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Infection, Pharmacology & VTE MCQs

Practice Set 41 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 801

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with an acutely swollen knee. Joint aspiration yields cloudy fluid with a white blood cell count of 45,000 cells/mcL (60% polymorphonuclear leukocytes). Polarized light microscopy reveals negatively birefringent, needle-shaped crystals. What is the most likely diagnosis?

. Septic arthritis
. Rheumatoid arthritis
. Gouty arthritis
. Pseudogout (CPPD)
. Osteoarthritis

Correct Answer & Explanation

. Gouty arthritis

Explanation

Gout is characterized by the presence of monosodium urate crystals, which appear needle-shaped and are strongly negatively birefringent under polarized light. The cell count (often 10,000 to 50,000 WBCs/mcL) is consistent with an acute inflammatory monoarthritis.

Question 802

Topic: Infection, Pharmacology & VTE

A 72-year-old patient requires emergent orthopedic surgery for a displaced femoral neck fracture. The patient is on Warfarin for atrial fibrillation, and the current INR is 3.5. Which of the following is the most rapid and effective method to reverse the coagulopathy prior to surgical intervention?

. Intravenous Vitamin K alone
. Fresh Frozen Plasma (FFP) and Intravenous Vitamin K
. Prothrombin Complex Concentrate (PCC) and Intravenous Vitamin K
. Cryoprecipitate and Subcutaneous Vitamin K
. Recombinant Factor VIIa

Correct Answer & Explanation

. Prothrombin Complex Concentrate (PCC) and Intravenous Vitamin K

Explanation

Prothrombin Complex Concentrate (PCC) is the most rapid and effective agent for reversing Warfarin-induced coagulopathy in an emergent setting. It contains concentrated Vitamin K-dependent factors (II, VII, IX, X). Intravenous Vitamin K is given simultaneously to provide sustained reversal once the half-life of the administered PCC factors expires. FFP requires thawing, necessitates large volumes (risk of fluid overload), and reverses INR more slowly than PCC.

Question 803

Topic: Infection, Pharmacology & VTE
A 55-year-old patient undergoing a total knee arthroplasty is prescribed Enoxaparin for deep vein thrombosis (DVT) prophylaxis. What is the primary molecular mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Binding to antithrombin III to preferentially inhibit Factor Xa
. Vitamin K antagonism through inhibition of epoxide reductase
. Direct inhibition of Factor Xa without antithrombin interaction

Correct Answer & Explanation

. Binding to antithrombin III to preferentially inhibit Factor Xa

Explanation

Enoxaparin is a Low Molecular Weight Heparin (LMWH). Unlike unfractionated heparin, which has roughly equal activity against Factor Xa and Factor IIa (thrombin), LMWH primarily binds to Antithrombin III, causing a conformational change that vastly accelerates its inhibition of Factor Xa, with much less effect on Factor IIa. Rivaroxaban and Apixaban are direct Factor Xa inhibitors (do not require ATIII).

Question 804

Topic: Infection, Pharmacology & VTE

A 9-year-old boy with sickle cell disease presents with an acute onset of fever, severe left femur pain, and an elevated C-reactive protein. Blood cultures are drawn. Statistically, what is the most common causative organism for hematogenous osteomyelitis in this specific patient population?

. Salmonella typhimurium
. Staphylococcus aureus
. Streptococcus pneumoniae
. Haemophilus influenzae
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

While Salmonella is classically associated with sickle cell disease and is highly unique to this population (due to hyposplenism and gastrointestinal microinfarctions), Staphylococcus aureus remains the most common overall cause of osteomyelitis in sickle cell patients worldwide in most large epidemiological studies. (Note: Many board questions test Salmonella as the 'classic' association, but careful wording regarding 'most common overall' leads to S. aureus; if asked for the 'classic unique organism', it is Salmonella).

