Antibiotics Review

Course #55073 • 5 Hours/Credits


Study Points

  1. Describe the general characteristics and mode of action of antibiotics commonly in use.
  2. Employ best practice principles for limiting the emergence and transmission of antimicrobial-resistant strains within the healthcare environment.
  3. Discuss the mechanism of action, pharmacokinetics, and spectrum of activity of natural and extended-spectrum penicillins.
  4. Select the most appropriate, cost-effective cephalosporin based on "generational" characteristics and spectrum of activity.
  5. Describe the role of carbapenems and monobactams.
  6. Discuss the characteristics, expected toxicities, and indications for the use of aminoglycosides, macrolides, and sulfonamides.
  7. Outline the mechanism of action, pharmacokinetics, and advantages inherent to quinolones and the tetracyclines.

    1 . Which of the following classes of antibiotics is associated with a risk for developing Clostridioides difficile-associated diarrhea?
    A) Macrolides
    B) Quinolones
    C) Cephalosporins
    D) All of the above

    GENERAL CHARACTERISTICS OF ANTIBIOTICS

    There are some characteristics that all antibiotics share. All antibiotics can elicit allergic responses, although some are more allergenic than others. Allergic reactions can range from mild, annoying rashes to life-threatening reactions like anaphylaxis and Stevens-Johnson syndrome. In some cases, there is a cross-sensitivity between agents in different classes. In addition, all antibiotics affect normal body flora as well as pathogens, which may result in overgrowth of Candida and pathogenic bacteria such as Clostridioides difficile. Overgrowth of C. difficile is a serious complication of antimicrobial therapy that can produce symptoms ranging from mild diarrhea to severe, life-threatening complications, such as pseudomembranous colitis [1]. Most cases resolve with supportive care and discontinuation of the offending antibiotic, but many require treatment. In addition, diarrhea and pseudomembranous colitis can develop weeks after antimicrobial therapy has been discontinued. A high degree of suspicion and judicious use of laboratory testing are the keys to recognizing and managing these complications.

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    2 . Bacteria become resistant to the effects of antibiotics by
    A) altered cellular permeability.
    B) increased efflux of the antibiotic from the cell.
    C) elaboration of deactivating enzymes that alter interactions at binding sites.
    D) All of the above

    ANTIBIOTIC RESISTANCE

    Repeated exposure to an antibiotic may lead to the emergence of selective subpopulations of the same or related bacteria now resistant to the therapeutic agent. The Centers for Disease Control and Prevention (CDC) note that approximately 2.8 million people become infected with bacteria that are resistant to antibiotics, and approximately 35,000 people die annually because of these infections [2]. Mechanisms of microbial resistance include altered cellular permeability (leading to greatly diminished intracellular concentration of the drug), increased efflux of the antibiotic from the cell, and elaboration of deactivating enzymes that alter the antibiotic's interaction at binding sites within the cell wall or cytoplasm [3].

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    3 . Which of the following are common ways for bacteria to gain antibiotic resistance?
    A) Genetic mutations
    B) Transfer of genetic information on plasmids
    C) Both A and B
    D) None of the above

    ANTIBIOTIC RESISTANCE

    These resistance mechanisms may be acquired through mutations in the genes that encode for the target or affected transport proteins. As the bacterial cells without the adaptive mutations succumb to the action of the antibiotic, the subpopulation that has the adaptive mutation continues to replicate, replacing the original population with a resistant one.

    Bacterial resistance can be transferred from one bacterium to another, or from one bacterial species to related group, by means of plasmids or transposons that gain entry to the cell. These agents are small segments of DNA that are readily exchanged between bacteria. A plasmid that contains a gene for an adaptive mutation can be shared with a large number of nearby bacteria, which may or may not be the same species. In this manner, resistance can quickly spread from species to species [5].

    In addition, new categories of antibiotics are being created in an attempt to stay ahead of the rapid evolution of bacterial resistance. Linezolid and tedizolid, the only two FDA-approved drugs in the oxazolidinone category, are examples of this, with linezolid being the first of the two to be developed. Oxazolidinones are a unique category of drugs that prevent formation of the 70S protein synthesis complex in bacteria, and may be useful in the treatment of vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus [6,7]. Nonetheless, development of resistance in bacteria is relentless.

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    4 . The first oxazolidinone created, which was developed in an attempt to stay ahead of the developing bacteria resistance, was
    A) linezolid.
    B) cefprozil.
    C) norfloxacin.
    D) meropenem.

