Pharmacotherapy - Infectious Diseases

INTRODUCTION
A systematic approach to the selection and evaluation of an antimicrobial
regimen is shown in Table 35-1. An “empiric” antimicrobial regimen is
begun before the offending organism is identified and sometimes prior to
the documentation of the presence of infection, while a “definitive”
regimen is instituted when the causative organism is known.
CONFIRMING THE PRESENCE OF INFECTION
FEVER
• Fever is defined as a controlled elevation of body temperature above the
normal range of 36.7 to 37.0°C (98.1 to 98.6°F) (measured orally). Fever is
a manifestation of many disease states other than infection.
• Many drugs have been identified as causes of fever. Drug-induced fever is
defined as persistent fever in the absence of infection or other underlying
condition. The fever must coincide temporally with the administration of
the offending agent and disappear promptly upon its withdrawal, after
which the temperature remains normal.
SIGNS AND SYMPTOMS
White Blood Cell Count
• Most infections result in elevated white blood cell (WBC) counts (leukocytosis)
because of the mobilization of granulocytes and/or lymphocytes to
destroy invading microbes. The generally accepted range of normal values
for WBC counts is between 4,000 and 10,000/mm3.
• Bacterial infections are associated with elevated granulocyte counts (neutrophils,
basophils), often with increased numbers of immature forms (band
neutrophils) seen in peripheral blood smears (left-shift). With infection,
peripheral leukocyte counts may be very high, but are rarely higher than
30,000 to 40,000/mm3. Low neutrophil counts (neutropenia) after the onset
of infection indicate an abnormal response and are generally associated with
a poor prognosis for bacterial infection.
• Relative lymphocytosis, even with normal or slightly elevated total WBC
counts, is generally associated with tuberculosis and viral or fungal
infections. Many types of infections, however, may be accompanied by a
completely normal WBC count and differential.

TABLE 35-1
Systematic Approach for Selection of Antimicrobials
Confirm the presence of infection
Careful history and physical
Signs and symptoms
Predisposing factors
Identification of the pathogen
Collection of infected material
Stains
Serologies
Culture and sensitivity
Selection of presumptive therapy considering every infected site
Host factors
Drug factors
Monitor therapeutic response
Clinical assessment
Laboratory tests
Assessment of therapeutic failure