Question 805

Topic: Infection, Pharmacology & VTE
Periprosthetic joint infections are notoriously difficult to eradicate due to bacterial biofilm formation. What is the primary chemical constituent of the extracellular polymeric substance (EPS) 'slime layer' formed by mature Staphylococcus epidermidis biofilms?
. Type III collagen
. Polysaccharides (Poly-N-acetylglucosamine)
. Peptidoglycan
. Lipopolysaccharide
. Teichoic acid

Correct Answer & Explanation

. Polysaccharides (Poly-N-acetylglucosamine)

Explanation

The biofilm matrix (Extracellular Polymeric Substance) in staphylococcal infections is largely composed of polysaccharide intercellular adhesin (PIA). PIA is biochemically identified as poly-N-acetylglucosamine (PNAG). This matrix protects the embedded bacteria from both host immune responses and systemic antibiotics.

Question 806

Topic: Infection, Pharmacology & VTE

During a regional block for orthopedic surgery, a patient experiences acute systemic toxicity from an accidental intravascular injection of bupivacaine, leading to severe cardiac dysrhythmias and impending arrest. What is the immediate first-line specific antidote for this local anesthetic systemic toxicity (LAST)?

. Flumazenil
. Naloxone
. 20% Intravenous Lipid Emulsion
. Intravenous calcium gluconate
. Atropine

Correct Answer & Explanation

. 20% Intravenous Lipid Emulsion

Explanation

Intravenous lipid emulsion (typically 20% Intralipid) is the rescue treatment of choice for local anesthetic systemic toxicity (LAST), particularly that induced by highly lipophilic amides like bupivacaine. The 'lipid sink' theory postulates that the lipid emulsion creates an expanded intravascular lipid phase that sequesters the lipophilic local anesthetic, removing it from target organs like the heart and brain.

Question 807

Topic: Infection, Pharmacology & VTE
Following total knee arthroplasty, a patient is prescribed rivaroxaban for chemical thromboprophylaxis. What is the specific pharmacological mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibition
. Vitamin K epoxide reductase inhibition
. Direct Factor Xa inhibition
. Activation of Antithrombin III
. ADP receptor (P2Y12) antagonism

Correct Answer & Explanation

. Direct Factor Xa inhibition

Explanation

Rivaroxaban is a direct oral anticoagulant (DOAC) that works by directly inhibiting Factor Xa, preventing the conversion of prothrombin to thrombin. Dabigatran, in contrast, is a direct thrombin inhibitor.

Question 808

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infection, biofilm formation provides bacteria with a physical barrier against host defenses and antibiotics. What is the primary extracellular polymeric substance produced by Staphylococcus epidermidis to facilitate this structural adhesion?

. Hyaluronic acid
. Polysaccharide intercellular adhesin (PIA)
. Peptidoglycan
. Lipopolysaccharide
. Fibronectin-binding protein

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Staphylococcus epidermidis is a notorious biofilm producer in implant-related infections. The crucial structural component of this biofilm matrix is the Polysaccharide Intercellular Adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG), which facilitates bacterial aggregation and immune evasion.

Question 809

Topic: Infection, Pharmacology & VTE
A 68-year-old patient undergoes elective total knee arthroplasty. Postoperatively, she is prescribed oral rivaroxaban for deep vein thrombosis (DVT) prophylaxis. What is the precise pharmacological target of this medication?
. Antithrombin III
. Vitamin K epoxide reductase
. Direct thrombin (Factor IIa)
. Factor Xa
. Platelet ADP receptor (P2Y12)

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa in the coagulation cascade. Dabigatran inhibits direct thrombin (Factor IIa). Warfarin inhibits vitamin K epoxide reductase. Clopidogrel blocks the P2Y12 ADP receptor on platelets.

Question 810

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for extended deep vein thrombosis prophylaxis following a total hip arthroplasty. 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
. Glycoprotein IIb/IIIa inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are oral direct Factor Xa inhibitors. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin is a vitamin K epoxide reductase inhibitor. Low molecular weight heparins (e.g., enoxaparin) act primarily by binding and activating antithrombin III, which then inactivates Factor Xa (and to a lesser extent IIa).

Question 811

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infection, biofilm formation protects bacteria from host defenses and systemic antibiotics. What is the primary constituent of the extracellular polymeric substance (EPS) matrix in a mature staphylococcal biofilm?

. Type I collagen
. Polysaccharide intercellular adhesin (PIA)
. Cross-linked fibrinogen
. Hyaluronic acid
. Fibronectin

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm matrix produced by staphylococci (especially S. epidermidis and S. aureus) is largely composed of an extracellular polymeric substance (EPS). A major component of this matrix is polysaccharide intercellular adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG), along with extracellular DNA (eDNA) and various proteins. It provides a structural scaffold and barrier against antimicrobials.

