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Infection, Pharmacology & VTE MCQs

Practice Set 46 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 901

Topic: Infection, Pharmacology & VTE
A 72-year-old man was scheduled for left total knee replacement. He has a history of hypertension and deep venous thrombosis (DVT) in his right lower extremity after an ankle fracture 2 years ago that was treated nonsurgically. The patient asked about the recommended types of DVT prophylaxis or investigations. Based on the 2011 AAOS Clinical Practice Guideline, Preventing Venous Thromboembolic Disease in Patients Undergoing Elective Hip and Knee Arthroplasty, what is an acceptable option?
. Six weeks of acetylsalicylic acid postsurgically beginning the evening of surgery
. Six weeks of low-molecular-weight heparin beginning the morning after surgery
. Routine duplex scans of both lower extremities before hospital discharge to ensure the patient has not developed another DVT
. Use of pneumatic calf compressors on both lower extremities while in the hospital and 4 weeks of warfarin starting the evening of surgery

Correct Answer & Explanation

. Use of pneumatic calf compressors on both lower extremities while in the hospital and 4 weeks of warfarin starting the evening of surgery

Explanation

The 2011 AAOS guideline, Preventing Venous Thromboembolic Disease in Patients Undergoing Elective Hip and Knee Arthroplasty, recommends the combined use of mechanical and pharmacological prophylaxis in patients who have a history of previous thromboembolism. This recommendation is a consensus opinion of the work group that established these guidelines because there is no other reliable evidence for this clinical scenario. There is strong evidence against the use of routine duplex scans in patients undergoing hip and knee replacement. The remaining two responses are less appropriate because they do not include the use of mechanical prophylaxis immediately after surgery.

Question 902

Topic: Infection, Pharmacology & VTE

The pharmacokinetics of which deep venous thrombosis (DVT) prophylactic agent are affected by liver function and dietary intake?

. Dalteparin
. Warfarin
. Fondaparinux
. Enoxaparin

Correct Answer & Explanation

. Dalteparin

Explanation

Warfarin is an oral vitamin K antagonist that is rapidly absorbed from the gastrointestinal tract. It accumulates in the liver, where it is metabolized and excreted. The pharmacokinetics of warfarin can be affected by certain drugs or disease states that influence liver function. Fondaparinux is a synthetic factor Xa inhibitor that is eliminated through the kidneys. Both Dalteparin and Enoxaparin are low-molecularweight heparins that activate antithrombin and inhibit factors Xa and IIa. Like Fondaparinux, they are eliminated through the kidneys and should be used with caution in patients with kidney disease.---

Question 903

Topic: Infection, Pharmacology & VTE
Rivaroxaban is an oral anticoagulant frequently used for DVT prophylaxis following total joint arthroplasty. What is its mechanism of action?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K antagonist
. Potentiates antithrombin III to inhibit Factor Xa and IIa
. Inhibits ADP-induced platelet aggregation

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban (Xarelto) and apixaban (Eliquis) are oral, direct inhibitors of Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin is a vitamin K antagonist. Heparin and low molecular weight heparins (LMWH) potentiate antithrombin III. Clopidogrel inhibits ADP-induced platelet aggregation.

Question 904

Topic: Infection, Pharmacology & VTE
Following a total knee arthroplasty, a patient is prescribed oral rivaroxaban for venous thromboembolism (VTE) prophylaxis. This medication exerts its anticoagulant effect by directly and reversibly inhibiting which of the following factors in the coagulation cascade?
. Antithrombin III
. Factor IIa (Thrombin)
. Factor Xa
. Vitamin K epoxide reductase
. Plasminogen

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by specifically and directly inhibiting free and clot-bound Factor Xa. This interrupts the intrinsic and extrinsic pathways of the blood coagulation cascade, inhibiting thrombin formation.

Question 905

Topic: Infection, Pharmacology & VTE

During the pathogenesis of periprosthetic joint infection, bacteria form a biofilm on the implant surface. The irreversible adherence of bacteria and subsequent biofilm maturation is primarily mediated by the production of:

. Planktonic proliferation
. Exopolysaccharide glycocalyx matrix
. Quorum sensing autoinducers
. Macrophage evasion proteins
. Antibiotic efflux pumps

Correct Answer & Explanation

. Planktonic proliferation

Explanation

Following initial reversible attachment, bacteria secure themselves to the implant by secreting an exopolysaccharide matrix (glycocalyx). This matrix creates a structural barrier that protects the colony from host immune cells and antibiotics.

