A 65-year-old man comes to the office due to a foot ulcer. The ulcer began 2 weeks ago, a few days after he scrubbed a callus off the bottom of his left foot. The patient tried over-the-counter antibiotic creams, but the ulcer gradually enlarged and started draining a foul discharge. The foot is not painful and he has had no fever. The patient has a history of hypertension, hyperlipidemia, and type 2 diabetes mellitus. His diabetes has been poorly controlled by oral medications, and he has refused to take insulin. The patient is a retired veteran and does not use tobacco, alcohol, or illicit drugs. Temperature is 37.2 C (99 F), blood pressure is 130/86 mm Hg, and pulse is 80/min. BMI is 32 kg/m². Examination of the left foot shows a 2×2 cm plantar ulcer with a necrotic base. No surrounding erythema or induration is present, and metal probing does not contact bone. Lower extremity pulses are diminished but palpable. Sensation to light touch and vibration is reduced, and ankle reflexes are absent bilaterally. Leukocyte count is 13,000 cells/mm³ and erythrocyte sedimentation rate is 95 mm/hr. Blood cultures and wound swab cultures are obtained. Imaging reveals soft tissue inflammation and cortical destruction. Blood cultures are negative, but the wound swab culture grows Staphylococcus epidermidis, Proteus mirabilis, and Bacteroides susceptible to all tested antibiotics. Debridement of the necrotic tissue and wound care is planned. Which of the following is the best approach for antibiotic selection in this patient?

Question

Quizplus · Accepted Answer

Explanation: This patient has radiographic evidence of osteomyelitis and requires antimicrobial treatment. Diabetic foot infections are often polymicrobial, and a diverse group of organisms may contribute to infection. Gram-positive cocci such as Staphylococcus aureus are isolated most commonly, but Pseudomonas aeruginosa and anaerobic bacteria (eg, Clostridium) are also frequently involved, particularly when wounds are deep and chronic. Because diabetic wound colonization rates are high, superficial wound cultures have little predictive value in identifying the underlying pathologic organisms and should not be used to guide therapy (Choices C and D). Positive blood cultures are far more predictive, especially in the setting of radiographic evidence of osteomyelitis. However, bone biopsy with culture is considered the gold standard for identifying pathologic organisms and is usually required to determine appropriate antimicrobial therapy. Diabetic foot infections with osteomyelitis are typically treated with a combination of glucose control, surgical debridement, weight off-loading, revascularization (if needed), and antibiotic therapy for >6 weeks. Serial inflammatory markers (eg, erythrocyte sedimentation rate) can help confirm treatment response. (Choice B) Because wound colonization rates are high and often do not correlate with the underlying organisms causing osteomyelitis, neither superficial wound swabs nor cultures from debrided tissue should be used to guide antimicrobial therapy in patients with osteomyelitis. (Choice E) Blood cultures are often negative (>60%) in patients with osteomyelitis; this limb-threatening infection requires aggressive treatment. Topical antibiotics are not sufficient. Educational objective: Patients with diabetic foot ulcers who have underlying osteomyelitis usually require bone biopsy to determine the pathogenic organisms. Superficial wound swabs and cultures from debrided tissue are not sufficient.

A 65-Year-Old Man Comes to the Office Due to a Foot