sure that the parent understands that the teaspoon in the prescription refers to a measuring teaspoon (5 mL). Inadvertent overdoses have been reported when parents used a kitchen teaspoon to measure out the child’s dose. Kitchen teaspoons vary greatly in volume. If a parent calls to report that the medicine is all gone on day 4 and it was supposed to be given for 7 days, check to see how the medicine is being measured. Teaching the parent when the drug is first ordered can prevent problems during the course of treatment. Safe medication administration

BACTERIA AND ANTIBIOTICS Bacteria can invade the human body through many routes: for example, respiratory, gastrointestinal (GI) and skin. Once the bacteria invade the body, the human immune response is activated, and signs and symptoms of an infection occur as the body tries to rid itself of the foreign cells. Fever, lethargy, slow-wave sleep induc- tion and the classic signs of inflammation (e.g. redness, swelling, heat and pain) all indicate that the body is responding to an invader. The body becomes the host for the bacteria and supplies proteins and enzymes the bacteria need for reproduction. Unchallenged, the invading bacteria can multiply and send out other bacteria to further invade tissue. The goal of antibiotic therapy is to decrease the population of invading bacteria to a point at which the human immune system can effectively deal with the invader. To determine which antibiotic will effectively interfere with the specific proteins or enzyme systems for treatment of a specific infection, the causative organism must be identified through a culture. Sensitivity testing is also done to determine the antibiotic to which that particular organism is most sensitive (e.g. which anti­ biotic best kills or controls the bacteria). Gram-positive bacteria are those whose cell walls retain a stain known as Gram’s stain or resist decol- ourisation with alcohol during culture and sensitivity testing. Gram-positive bacteria are commonly associated with infections of the respiratory tract and soft tissues. An example of a gram-positive bacterium is Strepto- coccus pneumoniae , a common cause of pneumonia. In contrast, gram-negative bacteria are those whose cell walls lose a stain or are decolourised by alcohol. These bacteria are frequently associated with infections of the genitourinary (GU) or GI tract. An example of a gram-negative bacterium is Escherichia coli , a common cause of cystitis. Aerobic bacteria depend on oxygen for