osteomyelitis
OSTEOMYELITIS
Osteomyelitis is an acute or chronic inflammation of the bone due to an infection resulting from hematogenous spread, contiguous spread from soft tissues and joints to bone, or direct inoculation into bone from surgery or trauma.
The infection is generally due to a single microorganism but polymicrobial infections may also occur.
Staphylococcus aureus is a major cause of infection.
Signs and symptoms include fever; inflammatory findings of erythema, warmth, pain and swelling over the involved area; draining sinus tracts over affected bone; limited movement of affected extremity; pain in the chest, back, abdomen or leg, and tenderness over involved vertebrae in patients with vertebral osteomyelitis; anorexia, vomiting and malaise.

Principles of Therapy

Factors to consider when choosing an antibiotic for empiric therapy

  • Suspected pathogens & their antimicrobial susceptibility pattern
    • Empiric antibiotic coverage for S aureus is indicated
  • Age of patient esp children
  • Severity of infection
  • History of recent antibiotic intake
  • Current Gram stain results
  • Underlying co-morbid conditions
  • Antibiotic safety & efficacy

Pharmacotherapy

Antibiotics for Empiric Therapy

  • Antibiotic treatment should be started after specimens for cultures are sent
    • However, treatment in an acutely ill patient should not be delayed to wait for bone debridement
  • Empirical therapy of acute hematogenous osteomyelitis  in both children & adults should include coverage against S aureus
  • IV antibiotics are given at the start of therapy; step-down to per orem treatment later may be possible based on clinical response

Antibacterial Combinations

  • Eg Co-trimoxazole [Sulfamethoxazole (SMZ) & Trimethoprim (TM)]
  • Effective against many Methicillin-resistant S aureus isolates but studies regarding effectiveness in osteomyelitis are limited
  • TMP-SMZ is also active against streptococci & enterobacteriaceae

Beta-lactam Antibiotics

  • Eg penicillins, cephalosporins, carbapenems
  • Achieve therapeutic concentrations in bone
  • 1st generation cephalosporins (eg Cefazolin) & Oxacillin are good initial choices for osteomyelitis suspected to be caused by methicillin-sensitive Staphylococcus aureus
    • Cefalexin & Cloxacillin are per orem agents that may be used to complete treatment
  • Benzylpenicillin is the drug of choice for treating osteomyelitis caused by group A streptococcus, susceptible S pneumoniae & enterococci
    • Amoxicillin or Phenoxymethylpenicillin are per orem agents recommended for completing treatment
  • Antipseudomonal penicillin, or Cefepime, or Ceftazidime &/or an aminoglycoside is an effective combination for osteomyelitis caused by Pseudomonas
  • Ampicillin is effective against Salmonella
    • Cefotaxime or Ceftriaxone may be used for resistant isolates
  • Most beta-lactam antibiotics are active against K kingae

Clindamycin

  • Achieves good bone penetration
  • May be used for empirical therapy of osteomyelitis suspected to be due to methicillin-sensitive Staphylococcus aureus & anaerobes
    • However, S aureus isolates susceptible to Clindamycin but resistant to Erythromycin should be tested for inducible macrolide-lincosamide-streptogramin B resistance through the D test
    • Treatment failure is more likely in the presence of inducible resistance
  • Active against most isolates of S pyogenes S pneumoniae

Linezolid

  • May be as effective as Vancomycin in treating infections caused by Methicillin-resistant S aureus
  • Active against streptococci & Vancomycin-resistant enterococci
  • Alternative to prolonged IV therapy because of excellent oral bioavailability

Quinolones

  • Eg Ciprofloxacin & Ofloxacin
  • May be used for PO treatment of osteomyelitis in adults because of good penetration into the bone & excellent oral absorption
    • Not routinely recommended for use in young children
  • May be used to treat osteomyelitis caused by gram-negative organisms including enterobacteriaceae
  • Quinolones have variable coverage against S aureus & S epidermidis; no coverage against Enterococcus spp; newer quinolones have better action against Streptococcus spp & some anaerobes
  • Should be combined w/ another antibiotic to achieve adequate coverage against S aureus during empiric therapy

Rifampicin

  • May be used in combination w/ cell-wall antibiotics for synergistic action against S aureus
  • Should never be used as monotherapy because resistance develops rapidly

Tetracyclines

  • Effective against many Methicillin-resistant S aureus isolates but studies regarding effectiveness in osteomyelitis are limited
  • Tetracycline use in young children may result in stunted bone & tooth growth; should only be considered in >8 yr of age
  • Should be avoided in pregnant patients

Vancomycin

  • Drug of choice for empiric therapy in areas where community acquired-Methicillin-resistant S aureus resistance to Methicillin & Clindamycin exceeds 10-15%
  • Active against most isolates of S pyogenes, S pneumoniae & Ampicillin-resistant enterococci
Local Antibiotic Therapy
  • Antibiotic-impregnated (usually w/ aminoglycosides or Vancomycin) acrylic beads may be placed to sterilize a dead space while waiting for definitive management
  • Limited studies are available to adequately support the superiority of local therapy over systemic antibiotic therapy, though local therapy is associated w/ markedly fewer adverse events

Suppressive Antibiotic Therapy

  • Considered for patients in whom surgical treatment is needed but is not feasible
  • Choose antibiotics that achieve adequate penetration into bone, have good bioavailability & low toxicity & are active against etiologic agents as based on sensitivity testing results
  • Choices include Fusidic acid, quinolones, TMP-SMZ, Rifampicin (combined w/ other antibiotics)
  • Treatment duration is usually 6 mth

Duration of Antibiotic Therapy

  • Based on extent of infection, etiologic agent & clinical course
  • Range is usually between 3-6 wk
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