Question 906

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total knee arthroplasty. This medication exerts its anticoagulant effect primarily by directly inhibiting:
. Thrombin (Factor IIa)
. Factor Xa
. Vitamin K epoxide reductase
. Antithrombin III
. Platelet ADP receptors

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban is a direct oral anticoagulant (DOAC) that selectively and reversibly blocks the active site of Factor Xa. This interrupts the intrinsic and extrinsic pathways of the blood coagulation cascade, inhibiting thrombin formation.

Question 907

Topic: Infection, Pharmacology & VTE

An 80-year-old male on warfarin for atrial fibrillation sustains a displaced femoral neck fracture. His admission INR is 3.5. To minimize mortality and morbidity, what is the most appropriate sequence of management?

. Delay surgery for 7 days to allow INR to normalize naturally
. Rapid reversal of anticoagulation and surgical intervention within 48 hours
. Non-operative management with prolonged bed rest
. Administration of tissue plasminogen activator (tPA)
. Immediate surgical intervention without any reversal

Correct Answer & Explanation

. Delay surgery for 7 days to allow INR to normalize naturally

Explanation

In geriatric hip fractures, surgical delay beyond 48 hours significantly increases mortality. Patients on warfarin should undergo rapid reversal (e.g., Vitamin K, PCC) to allow surgery within this critical 48-hour window.

Question 908

Topic: Infection, Pharmacology & VTE

A 30-year-old Ashkenazi Jewish man presents with severe, acute left thigh pain and fever, initially mimicking osteomyelitis. Radiographs of the femur show an 'Erlenmeyer flask' deformity of the distal femur with scattered lytic and sclerotic areas. He also has hepatosplenomegaly. Deficiency of which of the following enzymes is responsible for his skeletal manifestations?

. Alpha-L-iduronidase
. Sphingomyelinase
. Glucocerebrosidase
. Hexosaminidase A
. Iduronate sulfatase

Correct Answer & Explanation

. Alpha-L-iduronidase

Explanation

Gaucher disease is a lysosomal storage disorder caused by a deficiency of glucocerebrosidase (beta-glucosidase). The accumulation of glucocerebroside in macrophages inside the bone marrow leads to 'bone crises' mimicking osteomyelitis, avascular necrosis, and the classic 'Erlenmeyer flask' deformity of the distal femur.

Question 909

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, a limp, and refusal to bear weight. His temperature is 38.6°C (101.5°F), WBC count is 13.5 x 10^9/L, and ESR is 45 mm/hr. Based on the modified Kocher criteria, what is the approximate probability that this child has septic arthritis rather than transient synovitis?

. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 3%

Explanation

The Kocher criteria for differentiating septic arthritis from transient synovitis include: 1) Non-weight bearing on the affected side, 2) ESR > 40 mm/hr, 3) Fever > 38.5°C (101.3°F), and 4) WBC count > 12.0 x 10^9/L. This patient meets all 4 criteria. The probability of septic arthritis is approximately 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.

Question 910

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents to the emergency department refusing to bear weight on his right leg. His temperature is 38.8°C (101.8°F). You are attempting to differentiate between transient synovitis and septic arthritis of the hip using the Kocher criteria. Which of the following laboratory or clinical findings was NOT one of the four original criteria published by Kocher et al. in 1999?
. Inability to bear weight on the affected side
. Erythrocyte sedimentation rate (ESR) > 40 mm/hr
. Serum white blood cell (WBC) count > 12,000 cells/mm³
. C-reactive protein (CRP) > 2.0 mg/dL
. Temperature > 38.5°C (101.3°F)

Correct Answer & Explanation

. C-reactive protein (CRP) > 2.0 mg/dL

Explanation

The original four predictive criteria published by Kocher et al. (1999) for septic arthritis of the pediatric hip are: 1) Non-weight-bearing on affected side, 2) ESR > 40 mm/hr, 3) Fever > 38.5°C, and 4) Serum WBC count > 12,000 cells/mm³. C-reactive protein (CRP) > 2.0 mg/dL was later identified as an independent predictor and added by Caird et al. (2006), making it a five-part clinical prediction rule, but it was not one of the original four Kocher criteria.

