Answers

1. B. The patient has complicated urinary tract infection and nonsevere sepsis syndrome caused by P. aeruginosa. Effective antibiotics for Pseudomonas spp. include mezlocillin, piperacillin, piperacillin-tazobactam, ticarcillin, and ticarcillin-clavulanate. The carbapenems (imipenem and meropenem) and the monobactam (aztreonam) are also active against P. aeruginosa. Ampicillin-sulbactam and cefazolin are ineffective against P.

aeruginosa. The history defines a patient with type I allergic hypersensitivity to penicillin. The patient should avoid drugs in the penicillin class, including penicillin, nafcillin, oxacillin, cloxacillin, dicloxacillin, ampicillin, amoxicillin, ticarcillin, piperacillin, and mezlocillin. In addition, carbapenems (imipenem, meropenem) should not be administered to patients with a history of type I allergic response to penicillin or positive penicillin skin test. Cefazolin is a cephalosporin. Patients with type I allergy to penicillin and positive penicillin skin test have a 5.6% rate of allergic reactions to cephalosporins. Aztreonam may be used safely in patients with history of type I allergic response to penicillin.

2. B. The patient is pregnant and has latent syphilis of indeterminate duration. The pathogenic organism is T. pallidum. Benzathine penicillin G is the drug of first choice for treating latent syphilis. Doxycycline and tetracycline are alternatives treatments for non-pregnant patients with latent syphilis. Spectinomycin is not effective against syphilis; it is a treatment for disseminated gonorrhea in patients who are allergic to cephalosporins. Streptomycin is not effective against syphilis.

3. E. The patient has exudative pharyngitis, presumably secondary to group A streptococcus. Antibiotic treatment is indicated to reduce the duration and severity of symptoms and to prevent acute rheumatic fever. The antibiotic of first choice is penicillin V. Other reasonable alternatives are benzathine penicillin G, erythromycin, cephalosporin, clindamycin, azithromycin, and clarithromycin. Amikacin, lome-floxacin, metronidazole, and netilmicin are not active against group A streptococcus.

4. E. The patient has uncomplicated urethritis caused by N. gonorrhoeae. Effective antibiotics for gonorrhea include cephalosporins (ceftriaxone, cefixime, ceftizoxime, cefotaxime, cefotetan, cefoxitin), fluoroquinolones (ciprofloxacin, ofloxacin, enoxacin, lomefloxacin, gatifloxacin), and spectinomycin. Gonorrhea is resistant to trimethoprim and ri-fampin. Amphotericin B is an antifungal drug, and isoniazid is an antimycobacterial drug. Neither has antigonococcal activity. Cephalosporins and other (3-lactam antibiotics act to inhibit bacterial transpeptidase and block cross-linking of peptides in cell wall murein (peptidoglycan). Fluoroquinolone antibiotics inhibit DNA gyrase (topoisomerase) and interfere with bacterial DNA transcription and replication. Spectinomycin and doxycycline inhibit bacterial protein synthesis and act at the 30S ribosome subunit. Azithromycin inhibits bacterial protein synthesis and acts at the 50S ribosome subunit. Trimethoprim inhibits dihydrofo-late reductase and blocks formation of tetrahydro-folate required for purine synthesis. Rifampin in hibits RNA synthesis by binding to the psubunit of DNA-dependent RNA polymerase. Amphotericin B inhibits fungal cell membrane integrity by binding to ergosterols to create pores. Isoniazid inhibits KasA, a (3-ketoacyl carrier protein synthetase, and blocks mycolic acid synthesis.

5. B. The patient has impetigo. The causative organism is either Streptococcus pyogenes (group A) or S. au-reus. Recommended antibiotic treatment is di-cloxacillin or cloxacillin. Dapsone is used to treat skin infections with Mycobacterium leprae (leprosy) and to treat brown recluse spider (Loxosceles) bites. Doxycycline is used to treat skin infections with Bacillus anthracis (anthrax), Bartonella henselae (bacillary angiomatosis), Borrelia burgdorferi (Lyme disease, erythema migrans), Propionibacterium acnes (acne vulgaris), Vibrio vulnificus and Vibrio damsela (hemorrhagic bullous cellulitis). The question does not provide historical or epidemiological information to support these diagnoses. Ketoconazole is used to treat fungal infections of the skin (tinea capitis, tinea cruris, tinea corporis, tinea pedis, tinea versicolor). Dermatophyte infections are usually erythematous, with vesicles, fissures, and scaling. Penciclovir is a treatment for herpes simplex virus infections including herpes labialis fever blisters.

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