    ANTIBIOTIC RESISTANCE

    In light of the efficient means by which bacteria develop resistance, it is important to avoid practices that contribute to the process. In 2002, the CDC issued a position paper outlining recommendations for minimizing nosocomial infection and the emergence of resistant organisms [8]. In this paper, the CDC recommended a multistep approach that included: preventing infection (by paying careful attention to the proper use of invasive medical devices); tailoring medical treatment to fit the infection (by avoiding broad-spectrum antibiotics and prolonged treatment when possible); and preventing the transmission of resistant bacteria between patients (by emphasizing hand washing and implementing hospital infection control programs) [8]. Since issuance of the CDC's position paper, the agency has taken many additional steps and implemented coordinated, strategic action plans to change the course of antibiotic resistance. This includes publication of The National Action Plan for Combating Antibiotic-Resistant Bacteria (CARB), 2020–2025 [9]. The CARB builds on the first National Action Plan, released in 2015, and prioritizes infection prevention and control to slow the spread of resistant infections and reduce the need for antibiotic use. The CARB also integrates a "one health" approach, which recognizes the relationships between the health of humans, animals, plants, and the environment [9]. It has also been hypothesized that the response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and associated COVID-19 illness might increase use of antibiotics and other antimicrobial medicines (both appropriate and inappropriate) to address primary or secondary infections, with the potential to further accelerate the emergence of antibiotic resistance despite the rate of the development of new antibiotics [9].

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    5 . What recommendation has the CDC made regarding infection control to minimize the spread of antibiotic resistances among patients in hospitals and residential care facilities?
    A) Tailor treatment plans to the most likely pathogens
    B) Proper hand washing during and after patient care and implementation of hospital infection control programs
    C) Proper use of invasive medical devices only when they are necessary
    D) All of the above

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    6 . The antibacterial effect of penicillins is caused by the drugs' action of
    A) inhibiting protein synthesis.
    B) impairing cell wall synthesis.
    C) blocking the binding of aminoacyl transfer-RNA.
    D) displacing cations that link phospholipids together.

    PENICILLINS

    Penicillin is bactericidal, killing susceptible bacteria by interrupting cell wall synthesis. The drug exerts its effect by preventing cross-binding of the peptidoglycan polymers necessary for cell wall formation and by binding with carboxypeptidases, endopeptidases, and transpeptidase ("penicillin-binding proteins" [PBPs]) that participate in cell wall synthesis [12]. Although the exact mechanisms involved are not known, the end result is that the cell wall is structurally weakened and lyses, leading to cell death.

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    7 . Labeled uses for the natural penicillins include treatment of infections of the
    A) eye.
    B) meninges.
    C) gastrointestinal tract.
    D) upper and lower respiratory tracts.

    PENICILLINS

    The natural penicillins are active against gram-positive organisms such as streptococci, Enterococcus faecalis, and Listeria monocytogenes. However, most S. aureus isolates are now resistant. The natural penicillins are also active against anaerobic species, such as Bacteroides species and Fusobacterium species. At serum levels achieved by parenteral administration, the natural penicillins are effective against some gram-negative bacteria, such as Escherichia coli, H. influenzae, Neisseria gonorrhoeae, and Treponema pallidum. For the treatment of moderate-to-severe infections in which resistant organisms are considered a possibility, reliance upon penicillin alone should be avoided unless the identity and sensitivity of the infecting organism have been confirmed. Labeled uses include treatments for infections of the upper and lower respiratory tract, throat, skin, and genitourinary tract and prophylaxis of recurrent rheumatic fever and pneumococcal infections [6].

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    8 . Which of the following is an absolute contraindication for administering penicillins?
    A) Severe renal failure
    B) Severe hepatic failure
    C) Prior allergic reaction to a member of the class
    D) All of the above

    PENICILLINS

    Allergy to any of the penicillins is the only absolute contraindication to use of a penicillin agent. However, studies have found that penicillin allergy is less common than previously thought [22,23,24,25]. Traditionally, allergic reactions were believed to occur in up to 10% of patients; however, more recent studies have found the rate to be much lower. While penicillin-induced anaphylaxis death rate estimates are similar to previous statistics (i.e., approximately 0.002% among the general population), the percentage of individuals with a true penicillin allergy as defined by immunoglobulin E (IgE)-mediated reaction is generally less than 10%, with some studies showing a true penicillin allergy rate of only 0.7% [22,23,24,26]. It is also important to note that approximately 90% of patients previously diagnosed with a penicillin allergy will show no reactivity if not exposed to the antibiotic for 10 years or more, due to the absence of a true allergy or loss of allergy over time [22,24,25]. Allergy skin testing is the most reliable way to determine true penicillin allergy and may allow for previously avoided antibiotics to be used as indicated.

