Osteomyelitis/ Diabetic Foot Infections - Dr. Bulman

What is osteomyelitis + its 3 categories?

- Inflammation of the bone caused by infection

3 categories

- Hematogenous osteomyelitis (bacteria that spreads from the blood, common example = vertebral osteomyelitis in older adults)

- Osteomyelitis due to contiguous infection focus (bacteria that spreads from open wound, can result from surgery)

- Osteomyelitis associated with vascular insufficiency (e.g. diabetic foot infections)

Hematogenous osteomyelitis is often ____ (monomicrobial/ polymicrobial).

Monomicrobial

Osteomyelitis due to contiguous infection or diabetic foot infections are often ____ (monomicrobial/ polymicrobial).

Polymicrobial

Explain the pathophysiology of osteomyelitis.

- Bacteria expresses adhesins which promotes binding and growth in bones

- As the bacteria grows, it blocks blood supply and leads to pus formation

- Eventually, the bone will start to die (aka bone necrosis aka sequestra) + the body will try to compensate by building new bone (involucrum)

What is the difference between acute osteomyelitis and chronic osteomyelitis?

- Acute osteomyelitis: no bone necrosis yet --> often treated with abx

- Chronic osteomyelitis: bone necrosis (often 3+ months since the infection began) --> often requires surgical intervention

What pathogen is the most common cause of osteomyelitis?

S. aureus (50 - 75% of cases)... MRSA rates are HIGH

*more likely to cause osteomyelitis due to its ability to form biofilms

What are minor pathogens that cause osteomyelitis?

- Strep

- Gram (-) bacilli

- PSAE

- Anaerobes

What are the 4 risk factors for osteomyelitis?

- Previous bacteremia (esp if they have hardware like a prosthetic joint)

- Compound fracture (bones exposed to flora)

- Recent surgery

- Chronic/ poorly healing wounds

How is osteomyelitis diagnosed?

- Can use ESR and CRP but these are not sensitive

- Probe-to-bone test is useful for exclusion (+ test warrants for further testing)

- Common: Radiologic findings (usually MRI)

- Gold standard = bone biopsy (grow the bacteria + look at histologic findings to determine if there is inflammation and/or necrosis)

Why is appropriate diagnosis of osteomyelitis so important?

6+ weeks of treatment --> make sure you're using the RIGHT abx

*note: this is NOT generally a medical emergency, ok to wait for cultures to come back

Who typically receives surgery?

Chronic infection (> 3 months) --> no good access to the blood so systemic abx won't do much

If the patient is stable, is it appropriate to wait for culture/ sensitivity reports to come back?

Yes!

Are aminoglycosides recommended for osteomyelitis?

No, they have poor bone penetration

Is linezolid a good first line agent for osteomyelitis?

No! Good bone penetration but long-term use leads to side effects such as anemia + thrombocytopenia

In the past, IV abx were preferred over PO abx for osteomyelitis. Is this still the case?

No, the OVIVA trial showed that PO therapy was noninferior to IV therapy (oral therapy is definitely a reasonable option for patients with less severe infections)

*but he does not recommend oral beta lactams still

In what scenario would we consider empiric therapy for treating osteomyelitis? What empiric therapy are we recommending?

If the pt is hemodynamically unstable (i.e. septic)

Recommend: Vancomycin + Cefepime (can consider cipro or aztreonam instead of cefepime if the pt has a TRUE PCN allergy aka anaphylaxis)

In treating osteomyelitis, if the patient has MSSA, what are their first choice IV abx? *no need to know dosing

- Nafcillin 2g IV q4H or continuous infusion

- Oxacillin 2g IV q4H or continuous infusion

- Cefazolin 2g IV q8H

In treating osteomyelitis, if the patient has MSSA, what are their first choice PO abx? *no need to know dosing

Levofloxacin 750 mg q24H AND Rifampin 600 mg q24H

In treating osteomyelitis, if the patient has MRSA, what are their first choice IV abx? *no need to know dosing

- Vancomycin 15 - 20 mg/kg q12H

- Daptomycin 6 - 10 mg/kg q24H

In treating osteomyelitis, if the patient has MRSA, what are their first choice PO abx? *no need to know dosing

Levofloxacin 750 mg q24H AND Rifampin 600 mg q24H

Why do we do combo therapy when we select oral options?

Rifampin-Fluoroquinolone combos have synergistic activity against biofilms + promote disease-free survival

In what scenarios might we avoid adding a rifampin onto a FQ?

Risk > Benefit... esp when it comes to DDI/hepatic toxicity

In treating osteomyelitis, if the patient has penicillin-sensitive strep, what are their first choice IV abx? *no need to know dosing

- Ceftriaxone 2g IV q24H

- Penicillin G 20 - 24 million units IV continuously q24H or in 6 divided doses

In treating osteomyelitis, if the patient has penicillin-sensitive strep, what are their first choice PO abx? *no need to know dosing

Amoxicillin 875 mg q8H

In treating osteomyelitis, if the patient has penicillin-resistant strep, what are their first choice IV abx? *no need to know dosing

- Ceftriaxone 2g IV q24H

- Vancomycin 15 - 20 mg/kg q12H

In treating osteomyelitis, if the patient has penicillin-resistant strep, what are their first choice PO abx? *no need to know dosing

Levofloxacin 750 mg q24H

What strains of bacteria are included in Enterobacterales?

