General Information:  Antibiotics are generally classified as time- and concentration-dependent.

Concentration-dependent antibiotics

• Rate of kill is highly dependent on peak concentrations and is tissue-specific (generally 10x MIC needed for optimal bactericidal effect)
• As concentrations of the drug decrease, the bactericidal effect decreases
• Need less frequent dosing but higher doses
• Examples:

                    -Fluoroquinolones (i.e. Levofloxacin)

                    -Aminoglycosides (i.e. Gentamicin)

                    -Azithromycin

Relevance to the EM Physician:

Concentration-dependent antibiotics should be given at the highest appropriate dose for the target tissues (i.e. Levofloxacin 750mg for pneumonia is preferable to 500mg).  This is also the rationale for high dose, extended-interval dosing for Gentamicin (>5mg/kg initial dose).

University of Maryland Section of Global Emergency Health

Author:  Andi Tenner, MD, MPH

References

 

Levison ME and Levison JH.  Pharmacokinetics and Pharmacodynamics of Antibacterial Agents. Infect Dis Clin N Am.  23(2009): 791-815.