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Infection, Pharmacology & VTE MCQs

Practice Set 60 of 68

This practice set contains high-yield board review questions covering key concepts in Infection, Pharmacology & VTE. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1181

Topic: Infection, Pharmacology & VTE

According to the original Kocher criteria, the presence of four specific factors yields a 99% probability of septic arthritis in a pediatric hip. Which of the following is NOT one of the original four criteria?

. History of fever > 38.5 degrees Celsius
. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate > 40 mm/hr
. C-reactive protein > 2.0 mg/dL
. Serum white blood cell count > 12,000 cells/mm3

Correct Answer & Explanation

. C-reactive protein > 2.0 mg/dL

Explanation

The original Kocher criteria include: fever > 38.5 C, inability to bear weight, ESR > 40 mm/hr, and WBC > 12,000/mm3. While later studies (such as by Caird et al.) demonstrated that a CRP > 2.0 mg/dL is a strong independent predictor of septic arthritis, it was not part of the original four Kocher criteria.

Question 1182

Topic: Infection, Pharmacology & VTE
For postoperative deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty, multiple oral anticoagulants are now utilized. Which of the following agents exerts its clinical effect by directly and selectively inhibiting Factor Xa?
. Warfarin
. Dabigatran
. Apixaban
. Clopidogrel
. Enoxaparin

Correct Answer & Explanation

. Apixaban

Explanation

Apixaban and Rivaroxaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits vitamin K-dependent factors (II, VII, IX, X). Enoxaparin (LMWH) primarily potentiates Antithrombin III, which indirectly inhibits Factor Xa.

Question 1183

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with an acutely swollen knee. Synovial fluid analysis reveals a white blood cell count of 65,000 cells/mm3 with 85% polymorphonuclear leukocytes (PMNs), and a glucose level significantly lower than serum. What is the most likely diagnosis?

. Osteoarthritis
. Traumatic hemarthrosis
. Gout
. Septic arthritis
. Pigmented villonodular synovitis

Correct Answer & Explanation

. Septic arthritis

Explanation

Synovial fluid with a WBC count greater than 50,000 cells/mm3 (often >75% PMNs) and decreased glucose relative to serum is highly indicative of septic arthritis. Inflammatory arthropathies like gout typically present with WBC counts between 2,000 and 50,000 cells/mm3.

Question 1184

Topic: Infection, Pharmacology & VTE
According to recent guidelines for venous thromboembolism (VTE) prophylaxis following elective total joint arthroplasty in standard-risk patients, aspirin is considered non-inferior to other anticoagulants. What is the primary mechanism of action of aspirin?
. Direct factor Xa inhibition
. Direct thrombin inhibition
. Irreversible inhibition of cyclooxygenase (COX)
. Vitamin K epoxide reductase inhibition
. Activation of antithrombin III

Correct Answer & Explanation

. Irreversible inhibition of cyclooxygenase (COX)

Explanation

Aspirin acts by irreversibly inhibiting cyclooxygenase (COX-1 and COX-2) enzymes. This blocks the formation of thromboxane A2 in platelets, thereby producing a potent antiplatelet effect that lasts for the lifetime of the platelet (7-10 days).

Question 1185

Topic: Infection, Pharmacology & VTE

In the pathogenesis of implant-related orthopedic infections, Staphylococcus epidermidis utilizes a specific extracellular structure to form a protective biofilm. What is the primary constituent of this structure?

. Peptidoglycan
. Lipopolysaccharide
. Polysaccharide glycocalyx
. Teichoic acid
. Flagellin

Correct Answer & Explanation

. Polysaccharide glycocalyx

Explanation

Staphylococcus epidermidis produces an extracellular polysaccharide slime layer, known as the glycocalyx. This matrix facilitates adherence to abiotic implant surfaces and protects the bacteria from host immune responses and systemic antibiotics by forming a mature biofilm.

Question 1186

Topic: Infection, Pharmacology & VTE

A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the specific mechanism of action of this medication?

. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct Factor Xa inhibitor
. Low molecular weight heparin
. Antiplatelet agent via COX-1 inhibition

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that works by directly inhibiting Factor Xa, interrupting both the intrinsic and extrinsic pathways of the blood coagulation cascade. It does not require routine coagulation monitoring.

Question 1187

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, bacterial biofilms confer significant resistance to systemic antibiotics. Which phase of biofilm formation is characterized by the production of extracellular polymeric substance (EPS) and irreversible attachment?

