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Infection, Pharmacology & VTE MCQs

Practice Set 59 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 1161

Topic: Infection, Pharmacology & VTE

Aspiration of a 3 cm central, radiolucent bone lesion in the proximal humerus of an 8-year-old child yields clear, serosanguinous fluid. Laboratory analysis of this specific aspirate fluid is most likely to demonstrate markedly elevated levels of:

. Alkaline phosphatase
. Prostaglandins
. Matrix metalloproteinases
. Lactic acid
. Beta-2 microglobulin

Correct Answer & Explanation

. Prostaglandins

Explanation

The clinical presentation (central lucent lesion in proximal humerus in a child) and aspiration findings describe a Unicameral Bone Cyst (UBC). Fluid analysis of a UBC classically reveals high levels of prostaglandins (particularly PGE2), interleukins, and other inflammatory mediators. These factors stimulate osteoclastic bone resorption and prevent bone healing, leading to cyst expansion. This pathophysiology forms the rationale behind treating UBCs with intralesional corticosteroid injections, which inhibit prostaglandin synthesis.

Question 1162

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for deep vein thrombosis (DVT) prophylaxis following lower extremity total joint arthroplasty. What is its specific mechanism of action in the coagulation cascade?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via binding to antithrombin III
. Direct, competitive inhibition of Factor Xa
. Vitamin K antagonism via inhibition of epoxide reductase
. Irreversible inhibition of the P2Y12 ADP receptor on platelets

Correct Answer & Explanation

. Direct, competitive inhibition of Factor Xa

Explanation

Rivaroxaban (as well as Apixaban) is a direct oral anticoagulant (DOAC) that specifically and directly inhibits Factor Xa in the coagulation cascade, preventing the conversion of prothrombin to thrombin. Dabigatran directly inhibits thrombin (Factor IIa). Low molecular weight heparins (like enoxaparin) and fondaparinux indirectly inhibit Factor Xa by binding to antithrombin III. Warfarin is a vitamin K antagonist. Clopidogrel inhibits the ADP receptor on platelets.

Question 1163

Topic: Infection, Pharmacology & VTE
A 70-year-old woman is prescribed rivaroxaban for venous thromboembolism prophylaxis following a total knee arthroplasty. Which of the following best describes the mechanism of action of this medication?
. Inhibits the conversion of fibrinogen to fibrin
. Irreversibly binds and inhibits cyclooxygenase
. Directly inhibits Factor Xa
. Potentiates antithrombin III to inhibit Factor Xa and thrombin
. Inhibits Vitamin K epoxide reductase

Correct Answer & Explanation

. Directly inhibits Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa. Warfarin inhibits Vitamin K epoxide reductase. Low molecular weight heparin (LMWH) potentiates antithrombin III. Dabigatran is a direct thrombin inhibitor.

Question 1164

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, bacteria form a biofilm to evade host defenses and antibiotics. Which of the following terms describes the intercellular communication mechanism used by bacteria to coordinate gene expression and initiate biofilm formation?

. Opsonization
. Chemotaxis
. Quorum sensing
. Phagocytosis
. Transduction

Correct Answer & Explanation

. Quorum sensing

Explanation

Quorum sensing is a process of cell-to-cell communication that allows bacteria to share information about cell density and adjust gene expression accordingly. This process is a critical early step for the transition from planktonic (free-floating) bacteria to the complex, highly organized sessile structure of a biofilm.

Question 1165

Topic: Infection, Pharmacology & VTE

Rifampin is frequently utilized in the treatment of staphylococcal periprosthetic joint infections due to its ability to penetrate biofilms. What is its mechanism of action?

. Inhibits cell wall synthesis by binding to D-alanyl-D-alanine
. Inhibits bacterial DNA gyrase
. Inhibits DNA-dependent RNA polymerase
. Binds to the 50S ribosomal subunit
. Inhibits folic acid synthesis

Correct Answer & Explanation

. Inhibits DNA-dependent RNA polymerase

Explanation

Rifampin exerts its bactericidal effect by binding to the beta subunit of bacterial DNA-dependent RNA polymerase, thereby inhibiting RNA synthesis. It is highly active against stationary-phase bacteria within biofilms.

