Sulfonamides and trimethoprim — MCQs

A 68-year-old man comes to the physician because of headache, fatigue, and nonproductive cough for 1 week. He appears pale. Pulmonary examination shows no abnormalities. Laboratory studies show a hemoglobin concentration of 9.5 g/dL and an elevated serum lactate dehydrogenase concentration. A peripheral blood smear shows normal red blood cells that are clumped together. Results of cold agglutinin titer testing show a 4-fold elevation above normal. An x-ray of the chest shows diffuse, patchy infiltrates bilaterally. Treatment is begun with an antibiotic that is also used to promote gut motility. Which of the following is the primary mechanism of action of this drug?

A 49-year-old woman comes to the physician because of a 4-month history of fatigue and recurrent pain in both of her wrists and her fingers. During this time, she has also had stiffness of her joints for about 80 minutes after waking up in the morning. Examination shows swelling and tenderness of the wrists and metacarpophalangeal joints bilaterally. Her serum erythrocyte sedimentation rate is 42 mm/h and rheumatoid factor is positive. Treatment is begun with a drug that results in decreased synthesis of deoxythymidine monophosphate. This mechanism is most similar to the mechanism of action of which of the following drugs?

A 67-year-old man is seen on the surgical floor after a transplant procedure. The previous day, the patient had a renal transplant from a matched donor. He is currently recovering and doing well. The patient has a past medical history of IV drug use, diabetes mellitus, oral cold sores, hypertension, renal failure, and dyslipidemia. The patient's current medications include lisinopril, atorvastatin, insulin, and aspirin. Prior to the procedure, he was also on dialysis. The patient is started on cyclosporine. The patient successfully recovers over the next few days. Which of the following medications should be started in this patient?

A 15-year-old boy presents with his father to the urgent care department with a 5-day history of frequent diarrhea, occasionally mixed with streaks of blood. Stool cultures are pending, but preliminary stool samples demonstrate fecal leukocytes and erythrocytes. The patient's vital signs are within normal limits, and he is started on outpatient therapy for presumed Shigella infection. Which of the following was the young man most likely started on?

A 6-year-old boy is brought to the physician because of headache, cough, runny nose, and a low-grade fever since waking up that morning. He has been healthy except for a urinary tract infection one week ago that has resolved with trimethoprim-sulfamethoxazole therapy. Both parents have a history of allergic rhinitis. His temperature is 37.8°C (100°F). Physical exam shows rhinorrhea and tenderness over the frontal and maxillary sinuses. There is cervical lymphadenopathy. Laboratory studies show: Hemoglobin 14.2 g/dL Leukocyte count 2,700/mm3 Segmented neutrophils 30% Bands 1% Eosinophils 4% Basophils 0% Lymphocytes 56% Monocytes 9% Platelet count 155,000/mm3 Which of the following is the most likely underlying cause of this patient's symptoms?

A 55-year-old man with a history of hypertension and benign prostate hyperplasia presents for follow-up 4 days into the treatment of a urinary tract infection with trimethoprim-sulfamethoxazole. His symptoms have resolved, and he reports no problems with urination, with the exception of a weak urine stream and hesitancy, which he has had for the past 2 years. At the time of this visit, the patient is afebrile; the blood pressure is 130/88 mm Hg and the heart rate is 80/min. There is no flank tenderness. A urinalysis reveals no leukocytes and is negative for esterase. The urinalysis reveals 2 red blood cells (RBCs)/ high power field (HPF), and there are no casts on urinary sediment analysis. The physician, however, notices the following abnormality: Prior treatment BUN 12 mg/dL Creatinine 1.2 mg/dL Today’s visit BUN 13 mg/dL Creatinine 2.1 mg/dL

A 29-year-old female presents to her gynecologist complaining of a painful rash around her genitals. She has multiple sexual partners and uses condoms intermittently. Her last STD screen one year ago was negative. On examination, she has bilateral erosive vesicles on her labia majora and painful inguinal lymphadenopathy. She is started on an oral medication that requires a specific thymidine kinase for activation. Which of the following adverse effects is associated with this drug?

A 30-year-old man comes to the emergency department because of the sudden onset of back pain beginning 2 hours ago. Beginning yesterday, he noticed that his eyes started appearing yellowish and his urine was darker than normal. Two months ago, he returned from a trip to Greece, where he lived before immigrating to the US 10 years ago. Three days ago, he was diagnosed with latent tuberculosis and started on isoniazid. He has worked as a plumber the last 5 years. His temperature is 37.4°C (99.3°F), pulse is 80/min, and blood pressure is 110/70 mm Hg. Examination shows back tenderness and scleral icterus. Laboratory studies show: Hematocrit 29% Leukocyte count 8000/mm3 Platelet count 280,000/mm3 Serum Bilirubin Total 4 mg/dL Direct 0.7 mg/dL Haptoglobin 15 mg/dL (N=41–165 mg/dL) Lactate dehydrogenase 180 U/L Urine Blood 3+ Protein 1+ RBC 2–3/hpf WBC 2–3/hpf Which of the following is the most likely underlying cause of this patient's anemia?

An 8-year-old boy is brought to the emergency department by his parents because of sudden onset of abdominal pain beginning an hour ago. The parents report that their son has also had an episode of dark urine earlier that morning. Three days ago, he was diagnosed with a urinary tract infection and was treated with trimethoprim-sulfamethoxazole. He emigrated from Liberia to the US with his family 3 years ago. There is no personal history of serious illness. His immunizations are up-to-date. Vital signs are within normal limits. Examination shows diffuse abdominal tenderness and scleral icterus. The spleen is palpated 1–2 cm below the left costal margin. Laboratory studies show: Hemoglobin 10 g/dL Mean corpuscular volume 90 μm3 Reticulocyte count 3% Serum Bilirubin Total 3 mg/dL Direct 0.5 mg/dL Haptoglobin 20 mg/dL (N=41–165 mg/dL) Lactate dehydrogenase 160 U/L Urine Blood 3+ Protein 1+ RBC 2–3/hpf WBC 2–3/hpf Which of the following is the most likely underlying cause of this patient's symptoms?

A 45-year-old woman presents to the emergency department with fever, cough, tonsillar enlargement, and bleeding lips. She has a diffuse blistering rash that encompasses the palms and soles of her feet, in total covering 55% of her total body surface area (TBSA). The upper epidermal layer easily slips away with slight rubbing. Within 24 hours the rash progresses to 88% TBSA involvement and the patient requires mechanical ventilation for respiratory distress. Which of the following is the most likely etiology of this patient’s condition?