Menu

Infection, Pharmacology & VTE MCQs

Practice Set 57 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 1121

Topic: Infection, Pharmacology & VTE

A 65-year-old man presents with a delayed, low-grade periprosthetic joint infection of his total hip arthroplasty, caused by Staphylococcus epidermidis. The persistence and antibiotic resistance of this organism on the implant surface are primarily mediated by the production of which extracellular substance?

. Protein A
. Hyaluronidase
. Glycocalyx
. Coagulase
. Panton-Valentine leukocidin

Correct Answer & Explanation

. Glycocalyx

Explanation

Staphylococcus epidermidis is a common cause of indolent periprosthetic joint infections due to its ability to form a robust biofilm. The biofilm is composed of a self-produced extracellular polymeric substance known as glycocalyx, which shields the bacteria from host immune responses and antibiotics.

Question 1122

Topic: Infection, Pharmacology & VTE
A patient is prescribed subcutaneous enoxaparin for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the primary mechanism of action of this pharmacological agent?
. Directly inhibits thrombin (Factor IIa)
. Binds to antithrombin III, preferentially inhibiting Factor Xa over Factor IIa
. Inhibits the synthesis of vitamin K-dependent clotting factors
. Irreversibly binds to the ADP receptor on platelets
. Activates plasminogen to form plasmin

Correct Answer & Explanation

. Binds to antithrombin III, preferentially inhibiting Factor Xa over Factor IIa

Explanation

Enoxaparin is a low-molecular-weight heparin (LMWH) that binds to antithrombin III. This binding induces a conformational change that preferentially accelerates the inhibition of Factor Xa compared to thrombin (Factor IIa).

Question 1123

Topic: Infection, Pharmacology & VTE

A patient develops a periprosthetic joint infection caused by Staphylococcus epidermidis. The pathogenesis heavily relies on the formation of a biofilm. Which of the following primarily mediates the initial adherence of the bacteria to the orthopedic implant?

. Release of exotoxins
. Production of an extracellular polysaccharide glycocalyx
. Binding of fibronectin-binding proteins (FnBPs) to host proteins on the implant
. Phagocytosis by local macrophages
. Secretion of beta-lactamase

Correct Answer & Explanation

. Binding of fibronectin-binding proteins (FnBPs) to host proteins on the implant

Explanation

Initial adherence to an implant is mediated by bacterial adhesins like FnBPs binding to host proteins (such as fibronectin and fibrinogen) that immediately coat the implant surface. Following this attachment phase, the bacteria produce a polysaccharide glycocalyx to establish the mature biofilm.

Question 1124

Topic: Infection, Pharmacology & VTE
A patient is scheduled for a total hip arthroplasty and will receive rivaroxaban for postoperative venous thromboembolism prophylaxis. What is the specific mechanism of action of this drug?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K antagonist
. Enhances antithrombin III activity
. Irreversible cyclooxygenase inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that works by directly inhibiting Factor Xa, interrupting the common pathway of the coagulation cascade. Dabigatran, in contrast, is a direct thrombin (Factor IIa) inhibitor.

Question 1125

Topic: Infection, Pharmacology & VTE

A 3-year-old girl is brought to the emergency department with an acute limp and refuses to bear weight on her right leg. Joint aspiration of the hip reveals a synovial fluid white blood cell count of 85,000 cells/mm3 with 90% polymorphonuclear leukocytes. What is the most common causative organism of septic arthritis in this age group?

. Streptococcus pyogenes
. Staphylococcus aureus
. Kingella kingae
. Haemophilus influenzae
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus remains the single most common organism causing septic arthritis in children overall. While Kingella kingae is increasingly recognized in children under 4 years old, S. aureus represents the classic and most frequent isolate.

Question 1126

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the specific molecular mechanism of action of this medication?
. Inhibition of vitamin K epoxide reductase
. Direct inhibition of thrombin (Factor IIa)
. Direct inhibition of Factor Xa
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are oral anticoagulants that work by directly inhibiting Factor Xa. This efficiently prevents the conversion of prothrombin to thrombin within the common pathway of the coagulation cascade.

Question 1127

Topic: Infection, Pharmacology & VTE

A 28-year-old patient with homozygous sickle cell disease presents with acute hematogenous osteomyelitis of the femur. While Staphylococcus aureus remains the most common overall organism, which of the following pathogens has a uniquely high incidence in this specific demographic?

. Pseudomonas aeruginosa
. Escherichia coli
. Salmonella species
. Kingella kingae
. Streptococcus pneumoniae

Correct Answer & Explanation

. Salmonella species

Explanation

Patients with sickle cell disease suffer from functional asplenia and bowel ischemia, creating a uniquely high susceptibility to Salmonella osteomyelitis. However, S. aureus remains the most common overall cause of bone infection in this population.