Question 1166

Topic: Infection, Pharmacology & VTE
Rivaroxaban is a widely used oral anticoagulant for venous thromboembolism prophylaxis after total joint arthroplasty. Which step in the coagulation cascade does it directly inhibit?
. 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 work by competitively and reversibly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor.

Question 1167

Topic: Infection, Pharmacology & VTE

A 55-year-old male presents with acute severe pain in the first metatarsophalangeal joint. Aspiration yields negatively birefringent, needle-shaped crystals. For long-term management to prevent recurrent attacks, which of the following drugs acts by inhibiting xanthine oxidase?

. Colchicine
. Probenecid
. Allopurinol
. Indomethacin
. Anakinra

Correct Answer & Explanation

. Allopurinol

Explanation

Allopurinol is a xanthine oxidase inhibitor used for the chronic management of gout to decrease uric acid production. Colchicine inhibits microtubule assembly, probenecid is a uricosuric agent, and indomethacin is an NSAID used for acute attacks.

Question 1168

Topic: Infection, Pharmacology & VTE

Methicillin-resistant Staphylococcus aureus (MRSA) poses a severe challenge in periprosthetic joint infections. Its specific resistance to beta-lactam antibiotics is primarily mediated by which of the following mechanisms?

. Production of extended-spectrum beta-lactamases (ESBL)
. Upregulation and over-expression of membrane efflux pumps
. Alteration of penicillin-binding protein (PBP2a) encoded by the mecA gene
. Ribosomal methylation encoded by the erm gene
. Hyperproduction of biofilm exopolysaccharide matrix

Correct Answer & Explanation

. Alteration of penicillin-binding protein (PBP2a) encoded by the mecA gene

Explanation

MRSA resistance is directly conferred by the mecA gene, which encodes for an altered penicillin-binding protein, PBP2a. This mutant protein has an extremely low affinity for beta-lactam antibiotics, allowing cell wall cross-linking to continue even in their presence.

Question 1169

Topic: Infection, Pharmacology & VTE

A 45-year-old man presents with an acutely swollen, erythematous knee. Joint aspiration yields opaque synovial fluid. Which of the following synovial fluid analysis profiles is most diagnostic for acute bacterial septic arthritis?

. WBC 35,000 cells/mcL, 60% PMNs, normal glucose
. WBC 65,000 cells/mcL, 90% PMNs, negatively birefringent crystals
. WBC 85,000 cells/mcL, 95% PMNs, synovial glucose level < 50% of serum glucose
. WBC 40,000 cells/mcL, 80% PMNs, positively birefringent crystals
. WBC 15,000 cells/mcL, 50% PMNs, normal lactic acid

Correct Answer & Explanation

. WBC 85,000 cells/mcL, 95% PMNs, synovial glucose level < 50% of serum glucose

Explanation

Septic arthritis typically presents with a synovial fluid WBC count > 50,000 cells/mcL, > 90% polymorphonuclear leukocytes (PMNs), and decreased glucose compared to serum. While definitive diagnosis requires culture, these parameters dictate immediate empiric treatment.

Question 1170

Topic: Infection, Pharmacology & VTE
Following a total hip arthroplasty, a patient is prescribed rivaroxaban for routine venous thromboembolism prophylaxis. Which of the following best describes the precise molecular target of this medication?
. Direct thrombin (Factor IIa) inhibition
. Direct competitive inhibition of Factor Xa
. Potentiation of antithrombin III
. Vitamin K epoxide reductase antagonism
. Inhibition of platelet ADP (P2Y12) receptors

Correct Answer & Explanation

. Direct competitive inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa. This interrupts the intrinsic and extrinsic pathways of the blood coagulation cascade.

Question 1171

Topic: Infection, Pharmacology & VTE

According to current prophylactic guidelines, what is the most appropriate perioperative antibiotic regimen for a patient with a known, documented Type I IgE-mediated anaphylactic allergy to penicillin undergoing a primary total knee arthroplasty?

