WBR249

Author	[[PageAuthor::Gerald Chi (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Pulmonology
Prompt	[[Prompt::A 32-year-old man with a history of intravenous drug use is admitted with a worsening respiratory distress accompanied by fever and nonproductive cough. Arterial blood gas values are pH=7.52, PaCO2=28 mm Hg, HCO3=22 mEq/L, and PaO2=70 mm Hg when breathing room air. The patient's CD4+ count is 145 cells per microliter. Chest X-ray demonstrates bilateral perihilar interstitial infiltrates suggive of an infectious etiology. The causative organism is detected in bronchoalveolar lavage with silver stain. Two days following pharmacologic therapy, the patient returns to the emergency department with chest pain, dizziness, headache, cold extremities, and pale skin. Peripheral blood smear is remarkable for irregularly fragmented erythrocytes. Supravital stain of the smear demonstrates immature red blood cells with dark blue dots and curved linear structures in the cytoplasm. Which of the following drugs is most likely to be responsible for this patient's readmission?]]
Answer A	AnswerA::Atovaquone
Answer A Explanation	AnswerAExp::For mild-to-moderate PCP alternative therapeutic regimens include either dapsone plus TMP, primaquine plus clindamycin, or atovaquone. However, atovaquone generally does not cause hemolytic anemia.
Answer B	AnswerB::Clindamycin
Answer B Explanation	AnswerBExp::For mild-to-moderate PCP, alternative therapeutic regimens include dapsone plus TMP, primaquine plus clindamycin, or atovaquone. However, clindamycin generally does not cause hemolytic anemia.
Answer C	AnswerC::Methylprednisolone
Answer C Explanation	AnswerCExp::Patients with moderate-to-severe PCP should receive adjunctive corticosteroids as early as possible within 72 hours after starting specific PCP therapy. However, methylprednisolone generally does not cause hemolytic anemia.
Answer D	AnswerD::Pentamidine
Answer D Explanation	AnswerDExp::For moderate-to-severe PCP, either clindamycin-primaquine or pentamidine may be administered. However, pentamidine generally does not cause hemolytic anemia.
Answer E	AnswerE::Primaquine
Answer E Explanation	[[AnswerEExp::For mild-to-moderate PCP, alternative therapeutic regimens include either dapsone plus TMP, primaquine plus clindamycin, or atovaquone. Common triggers of hemolytic anemia include sulfonamides and other drugs such as chloroquine, isoniazid, nalidixic acid, nitrofurantoin, and primaquine.]]
Right Answer	RightAnswer::E
Explanation	[[Explanation::Pneumocystis jiroveci/carinii pneumonia (PCP) is an opportunistic infection caused by Pneumocystis jiroveci. The risk of PCP increases among HIV-positive patients when CD4+ cell concentrations are less than 200 cells/μl. Symptoms include fever, non-productive cough, shortness of breath, weight loss, and night sweats. Chest films typically demonstrate diffuse, symmetrical, perihilar interstitial infiltration that may progress to a homogenous, ground-glass opacification of the lung fields. Hypoxemia, the most characteristic laboratory abnormality, may range from mild (room air arterial oxygen ≥70 mm Hg or alveolar-arterial O2 difference <35 mm Hg) to moderate (A-a DO2 ≥35 and <45 mm Hg) to severe (A-a DO2 ≥45 mm Hg). TMP-SMX is the treatment of choice for PCP. For mild-to-moderate disease, alternative therapeutic regimens include either dapsone plus TMP, primaquine plus clindamycin, or atovaquone. For moderate-to-severe disease, either clindamycin-primaquine or pentamidine may be administered. Patients with moderate-to-severe disease should receive adjunctive corticosteroids as early as possible within 72 hours after starting specific PCP therapy. This patient's hospital course is complicated by hemolytic anemia due to increased oxidative stress, which typically occurs among patients with glucose-6-phosphate dehydrogenase deficiency. Heinz bodies, bite cells, spherocytes, and reticulocytes may be evident on peripheral blood smear. Educational Objective: For mild-to-moderate PCP, alternative therapeutic regimens include either dapsone plus TMP, primaquine plus clindamycin, or atovaquone. Common triggers of hemolytic anemia include sulfonamides and other drugs such as chloroquine, isoniazid, nalidixic acid, nitrofurantoin, and primaquine. References: Kaplan JE, Benson C, Holmes KK, et al. Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. Centers for Prevention and Disease Control. 2009;58(RR04);1-198. First Aid 2015 page 168, 170.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Pneumocystis jiroveci, WBRKeyword::HIV, WBRKeyword::PCP, WBRKeyword::Pneumocystis carinii pneumonia, WBRKeyword::Dapsone, WBRKeyword::Antimicrobial therapy
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::