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

Chapter 46: Sulfonamides, Trimethoprim, & Fluoroquinolones

Trimethoprim-sulfamethoxazole is established to be effective against which of the following opportunistic infections in the AIDS patient?

(A) Cryptococcal meningitis

(B) Herpes simplex

(C) Oral candidiasis

(D) Toxoplasmosis

(E) Tuberculosis

Trimethoprim-sulfamethoxazole is not effective in the treatment of infections caused by viruses, fungi, or mycobacteria. However, the drug combination is active against certain protozoans, including Toxoplasma, and can be used for both prevention and treatment of toxoplasmosis in the severely immunocompromised AIDS patient. The answer is D.

A 65-year-old woman has returned from a vacation abroad suffering from traveler’s diarrhea, and her problem has not responded to antidiarrheal drugs. A pathogenic Gram-negative bacillus is suspected. Which drug is most likely to be effective in the treatment of this patient?

(A) Ampicillin

(B) Ofloxacin

(C) Sulfadiazine

(D) Trimethoprim

(E) Vancomycin

The second-generation fluoroquinolones are very effective in diarrhea caused by bacterial Gram-negative pathogens, including E coli, Shigella, and Salmonella. None of the other drugs listed would be appropriate. Many coliforms are now resistant to amoxicillin and ampicillin. Although trimethoprim is available as a single drug, resistance emerges rapidly during treatment unless it is used for urinary tract infections, in which high concentrations can be achieved. Vancomycin has no activity against Gram-negative bacilli. The answer is B.

Which statement about the clinical use of sulfonamides is correct?

(A) Cannot be used topically for treatment of chlamydial infections of the eye

(B) Effective as sole agents in the treatment of prostatitis

(C) Effective in Rocky Mountain spotted fever

(D) In some bacterial strains resistance occurs via reduced PABA formation

(E) Reduced intracellular uptake is a mechanism of sulfonamide resistance in some bacterial strains

Reduced uptake of sulfonamides is one way organisms can become resistant. All of the other statements about sulfonamide antimicrobial drugs are incorrect. The answer is E.

A 31-year-old man has gonorrhea. He has no drug allergies, but a few years ago acute hemolysis followed use of an antimalarial drug. The physician is concerned that the patient has an accompanying urethritis caused by C trachomatis, although no cultures or enzyme tests have been performed. Which of the following drugs will be reliably effective against both gonococci and C trachomatis and safe to use in this patient?

(A) Cefixime

(B) Ciprofloxacin

(C) Spectinomycin

(D) Sulfamethoxazole-trimethoprim

(E) None of the above

Cefixime in a single oral dose is effective in gonorrhea (Chapter 43), but it has no activity against organisms causing nongonococcal urethritis. Spectinomycin (Chapter 45) is active against most gonococci, but does not eradicate a urogenital chlamydial infection. Although ciprofloxacin might be effective in both gonorrhea and chlamydial urethritis, it is no longer recommended for treatment of gonorrhea in the United States, since resistance is now common. This patient could be treated by single oral doses of cefixime plus azithromycin (not listed). Sulfamethoxazole or TMP-SMZ would not be useful and may cause acute hemolysis in this patient. The answer is E.

Which statement about the fluoroquinolones is accurate?

(A) Antacids increase their oral bioavailability

(B) Contraindicated in patients with hepatic dysfunction

(C) Fluoroquinolones are drugs of choice in a 6-year-old child with a urinary tract infection

(D) Gonococcal resistance to fluoroquinolones may involve changes in DNA gyrase

(E) Modification of moxifloxacin dosage is required in patients when creatinine clearance is less than 50 mL/min

Antacids can decrease oral bioavailability of fluoroquinolones. Neither hepatic nor renal dysfunction is a contraindication to the use of fluoroquinolones. Most fluoroquinolones undergo renal elimination and dosage should be modified with creatinine clearance <50 mL/min. Moxifloxacin elimination occurs mainly via the liver. The fluoroquinolones should not be used to treat uncomplicated first-time urinary tract infections in children because of possible effects on cartilage development. Uncomplicated urinary tract infections in children are usually due to a strain of E coli that is sensitive to many other drugs, including beta-lactam antibiotics. The answer is D.

