Chapter 8: Antiinfective Agents

The central principle guiding this therapy is selective toxicity, the critical ability of the drug to affect specific proteins or enzyme systems utilized by the invading pathogen without causing undue damage to the host’s human cells, though achieving total selective toxicity remains an ongoing challenge. Antiinfective drugs function by several mechanisms, including interfering with cell wall synthesis (like penicillins or vancomycin), disrupting protein synthesis (such as gentamicin), blocking DNA synthesis, or inhibiting the utilization of essential nutrients necessary for pathogen survival and replication. These agents are characterized by their spectrum of activity, categorized as narrow-spectrum (effective against only highly selective organisms) or broad-spectrum (effective against a wide variety of microbes). They may be bactericidal (directly causing cell death) or bacteriostatic (preventing reproduction). A major concern in treatment is the development of resistance, which can be natural or acquired. Microbes acquire resistance by developing enzymes (like penicillinase) that deactivate the drug, altering cellular permeability to prevent drug entry, or modifying binding sites. Healthcare professionals mitigate the emergence of resistant strains by limiting the indiscriminate use of antiinfectives, ensuring drug selection is guided by culture and sensitivity testing, and stressing to patients the importance of maintaining therapeutic drug levels through timely, around-the-clock dosing for the full prescribed duration. Antiinfective use is associated with several serious adverse reactions, including direct toxicity to the host’s organs, such as renal toxicity (kidney damage), neurotoxicity (nerve damage leading to effects like ototoxicity or dizziness), and GI toxicity (nausea, vomiting, diarrhea, and potentially fatal pseudomembranous colitis), in addition to hypersensitivity reactions and the risk of superinfections, which occur when the normal flora is destroyed, allowing opportunistic pathogens (like Candida or C. difficile) to proliferate. Antiinfectives are also sometimes used for prophylaxis, preventing infection before it occurs, such as before certain surgeries or dental procedures in high-risk patients.