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Infection, Pharmacology & VTE MCQs

Practice Set 61 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 1201

Topic: Infection, Pharmacology & VTE

In the formation of a bacterial biofilm on an orthopedic implant, which phase is primarily characterized by the irreversible attachment of bacteria and the robust production of an extracellular polymeric substance (EPS) matrix?

. Planktonic phase
. Adhesion phase
. Maturation phase
. Dispersion phase
. Stationary phase

Correct Answer & Explanation

. Maturation phase

Explanation

The maturation phase of a biofilm involves irreversible bacterial attachment and the secretion of an extensive exopolysaccharide (EPS) matrix. This matrix shields the bacterial colony from host cellular immunity and systemic antibiotics.

Question 1202

Topic: Infection, Pharmacology & VTE
A 68-year-old man requires elective total knee arthroplasty. He is currently taking rivaroxaban for atrial fibrillation. What is the specific mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K epoxide reductase inhibitor
. Antithrombin III activator
. ADP receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are oral direct Factor Xa inhibitors used for DVT prophylaxis and stroke prevention. Dabigatran, conversely, functions as a direct thrombin (Factor IIa) inhibitor.

Question 1203

Topic: Infection, Pharmacology & VTE

A 45-year-old man presents with an acute, swollen, painful knee. Synovial fluid aspiration yields an opaque, yellow fluid with a WBC count of 85,000 cells/mm3 and 90% polymorphonuclear leukocytes. What is the most likely diagnosis?

. Osteoarthritis
. Gout
. Septic arthritis
. Rheumatoid arthritis
. Traumatic hemarthrosis

Correct Answer & Explanation

. Septic arthritis

Explanation

Synovial fluid with a WBC count greater than 50,000 cells/mm3 (with a highly elevated PMN percentage) is strongly indicative of septic arthritis. Inflammatory arthropathies like gout typically present with WBC counts between 2,000 and 50,000 cells/mm3.

Question 1204

Topic: Infection, Pharmacology & VTE
A 45-year-old farmer sustains a highly contaminated Gustilo-Anderson Grade IIIA open tibia fracture from a tractor rollover. According to evidence-based guidelines, which antibiotic regimen is most appropriate for initial management?
. Cefazolin alone
. Cefazolin and gentamicin
. Cefazolin, gentamicin, and penicillin
. Vancomycin and ceftriaxone
. Clindamycin alone

Correct Answer & Explanation

. Cefazolin, gentamicin, and penicillin

Explanation

For farm injuries with gross soil contamination, high-dose penicillin is added to a first-generation cephalosporin and an aminoglycoside. This provides necessary coverage for Clostridium species to prevent gas gangrene.

Question 1205

Topic: Infection, Pharmacology & VTE

A 60-year-old male presents with a swollen, acutely painful knee. Synovial fluid aspiration reveals a white blood cell count of 65,000 cells/mm3 with 85% polymorphonuclear leukocytes. Crystals are absent. What is the most likely diagnosis?

. Osteoarthritis
. Rheumatoid arthritis flare
. Gouty arthropathy
. Septic arthritis
. Lyme arthritis

Correct Answer & Explanation

. Septic arthritis

Explanation

A synovial fluid WBC count greater than 50,000 cells/mm3 with a high percentage of PMNs strongly suggests septic arthritis. The absence of crystals further lowers the likelihood of gout or pseudogout.

Question 1206

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis (DVT) prophylaxis following a total hip arthroplasty. What is the specific mechanism of action of this medication?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III
. Direct inhibition of Factor Xa
. Inhibition of vitamin K epoxide reductase
. Inhibition of ADP-induced platelet aggregation

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct inhibitors of Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Low-molecular-weight heparins (like enoxaparin) work indirectly by binding to antithrombin III, which in turn inhibits Factor Xa. Warfarin inhibits vitamin K epoxide reductase.

Question 1207

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, which phase of biofilm formation is characterized by the irreversible attachment of bacteria to the implant surface mediated by exopolysaccharides?

. Planktonic phase
. Adhesion phase
. Aggregation phase
. Maturation phase
. Dispersion phase

Correct Answer & Explanation

. Aggregation phase

Explanation

Biofilm formation follows distinct stages: 1) Reversible attachment (planktonic bacteria initially adhere), 2) Irreversible attachment (aggregation phase mediated by extracellular polymeric substances/exopolysaccharides), 3) Maturation (growth and development of complex 3D architecture), and 4) Detachment/Dispersion.

