OSTEOMYELITIS

OSTEOMYELITIS is a topic covered in the Harrison's Manual of Medicine.

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  • Pathogenesis and epidemiology: Osteomyelitis cases can be classified by pathogenesis, duration of infection, location of infection, and whether prosthetic material is present. Osteomyelitis is typically caused by hematogenous spread, spread from a contiguous site following surgery, and/or secondary infection in the setting of vascular insufficiency or concomitant neuropathy (e.g., in diabetes). The most common primary foci of infection are the urinary tract, skin and soft tissues, intravascular catheterization sites, and the endocardium. Hematogenous osteomyelitis in adults most commonly results in vertebral infection, with 6.5 cases/100,000 at ages >70 years.
  • Microbiology: Irrespective of the anatomic location involved, S. aureus is the most common cause, accounting for ∼40–50% of cases.
    • Gram-negative bacilli account for 10–20% of cases.
  • Clinical manifestations: Pts generally have a febrile illness, with localized pain and tenderness. A history of surgery or trauma in the affected region—even in the remote past—should raise suspicion.
  • Diagnosis
    • Radiographic studies and occasionally invasive sampling of lesions are needed to confirm the diagnosis.
    • Blood cultures are positive in 30–78% of cases, with lower rates if the pt has previously received antibiotics.
    • CT and especially MRI scans offer increased sensitivity in detecting osteomyelitis.
  • Treatment
    • Table 87-2 lists antibiotics for the treatment of osteomyelitis in the absence of implants.
    • The optimal route and duration of therapy remain controversial, but a 6-week course of IV therapy is usually recommended for acute osteomyelitis. If evidence indicates clinical efficacy of an oral antibiotic to which the organism is susceptible and if the pt has normal intestinal function (without vomiting), a transition from IV to PO therapy can be considered.
    • Serial measurements of inflammatory markers (ESR, C-reactive protein) can serve as surrogates for response to treatment in some infections (particularly those due to S. aureus).
    • Surgical intervention is usually required in chronic osteomyelitis and cases involving prosthetic implants.
TABLE 87-2: Antibiotic Therapy for Osteomyelitis in Adults Without Implantsa
MICROORGANISMANTIMICROBIAL AGENT (DOSE,b ROUTE)
Staphylococcus spp. 
 Methicillin-susceptible

Nafcillin or oxacillinc (2 g IV q6h)

followed by

Rifampin (300–450 mg PO q12h) plus levofloxacin (750 mg PO q24h or 500 mg PO q12h)

 Methicillin-resistant

Vancomycind (15 mg/kg IV q12h) or daptomycin (>6–8 mg/kg IV q24h)

followed by

Rifampin (300–450 mg PO q12h)

plus

Levofloxacin (750 mg PO q24h or 500 mg PO q12h) or TMP-SMXe (1 double-strength tablet PO q8h) or fusidic acid (500 mg PO q8h)

Streptococcus spp.Penicillin Gc (5 million units IV q6h) or ceftriaxone (2 g IV q24h)

Enterobacteriaceae

 Quinolone-susceptible

 Quinolone-resistantf

Ciprofloxacin (750 mg PO q24h)

Imipenem (500 mg IV q6h)

Pseudomonas aeruginosa

Cefepime or ceftazidime (2 g IV q8h) plus an aminoglycosideg

or

Piperacillin-tazobactam (4.5 g IV q8h) plus an aminoglycosideg for 2–4 weeks

followed by

Ciprofloxacinh (750 mg PO q12h)

Anaerobes

Clindamycin (600 mg IV q6–8h) for 2–4 weeks

followed by

Clindamycini (300 mg PO q6h)

aUnless otherwise indicated, the total duration of antimicrobial treatment is generally 6 weeks.
bAll dosages are for adults with normal renal function.
cWhen the pt has delayed-type penicillin hypersensitivity, cefuroxime (1.5 g IV q6–8h) can be administered. When the pt has immediate-type penicillin hypersensitivity, the penicillin should be replaced by vancomycin (1 g IV q12h).
dTarget vancomycin trough level: 15–20 µg/mL.
eTrimethoprim-sulfamethoxazole. A double-strength tablet contains 160 mg of trimethoprim and 800 mg of sulfamethoxazole.
fIncluding isolates producing extended-spectrum β-lactamase.
gThe need for addition of an aminoglycoside has not yet been proven. However, this addition may decrease the risk of emergence of resistance to the β-lactam.
hThe rationale for starting ciprofloxacin treatment only after pretreatment with a β-lactam is the increased risk of emergence of quinolone resistance in the presence of a heavy bacterial load.
iAlternatively, penicillin G (5 million units IV q6h) or ceftriaxone (2 g IV q24h) can be used against gram-positive anaerobes (e.g., Propionibacterium acnes), and metronidazole (500 mg IV/PO q8h) can be used against gram-negative anaerobes (e.g., Bacteroides spp.).
Source: From Zimmerli W: Vertebral Osteomyelitis. N Engl J Med 362:1022, 2010. © Massachusetts Medical Society. Reprinted with permission.

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