. Cefazolin
. Cefuroxime
. Vancomycin
. Aztreonam
. Ertapenem

Correct Answer & Explanation

. Vancomycin

Explanation

For patients with a documented IgE-mediated (anaphylactic) allergy to penicillin, cephalosporins (like cefazolin and cefuroxime) have historically been avoided due to potential cross-reactivity, though modern evidence suggests the true cross-reactivity is very low. However, standard AAOS/CDC guidelines still recommend an alternative such as Vancomycin or Clindamycin as the preferred prophylactic agent in the setting of true anaphylaxis to beta-lactams.

Question 1172

Topic: Infection, Pharmacology & VTE

Biofilm formation on orthopedic implants represents a major barrier to eradicating periprosthetic joint infections. During which distinct phase of biofilm development are the offending bacteria most highly resistant to systemic antibiotic therapy?

. Initial reversible attachment mediated by van der Waals forces and hydrophobic interactions
. Irreversible attachment via the early secretion of extracellular polymeric substance (EPS)
. Exponential bacterial growth and microcolony formation
. Stationary phase within a mature, complex biofilm community
. Planktonic dispersion phase when bacteria are actively shed into surrounding tissues

Correct Answer & Explanation

. Stationary phase within a mature, complex biofilm community

Explanation

Bacteria within a mature biofilm (stationary phase) exhibit the highest resistance to antibiotics. In this phase, bacteria drastically reduce their metabolic rate and cell division, entering a dormant, nutrient-deprived state. Since the vast majority of systemic antibiotics target metabolically active processes (such as cell wall synthesis or active protein translation), these dormant 'persister' cells survive treatment. Additionally, the dense extracellular polymeric substance (EPS) matrix serves as a physical and chemical barrier.

Question 1173

Topic: Infection, Pharmacology & VTE

A patient develops a delayed periprosthetic joint infection 14 months after a total hip arthroplasty. Cultures grow Staphylococcus epidermidis. The pathogenesis of this infection relies primarily on the bacteria's ability to produce which of the following?

. Protein A
. Panton-Valentine leukocidin
. Glycocalyx
. Beta-lactamase
. Alpha toxin

Correct Answer & Explanation

. Glycocalyx

Explanation

Staphylococcus epidermidis is a leading cause of implant-associated infections due to its ability to produce a glycocalyx slime layer, which facilitates biofilm formation. Biofilms protect the bacteria from both host immune responses and antibiotics.

Question 1174

Topic: Infection, Pharmacology & VTE

A patient with an infected tibial nonunion is found to have methicillin-resistant Staphylococcus aureus (MRSA) cultured from intraoperative bone biopsies. The resistance of this organism to beta-lactam antibiotics is primarily mediated by which of the following mechanisms?

. Efflux pumps
. Production of beta-lactamase
. Alteration of penicillin-binding protein (PBP2a)
. Mutation in DNA gyrase
. Decreased outer membrane permeability

Correct Answer & Explanation

. Alteration of penicillin-binding protein (PBP2a)

Explanation

MRSA resistance is mediated by the mecA gene, which encodes for a novel penicillin-binding protein, PBP2a. This altered protein has a very low affinity for beta-lactam antibiotics, rendering them ineffective.

Question 1175

Topic: Infection, Pharmacology & VTE

During the pathogenesis of a periprosthetic joint infection, which of the following organisms relies primarily on the production of a polysaccharide glycocalyx slime layer to facilitate initial adherence and biofilm formation on the implant surface?

. Staphylococcus aureus
. Staphylococcus epidermidis
. Pseudomonas aeruginosa
. Cutibacterium acnes
. Streptococcus pyogenes

Correct Answer & Explanation

. Staphylococcus epidermidis

Explanation

Staphylococcus epidermidis is a ubiquitous skin commensal and a major pathogen in implant-related infections. It produces an exopolysaccharide glycocalyx slime layer that facilitates adherence to hardware and protects the bacteria from both host immunity and systemic antibiotics.