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    9 . Which of the following is considered a first-generation cephalosporin?
    A) Cefixime
    B) Cefepime
    C) Cefadroxil
    D) Loracarbef

    CEPHALOSPORINS

    THE CEPHALOSPORINS

    AgentAdult Dosing RangePediatric Dosing RangeRouteCommon Side EffectsComments
    1st Generation
    Cefadroxil1–2 g/day in 2 divided doses
    30 mg/kg/day in 2 divided doses
    Max: 2 g/day
    PORash, diarrheaCan interfere with some urine glucose tests.
    Cefazolin
    1–2 g every 8 hrs
    Max: 12 g/day
    >1 mo: 25–100 mg/kg/day divided every 6 to 8 hrs
    Max: 6 g/day
    IV, IMPhlebitis at infusion site, seizure,rash, diarrheaCan interfere with some urine glucose tests.
    Cephalexin
    250–1,000 mg every 6 to 12 hrs
    Max: 4 g/day
    >1 yr to <15 yrs: 25–100 mg/kg/day in 3 to 4 divided doses
    Max: 4 g/day
    POGI upset, rashCan interfere with some urine glucose tests.
    2nd Generation
    Cefaclor250–500 mg every 8 hrs
    >1 mo: 20–40 mg/kg/day in 2 to 3 divided doses
    Max: 1 g/day
    PORash, GI upsetCan interfere with some urine glucose tests.
    Cefotetan
    1–2 g every 12 hrs
    Max: 4–6 g/day
    AAP recommendation: 30–50 mg/kg/dose every 12 hrs
    Max: 4,000 mg/day
    IV, IMPhlebitis at infusion site, rash, GI upset
    Disulfiram-like reaction with alcohol. Can interfere with some urine glucose tests.
    Not recommended for treatment of community-acquired intra-abdominal infections.
    Cefoxitin
    1–2 g every 6 to 8 hrs
    Max: 12 g/day
    >3 mos: 80–160 mg/kg/day in 4 to 6 divided doses
    Max: 12 g/day
    IV, IMPhlebitis at infusion site, rash
    IM injection is painful. Can interfere with some urine glucose tests.
    In pediatrics, for group A beta-hemolytic streptococcal infections, antimicrobial therapy should be given for at least 10 days to guard against the risk of rheumatic fever or glomerulonephritis.
    Cefprozil250–500 mg every 12 to 24 hrs
    >6 mos: 7.5–20 mg/kg every 12 hrs
    >2 yrs: 7.5–15 mg/kg/day in 2 divided doses, or 20 mg/kg every 24 hrs
    Max: 1 g/day
    PORash, GI upset, elevated liver enzymesAvoid use in phenylketonuria. Can interfere with some urine glucose tests.
    Cefuroxime
    PO: 250–500 mg every 12 hrs for 10 days
    IV, IM: 0.5–1.5 g every 6 to 8 hrs
    Max: 6 g/day
    PO: 20–30 mg/kg/day in 2 divided doses
    IV, IM: 75–150 mg/kg/day in 3 divided doses
    Max: 6 g/day
    PO, IV, IMPhlebitis at infusion site, rash, GI upset
    Tablets and oral suspension forms require different dose. Oral doses noted here are for tablet formulation.
    Higher doses can be used for severe infection.
    3rd Generation
    Cefdinir300 mg every 12 hrs, or 600 mg every 24 hrs for 10 days
    7 mg/kg/dose twice daily or 14 mg/kg/dose for 10 days
    Max: 600 mg/day
    PORash, diarrheaIron and antacids can reduce absorption. Can interfere with some urine glucose tests.
    Cefditoren200–400 mg every 12 hrs for 10 to 14 daysNot studied for patients <12 yrsPOGI upset, headacheInteraction with proton-pump inhibitors, H2 blockers, antacids. Contraindicated with milk protein allergy.
