Source: Burgess DS. Antimicrobial
Regimen Selection. In: DiPiro, JT, Talbert RL, Yee GC, Matzke GR, Wells
BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 8 ed. http://accesspharmacy.com/content.aspx?aid=8001114.
Accessed June 23, 2012.
- “Empiric” regimen: initiated before
offending organism is identified and sometimes prior to documentation
of presence of infection.
- “Definitive” regimen: instituted when causative
organism is known.
- Obtain careful history and physical.
- Signs and Symptoms
temperature above normal range of 36.7–37°C
(98.1–98.6°F; measured orally)
- Hallmark of infectious disease
- May be caused by drugs in absence of infection or other underlying
- Elevated white blood cell (WBC) count
and/or lymphocytes are mobilized to destroy invading microbes.
- Bacterial infections associated with
granulocyte counts (neutrophils and basophils)
- Increased band neutrophils in peripheral smear (left-shift)
- Low neutrophil counts (neutropenia), indicating abnormal response;
associated with poor prognosis
- Tuberculosis, viral, or fungal infections associated with
relative lymphocytosis even with normal or slightly elevated total
- Local signs
- Pain and inflammation
- Purulent drainage
- Collect infected body material.
with Gram stain.
- Perform blood cultures and sensitivities.
- Perform serologic tests for presence of antibodies.
- Collect suspected fluids or tissues (e.g., spinal fluid in
- Assess inflammation with deep-seated infections by examining
tissues or fluids (e.g., examine sputum to assess pneumonia).
- Factors to consider
- Severity and acuity
- Local susceptibility data rather than national compilations
- Host factors
- Allergy or history of adverse
- Age of patient
- Metabolic abnormalities
- Renal and hepatic function: Adjust dosage with diminished
renal and/or hepatic function to avoid drug accumulation.
- Concomitant drug therapy: Potential for drug interactions
- Concomitant disease states
- Drug factors
- Use generally accepted drugs
based on pathogen (Table 2)
- Consider pharmacokinetic and pharmacodynamic properties of
- Bactericidal effects may be concentration-dependent
(aminoglycosides and fluoroquinolones) or time-dependent (β-lactams).
- Treatment outcome can be predicted by area under concentration-time
curve (AUC) and maximal plasma concentration.
- Duration that drug concentration exceeds minimal inhibitory
concentration (MIC) is most important pharmacodynamic relationship
for antimicrobials that display time-dependent bactericidal effects.
- Antibiotic tissue penetration varies with site of infection.
- Clinically relevant drug concentrations found in blood,
urine, synovial fluid, and peritoneal fluid.
- Combination therapy should be considered to:
the spectrum of coverage for empiric therapy
when multiple aerobic and anaerobic bacteria are likely to be present
(e.g., in intraabdominal and female pelvic infections)
- Achieve synergistic activity against infecting organism
- Advantageous for infections caused by gram-negative bacilli
in immunosuppressed patients.
- May produce better results in infections caused by Pseudomonas aeruginosa and certain
infections caused by Enterococcus spp.
- Prevent the emergence of resistance
Table 1. Major Drug Interactions with Antimicrobials |Favorite Table|Download (.pdf)
Table 1. Major Drug Interactions with Antimicrobials
Mechanism of Action/Effect
Neuromuscular blocking agents
Additive adverse effects
Nephrotoxins (N) or ototoxins (O) (e.g., amphotericin
B (N) cisplatin (N/O), cyclosporine ...
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