A 40-year-old man complains of periodic bouts of diarrhea with lower abdominal cramping and intermittent rectal bleeding. Seen in the clinic, he appears well nourished, with blood pressure in the normal range. Examination reveals moderate abdominal pain and tenderness. His current medications are limited to loperamide for his diarrhea. Sigmoidoscopy reveals mucosal edema, friability, and some pus. Laboratory findings include mild anemia and decreased serum albumin. Microbiologic examination via stool cultures and mucosal biopsies do not reveal any evidence for bacterial, amebic, or cytomegalovirus involvement. The most appropriate drug to use in this patient is

(A) Ampicillin

(B) Doxycycline

(C) Norfloxacin

(D) Sulfasalazine

(E) Trimethoprim-sulfamethoxazole

In the absence of any evidence pointing toward a definite microbial cause for the colitis in this patient, a drug that decreases inflammation is indicated. Sulfasalazine has significant anti-inflammatory action, and its oral use results in symptomatic improvement in 50–75% of patients suffering from ulcerative colitis. The drug is also used for its anti-inflammatory effects in rheumatoid arthritis. The answer is D.

Which adverse effect is most common with sulfonamides?

(A) Fanconi’s aminoaciduria syndrome

(B) Hematuria

(C) Kernicterus in the newborn

(D) Neurologic dysfunction

(E) Skin rash

The most common adverse effect of the sulfonamides is a skin rash caused by hypersensitivity. Neurologic dysfunction and hematuria occur less frequently. Sulfonamides are usually avoided in the third trimester of pregnancy or in neonates, so kernicterus is rare. Fanconi’s syndrome is associated with the use of outdated tetracyclines. The answer is E.

Which drug is effective in the treatment of nocardiosis and, in combination with pyrimethamine, is prophylactic against Pneumocystis jirovecii infections in AIDS patients?

(A) Amoxicillin

(B) Erythromycin

(C) Levofloxacin

(D) Sulfadiazine

(E) Trimethoprim

Sulfadiazine and TMP-SMZ are drugs of choice in nocardiosis. In combination with pyrimethamine (an effective dihydrofolate reductase inhibitor in protozoa), sulfadiazine is effective in toxoplasmosis and is prophylactic against pneumocystis pneumonia in the AIDS patient. However, TMP-SMZ is more commonly used for the latter purpose. The answer is D.

Which statement about ciprofloxacin is accurate?

(A) Antagonism occurs if used with dihydrofolate reductase inhibitors

(B) Ciprofloxacin is active against MRSA strains of staphylococci

(C) Most “first-time” urinary tract infections are resistant to ciprofloxacin

(D) Organisms that commonly cause ear infections are highly resistant

(E) Tendinitis may occur during treatment

Ciprofloxacin is commonly used for the treatment of urinary tract infections and is active against most strains of common causative agents of otitis media, including H influenzae and pneumococci. However, up to 50% of strains of MRSA are now resistant to ciprofloxacin. No clinical antagonism has been reported between fluoroquinolones and inhibitors of folic acid synthesis. Fluoroquinolones are not recommended for use in pregnancy or for children less than 10 years of age because they may damage growing cartilage. Tendonitis and tendon rupture are adverse effects of the fluoroquinolones. The answer is E.

Supplementary folinic acid may prevent anemia in folate-deficient persons who use this drug; it is a weak base achieving tissue levels similar to those in plasma.

(A) Ciprofloxacin

(B) Levofloxacin

(C) Linezolid

(D) Sulfamethoxazole

(E) Trimethoprim

Trimethoprim is the only weak base listed (fluoroquinolones and sulfonamides are acidic compounds), and its high lipid solubility at blood pH allows penetration of the drug into prostatic and vaginal fluid to reach levels similar to those in plasma. Leukopenia and thrombocytopenia may occur in folate deficiency when the drug is used alone or in combination with sulfamethoxazole. Fluoroquinolones and linezolid do not exacerbate symptoms of folic acid deficiency. The answer is E.

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Chapter 46: Sulfonamides, Trimethoprim, & Fluoroquinolones

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