Home Books Katzung & Trevor's Pharmacology: Examination & Board Review, 12e

Chapter 50: Miscellaneous Antimicrobial Agents & Disinfectants, Antiseptics, & Sterilants

Infections caused by Gram-negative bacilli have occurred when this cationic surfactant has been used as a skin antiseptic.

(A) Acetic acid

(B) Benzalkonium chloride

(C) Lindane

(D) Hexachlorophene

(E) Thimerosal

Pseudomonas and other Gram-negative bacteria have caused infections after the use of cationic surfactants such as benzalkonium and cetylpyridinium chlorides, partly because they form a film on the skin under which microorganisms can survive. In addition, some Gram-negative bacilli are able to grow in solutions containing benzalkonium salts. Bacterial growth may also occur in solutions of povidone-iodine. The answer is B.

A young woman is brought to a hospital emergency department with intense abdominal pain of 2 days duration. The pain has spread to the right lower quadrant and is accompanied by nausea, vomiting, and fever. She arrives at the emergency department with a blood pressure of 85/45, pulse 120/min, and temperature 40°C. Her abdomen has a board-like rigidity with diffuse pain to palpation. Laboratory values include the following: WBC 20,000/µL and creatinine 1.5 mg/dL. After abdominal x-ray films are taken, a preliminary diagnosis of abdominal sepsis is made, possibly resulting from bowel perforation. After appropriate samples are sent to the laboratory for culture, the patient is hospitalized, and antimicrobial therapy is started with intravenous ampicillin and gentamicin.

Regarding the treatment of this patient, which statement is accurate?

(A) A drug active against anaerobes should be included in the antimicrobial drug regimen

(B) Cultures are pointless because this is probably a mixed infection

(C) Empiric antibiotic therapy of abdominal sepsis should always include a third-generation cephalosporin

(D) Gram stain of the blood would provide positive identification of the specific organism involved in this infection

(E) The combination of ampicillin and gentamicin provides good coverage for all likely pathogens

Abdominal sepsis is commonly a mixed infection; the most likely pathogens are Bacteroides fragilis, Enterobacteriaceae, and Enterococcus faecalis. An antibiotic regimen that includes only ampicillin and gentamicin does not control B fragilis. Empiric treatment in this case should include a drug active against this pathogen (eg, metronidazole, cefoxitin, cefotetan, or clindamycin). The answer is A.

If the antibiotic regimen in this patient is modified to include metronidazole

(A) Ampicillin should be excluded from the regimen

(B) Coverage will be extended to methicillin-resistant staphylococci

(C) Gentamicin should be excluded from the regimen

(D) Metronidazole should not be administered intravenously

(E) The patient should be monitored for candidiasis

Fungal superinfections, especially from Candida albicans, occur frequently during treatment with metronidazole. In most cases of abdominal sepsis, metronidazole would be given by slow intravenous infusion. Both ampicillin and gentamicin should be maintained until the infection is controlled, at which time surgery is indicated. Metronidazole has no activity against aerobes. The combination of ampicillin, gentamicin, and metronidazole does not provide coverage for methicillin-resistant staphylococci. The answer is E.

Which compound is the safest drug to use topically to treat scabies and pediculosis?

(A) Benzoyl peroxide

(B) Chlorhexidine

(C) Lindane

(D) Permethrin

(E) Silver sulfadiazine

Of the agents listed, both lindane and permethrin are effective scabicides and pediculicides. However, there is some concern about systemic absorption of lindane, which may cause neurotoxicity and hematotoxicity. Accidental ingestion of lindane in children has caused seizures. The answer is D.

Methenamine salts are used as urinary antiseptics. The reason they lack systemic antibacterial action is that they are

(A) Converted to formaldehyde only at low pH

(B) Metabolized rapidly by hepatic drug-metabolizing enzymes

(C) More than 98% bound to plasma proteins

(D) Not absorbed into the systemic circulation after oral ingestion

(E) Substrates for active tubular secretion

Below pH 5.5, methenamine releases formaldehyde, which is antibacterial. This pH is achieved in the urine but nowhere else in the body. Ascorbic acid is sometimes given with methenamine salts to ensure a low urinary pH. The answer is A.

Which statement about the actions of antimicrobial agents is false?

(A) Metronidazole has activity against C difficile

(B) Neonatal gonococcal ophthalmia can be prevented by silver nitrate

(C) Polymyxins act as cationic detergents to disrupt bacterial cell membranes

(D) Resistance to nitrofurans emerges rapidly, and there is cross-resistance with sulfonamides

(E) Salicylic acid has useful antidermatophytic activity when applied locally

Resistance emerges very slowly when nitrofurantoin is used as a urinary antiseptic. There is no cross-resistance between the drug and other drugs used in the treatment of bacterial infections of the urinary tract. The answer is D.

Which antiseptic promotes wound healing?

(A) Cetylpyridinium chloride

(B) Chlorhexidine

(C) Hexachlorophene

(D) Phenol

(E) None of the above

No antiseptic in current use is able to promote wound healing, and most agents do the opposite. In general, cleansing of abrasions and superficial wounds with soap and water is just as effective as and less damaging than the application of topical antiseptics. Phenol is only used as a disinfectant of inanimate objects! The answer is E.

A 22-year-old man with gonorrhea is to be treated with cefixime and will need another drug to provide coverage for possible urethritis caused by C trachomatis. Which of the following drugs is least likely to be effective in nongonococcal urethritis?

(A) Azithromycin

(B) Ciprofloxacin

(C) Erythromycin

(D) Nitrofurantoin

(E) Tetracycline

Urinary tract infections resulting from C trachomatis are likely to respond to all of the drugs listed except nitrofurantoin. However, nitrofurantoin is effective against many bacterial urinary tract pathogens with the exception of Pseudomonas aeruginosa and strains of Proteus. The answer is D.

A patient with AIDS has an extremely high viral RNA titer. While blood is being drawn from this patient, the syringe is accidentally dropped, contaminating the floor, which is made of porous material. The best way to deal with this is to

(A) Clean the floor with a 10% solution of household bleach

(B) Clean the floor with soap and water

(C) Completely replace the contaminated part of the floor

(D) Neutralize the spill with a solution of potassium permanganate

(E) Seal the room and decontaminate with ethylene oxide

Household bleach contains sodium hypochlorite. A 1:10 dilution of bleach is effective for disinfection of a direct blood spill on a porous surface. In addition to inactivating HIV, sodium hypochlorite solutions have disinfectant activity against other viruses, including hepatitis B virus. The answer is A.

Neuropathies are more likely to occur with this agent when it is used in patients with renal dysfunction. The drug may cause acute hemolysis in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency.

(A) Chlorhexidine

(B) Halazone

(C) Methenamine

(D) Metronidazole

(E) Nitrofurantoin

Acute hemolytic reactions in G6PD deficiency occur with drugs that are oxidizing agents, including antimalarials, sulfonamides, and nitrofurans. Severe polyneuropathies may occur with nitrofurantoin, and they are more likely to occur in patients with renal dysfunction. The answer is E.

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Chapter 50: Miscellaneous Antimicrobial Agents & Disinfectants, Antiseptics, & Sterilants

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