Question 1208

Topic: Infection, Pharmacology & VTE

Biofilm formation on orthopedic implants makes periprosthetic joint infections highly resistant to host immunity and antibiotics. What represents the first distinct phase of biofilm formation?

. Irreversible attachment via exopolysaccharides
. Maturation and quorum sensing
. Reversible attachment of planktonic bacteria
. Dispersion of sessile bacteria
. Formation of the glycocalyx

Correct Answer & Explanation

. Reversible attachment of planktonic bacteria

Explanation

The first step in biofilm formation is the reversible attachment of free-floating (planktonic) bacteria to the implant surface. This is initially mediated by weak forces such as van der Waals forces and hydrophobic interactions.

Question 1209

Topic: Infection, Pharmacology & VTE
Low-molecular-weight heparin (LMWH) is commonly prescribed for deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty. LMWH exerts its primary anticoagulant effect by binding to antithrombin III, which predominantly inactivates which of the following?
. Factor IIa (Thrombin)
. Factor VIIa
. Factor IXa
. Factor Xa
. Factor XIIa

Correct Answer & Explanation

. Factor Xa

Explanation

LMWH binds to antithrombin III and primarily accelerates the inactivation of Factor Xa. Due to its shorter chain length compared to unfractionated heparin, it has much less inhibitory effect on Factor IIa (thrombin).

Question 1210

Topic: Infection, Pharmacology & VTE

A 6-year-old boy presents with high fever and refusal to bear weight on his right leg. MRI confirms acute hematogenous osteomyelitis of the proximal tibia. What is the primary anatomical location for the initial bacterial seeding in this age group?

. Diaphysis
. Metaphysis
. Epiphysis
. Physis
. Periosteum

Correct Answer & Explanation

. Metaphysis

Explanation

In children, acute hematogenous osteomyelitis most commonly begins in the metaphysis of long bones. Sluggish blood flow in the venous sinusoids adjacent to the physis provides an ideal environment for bacterial deposition and proliferation.

Question 1211

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections caused by Staphylococcus epidermidis, which of the following is primarily responsible for facilitating the initial adherence to the implant and subsequent biofilm formation?

. Protein A
. Alpha toxin
. Polysaccharide intercellular adhesin (PIA)
. Panton-Valentine leukocidin (PVL)
. Coagulase

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Polysaccharide intercellular adhesin (PIA) is crucial for the cell-to-cell adhesion and biofilm formation of Staphylococcus epidermidis on foreign bodies. This biofilm protects the bacteria from host immune responses and antibiotics.

Question 1212

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a frequent and tenacious pathogen in prosthetic joint infections, primarily due to its ability to form a robust biofilm. Which phase of biofilm formation critically involves the production of poly-N-acetylglucosamine (PNAG)?

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

Correct Answer & Explanation

. Maturation phase

Explanation

During the maturation phase (also known as the accumulation phase) of biofilm formation, bacteria produce an extracellular polymeric substance (EPS). In S. epidermidis, a major component of this matrix is polysaccharide intercellular adhesin (PIA), which is primarily composed of poly-N-acetylglucosamine (PNAG). This matrix protects the bacteria from host immunity and antibiotics.

Question 1213

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for venous thromboembolism (VTE) prophylaxis following major orthopedic adult reconstruction surgery. What is its specific mechanism of action within the coagulation cascade?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via complexing with antithrombin III
. Direct and selective inhibition of Factor Xa
. Inhibition of the vitamin K epoxide reductase enzyme
. Irreversible antagonism of the P2Y12 ADP receptor on platelets

Correct Answer & Explanation

. Direct and selective inhibition of Factor Xa

Explanation

Rivaroxaban is an oral anticoagulant that functions as a direct, highly selective inhibitor of Factor Xa. Unlike low-molecular-weight heparins (LMWH) and fondaparinux, which require antithrombin III to indirectly inhibit factor Xa, rivaroxaban binds directly to the active site of Factor Xa, interrupting the common pathway of the coagulation cascade.

Question 1214

Topic: Infection, Pharmacology & VTE

During the development of a periprosthetic joint infection, biofilm formation protects the offending bacteria from host immune defenses and systemic antibiotics. What is the initiating biological step in the formation of a bacterial biofilm on an orthopedic implant?

