- Antimicrobial therapy can be optimized for a given patient if you go beyond “Drugs of Choice” lists. The usual drug of first choice may be inappropriate for a given patient. Antimicrobial selection can be based on the following approach: List antimicrobials which are likely to have activity against bacteria causing the infection. The list can be improved if the antimicrobials can be ranked as to likely efficacy (MIC90, MIC80, etc.). It also follows that the more you know about the infection (I think there is an infection vs. I have isolated a pure culture of E. coli with the following susceptibilities….) the easier this list is to construct. Consider the likely toxicity, drug interactions, etc. of the antimicrobials. Are the toxicities more or less likely because of the patient’s condition, age, etc.? (There are probably no absolute contraindications. There are probably no absolutely safe drugs.)
Consider the route of administration appropriate for the patient and the clinical condition being treated.
- Determine the correct dose and interval for the drug, the patient, and the condition. (Activity of some drugs is highly dependent on concentrations to which bacteria are exposed.) Antimicrobials can be safe and efficacious at doses other than those found in formularies. Changing the dosage of an antimicrobial can improve its efficacy. Also, it is possible to “cheat” the dose or the interval and maintain activity but you need to understand what you are doing. Label doses are rarely optimum for a given patient.
- Consider the cost of the antimicrobial. Depending on the value of the animal and the depth of client pockets this may be the second consideration after listing those drugs likely to be efficacious. Cost should never be the first consideration. (If the drug you choose is not efficacious, any amount of money you spend is wasted).
- Advances in susceptibility testing suggest that the disk diffusion assay (Kirby- Bauer) will be phased out during your career! Get familiar with the interpretation of MIC-based susceptibility testing. These tests provide the same basic information as the Kirby-Bauer plus information about relative efficacy of drugs not available by KB.
