Figure 6-1 Drawbacks of the antibiotic era: the accelerating cycle of antibiotic resistance. Source: Modified from the work produced by John McGowan, Professor, Rollins School of Public Health, Emory University, Atlanta, Georgia.

Presented by Jerome J. Schentag, Pharm. D.

Professor of Pharmacy, State University of New York at Buffalo and Director, Clinical Pharmacokinetics Laboratory, Millard Fillmore Health System

It has become difficult to target the causes of antibiotic resistance in the current health care environment. There is reason for concern because the cycle of antibiotic resistance is not only complex but it also seems to be intensifying (Figure 6-1).

Several principal causes of endemic antimicrobial resistance have been proposed. Resistance patterns are believed to be the consequence of the many bacterial genetic pressures and antibiotics that humans have introduced into the environment. Subsequently, the importance of antibiotic selective pressure is increasingly a concern. The organisms that infect patients may develop resistance on the basis of the dose of the prescribed drug relative to the organism's susceptibility, a problem generally overlooked and understudied. In one study, researchers analyzing the relationship between dose and resistance for methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae, and vancomycin-resistant Enterococcus faecium (VREF) in a large population of the Millard Fillmore Health System in Buffalo, New York, found that the manifestations of these infections resulted in an increasing incidence of serious infections. The use of suboptimal doses produced resistance in organisms from 93 percent of patients, whereas the use of optimal doses produced resistance in organisms from only 8 percent of patients.