Question 1176

Topic: Infection, Pharmacology & VTE
A 4-year-old child presents with a 2-day history of refusal to bear weight on the right leg. Clinical evaluation reveals a temperature of 38.6°C (101.5°F). Laboratory workup shows a WBC count of 14,000/mm³, an ESR of 50 mm/hr, and a CRP of 3.5 mg/dL. According to the classic Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 10%
. 40%
. 71%
. 99%
. 100%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria are used to differentiate septic arthritis from transient synovitis in children. The four classic criteria are: history of fever (>38.5°C), non-weight bearing, ESR >40 mm/hr, and serum WBC >12,000/mm³. The probability of septic arthritis based on the number of criteria present is approximately: 1 predictor = 3%, 2 predictors = 40%, 3 predictors = 93%, and 4 predictors = 99%. This patient meets all 4 criteria.

Question 1177

Topic: Infection, Pharmacology & VTE

Bacterial biofilms on orthopedic implants render infections highly resistant to antibiotics and host immune clearance. The life cycle of a biofilm occurs in distinct stages. What is the final stage that facilitates the spread of infection to distant sites?

. Reversible attachment
. Irreversible attachment and exopolysaccharide production
. Microcolony formation
. Dispersion (Detachment)
. Quorum sensing activation

Correct Answer & Explanation

. Irreversible attachment and exopolysaccharide production

Explanation

The stages of biofilm formation are: 1) Reversible attachment of planktonic bacteria to the surface, 2) Irreversible attachment, 3) Maturation (growth, exopolysaccharide matrix production, quorum sensing), and 4) Dispersion/Detachment, where single cells or clumps of bacteria shed from the biofilm to disseminate and colonize new surfaces.

Question 1178

Topic: Infection, Pharmacology & VTE
The progressive loss of articular cartilage characteristic of osteoarthritis is primarily mediated by the enzymatic cleavage of aggrecan and Type II collagen. Which class of enzymes is the primary driver of this catabolic degradation?
. Cyclooxygenases (COX-1, COX-2)
. Matrix metalloproteinases (MMPs)
. Cathepsin K
. Alkaline phosphatase
. Lipoxygenases

Correct Answer & Explanation

. Matrix metalloproteinases (MMPs)

Explanation

Matrix metalloproteinases (MMPs), specifically MMP-13 (collagenase 3) and ADAMTS-5 (an aggrecanase), are the principal enzymes that degrade the cartilage extracellular matrix in osteoarthritis.

Question 1179

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a limp and refuses to bear weight on his right leg. According to the modified Kocher criteria, which of the following combinations gives the highest probability of septic arthritis of the hip?

. Fever > 38.5C, non-weight bearing, ESR > 40, WBC > 12,000
. Fever > 38.0C, limp, ESR > 20, WBC > 10,000
. Normal temperature, non-weight bearing, CRP > 1.0, WBC > 15,000
. Fever > 39.0C, non-weight bearing, ESR > 40, platelet count > 400,000
. Fever > 38.5C, limp, CRP > 2.0, WBC > 8,000

Correct Answer & Explanation

. Fever > 38.5C, non-weight bearing, ESR > 40, WBC > 12,000

Explanation

The four classic Kocher criteria for septic arthritis in a child are: non-weight bearing on the affected side, ESR > 40 mm/hr, Fever > 38.5 C (101.3 F), and WBC count > 12,000 cells/mm3. The presence of all four criteria indicates a >99% probability of septic arthritis.

Question 1180

Topic: Infection, Pharmacology & VTE

Methicillin-resistant Staphylococcus aureus (MRSA) is a major concern in prosthetic joint infections. Its resistance to beta-lactam antibiotics is primarily mediated by the mecA gene, which encodes for:

. Beta-lactamase enzymes that degrade the antibiotic
. Efflux pumps that actively remove the antibiotic from the cell
. An altered penicillin-binding protein (PBP2a) with low affinity for beta-lactams
. Porin channel modifications that prevent antibiotic entry
. Ribosomal methylation preventing antibiotic binding

Correct Answer & Explanation

. An altered penicillin-binding protein (PBP2a) with low affinity for beta-lactams

Explanation

The mecA gene encodes for PBP2a, an altered penicillin-binding protein that has a significantly reduced affinity for beta-lactam antibiotics. This structural change allows MRSA to maintain cell wall synthesis even in the presence of these drugs.

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