• Penicillin G and Penicillin V Pharmacology and Therapeutics

  • Therapeutic uses

    • Serious Clostridial Infections

      Serious Clostridial Infections  Audio Overview

      • High-dose penicillin G along with surgical debridement is indicated for gas gangrene and Clostridium wound infections, as clostridial species (e.g. C. perfringens) are generally penicillin-susceptible.¹

        • Clostridium perfringens

          "This illustration depicts a three-dimensional (3D), computer-generated image of the cluster of barrel-shaped, Clostridium perfringens bacteria. The artistic recreation was based upon scanning electron microscopic (SEM) imagery." Attribution Illustrator: Jennifer Oosthuizen, CC0, via Wikimedia Commons https://commons.wikimedia.org/wiki/File:21913_lores.jpg

      • For patients with suspected clostridial infection, empiric antibiotic treatment should not be delayed.

        • Some broad spectrum drugs used in this setting could include vancomycin, tazobactam, a carbapenem, or ceftriaxone with metronidazole.

        • However, if necrotizing soft tissue infection or gas gangrene is suspected, then penicillin in combination with clindamycin should be added, treating group A streptococcal necrotizing fasciitis.¹

      • Penicillin G may be given IV in large doses for tetanus (caused by Clostridium tetani) as an adjunct to antitoxin, to eradicate the vegetative bacteria.

        • However, penicillin G which in the past was first-line treatment is now considered an acceptable alternative with metronidizole being the contemporary first-line treatment approach.

          • For patients with the history of serious allergic reactions to penicillin or metronidazole, desensitization of the patient to penicillin may be appropriate before trying alternatives.

      • Penicillin G is also used for botulism (wound botulism) as adjunct therapy after antitoxin, botulinum antitoxin, heptavalent (Rx).³

    • Meningitis and Brain Abscess

      • Penicillin G can treat meningococcal meningitis (caused by Neisseria meningitidis) if the strain is penicillin-susceptible.⁴

        • Initial empiric treatment (prior to susceptibility testing) would likely include an extended-spectrum cephalosporin, e.g. cefotaxime or ceftriaxone.

          • If the meningococcal isolate is susceptible to penicillin, treatment could be changed to penicillin G or ampicillin.

          • Alternatively, definitive treatment could also continue to utilize cefotaxime or ceftriaxone.⁴

        • At initial patient presentation meningitis due to Neisseria meningitidis may not be easily distinguished from other types of meningitis.⁵ 

          • Therefore, empirical treatment is important to initiate, given the seriousness of the infection.

            • Another initial empirical therapeutic approach would include dexamethosone, ceftriaxone, cefotaxime (third-generation cephalosporins) and vancomycin.⁵ 

              • Acyclovir would be considered in accordance with the initial CSF evaluation.

            • Upon establishing at an accurate diagnosis of meningococcal meningitis, ceftriaxone or cefotaxime appears to be a drug of choice for treatment; moreover, penicillin G, ampicillin, chloramphenicol, fluoroquinolones, and aztreonam are described as alternative therapeutic approaches.⁵

      • Antibiotic selection for treating brain abscess is challenging, given the likelihood of polymicrobial presentations.^6,7  

        •  

          Brain Abscess (Magnetic Resonance Image (MRI))

          Brain MRI in lung cancer patient. Abscess localized in Red Square. Attribution © Nevit Dilmen, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons https://commons.wikimedia.org/wiki/File:Brain_MRI_131749_rgbca-.png

        • Therefore, empiric antibiotic therapy should cover oral streptococci, methicillin-susceptible staphylococci, anaerobes and Enterobacteriaceae.

          • Anaerobic coverage should also be considered.

            • Following culture, any initial empiric treatment protocol may be changed.

              • Streptococci coverage can be obtained with high-dose penicillin G or a third-generation cephalosporin (cefotaxime or ceftriaxone).

              • Metronidizole would be included to cover penicillin-resistant anaerobes.

              • If S. aureus is a concern, vancomycin may be utilized to address methicillin-resistant bacteria.⁶

August, 2025