What is the antibiotic for right lower extremity (RLE) cellulitis in a patient with a history of total knee arthroplasty (TKA) of the right lower extremity (RLE)?

From the Guidelines

For cellulitis of the right lower extremity (RLE) in a patient with a history of total knee arthroplasty (TKA), I recommend empiric treatment with intravenous vancomycin (15-20 mg/kg every 12 hours) plus either cefepime (2g IV every 8 hours) or piperacillin-tazobactam (4.5g IV every 6-8 hours). This combination provides coverage against methicillin-resistant Staphylococcus aureus (MRSA) and gram-negative organisms, which is crucial given the prosthetic joint, as supported by the guidelines from the Infectious Diseases Society of America 1. The guidelines suggest that vancomycin plus either piperacillin-tazobactam or imipenem-meropenem is a reasonable empiric regimen for severe infection, which may be applicable in this case due to the presence of a prosthetic joint 1.

Key Considerations

• Blood cultures should be obtained before starting antibiotics to guide subsequent therapy 1.
• The total duration of treatment should be 2-4 weeks depending on clinical response and whether the prosthesis is involved.
• If the patient is stable without systemic symptoms, oral alternatives after initial IV therapy could include trimethoprim-sulfamethoxazole DS (1-2 tablets twice daily) plus ciprofloxacin (500-750mg twice daily), although the activity of doxycycline and SMX-TMP against β-hemolytic streptococci is not well established 1.
• Close monitoring for improvement is essential, and orthopedic consultation is warranted to evaluate for possible prosthetic joint involvement requiring surgical intervention.
• Elevation of the affected area and treatment of predisposing factors, such as edema or underlying cutaneous disorders, are also recommended to promote recovery 1.

From the FDA Drug Label

The two trials were similar in design but differed in patient characteristics, including history of diabetes and peripheral vascular disease. There were a total of 534 adult patients treated with daptomycin for injection and 558 treated with comparator in the two trials. The efficacy endpoints in both trials were the clinical success rates in the intent-to-treat (ITT) population and in the clinically evaluable (CE) population. The success rates by pathogen for microbiologically evaluable patients are presented in Table 16 Pathogen Success Rate n/N (%) Daptomycin for Injection Comparator* Methicillin-susceptible Staphylococcus aureus (MSSA) † 170/198 (86%) 180/207 (87%) Methicillin-resistant Staphylococcus aureus (MRSA) † 21/28 (75%) 25/36 (69%) Streptococcus pyogenes 79/84 (94%) 80/88 (91%) Streptococcus agalactiae 23/27 (85%) 22/29 (76%) Streptococcus dysgalactiae subsp. equisimilis 8/8 (100%) 9/11 (82%) Enterococcus faecalis (vancomycin-susceptible only) 27/37 (73%) 40/53 (76%)

The antibiotic for RLE cellulitis S/p TKA RLE is daptomycin or comparator (vancomycin or an anti-staphylococcal semi-synthetic penicillin) 2.

• Key points:
  • Daptomycin is effective against various pathogens, including MSSA, MRSA, Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus dysgalactiae subsp. equisimilis, and Enterococcus faecalis.
  • Clinical success rates for daptomycin and comparator were similar in the ITT and CE populations.
  • The choice of antibiotic should be based on the specific pathogen and patient characteristics.

From the Research

Antibiotic Treatment for RLE Cellulitis

The treatment of cellulitis, particularly in the context of a recent total knee arthroplasty (TKA) in the right lower extremity (RLE), involves the selection of appropriate antibiotics based on the suspected causative pathogens and the patient's specific risk factors.

• The choice of antibiotic may depend on the severity of the infection, the presence of any underlying health conditions, and the results of any microbiological tests that have been performed.
• Studies have compared the efficacy of different antibiotics, such as ceftriaxone and cefazolin, in the treatment of methicillin-susceptible Staphylococcus aureus (MSSA) infections 3, 4, 5.
• Cefazolin is often considered a first-line treatment option for MSSA infections due to its effectiveness and relatively low risk of adverse effects.
• Ceftriaxone has also been evaluated as a potential treatment option for MSSA infections, with some studies suggesting that it may be associated with a lower risk of toxicity compared to traditional antistaphylococcal antibiotics 3.
• However, other studies have raised concerns about the use of ceftriaxone for the treatment of MSSA bacteremia, citing higher rates of treatment failure compared to cefazolin 5.

Considerations for Antibiotic Selection

When selecting an antibiotic for the treatment of RLE cellulitis in a patient with a recent TKA, it is essential to consider the following factors:

• The suspected causative pathogen(s) and their likely antibiotic susceptibility patterns.
• The patient's medical history, including any underlying health conditions that may affect the choice of antibiotic.
• The results of any microbiological tests that have been performed, such as blood cultures or wound swabs.
• The potential risks and benefits of different antibiotic treatment options, including the risk of adverse effects and the development of antibiotic resistance.
• According to 6, antibiotic selection is determined by patient history and risk factors, severity of clinical presentation, and the most likely microbial culprit.