All practice questions

A 62-year-old man is hospitalized for the management of urosepsis. Blood and urine cultures obtained on admission grow *Enterobacter cloacae*. Initial susceptibility testing indicates the isolate is susceptible to ceftriaxone, cefepime, and meropenem. The patient is started on intravenous ceftriaxone, and his fever and leukocytosis improve over the next 72 hours. However, on day 5 of hospitalization, he develops recurrent fever, tachycardia, and altered mental status. Repeat blood cultures are drawn and again grow *Enterobacter cloacae*. Susceptibility testing of the new isolate reveals resistance to ceftriaxone, but it remains susceptible to cefepime and meropenem. Which of the following is the most likely molecular mechanism responsible for this patient's treatment failure?

During routine inpatient monitoring, blood cultures drawn from a $58$-year-old male return positive for Gram-positive cocci in clusters. The patient was admitted $18$ days ago for right-sided infective endocarditis and was initially treated with intravenous vancomycin. On hospital day $6$, his regimen was changed to daptomycin due to a rising vancomycin minimum inhibitory concentration (MIC) and persistent bacteremia. He initially improved, but over the last $48$ hours, he has developed recurrent high-grade fevers. Repeat susceptibility testing of the new isolate demonstrates a daptomycin MIC of $8 \text{ \mu g/mL}$ (susceptible is $\leq 1 \text{ \mu g/mL}$). Which of the following best describes the underlying molecular mechanism responsible for this pathogen's newly acquired drug resistance?

A 62-year-old man comes to the clinic due to a 2-day history of severe muscle aches and dark urine. He has a history of hyperlipidemia and hypertension, for which he takes stable doses of simvastatin and amlodipine. One week ago, he was diagnosed with community-acquired pneumonia and was prescribed a 7-day course of clarithromycin. Laboratory studies today show a serum creatine kinase level of 12,000 U/L. Which of the following pharmacokinetic mechanisms best explains this patient's current presentation?

A 45-year-old man who works in a sheep wool processing facility is brought to the emergency department with a rapidly progressing illness characterized by high fever, severe dyspnea, and retrosternal chest pain. A chest radiograph reveals a significantly widened mediastinum and bilateral pleural effusions. Blood cultures subsequently grow large, Gram-positive, spore-forming rods in chains. The rapid clinical deterioration seen in this patient is largely mediated by a tripartite exotoxin.

Arrange the following cellular events in the correct chronological sequence regarding the cellular entry and activation of this pathogen's primary virulence complex.

A 62-year-old man comes to the emergency department complaining of severe, diffuse muscle pain and dark urine for the past 2 days. He has a history of hypertension, hyperlipidemia, and type 2 diabetes mellitus. His daily medications include lisinopril, amlodipine, metformin, and atorvastatin. Ten days ago, he was evaluated at an urgent care clinic for community-acquired pneumonia and was prescribed a 7-day course of clarithromycin, which he completed 3 days ago. His temperature is 37.2°C (99.0°F), blood pressure is 134/82 mm Hg, and pulse is 78/min. Physical examination shows diffuse muscle tenderness on palpation. Laboratory studies show a serum creatine kinase level of 8,500 U/L and an elevated serum creatinine of 1.9 mg/dL (baseline 1.0 mg/dL). Urinalysis is positive for blood but shows no red blood cells on microscopy. Which of the following mechanisms best explains this patient's current presentation?

Match each medically important fungal pathogen with its primary morphologic or biochemical mechanism for evading host immune defenses.

A 45-year-old agricultural worker presents to the emergency department with a 2-day history of progressively worsening jaw stiffness, difficulty swallowing, and painful, uncontrollable muscle spasms in his back. Vital signs show a heart rate of 112/min and blood pressure of 165/95 mm Hg. Physical examination is notable for severe trismus, risus sardonicus, and opisthotonos. He reports stepping on a rusty nail in a barn two weeks ago and has not received any vaccinations since early childhood. The pathogenic mechanism underlying this patient's condition is driven by a potent protein exotoxin. Arrange the following steps in the correct chronological sequence to describe the molecular pathogenesis of this exotoxin, from initial neuronal contact to its ultimate synaptic effect.