Question 911

Topic: Infection, Pharmacology & VTE

A 2-week-old neonate presents with decreased spontaneous movement of the right lower extremity, swelling of the right thigh, and pain with passive hip motion. Ultrasound demonstrates a large hip effusion. What anatomical feature unique to infants younger than 18 months predisposes them to concurrent osteomyelitis and septic arthritis in this location?

. An incomplete physical barrier at the articular cartilage
. A highly cellular hypertrophic zone of the physis
. The presence of transphyseal blood vessels connecting the metaphysis and epiphysis
. A thick, non-yielding periosteum surrounding the femoral neck
. The absence of an intra-articular ligamentum teres

Correct Answer & Explanation

. An incomplete physical barrier at the articular cartilage

Explanation

In neonates and infants younger than 12-18 months, there are transphyseal blood vessels that cross the physis, establishing direct communication between the metaphysis and the epiphysis (and by extension, the intra-articular space). This unique vascular anatomy allows an infection that begins as metaphyseal osteomyelitis to easily cross into the joint space, resulting in concomitant septic arthritis, which rapidly destroys the chondroepiphysis and increases the risk of avascular necrosis of the femoral head.

Question 912

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents to the emergency department with acute right hip pain, a severe limp, and a refusal to bear weight. His temperature is 38.6°C. Laboratory workup reveals a WBC count of 13,500/mm³ and an ESR of 45 mm/hr. According to the Kocher criteria, what is the approximate statistical probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for differentiating septic arthritis from transient synovitis include four predictors: fever >38.5°C, non-weight bearing status, ESR >40 mm/hr, and WBC >12,000/mm³. This patient has all 4 criteria. According to the original study, the probability of septic arthritis is approximately: 1 criterion = 3%, 2 criteria = 40%, 3 criteria = 93%, and 4 criteria = 99%.

Question 913

Topic: Infection, Pharmacology & VTE

A 3-year-old presents with a 2-day history of right hip pain, refusal to bear weight, and a temperature of 38.8°C. According to the updated Kocher criteria by Caird et al., which laboratory value was added as a strong independent predictor for septic arthritis of the hip?

. Procalcitonin > 0.5 ng/mL
. C-reactive protein (CRP) > 2.0 mg/dL
. Erythrocyte sedimentation rate (ESR) > 20 mm/hr
. Peripheral WBC count > 10,000 cells/mm3
. Synovial fluid WBC > 25,000 cells/mm3

Correct Answer & Explanation

. Procalcitonin > 0.5 ng/mL

Explanation

Caird et al. modified the original Kocher criteria by adding a C-reactive protein (CRP) level > 2.0 mg/dL. The presence of all five predictors yields a >97% probability of septic arthritis.

Question 914

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with a 2-day history of right hip pain and inability to bear weight. His temperature is 38.8°C (101.8°F), WBC count is 14,000/mm3, ESR is 55 mm/hr, and CRP is 3.5 mg/dL. Radiographs of the hip are normal. What is the most appropriate next step in management?

. MRI of the pelvis with and without contrast
. Ultrasound-guided aspiration of the right hip
. Intravenous antibiotics and clinical observation
. Immediate hip arthrotomy and washout
. Bone scan of the lower extremities

Correct Answer & Explanation

. MRI of the pelvis with and without contrast

Explanation

This patient meets all four Kocher criteria (fever, non-weight-bearing, ESR >40, WBC >12,000), giving him a >93% probability of septic arthritis. The definitive diagnostic next step is an ultrasound-guided hip aspiration to confirm the diagnosis before proceeding to surgical washout.

Question 915

Topic: Infection, Pharmacology & VTE

A 55-year-old diabetic male presents with unrelenting, severe lower back pain and fevers. MRI with gadolinium contrast reveals increased T2 signal and enhancement in the L3-L4 disc space and adjacent vertebral endplates. Blood cultures are drawn. What is the most common causative organism for spontaneous pyogenic spondylodiscitis in the adult population?

. Streptococcus pneumoniae
. Staphylococcus aureus
. Pseudomonas aeruginosa
. Escherichia coli
. Mycobacterium tuberculosis

Correct Answer & Explanation

. Streptococcus pneumoniae

Explanation

Staphylococcus aureus is the single most common causative organism of pyogenic spondylodiscitis and vertebral osteomyelitis in the general adult population, accounting for more than 50% of cases. While IV drug users may have a higher risk of Pseudomonas or MRSA, and genitourinary sources may seed gram-negatives like E. coli, S. aureus remains the overall most prevalent pathogen.