Question 812

Topic: Infection, Pharmacology & VTE

A 5-year-old boy presents with a limp, fever of 39.0°C, a WBC count of 14,000/mm3, an ESR of 50 mm/hr, and inability to bear weight. According to the Kocher criteria, what is the approximate probability of septic arthritis?

. 10%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The four Kocher criteria are fever >38.5°C, non-weight bearing, ESR >40, and WBC >12,000. With all four criteria present, the probability of septic arthritis is approximately 99%.

Question 813

Topic: Infection, Pharmacology & VTE

A 28-year-old construction worker presents with pain, swelling, and redness over the olecranon bursa, with no history of trauma. He reports a low-grade fever. Aspiration reveals cloudy fluid with elevated white blood cell count and positive Gram stain for Staphylococcus aureus. What is the most appropriate initial management?

. Oral NSAIDs and rest
. Corticosteroid injection into the bursa
. Surgical excision of the bursa
. Oral antibiotics targeting Staphylococcus aureus
. Repeated aspiration and compression

Correct Answer & Explanation

. Oral antibiotics targeting Staphylococcus aureus

Explanation

The presence of signs of infection (redness, swelling, fever, cloudy fluid with elevated WBCs and positive Gram stain for S. aureus) indicates septic olecranon bursitis. The most appropriate initial management is oral antibiotics targeting S. aureus (e.g., a first-generation cephalosporin or clindamycin if MRSA is suspected locally). NSAIDs, rest, and corticosteroid injections are for aseptic bursitis. Surgical excision is reserved for chronic, recurrent, or refractory septic bursitis. Repeated aspiration alone without antibiotics is insufficient for infection.

Question 814

Topic: Infection, Pharmacology & VTE

In the management of chronic osteomyelitis, what is the most important factor for successful treatment?

. Long-term intravenous antibiotics alone
. Surgical debridement of infected and necrotic bone
. Hyperbaric oxygen therapy
. Bone graft application
. External fixation

Correct Answer & Explanation

. Surgical debridement of infected and necrotic bone

Explanation

Surgical debridement of infected and necrotic (non-viable) bone is the cornerstone of successful treatment for chronic osteomyelitis. Antibiotics alone are often insufficient due to poor penetration into avascular necrotic tissue and biofilm formation. While long-term antibiotics are crucial post-debridement, they are ineffective without source control. Hyperbaric oxygen therapy can be an adjunctive treatment but is not primary. Bone grafting and external fixation are reconstructive or stabilizing procedures performed after successful debridement.

Question 815

Topic: Infection, Pharmacology & VTE

What is the most common cause of acute hematogenous osteomyelitis in children?

. Pseudomonas aeruginosa
. Escherichia coli
. Staphylococcus aureus
. Group A Streptococcus
. Kingella kingae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus is by far the most common causative organism of acute hematogenous osteomyelitis in children across all age groups. While other organisms can cause osteomyelitis (e.g., Kingella kingae in infants/toddlers, Pseudomonas in puncture wounds through sneakers), S. aureus remains the predominant pathogen.

Question 816

Topic: Infection, Pharmacology & VTE

A patient presents with acute, severe pain, swelling, and exquisite tenderness of the great toe metatarsophalangeal joint. Aspiration reveals negatively birefringent, needle-shaped crystals. What is the most likely diagnosis?

. Pseudogout (Calcium pyrophosphate deposition disease)
. Septic arthritis
. Rheumatoid arthritis
. Gout
. Osteoarthritis

Correct Answer & Explanation

. Gout

Explanation

The classic presentation of acute, severe pain, swelling, and exquisite tenderness of the great toe MTP joint (podagra), combined with the finding of negatively birefringent, needle-shaped crystals on synovial fluid analysis, is pathognomonic for gout. Pseudogout involves positively birefringent, rhomboid-shaped crystals. Septic arthritis would have pus and bacteria. Rheumatoid arthritis typically affects smaller joints symmetrically and has specific serologic markers. Osteoarthritis is a degenerative condition and does not present with acute inflammation or crystal findings like gout.

