What is the rationale for adding doxycycline (Doxycycline) to cefazolin (Cefazolin) in a patient with severe foot cellulitis and fever, given a wound culture positive for pan-sensitive Methicillin-Sensitive Staphylococcus aureus (MSSA) and Group A Streptococcus (GAS)?

From the Guidelines

Doxycycline can be discontinued in this patient with severe foot cellulitis and fever, as cefazolin alone provides adequate coverage against the pan-sensitive Methicillin-Sensitive Staphylococcus aureus (MSSA) and Group A Streptococcus (GAS) identified in the wound culture. The initial addition of doxycycline to cefazolin was likely empiric, aiming to cover a broader spectrum of pathogens, including potential resistant strains, until culture results were available 1. However, given the culture results showing sensitivity to cefazolin, the rationale for continuing doxycycline is diminished. Cefazolin, a first-generation cephalosporin, has well-documented efficacy against MSSA and group A streptococcus, making it sufficient for the treatment of this patient's infection 1.

Key points to consider in this decision include:

• The patient's wound culture is positive for pan-sensitive MSSA and GAS, both of which are adequately covered by cefazolin.
• Cefazolin has excellent tissue penetration, which is beneficial for skin and soft tissue infections like cellulitis.
• Continuing unnecessary antibiotics like doxycycline can contribute to antibiotic resistance, increase the risk of side effects, and add to the cost of treatment without providing additional clinical benefit.
• The practice guidelines for the diagnosis and management of skin and soft tissue infections support the use of antibiotics active against streptococci, such as cefazolin, for the treatment of cellulitis 1.

Given these considerations and the evidence from the Infectious Diseases Society of America's 2014 update on the practice guidelines for skin and soft tissue infections 1, the most appropriate course of action is to discontinue doxycycline and continue treatment with cefazolin alone, ensuring effective treatment of the identified pathogens while minimizing unnecessary antibiotic exposure.

From the FDA Drug Label

INDICATIONS AND USAGE Cefazolin for Injection, USP is indicated in the treatment of the following serious infections due to susceptible organisms: ... Skin and Skin Structure Infections: Due to S. aureus (including beta-lactamase-producing strains), S. pyogenes, and other strains of streptococci. Appropriate culture and susceptibility studies should be performed to determine susceptibility of the causative organism to cefazolin The rationale for adding doxycycline to cefazolin in a patient with severe foot cellulitis and fever, given a wound culture positive for pan-sensitive Methicillin-Sensitive Staphylococcus aureus (MSSA) and Group A Streptococcus (GAS), is not directly supported by the provided drug label, as it does not discuss the use of doxycycline or combination therapy with cefazolin for this specific indication 2.

• The label indicates cefazolin is effective against S. aureus and S. pyogenes, but does not provide information on adding doxycycline to cefazolin for treatment of infections caused by these organisms.
• No conclusion can be drawn regarding the rationale for adding doxycycline to cefazolin based on the provided drug label.

From the Research

Rationale for Adding Doxycycline to Cefazolin

The rationale for adding doxycycline to cefazolin in a patient with severe foot cellulitis and fever, given a wound culture positive for pan-sensitive Methicillin-Sensitive Staphylococcus aureus (MSSA) and Group A Streptococcus (GAS), is not directly supported by the provided evidence. However, some points can be considered:

• The use of cefazolin as a treatment for MSSA infections is supported by several studies 3, 4, 5, 6.
• Cefazolin has been shown to be effective in treating MSSA infections, including bacteremia 3, 4, 5, 6.
• The need for empirical coverage of MSSA in cellulitis/erysipelas is debated, and some studies suggest that streptococci are responsible for the vast majority of cases 7.
• Doxycycline is often used to treat infections caused by GAS, but its use in combination with cefazolin for MSSA and GAS infections is not explicitly mentioned in the provided studies.

Considerations for Treatment

Some considerations for treatment include:

• The effectiveness of cefazolin in treating MSSA infections, as shown in several studies 3, 4, 5, 6.
• The potential for doxycycline to provide coverage for GAS, although its use in combination with cefazolin is not explicitly supported by the provided evidence.
• The need for further studies to determine the optimal treatment regimen for patients with severe foot cellulitis and fever, given a wound culture positive for pan-sensitive MSSA and GAS.

Treatment Options

Treatment options may include:

• Cefazolin as a first-line treatment for MSSA infections, as supported by several studies 3, 4, 5, 6.
• Doxycycline as a potential addition to cefazolin for coverage of GAS, although further studies are needed to support this combination.
• Other treatment options, such as antistaphylococcal penicillins or ampicillin/sulbactam, may also be considered, as mentioned in the provided studies 3, 4, 6.