    Cefixime400 mg/day in 1 or 2 doses
    >6 mos and <45 kg:8–20 mg/kg/day every 12 to 24 hrs
    Max: 400 mg/day
    >12 yrs or >50 kg: Use adult dosing
    PODiarrhea, rashCan interfere with some urine glucose tests.
    Cefotaxime1–2 g every 4 to 12 hrs1 mo to 12 yrs and <50 kg: 50–225 mg/kg/day in 3 to 4 divided dosesIV, IMPhlebitis at infusion site, rash, GI upsetSingle dose can be given for GC. Transient arrhythmias have developed after administration of this agent through central venous catheter.
    Cefpodoxime100–400 mg every 12 hrs for 7 to 14 days10 mg/kg/day in 2 divided dosesPODiarrhea, nausea, vomitingDecreased absorption with antacids and H2 blockers. Can be given as a single dose for GC.
    Ceftazidime500–1,000 mg every 8 hrs
    IV: 30–50 mg/kg every 8 hrs
    Max: 6 g/day
    AAP recommendation for IV: 90–200 mg/kg/day every 8 hours
    Max: 6 g/day
    IV, IMPhlebitis at infusion site, rash, GI upsetCan interfere with some urine glucose tests. The L-arginine formulation should not be used in children.
    Ceftibuten400 mg every 24 hrs for 10 days
    9 mg/kg/day
    Max: 400 mg/day for 10 days
    PORash, GI upset, headacheCan interfere with some urine glucose tests.
    CeftriaxoneIV, IM: 1–2 g every 12 to 24 hrs
    50–100 mg/kg/day in 1 to 2 divided doses
    Max: 4 g/day
    IV, IMPhlebitis at infusion site, rashAvoid in neonates with hyperbilirubinemia. Higher doses are used for meningitis. A ceftriaxone-calcium salt can precipitate in the gallbladder, causing sonographically detectable abnormalities.
    4th Generation
    Cefepime
    IV:1–2 g every 8 to 12 hrs
    IM: 0.5–1 g every 12 hrs
    IV, IM: 50 mg/kg every 8 to 12 hrs
    Not to exceed adult dosing
    IV, IMPhlebitis at infusion site, GI upsetCan interfere with some urine glucose tests.
    Cefiderocol2 g every 8 hours for 7 to 10 daysIVPhlebitis at infusion site, rash, GI upsetCan interfere with some urine glucose tests.
    5th Generation
    Ceftaroline fosamil600 mg every 12 hours for 5 to 14 days
    >2 mos to <2 yrs: 8 mg/kg/dose every 8 hrs for 5 to 14 days
    >2 yrs to <18 yrs and <33 kg: 12 mg/kg/dose every 8 hrs for 5 to 14 days
    >2 yrs to <18 yrs and >33 kg: 400–600 mg every 8 to 12 hrs for 5 to 14 days
    IVPhlebitis at infusion site, GI upset, headacheSlow IV infusion over 60 minutes. Can interfere with some urine glucose tests.
    Ceftobiprole500 mg every 8 hoursIVHyponatremia, phlebitis at infusion site, headache, nausea/vomiting
    Approved for use in Canada but not the United States.
    Not for use in patients with ventilator-associated pneumonia.
    Prescribing information is given for comparison purposes only. The higher dosage ranges reflect dosages for more severe infections. Please consult the manufacturer's package insert for the antibiotic for complete prescribing information, maximum dosages, and indications.
    GC = gonococcal infection.
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    10 . What route of elimination is used by members of the cephalosporin class of antibiotics?
    A) Renal
    B) Mixed renal/hepatic
    C) Hepatic metabolism with excretion into the bile
    D) All of the above