. Maturation of the extracellular polymeric substance
. Irreversible adhesion of sessile bacterial colonies
. Reversible attachment of planktonic bacteria to the surface
. Quorum sensing activation and subsequent bacterial dispersal
. Enzymatic degradation of the host-derived glycocalyx

Correct Answer & Explanation

. Reversible attachment of planktonic bacteria to the surface

Explanation

Biofilm formation is a sequential process that begins with the reversible attachment of free-floating (planktonic) bacteria to the implant surface. This initial stage is followed by irreversible adhesion, extracellular matrix production, structural maturation, and eventual bacterial dispersal.

Question 1215

Topic: Infection, Pharmacology & VTE

Deep vein thrombosis (DVT) prophylaxis is a critical component of postoperative orthopedic care. Which of the following commonly utilized oral prophylactic agents exerts its anticoagulant effect via direct, reversible inhibition of thrombin (Factor IIa)?

. Rivaroxaban
. Apixaban
. Dabigatran
. Warfarin
. Enoxaparin

Correct Answer & Explanation

. Dabigatran

Explanation

Dabigatran is a direct oral anticoagulant (DOAC) that specifically and reversibly binds to and inhibits the active site of thrombin (Factor IIa). In contrast, rivaroxaban and apixaban exert their anticoagulant effects by directly inhibiting Factor Xa.

Question 1216

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, Staphylococcus epidermidis evades the host immune system and antibiotics primarily through biofilm formation. What is the major structural component of this biofilm?

. Peptidoglycan
. Lipopolysaccharide
. Polysaccharide intercellular adhesin (PIA)
. Teichoic acid
. Hyaluronic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm matrix produced by Staphylococcus epidermidis is primarily composed of poly-N-acetylglucosamine, commonly known as polysaccharide intercellular adhesin (PIA). This protective glycocalyx severely limits antibiotic penetration and efficacy.

Question 1217

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infections, which step is considered the critical threshold for the development of a mature, antibiotic-resistant biofilm?

. Planktonic bacterial attachment
. Secretion of extracellular polymeric substance (EPS)
. Bacterial replication
. Quorum sensing
. Dispersion of bacteria

Correct Answer & Explanation

. Secretion of extracellular polymeric substance (EPS)

Explanation

The secretion of the extracellular polymeric substance (EPS) matrix creates an impermeable barrier that protects bacteria from host immune responses and antibiotics. This step marks the transition from reversible attachment to an established, highly resistant biofilm.

Question 1218

Topic: Infection, Pharmacology & VTE

Which of the following systemic antibiotics exhibits the highest penetration into both cortical and cancellous bone, making it particularly useful for treating chronic osteomyelitis?

. Cefazolin
. Vancomycin
. Clindamycin
. Gentamicin
. Penicillin G

Correct Answer & Explanation

. Clindamycin

Explanation

Clindamycin is highly lipophilic and has excellent penetration into both cortical and cancellous bone, often reaching concentrations equal to or greater than those in serum. This makes it highly effective for treating deep tissue and bone infections like osteomyelitis.

Question 1219

Topic: Infection, Pharmacology & VTE

A 65-year-old male on dabigatran for atrial fibrillation sustains a displaced femoral neck fracture. Which of the following agents is the specific reversal agent for this anticoagulant?

. Vitamin K
. Protamine sulfate
. Andexanet alfa
. Idarucizumab
. Four-factor prothrombin complex concentrate (PCC)

Correct Answer & Explanation

. Idarucizumab

Explanation

Idarucizumab is a monoclonal antibody fragment that serves as the specific reversal agent for dabigatran, a direct thrombin inhibitor. Andexanet alfa is used to reverse direct Factor Xa inhibitors like rivaroxaban.

Question 1220

Topic: Infection, Pharmacology & VTE

Which of the following phases of biofilm formation on an orthopedic implant is characterized by irreversible bacterial attachment and exopolysaccharide matrix production?

. Planktonic phase
. Adhesion phase
. Aggregation phase
. Maturation phase
. Dispersion phase

Correct Answer & Explanation

. Aggregation phase

Explanation

Following initial reversible attachment, the aggregation phase involves bacteria firmly attaching and secreting an extracellular polymeric substance (EPS). This slime layer protects the bacteria from the host immune system and antibiotics.

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