Question 817

Topic: Infection, Pharmacology & VTE

A 72-year-old female undergoes an elective total hip arthroplasty for severe osteoarthritis. On postoperative day 2, she develops acute shortness of breath, pleuritic chest pain, and hypoxemia. What is the MOST likely diagnosis?

. Pneumonia
. Myocardial infarction
. Atelectasis
. Pulmonary embolism
. Fat embolism syndrome

Correct Answer & Explanation

. Pulmonary embolism

Explanation

Pulmonary embolism (PE) is a serious and well-recognized complication after total hip arthroplasty, especially within the first few weeks post-op. The symptoms of acute shortness of breath and pleuritic chest pain in a postoperative patient are highly suggestive of PE. While pneumonia, MI, and atelectasis are possibilities, PE must be ruled out urgently. Fat embolism syndrome, though possible after orthopedic trauma, is less common after elective arthroplasty and typically presents with a classic triad of respiratory insufficiency, neurological impairment, and petechial rash.

Question 818

Topic: Infection, Pharmacology & VTE

A 4-year-old child presents with acute onset severe right hip pain, refusal to bear weight, and fever. On examination, the hip is held in flexion, abduction, and external rotation, and any attempt at passive range of motion elicits significant pain. ESR and CRP are markedly elevated. What is the MOST critical immediate management step?

. Start broad-spectrum oral antibiotics
. Obtain plain radiographs of the hip
. Urgent hip aspiration and initiation of intravenous antibiotics
. Bed rest and anti-inflammatory medications
. MRI of the hip to rule out osteomyelitis

Correct Answer & Explanation

. Urgent hip aspiration and initiation of intravenous antibiotics

Explanation

This clinical scenario is highly concerning for septic arthritis of the hip, which is an orthopedic emergency. The most critical immediate management step is urgent hip aspiration to obtain synovial fluid for cell count, culture, and gram stain. This is essential for definitive diagnosis and guiding antibiotic therapy. Concurrently, broad-spectrum intravenous antibiotics should be initiated immediately after aspiration. Delay in diagnosis and treatment can lead to rapid cartilage destruction and long-term joint damage. Radiographs are often normal early on, and oral antibiotics are insufficient.

Question 819

Topic: Infection, Pharmacology & VTE

A 10-year-old boy presents with a 2-week history of worsening right tibia pain, fever, and refusal to bear weight. Blood tests show elevated ESR and CRP. Radiographs show subtle periosteal reaction. What is the MOST sensitive imaging modality for early diagnosis of acute osteomyelitis?

. Plain radiographs
. CT scan
. Bone scintigraphy (Technetium-99m)
. Magnetic resonance imaging (MRI)
. Ultrasound

Correct Answer & Explanation

. Magnetic resonance imaging (MRI)

Explanation

Magnetic Resonance Imaging (MRI) is the MOST sensitive imaging modality for early diagnosis of acute osteomyelitis, especially in children. It can detect bone marrow edema and early changes before they are visible on plain radiographs or CT scans. Bone scintigraphy can also detect early changes but is less specific than MRI. Plain radiographs often lag behind clinical symptoms by 10-14 days. CT is good for cortical bone but less for marrow changes.

Question 820

Topic: Infection, Pharmacology & VTE

A 55-year-old diabetic male with a history of open tibia fracture 10 years ago presents with a chronic draining sinus tract in his lower leg. Radiographs show sclerotic bone and a sequestrum. What is the definitive management for chronic osteomyelitis with a sequestrum?

. Long-term oral antibiotics
. Surgical debridement and sequestrectomy
. Hyperbaric oxygen therapy
. Amputation
. Bone grafting without debridement

Correct Answer & Explanation

. Surgical debridement and sequestrectomy

Explanation

Chronic osteomyelitis with a sequestrum (a piece of dead, infected bone) requires surgical debridement and sequestrectomy (removal of the sequestrum) for definitive treatment. The sequestrum acts as a nidus for infection and cannot be eradicated by antibiotics alone. Antibiotics are adjunctive to surgery. Long-term oral antibiotics alone will not cure it. Amputation is a last resort. Bone grafting should be performed after infection eradication.

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