Question 1128

Topic: Infection, Pharmacology & VTE

According to the original Kocher criteria for differentiating pediatric septic arthritis of the hip from transient synovitis, which of the following is NOT one of the classic four predictive variables?

. Temperature greater than 38.5 degrees Celsius
. Inability to bear weight on the affected limb
. Erythrocyte sedimentation rate (ESR) greater than 40 mm/hr
. Serum C-reactive protein (CRP) greater than 2.0 mg/dL
. White blood cell (WBC) count greater than 12,000 cells/mm3

Correct Answer & Explanation

. Serum C-reactive protein (CRP) greater than 2.0 mg/dL

Explanation

The original four Kocher criteria are non-weight-bearing status, ESR > 40, WBC > 12,000, and Temperature > 38.5 C. CRP > 2.0 mg/dL was later added as a fifth independent predictor by Caird et al., but was not part of the original Kocher study.

Question 1129

Topic: Infection, Pharmacology & VTE

An orthopedic study reports that a new deep vein thrombosis (DVT) prophylaxis protocol reduces the absolute risk of DVT from 8% to 3% compared to the standard protocol. What is the Number Needed to Treat (NNT) to prevent one DVT?

. 5
. 10
. 20
. 50
. 100

Correct Answer & Explanation

. 20

Explanation

The Number Needed to Treat (NNT) is calculated as the inverse of the Absolute Risk Reduction (ARR). The ARR here is 8% - 3% = 5% (0.05). Therefore, NNT = 1 / 0.05 = 20.

Question 1130

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with a limp. Which of the following is NOT one of the classic four Kocher criteria used to differentiate septic arthritis from transient synovitis of the pediatric hip?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate greater than 40 mm/hr
. Fever greater than 38.5 C
. Presence of a joint effusion on ultrasound
. Serum white blood cell count greater than 12,000/mm3

Correct Answer & Explanation

. Presence of a joint effusion on ultrasound

Explanation

The four classic Kocher criteria are fever > 38.5 C, non-weight-bearing status, ESR > 40 mm/hr, and WBC > 12,000 cells/mm3. While a joint effusion is supportive of hip pathology, it is not one of the specific predictive criteria.

Question 1131

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for DVT 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
. Antithrombin III activator
. Platelet ADP receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that selectively and directly inhibits Factor Xa. This interrupts both the intrinsic and extrinsic pathways of the blood coagulation cascade.

Question 1132

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, organisms often form a biofilm. Which phase of biofilm formation is characterized by the production of an extracellular polymeric substance (EPS) matrix that confers profound antibiotic resistance?

. Reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic shedding

Correct Answer & Explanation

. Maturation

Explanation

During the maturation phase, bacteria secrete an abundant extracellular polymeric substance (EPS) matrix. This matrix shields the community from host immune responses and dramatically increases resistance to antimicrobial agents.

Question 1133

Topic: Infection, Pharmacology & VTE

A 65-year-old man is scheduled for a total hip arthroplasty. He has a documented severe, IgE-mediated anaphylactic allergy to penicillin. Which of the following is the most appropriate preoperative prophylactic antibiotic regimen?

. Cefazolin
. Cefuroxime
. Vancomycin
. Clindamycin and gentamycin
. Ampicillin-sulbactam

Correct Answer & Explanation

. Vancomycin

Explanation

In patients with a severe, IgE-mediated allergy (e.g., anaphylaxis, bronchospasm, hives) to penicillins, first- and second-generation cephalosporins (like cefazolin and cefuroxime) are generally contraindicated due to the risk of cross-reactivity. Vancomycin or Clindamycin are the standard evidence-based alternative prophylactic agents for joint arthroplasty in this scenario.

Question 1134

Topic: Infection, Pharmacology & VTE

A 45-year-old farmer sustains an open tibia fracture highly contaminated with soil. He is given broad-spectrum antibiotics and undergoes emergent irrigation and debridement. Which specific antibiotic should be added to his regimen to cover the most likely atypical pathogen associated with this environment?

. Vancomycin
. Ceftriaxone
. High-dose Penicillin
. Gentamicin
. Clindamycin

Correct Answer & Explanation

. High-dose Penicillin

Explanation

Farm injuries or fractures heavily contaminated with soil are at high risk for Clostridium perfringens infection. High-dose penicillin is added to the standard broad-spectrum regimen to provide specific coverage against these anaerobic, spore-forming bacteria.

Question 1135

Topic: Infection, Pharmacology & VTE

A 68-year-old male is scheduled for a total hip arthroplasty. He has a history of atrial fibrillation and is currently taking Rivaroxaban. According to current perioperative guidelines, when should the Rivaroxaban be discontinued prior to surgery?