Match each pharmacodynamic agent or modulator to its corresponding effect on the dose-response curve.

A 52-year-old man visits the clinic for a follow-up appointment. He has a history of chronic hepatitis C virus (HCV) infection, genotype 1a. He has just taken the final dose of a 12-week regimen of daily glecaprevir-pibrentasvir. Prior to initiating therapy, baseline testing for hepatitis B virus and HIV was negative, and liver transient elastography demonstrated a fibrosis score of F2 (moderate fibrosis). The patient reports feeling well and has experienced no adverse effects from the medication. He has no history of alcohol use disorder. Physical examination shows no jaundice, spider angiomata, or hepatosplenomegaly.

Serial laboratory results are as follows:

The patient asks how the clinical team will determine if his liver infection has been fully cured by the antiviral regimen. Which of the following is the most appropriate next step in evaluating the success of this patient's treatment?

Five patients are currently awaiting transition from an acute care hospital. The attending physician must determine the correct post-acute environment for each based on their current clinical stability, rehabilitation tolerance, and functional deficits. Match each patient scenario with the most appropriate post-acute care setting.

A $45$-year-old man is admitted to the intensive care unit with septic shock secondary to severe *Staphylococcus aureus* pneumonia. He requires massive intravenous fluid resuscitation and initiation of vasopressor support. Laboratory studies reveal a serum creatinine of $3.2\text{ mg/dL}$, representing a $75\%$ reduction in his estimated glomerular filtration rate compared to his baseline. Intravenous vancomycin therapy is planned. Capillary leak syndrome and aggressive fluid resuscitation have significantly increased this patient's extracellular fluid compartment, effectively doubling the drug's apparent volume of distribution ($V_d$). Assuming the target steady-state peak plasma concentration remains unchanged, which of the following pharmacokinetic-based dosing adjustments is most appropriate for this patient compared to a healthy adult of the same weight?

A 34-year-old woman with a history of bipolar disorder has been well-controlled on a stable daily dose of lithium carbonate for the past two years. She recently joined a local running club and developed bilateral knee pain. To manage the discomfort, she started taking over-the-counter naproxen regularly. Five days later, she presents to her primary care physician complaining of new-onset nausea, coarse hand tremors, and feeling unsteady when walking. Her vital signs are within normal limits. Laboratory testing reveals a serum lithium concentration of 1.9 mEq/L (therapeutic range: 0.6-1.2 mEq/L). Which of the following pharmacokinetic mechanisms best explains this patient's laboratory findings and clinical presentation?

A 68-year-old woman is evaluated in the hospital for a deep vein thrombosis of the left lower extremity. She is prescribed oral warfarin. However, a bridging parenteral anticoagulant is not initiated. Three days later, the patient develops painful, well-demarcated, erythematous lesions on her abdomen and breasts that rapidly progress to purpuric necrosis and eschar formation. This patient's dermatologic complication is most directly caused by a precipitous decline in the plasma activity of which of the following?

A 52-year-old man with locally advanced oropharyngeal squamous cell carcinoma is currently undergoing the third week of a definitive fractionated radiation therapy regimen. He presents with severe oral pain, erythema, and ulcerations of the buccal mucosa, consistent with radiation-induced mucositis. The ionizing radiation causes extensive DNA double-strand breaks in the rapidly dividing basal epithelial cells, ultimately committing these cells to programmed cell death. Arrange the following subcellular biochemical events in the correct chronological order from the initial molecular trigger to the execution of this cellular injury pathway.

