Fosfomycin

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Background

Mechanism of Action

  • Inhibits an enzyme-catalyzed reaction in cell wall synthesis
  • Bacteridical

Spectrum of Activity

PK/PD

  • Efficacy predicted by time above MIC
  • Oral bioavailability 34 to 58%; higher if taken on an empty stomach
  • Elimination half-life of 5.7 hours, 93 to 99% excreted unchanged in the urine

Breakpoints

Dosing

  • Uncomplicated UTI: fosfomycin 3 g PO once
  • Complicated UTI: fosfomycin 3 g PO q72h for 2 to 3 doses
  • Intravenous: fosfomycin disodium 8 g IV q12h
  • CNS or other severe infection: fosfomycin disodium 8 to 12 g IV q12h
  • Continuous infusion may result in better PK/PD: 8 g IV load followed by 16-24 g continuous infusion over 24 hours[1]

Renal Dosing

  • Oral: no dosage adjustment necessary for oral, though elimination may be prolonged
  • Intravenous
    • CrCl >=130 mL/min: maximum indicated dose for indication (up to 24 g/day in 3 to 4 divided doses)
    • CrCl 40-129 mL/min: normal dose, in 2 to 4 divided doses
    • CrCl 30-39: 70-80% of normal daily dose, in 2 to 3 divided doses
    • CrCl 20-29: 50-70% of normal daily dose, in 2 to 3 divided doses
    • CrCl 10-19: 30-50% of normal daily dose, in 2 to 3 divided doses
    • CrCl <10: 20% of normal daily dose, in 1 to 2 divided doses
    • Intermittent hemodialysis: 2 g after each session (up to 4 g for severe or less susceptible infections)

Safety

Monitoring

  • Hypokalemia, high sodium content, dose-limiting nausea, vomiting, and diarrhea

Pregnancy

  • Safe in pregnancy
  1. Antonello RM, Di Bella S, Maraolo AE, Luzzati R. Fosfomycin in continuous or prolonged infusion for systemic bacterial infections: a systematic review of its dosing regimen proposal from in vitro, in vivo and clinical studies. Eur J Clin Microbiol Infect Dis. 2021 Jun;40(6):1117-1126. doi: 10.1007/s10096-021-04181-x. Epub 2021 Feb 18. PMID: 33604721; PMCID: PMC8139892.