Does doxycycline (Doxycycline) cover Gram-negative rods?

From the Guidelines

Doxycycline has limited coverage against gram-negative rods, and its use should be guided by local resistance patterns and specific infection types. As a tetracycline antibiotic, doxycycline works by inhibiting bacterial protein synthesis, making it effective against certain gram-negative rod bacteria, including Pasteurella multocida and Eikenella species 1. However, doxycycline has important limitations in its gram-negative coverage, as it is not reliably effective against Pseudomonas aeruginosa, Acinetobacter, or many Proteus species. The typical adult dosage is 100 mg twice daily, and it's particularly useful for treating infections caused by Rickettsia, Brucella, and certain anaerobes.

Key Points to Consider

• Doxycycline's effectiveness against gram-negative rods is limited, and it should not be used as a first-line treatment for severe gram-negative infections 1.
• Local resistance patterns and specific infection types should guide the use of doxycycline, and other antibiotics like carbapenems, fluoroquinolones, or aminoglycosides may be preferred for severe gram-negative infections.
• Doxycycline's mechanism of action involves binding to the 30S ribosomal subunit, preventing the attachment of aminoacyl-tRNA to the mRNA-ribosome complex, thus inhibiting bacterial protein synthesis.

Recommended Use

• Doxycycline can be used to treat infections caused by gram-negative rods, such as Pasteurella multocida and Eikenella species, but its use should be guided by local resistance patterns and specific infection types 1.
• The typical adult dosage is 100 mg twice daily, and the treatment duration depends on the infection being treated.
• Doxycycline should not be used as a first-line treatment for severe gram-negative infections, and other antibiotics may be preferred in these cases.

From the FDA Drug Label

Doxycycline is indicated for the treatment of infections caused by the following gram-negative microorganisms: Chancroid caused by Haemophilus ducreyi. Plague due to Yersinia pestis (formerly Pasteurella pestis). Tularemia due to Francisella tularensis (formerly Pasteurella tularensis). Cholera caused by Vibrio cholerae (formerly Vibrio comma). Campylobacter fetus infections caused by Campylobacter fetus (formerly Vibrio fetus). Brucellosis due to Brucella species (in conjunction with streptomycin). Bartonellosis due to Bartonella bacilliformis. Granuloma inguinale caused by Calymmatobacterium granulomatis. Doxycycline is indicated for treatment of infections caused by the following gram-negative microorganisms, when bacteriologic testing indicates appropriate susceptibility to the drug: Escherichia coli. Enterobacter aerogenes (formerly Aerobacter aerogenes). Shigella species. Acinetobacter species (formerly Mima species and Herellea species). Respiratory tract infections caused by Haemophilus influenzae. Respiratory tract and urinary tract infections caused by Klebsiella species.

Doxycycline covers certain gram-negative rods, including:

• Haemophilus ducreyi
• Yersinia pestis
• Francisella tularensis
• Vibrio cholerae
• Campylobacter fetus
• Brucella species (in conjunction with streptomycin)
• Bartonella bacilliformis
• Calymmatobacterium granulomatis
• Escherichia coli (when susceptible)
• Enterobacter aerogenes (when susceptible)
• Shigella species (when susceptible)
• Acinetobacter species (when susceptible)
• Haemophilus influenzae (respiratory tract infections)
• Klebsiella species (respiratory tract and urinary tract infections) 2

From the Research

Doxycycline Coverage of Gram-Negative Rods

• Doxycycline displays excellent activity against gram-positive and gram-negative aerobic and anaerobic pathogens, including gram-negative rods 3.
• The antibiotic is effective against various gram-negative bacteria, such as those causing respiratory tract infections, including atypical pneumonias, and genitourinary infections, including gonorrhea and syphilis 3.
• However, some gram-negative rods, like P. aeruginosa, E. cloacae, and S. marcescens, show resistance to many antibacterial agents, including some that doxycycline may not be effective against 4.
• Klebsiella spp. and Enterobacter spp. are intrinsically resistant to certain antibiotics, but most isolates are susceptible to fluoroquinolones, trimethoprimsulfamethoxazole, aminoglycosides, and carbapenems, with doxycycline being an option for some cases 5.
• A scoping review found that doxycycline showed promising results in treating multidrug-resistant gram-negative bacterial infections, with clinical and microbiologic improvements achieved in 81.3% and 87% of patients, respectively 6.
• A case report also demonstrated the successful use of doxycycline in treating a patient with a multidrug-resistant Klebsiella pneumoniae urinary tract infection 7.

Specific Gram-Negative Rods Covered by Doxycycline

• Doxycycline may be effective against certain gram-negative rods, such as:
  • Enterobacteriaceae, including Klebsiella spp. and Enterobacter spp. 5, 6, 7
  • Escherichia coli 7
• However, the effectiveness of doxycycline against other gram-negative rods, like P. aeruginosa, is less clear and may depend on the specific strain and resistance pattern 4.