- E. coli

- Klebsiella

- Enterobacter

- Citrobacter

In treating osteomyelitis, if the patient has Enterobacterales, what are their first choice IV abx? *no need to know dosing

- Cefepime 2g IV q12H

- Ertapenem 1g IV q24H

In treating osteomyelitis, if the patient has PSAE, what are their first choice IV abx? *no need to know dosing

- Cefepime 2g IV q12H

- Meropenem 1g IV q8H

In treating osteomyelitis, if the patient has salmonella, what are their first choice IV abx? *no need to know dosing

Ceftriaxone 2g IV q24H

Salmonella is a common cause of osteomyelitis in patients with _____.

Sickle cell disease!

If the patient has any gram-negative cause of osteomyelitis (Enterobacterales + PSAE + Salmonella), what is their first choice PO antibiotic?

Cipro!

When would we suspect vertebral osteomyelitis?

- Pt presents with acutely worsening back pain focused to one location with other general signs of infection such as fever or increased WBC

- Risk factors to look out for include IVDU, hemodialysis, and immunocompromised hosts

*we care about diagnosing this particular type of osteomyelitis because it impacts duration of treatment

Patients with compound fracture are indicated for _____.

- Prophylaxis!

- Prophylaxis should occur within 6 hours of trauma to reduce osteomyelitis risk! About 1/4 of patients with compound fractures will get osteomyelitis

- Prophylaxis should occur for 72 hours

- Grade I/II fracture --> vancomycin

- Grade III fracture --> vancomycin + cefepime

What is the typical duration of treatment for patients with osteomyelitis?

x 6 weeks (start counting days of therapy after last debridement)

EXCEPTION: 8 weeks or more for patients with vertebral osteomyelitis AND high risk for recurrence

Who has a high risk for recurrence of vertebral osteomyelitis?

a) Paravetebral abscess

b) MRSA infection

*if the pt has either/both of these risk factors AND vetebral osteomyelitis, we extend their treatment duration to 8 weeks or more!

Explain the progression of diabetic foot infections.

Diabetic foot ulcer --> diabetic foot infection --> osteomyelitis

Patients with diabetes should be counseled to _________ to prevent diabetic foot infections.

Inspect their feet daily to check for redness/ ulcers

What is the most common causative organism for diabetic foot infections?

Gram-positive cocci, especially staph!

What are the MRSA risk factors?

- Prior hx of MRSA

- Recent hospitalization

- Recent antibiotic use

- Residence in long-term care facility

What are the PSAE risk factors?

- Tropical/ subtropical climates

- Previous isolation of PSAE in wound

If the patient has a Class 2 (mild) diabetic foot infection, do we initiate oral or IV abx and what coverage are we providing?

- Oral!

- Target: MSSA and Strep (can add PO MRSA or PSAE coverage if risk factor are present)

If the patient has a Class 3 (moderate) diabetic foot infection, do we initiate oral or IV abx and what coverage are we providing?

- Oral or IV!

- Target: MSSA + Strep + Enterobacterales (can add IV MRSA or PSAE coverage if risk factors are present)

If the patient has a Class 4 (severe) diabetic foot infection, do we initiate oral or IV abx and what coverage are we providing?

- IV!

- Target: MRSA + Strep + Enterobacterales + Anaerobes + PSAE (everything)

If a patient has a Class 2 (mild) diabetic foot infection with no risk factors, what abx should we initiate?

ORAL Cephalexin (or Clindamycin if PCN allergy)

If a patient has a Class 2 (mild) diabetic foot infection with MRSA risk factor, what abx should we initiate?

ORAL Linezolid or Bactrim

If a patient has a Class 2 (mild) diabetic foot infection with PSAE risk factor, what abx should we initiate?

ORAL Cephalexin + Cipro

If a patient has a Class 3 (Moderate) diabetic foot infection with no risk factors, what abx should we initiate?

Oral or IV--> Amoxicillin/Clavulanate OR Ampicillin/Sulbactam OR Ertapenem

If a patient has a Class 3 (Moderate) diabetic foot infection with MRSA risk factor, what abx should we initiate?

IV Ampicillin/sulbactam + Vancomycin

If a patient has a Class 3 (Moderate) diabetic foot infection with PSAE risk factor, what abx should we initiate?

IV Pip/Tazo

If a patient has a Class 4 (severe) diabetic foot infection, what abx should we initiate?

- IV Vancomycin + Cefepime + Metronidazole

- IV Vancomycin + Meropenem

How often should diabetic foot infection therapy be monitored?

- Daily if inpatient

- Every 2-7 days if outpatient

- If their condition is worsening, reassess need for surgery + potentially broaden therapy

- If their condition is improving, switch from IV to PO in 5-7 days ideally + consider narrowing to target the identified organism

How do we determine treatment duration for diabetic foot infection? *without osteomyelitis

Administer abx until the infection has cleared (1-2 weeks for many infections, 3-4 weeks for extensive infection)