    CEPHALOSPORINS

    Most cephalosporins are eliminated by the kidney. The exception in the oral cephalosporins is cefixime, half of which is excreted in the urine [6]. The remaining half is partly metabolized to inactive metabolites and partly excreted in the bile. Cefotaxime is deacetylated by the liver to a bioactive metabolite and inactive forms. The deacetylated metabolites are excreted by the kidney. Cefditoren is excreted predominantly in the bile.

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    11 . Probenecid increases serum levels of which cephalosporin?
    A) Cefotetan
    B) Cefotaxime
    C) Ceftriaxone
    D) All of the above

    CEPHALOSPORINS

    The serum levels of all the cephalosporins are increased with co-administration of probenecid. The effects of warfarin may be enhanced by co-administration of cefotetan, cefazolin, cefoxitin, and ceftriaxone [6].

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    12 . Meropenem is approved by the FDA for the treatment of
    A) pneumonia.
    B) urinary tract infections.
    C) intra-abdominal infections.
    D) meningitis in patients younger than 3 months of age.

    CARBAPENEMS

    Imipenem and ertapenem have a wide antimicrobial spectrum with excellent activity against anaerobic bacteria, including Bacteroides species. They also cover many gram-positive cocci, such as Enterococcus and Streptococcus, as well as many gram-negative bacteria [60]. Meropenem has somewhat greater activity against gram-negative bacteria, which are not affected by most beta-lactamases. Doripenem has good activity against Pseudomonas aeruginosa. Imipenem and ertapenem are approved by the FDA for use in urinary tract infections, pneumonia, intra-abdominal infections, and skin and soft-tissue infections [6]. Meropenem is approved by the FDA for treatment of intra-abdominal infections, skin and skin structure infections, and meningitis in patients older than 3 months of age [6]. Combination meropenem/vaborbactam is approved for the treatment of complicated urinary tract infections caused by susceptible micro-organisms [6,61]. The combination imipenem/cilastatin/relebactam was approved by the FDA in 2019 for the treatment of complicated urinary tract infections and complicated intra-abdominal infections [6,62].

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    13 . One side effect associated with the use of imipenem/cilastatin is
    A) diarrhea.
    B) headache.
    C) hypotension.
    D) phlebitis at the infusion site.

    CARBAPENEMS

    The carbapenems are generally well tolerated. Occasional reactions include nausea and vomiting, phlebitis at the infusion site, elevation of liver enzymes, and leukopenia. Seizures may occur. The risk is higher in patients with underlying central nervous system (CNS) disease and in patients with renal disease, which results in high serum levels of the drug [66]. Hypersensitivity reactions may occur, and while there is a degree of cross-sensitivity with penicillins, this risk is lower than previously believed [22,23,24]. Carbapenems should be used with caution in patients allergic to the carbapenems or penicillins [6].

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    14 . Aztreonam is considered pregnancy category
    A) A.
    B) B.
    C) C.
    D) D.

    MONOBACTAMS

    Aztreonam is pregnancy category B, based on animal studies that have shown no ill effects of the drug. There are no human data available [6].

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    15 . Aminoglycosides are effective for the treatment of
    A) anaerobic bacilli.
    B) gram-positive bacilli.
    C) aerobic gram-negative bacilli.
    D) All of the above

    AMINOGLYCOSIDES

    The aminoglycosides are effective for the treatment of aerobic gram-negative bacilli, such as Klebsiella species, Enterobacter, and P. aeruginosa. There is very little activity against anaerobes and gram-positive organisms, so combination therapy with a beta-lactam, vancomycin, or other agents active against gram-positive organisms and anaerobes is commonly used. The aminoglycosides are indicated for infections caused by susceptible organisms of the urinary tract, respiratory tract, skin and soft tissues, and sepsis due to gram-negative aerobic bacilli.

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    16 . Which of the following aminoglycosides is taken orally as a bowel decontaminant due to its minimal absorption?
    A) Neomycin
    B) Gentamicin
    C) Tobramycin
    D) Streptomycin

    AMINOGLYCOSIDES

    The aminoglycosides commonly used at present for treatment of systemic bacterial infection include gentamicin, tobramycin, and amikacin. Kanamycin is discontinued [17]. Aminoglycosides have negligible oral absorption and thus require parenteral administration. They also can be administered directly into body cavities and have a role in the management of pleural and peritoneal infection. Tobramycin is particularly useful for treatment of recurrent Pseudomonas infection in patients with cystic fibrosis and can be administered by aerosolized inhalation to facilitate optimal local antimicrobial effect [79]. Neomycin is often used orally as part of a pre-operative bowel decontamination protocol.

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    17 . Which of the following is a well-established side effect of the aminoglycosides?
    A) Ototoxicity
    B) Nephrotoxicity
    C) Both A and B
    D) None of the above

    AMINOGLYCOSIDES

    The most common adverse effect associated with aminoglycoside usage is renal failure, occurring in 10% to 25% of therapeutic courses [84]. Aminoglycosides are freely filtered by the glomeruli and quickly taken up by the proximal tubular epithelial cells, where they exert their main toxic effect by altering phospholipid metabolism. Aminoglycosides also cause renal vasoconstriction [85]. Critical factors in the development of acute kidney injury secondary to aminoglycoside nephrotoxicity are dosing and duration of therapy. A single daily large dose is preferable to more frequent dosing, as it appears to cause less accumulation in the tubular cells once the saturation point is reached [84]. Additionally, extending the dose interval to more than 24 hours in patients with renal impairment has been found to be effective, with irreversible nephrotoxicity reported in only 1% of patients studied [86].