. 12 hours prior
. 24 hours prior
. 3 days prior
. 5 days prior
. 7 days prior

Correct Answer & Explanation

. 3 days prior

Explanation

Rivaroxaban is a direct Factor Xa inhibitor. For major orthopedic surgery with a high bleeding risk, current guidelines generally recommend discontinuing Rivaroxaban 3 days (approx. 72 hours) prior to surgery in patients with normal renal function to allow for adequate drug clearance.

Question 1136

Topic: Infection, Pharmacology & VTE

In evaluating synovial fluid from a painful knee, which of the following profiles is most characteristic of an inflammatory arthropathy such as Rheumatoid Arthritis?

. Clear, highly viscous fluid with 1,500 WBC/mm3 and <25% PMNs
. Yellow, translucent fluid with 4,000 WBC/mm3 and 30% PMNs
. Opaque, yellow-green fluid with 45,000 WBC/mm3 and 80% PMNs
. Opaque, purulent fluid with 120,000 WBC/mm3 and 95% PMNs
. Bloody fluid with lipid droplets

Correct Answer & Explanation

. Opaque, yellow-green fluid with 45,000 WBC/mm3 and 80% PMNs

Explanation

Inflammatory synovial fluid (Group II) is typically translucent to opaque, yellow/green, with decreased viscosity and a WBC count ranging from 2,000 to 50,000 cells/mm3, containing >50% PMNs. Non-inflammatory (OA) fluid has <2,000 WBCs. Septic arthritis fluid typically has >50,000 WBCs with >90% PMNs.

Question 1137

Topic: Infection, Pharmacology & VTE

During the pathogenesis of prosthetic joint infections, Staphylococcus epidermidis utilizes which of the following components to facilitate initial adherence and biofilm formation on the metal implant surface?

. Exotoxins
. Polysaccharide intercellular adhesin (PIA)
. Peptidoglycan
. Lipopolysaccharide
. Protein A

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Staphylococcus epidermidis establishes infections on implants by forming a biofilm, which begins with adherence followed by the production of a protective slime layer. This process is heavily mediated by the production of polysaccharide intercellular adhesin (PIA).

Question 1138

Topic: Infection, Pharmacology & VTE

A patient develops a methicillin-resistant Staphylococcus aureus (MRSA) infection following a total knee arthroplasty and is treated with intravenous vancomycin. What is the specific mechanism of action of this antibiotic?

. Inhibition of DNA gyrase
. Binding to the 50S ribosomal subunit
. Binding to the D-ala-D-ala terminus of peptidoglycan precursors
. Disruption of the bacterial cell membrane via depolarization
. Competitive inhibition of folic acid synthesis

Correct Answer & Explanation

. Binding to the D-ala-D-ala terminus of peptidoglycan precursors

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits bacterial cell wall synthesis. It acts by binding tightly to the D-alanyl-D-alanine terminus of cell wall precursor units, preventing their incorporation into the growing peptidoglycan matrix.

Question 1139

Topic: Infection, Pharmacology & VTE

A patient develops a late chronic prosthetic joint infection caused by Staphylococcus epidermidis. The profound resistance of this organism to systemic antimicrobial therapy is primarily mediated by which of the following mechanisms?

. Alteration of penicillin-binding proteins (PBP2a)
. Production of beta-lactamase enzymes
. Expression of active drug efflux pumps
. Formation of a polysaccharide glycocalyx biofilm
. Secretion of Panton-Valentine leukocidin

Correct Answer & Explanation

. Formation of a polysaccharide glycocalyx biofilm

Explanation

S. epidermidis produces an extracellular polysaccharide matrix (glycocalyx) that allows it to adhere to implants and form a robust biofilm. This biofilm physically shields the bacteria from both host immunity and systemic antibiotics.

Question 1140

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with an acutely hot, swollen first metatarsophalangeal joint. Aspiration reveals yellow, cloudy fluid with a leukocyte count of 55,000 cells/mm3 (70% PMNs). Polarized microscopy demonstrates negatively birefringent, needle-shaped crystals. What is the most appropriate initial management?

. Immediate operative irrigation and debridement
. Intravenous vancomycin and ceftriaxone
. Indomethacin and colchicine
. Intra-articular hyaluronic acid
. Allopurinol load

Correct Answer & Explanation

. Indomethacin and colchicine

Explanation

The microscopic finding of negatively birefringent, needle-shaped monosodium urate crystals confirms acute gout. The first-line treatment for an acute attack is NSAIDs (e.g., indomethacin), colchicine, or corticosteroids; allopurinol is contraindicated during an acute flare.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page