Question 916

Topic: Infection, Pharmacology & VTE

In periprosthetic joint infections, bacteria adhere to the implant and form a biofilm. The bacteria within this biofilm coordinate their behavior and gene expression based on population density through a communication mechanism known as:

. Chemotaxis
. Quorum sensing
. Opsonization
. Transduction
. Conjugation

Correct Answer & Explanation

. Chemotaxis

Explanation

Quorum sensing is the mechanism by which bacteria communicate using secreted signaling molecules (autoinducers). Once a critical population density is reached, it triggers changes in gene expression, facilitating processes like biofilm formation, virulence factor production, and antibiotic resistance.

Question 917

Topic: Infection, Pharmacology & VTE
A patient undergoing total knee arthroplasty is prescribed rivaroxaban for deep vein thrombosis (DVT) prophylaxis. Based on the coagulation cascade, rivaroxaban exerts its anticoagulant effect by directly inhibiting:
. Thrombin (Factor IIa)
. Factor Xa
. Vitamin K epoxide reductase
. Antithrombin III
. Platelet P2Y12 receptors

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and apixaban are direct, oral Factor Xa inhibitors. They do not require antithrombin for their activity. Dabigatran is a direct thrombin (IIa) inhibitor. Warfarin inhibits vitamin K epoxide reductase.

Question 918

Topic: Infection, Pharmacology & VTE
A 68-year-old patient with a documented history of deep vein thrombosis is undergoing a staged bilateral total knee arthroplasty. The patient is placed on oral apixaban for postoperative venous thromboembolism prophylaxis. What is the precise pharmacological mechanism of action of apixaban?
. Direct, competitive thrombin (Factor IIa) inhibitor
. Indirect Factor Xa inhibitor mediated via antithrombin III
. Direct, selective, and reversible Factor Xa inhibitor
. Vitamin K epoxide reductase complex subunit 1 (VKORC1) inhibitor
. Tissue plasminogen activator (tPA) competitive inhibitor

Correct Answer & Explanation

. Direct, selective, and reversible Factor Xa inhibitor

Explanation

Apixaban (along with rivaroxaban and edoxaban) is a direct, selective, and reversible inhibitor of Factor Xa, blocking the conversion of prothrombin to thrombin. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Low-molecular-weight heparins (like enoxaparin) and fondaparinux act as indirect Factor Xa inhibitors by profoundly accelerating the activity of antithrombin III. Warfarin inhibits the vitamin K epoxide reductase enzyme.

Question 919

Topic: Infection, Pharmacology & VTE



Staphylococcus aureus forms a robust biofilm on orthopaedic implants. Which extracellular matrix component is synthesized by the bacteria to initiate irreversible adhesion to the implant surface?

. Fibronectin
. Polysaccharide intercellular adhesin (PIA)
. Collagenase
. Teichoic acid
. Hyaluronidase

Correct Answer & Explanation

. Fibronectin

Explanation

Following initial reversible attachment, S. aureus synthesizes polysaccharide intercellular adhesin (PIA) encoded by the ica operon. This component forms the structural backbone of the biofilm's glycocalyx, allowing irreversible adhesion.

Question 920

Topic: Infection, Pharmacology & VTE

A 40-year-old aquarium maintenance worker presents with an indolent, slowly progressive swelling and restricted motion of his right index finger, accompanied by a painless nodule on the dorsum of his hand that seems to be spreading proximally up his arm.

A biopsy reveals non-caseating granulomas and acid-fast bacilli. Which of the following antimicrobial regimens is most appropriate?

. Intravenous penicillin G
. Oral cephalexin
. Clarithromycin and ethambutol
. Intravenous vancomycin
. Oral terbinafine

Correct Answer & Explanation

. Intravenous penicillin G

Explanation

This patient has a Mycobacterium marinum infection, historically known as 'fish tank granuloma'. It typically causes a chronic tenosynovitis and can exhibit sporotrichoid spread (nodules tracking proximally along lymphatics). Because it is an atypical mycobacterium, it is resistant to standard anti-staphylococcal antibiotics. First-line medical therapy often includes a multidrug regimen such as clarithromycin, ethambutol, or rifampin, usually for a prolonged course.

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