. Planktonic phase
. Reversible attachment
. Maturation phase
. Dispersion phase
. Quorum sensing initiation

Correct Answer & Explanation

. Maturation phase

Explanation

Following initial reversible attachment, bacteria undergo irreversible attachment and begin the maturation phase, which is characterized by the robust production of the extracellular polymeric substance (EPS) matrix. This matrix shields the bacteria from host defenses and antimicrobials.

Question 1188

Topic: Infection, Pharmacology & VTE
A 68-year-old woman is scheduled for a total hip arthroplasty. She is currently taking rivaroxaban for non-valvular atrial fibrillation. What is the specific mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K epoxide reductase inhibitor
. Direct factor Xa inhibitor
. Anti-thrombin III activator
. Glycoprotein IIb/IIIa inhibitor

Correct Answer & Explanation

. Direct factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that specifically inhibit Factor Xa. Dabigatran is a direct thrombin inhibitor, while warfarin inhibits Vitamin K epoxide reductase.

Question 1189

Topic: Infection, Pharmacology & VTE

During the establishment of an orthopedic implant-associated infection, bacteria within a biofilm begin to communicate and coordinate group behaviors (such as altering gene expression and increasing virulence) once a critical population density is reached. What is this communication process called?

. Glycocalyx shedding
. Quorum sensing
. Planktonic dispersion
. Opsonization
. Chemotaxis

Correct Answer & Explanation

. Quorum sensing

Explanation

Quorum sensing is the mechanism by which bacteria monitor their own population density through the secretion and detection of autoinducer molecules. Once a critical threshold is reached, it triggers a coordinated change in gene expression, promoting biofilm maturation, virulence factor production, and metabolic dormancy.

Question 1190

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for chemical venous thromboembolism (VTE) prophylaxis following a total hip arthroplasty. This medication achieves its anticoagulant effect by directly inhibiting which of the following?
. Thrombin (Factor IIa)
. Factor Xa
. Vitamin K epoxide reductase
. Antithrombin III
. Factor VIII

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa, the first step in the common pathway of the coagulation cascade. Dabigatran, by contrast, is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase.

Question 1191

Topic: Infection, Pharmacology & VTE

A 7-year-old girl with homozygous sickle cell disease presents with high fever, localized bone pain, and erythema over her left proximal humerus. Blood cultures and a bone aspirate subsequently grow a Gram-negative bacillus. Which of the following is the most likely causative organism?

. Staphylococcus aureus
. Pseudomonas aeruginosa
. Salmonella typhimurium
. Haemophilus influenzae
. Kingella kingae

Correct Answer & Explanation

. Salmonella typhimurium

Explanation

While Staphylococcus aureus remains a common cause of osteomyelitis, patients with sickle cell disease have a unique and highly increased susceptibility to osteomyelitis caused by Salmonella species. This is thought to be secondary to functional asplenia and bowel wall microinfarctions.

Question 1192

Topic: Infection, Pharmacology & VTE

Which phase of biofilm formation on an orthopedic implant is characterized by the production of an extracellular polymeric substance (EPS) matrix that protects the bacteria from systemic antibiotics and host immune responses?

. Reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic phase

Correct Answer & Explanation

. Maturation

Explanation

The maturation phase of biofilm formation is marked by the secretion of the extracellular polymeric substance (EPS) matrix. This slimy matrix creates a protective microenvironment, rendering the bacteria highly resistant to standard antibiotic therapies.

Question 1193

Topic: Infection, Pharmacology & VTE
Low-molecular-weight heparin (LMWH) is frequently used for DVT prophylaxis following orthopedic surgery. LMWH primarily exerts its anticoagulant effect by inhibiting which of the following coagulation factors?
. Factor IIa (Thrombin)
. Factor VIIa
. Factor IXa
. Factor Xa
. Factor XIIa

Correct Answer & Explanation

. Factor Xa

Explanation

Low-molecular-weight heparin (LMWH) primarily binds to and potentiates antithrombin III, which selectively inhibits Factor Xa. It has significantly less effect on Factor IIa (thrombin) compared to unfractionated heparin.