    Less commonly, vestibular and auditory impairment may develop during treatment with aminoglycosides. These effects are usually reversible, and because there is some data suggesting that there is a genetic predisposition to ototoxicity, this drug class should be avoided in patients who have a family history of ototoxicity with aminoglycosides [87]. When aminoglycoside therapy is expected to exceed five to seven days, baseline testing of auditory function should be performed and monitored weekly for the duration of treatment.

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    18 . Which of the following is a topical sulfonamide?
    A) Sulfadiazine
    B) Sulfasalazine
    C) Sulfacetamide
    D) Sulfadoxine/pyrimethamine

    SULFONAMIDES

    THE SULFONAMIDES

    AgentAdult Dosing RangePediatric Dosing RangeRouteCommon Side EffectsComments
    Short- to Medium-Acting
    Sulfadiazine2–4 g/day in 3 to 6 divided doses
    >2 mos (initial): 75–150 mg/kg/day in 4 to 6 divided doses
    >2 mos (maintenance): 150 mg/kg/day in 4 to 6 divided doses
    Max: 6 g/day
    PORash, pruritus
    Multiple drug interactions.
    Contraindicated in infants <2 mos of age.
    Sulfamethoxazole/trimethoprim (TMP/SMX)
    PO: 1–2 DS tablets every 12 to 24 hrs
    IV: 8–20 mg TMP/kg/day in 2 to 4 divided doses
    >2 mos PO:6–20 mg TMP/kg/day in 2 divided doses
    IV: 6–20 mg TMP/kg/day every 12 to 24 hours
    Max single dose: 160 mg TMP/dose
    PO, IVRash, pruritus
    Multiple drug interactions.
    Weight-based dosing recommendations based on trimethoprim content.
    Limited to GI Tract
    Sulfasalazine
    RA: Initial: 0.5–1 g every 6 to 8 hrs Maintenance: 2 g/day in divided doses
    UC: Initial: 3–4 g in evenly divided doses every 8 hours
    Titrate to 4–6 g in 4 divided doses
    >2 yrs: 40–60 mg/kg/day in 3 to 6 divided dosesPOAnorexia, headache, GI upsetContraindicated with hypersensitivity to salicylates, sulfasalazine, sulfonamides, or mesalamine.
    Topical
    Mafenide
    Cream: Apply 1.6 mm thick layer to burn area every 12 or 24 hrs
    Solution: Wet dressing gauze every 4 hrs or as needed
    Use adult dosingCream, powder for solutionBurning at application site, rash, allergic reaction
    Used for treatment of second- and third-degree burns to prevent infection.
    Burn area should be covered with cream/wet at all times.
    Apply with sterile gloved hand.
    Silver sulfadiazineApply 1.6-mm layer to burn area once or twice dailyUse adult dosingCreamRash, allergic reaction
    SulfacetamideDosage varies with the preparation.Use adult dosingPrepared in complex with other topical medications as a solution or ointmentRash, local irritationCombinations with fluorometholone, prednisolone, and phenylephrine are available, each with differing dosing, indications, and contraindications. Common for ophthalmic and topical use.
    Prescribing information is given for comparison purposes only. The higher dosage ranges reflect dosages for more severe infections. Please consult the manufacturer's package insert for the antibiotic for complete prescribing information, maximum dosages, and indications.
    DS = double strength; RA = rheumatoid arthritis; TMP = trimethoprim; UC = ulcerative colitis.
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    19 . Of the tetracyclines, which drug is mainly excreted in the urine?
    A) Tetracycline
    B) Minocycline
    C) Doxycycline
    D) All of the above

    TETRACYCLINES

    Most of the tetracycline dose is excreted unchanged into the urine by glomerular filtration, although there is some biliary excretion as well. Nonrenal, possibly hepatic, mechanisms account in large part for excretion of doxycycline and minocycline. Approximately 23% to 40% of doxycycline and 5% to 12% of minocycline is excreted in the urine [6].

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    20 . Which of the following is a contraindication for administering tetracycline?
    A) Age older than 65 years
    B) Age younger than 8 years
    C) Patient history of syndrome of inappropriate antidiuretic hormone secretion
    D) Both A and B

    TETRACYCLINES

    Allergic reactions to tetracyclines are not common but may range from mild rashes to anaphylaxis. Tetracyclines are contraindicated in patients who have shown hypersensitivity to any tetracyclines.

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