A 75-year-old man is transferred from a skilled nursing facility to the intensive care unit for hypotension, fever, and severe abdominal pain. He recently completed a 10-day course of clindamycin for aspiration pneumonia. Vital signs show a temperature of 38.9°C (102.0°F), pulse of 122/min, and blood pressure of 86/50 mm Hg. Physical examination reveals a distended abdomen with diffuse tenderness and guarding. Laboratory studies show a leukocyte count of 32,000/mm³ and serum creatinine of 2.4 mg/dL. A non-contrast CT scan of the abdomen demonstrates severe, diffuse colonic wall thickening with mucosal edema (thumbprinting). Stool polymerase chain reaction is positive for Clostridioides difficile toxin genes. Arrange the following steps in the correct chronological sequence detailing the cellular pathogenesis of the primary toxin (Toxin B) responsible for this patient's mucosal necrosis.

A 24-year-old healthy male sustains a minor laceration to his forearm while cooking. Bleeding from the wound ceases within a few minutes due to an intact physiological hemostatic response. Arrange the following cellular and molecular events of hemostasis in the correct chronological order, beginning immediately after the initial vascular injury.

A 60-year-old man is admitted to the intensive care unit for a severe exacerbation of chronic obstructive pulmonary disease. He is started on a continuous intravenous infusion of theophylline at a rate of $40 \text{ mg/hr}$. Forty-eight hours later, his steady-state serum theophylline concentration is measured at $10 \text{ mg/L}$ (therapeutic range: $10-20 \text{ mg/L}$). His estimated volume of distribution ($V_d$) for theophylline is $40 \text{ L}$.

On hospital day 4, the patient develops a catheter-associated urinary tract infection, and empiric intravenous ciprofloxacin is added to his regimen. On hospital day 8, the patient complains of intractable nausea, palpitations, and tremors. An electrocardiogram shows sinus tachycardia. A repeat serum theophylline concentration is found to be $20 \text{ mg/L}$. The theophylline infusion rate had remained constant at $40 \text{ mg/hr}$.

The physician immediately stops the theophylline infusion to allow the drug concentration to fall to $10 \text{ mg/L}$ before restarting at a lower rate.

Assuming first-order elimination kinetics and that the volume of distribution remains unchanged, approximately how many hours will it take from the time the infusion is stopped for the serum theophylline concentration to decrease to $10 \text{ mg/L}$?

A 68-year-old man is hospitalized in the intensive care unit for septic shock secondary to a complicated intra-abdominal infection following a ruptured appendix. He has a prolonged hospital course complicated by acute respiratory distress syndrome requiring mechanical ventilation. During his third week of hospitalization, he develops a new-onset fever, increased vasopressor requirements, and purulent endotracheal secretions. Blood and sputum cultures grow Klebsiella pneumoniae. Initial antimicrobial susceptibility testing reveals resistance to all tested penicillins, cephalosporins, and carbapenems. The patient is treated empirically with ceftazidime-avibactam based on local antibiogram data. However, 72 hours later, he remains febrile and hemodynamically unstable. Repeat susceptibility testing confirms that the isolate is resistant to ceftazidime-avibactam. Further specialized susceptibility testing reveals the isolate is susceptible to the combination of aztreonam and avibactam, as well as to cefiderocol. Which of the following best describes the underlying molecular mechanism responsible for this organism's specific resistance profile?

A 34-year-old man comes to the emergency department due to a 3-day history of high fever, severe sore throat, and easy bruising. Four weeks ago, he was diagnosed with severe ileocolonic Crohn disease and was started on a tapering dose of oral prednisone and azathioprine. His temperature is 39.2°C (102.6°F), blood pressure is 105/65 mm Hg, and pulse is 115/min. Physical examination shows pale conjunctivae, pharyngeal erythema with exudates, and scattered petechiae over the lower extremities.

Laboratory studies show:
Leukocyte count: 1,100/mm³
Absolute neutrophil count: 200/mm³
Hemoglobin: 8.2 g/dL
Platelet count: 35,000/mm³

The patient's condition is most likely due to an underlying genetic defect in which of the following molecular processes?

Match each clinical scenario describing a pharmacokinetic drug interaction to the primary underlying molecular mechanism responsible for the altered drug levels.