Question 1194

Topic: Infection, Pharmacology & VTE
Rivaroxaban is an oral anticoagulant increasingly used for DVT prophylaxis following total joint arthroplasty. At which specific point in the coagulation cascade does it exert its primary effect?
. Direct inhibition of Thrombin (Factor IIa)
. Direct inhibition of Factor Xa
. Potentiation of Antithrombin III
. Inhibition of Vitamin K epoxide reductase
. Inhibition of von Willebrand factor cross-linking

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that specifically bind to and inhibit Factor Xa. This interrupts the common pathway of the coagulation cascade, preventing the conversion of prothrombin to thrombin.

Question 1195

Topic: Infection, Pharmacology & VTE
A patient undergoing total knee arthroplasty is prescribed apixaban for VTE prophylaxis. Which step in the coagulation cascade is directly inhibited by this medication?
. Conversion of fibrinogen to fibrin
. Activation of antithrombin III
. Factor Xa
. Vitamin K epoxide reductase
. Direct inhibition of thrombin (Factor IIa)

Correct Answer & Explanation

. Factor Xa

Explanation

Apixaban and rivaroxaban are direct, highly selective, and reversible inhibitors of Factor Xa. They block the conversion of prothrombin to thrombin without requiring antithrombin III as a mediator.

Question 1196

Topic: Infection, Pharmacology & VTE
A patient on rivaroxaban for deep vein thrombosis prophylaxis sustains a traumatic closed femur fracture requiring urgent intramedullary nailing. What is the specific molecular target of rivaroxaban?
. Thrombin (Factor IIa)
. Factor Xa
. Antithrombin III
. Vitamin K epoxide reductase
. Plasminogen

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that specifically inhibit Factor Xa. Dabigatran, in contrast, is a direct thrombin (Factor IIa) inhibitor.

Question 1197

Topic: Infection, Pharmacology & VTE

A 9-year-old boy with sickle cell disease presents with acute osteomyelitis of the diaphyseal femur. While Staphylococcus aureus remains the most common overall pathogen, he is at uniquely high risk for Salmonella osteomyelitis. What is the primary mechanism for this specific susceptibility?

. Impaired splenic opsonization of encapsulated organisms
. Microvascular bowel infarcts allowing transmural bacterial migration
. Defective neutrophil oxidative burst
. Decreased complement pathway activation
. Increased bone marrow iron stores promoting bacterial growth

Correct Answer & Explanation

. Microvascular bowel infarcts allowing transmural bacterial migration

Explanation

Patients with sickle cell disease suffer from microvascular occlusion, which in the gastrointestinal tract can cause microinfarcts. This allows Salmonella species to translocate from the bowel lumen into the bloodstream, eventually seeding ischemic bone.

Question 1198

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. At which point in the coagulation cascade does this medication exert its primary effect?
. Inhibition of Factor IIa (Thrombin)
. Inhibition of Factor Xa
. Activation of Antithrombin III
. Inhibition of Vitamin K epoxide reductase
. Inhibition of ADP-induced platelet aggregation

Correct Answer & Explanation

. Inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa in the coagulation cascade. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. LMWH primarily activates antithrombin III, which then inhibits Factor Xa.

Question 1199

Topic: Infection, Pharmacology & VTE

A 70-year-old man undergoes an extended spinal fusion lasting 6 hours. He received 2 grams of IV cefazolin 30 minutes prior to incision. According to current guidelines, what is the optimal timing for redosing the cefazolin?

. It does not need to be redosed
. 2 hours after the initial dose
. 4 hours after the initial dose
. 6 hours after the initial dose
. Only if estimated blood loss exceeds 2000 mL

Correct Answer & Explanation

. 4 hours after the initial dose

Explanation

Cefazolin has a half-life of approximately 1.8 to 2 hours. Current surgical antimicrobial prophylaxis guidelines recommend redosing cefazolin every 4 hours during the procedure to maintain adequate minimal inhibitory concentrations (MIC) in the tissues. Redosing is also recommended if estimated blood loss exceeds 1500 mL.

Question 1200

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis frequently causes periprosthetic joint infections due to its ability to form a robust biofilm. Which component is crucial for the intercellular adhesion phase of this biofilm formation?

. Protein A
. Polysaccharide intercellular adhesin (PIA)
. Panton-Valentine leukocidin
. Alpha-toxin
. Fibronectin-binding protein

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Polysaccharide intercellular adhesin (PIA) is synthesized by products of the ica operon in S. epidermidis. It mediates the critical cell-to-cell adhesion during biofilm accumulation on orthopedic implants.

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