Antimicrobial Agents

Introduction: Antimicrobial Agents Although they are often over-prescribed, antimicrobial agents are a critical defense against microbial infections. The sources of microbial infections include bacteria, viruses, funguses, and parasites. Therefore, the key categories of antimicrobial pharmaceutical agents are antibiotics, antifungals, antiprotozoal, and antiviral drugs. Sometimes the terms antibiotic, antimicrobial, and anti-infective are used interchangeably, but it is crucial to differentiate between the type of infection in order to choose the appropriate antimicrobial agent (Leekha, Terrell, & Edson, 2011, p. 156). Incorrect treatment can lead to deleterious results including resistance.

There are several different ways to classify antimicrobial agents, and likewise, different methods of determining whether the infection is related to a virus, bacteria, or otherwise. Classifying Antimicrobial Agents One method of classifying antimicrobial agents is via their chemical composition or molecular structure.

Another method of classifying antimicrobial agents is via their mechanism of action, and a third method is their level of importance overall in human medicine, which pragmatic implications for public policy, public health policy, and healthcare procurement and logistics (“Categorization of Antimicrobial Drugs Based on Importance in Human Medicine,” 2009). Antimicrobials can also be classified based on their antibacterial activity, referring to features like mechanisms of resistance, sensitivity, and predicted spectrum (Purdue Research Foundation, 1996).

In fact, antimicrobials can also be classified according to their source: as they are typically derived from at least three sources including molds or fungi, bacteria themselves, or from synthetic analysis (Purdue Research Foundation, 1996). The broadest means by which to classify antimicrobial agents would be to focus on what they target: such as a fungus, a virus, a parasite, or bacteria (“Antimicrobial Agents – An Overview,” 2015). Chemical Classifications Chemical classification systems divide antimicrobials into categories based on their chemical features.

For example, penicillins differ from polypeptides, which differ from tetracyclines. Penicillins and cephalosporins together are sub-categories of the parent class of Beta-lactam antibiotics (Becker, 2013; Purdue Research Foundation, 1996). There are also macrolides, lincosamides, aminoglycosides, sulfanomides, fluoroquinolones, metronidazoles, clindamycin, and innumerable other sub-categories of antimicrobial agents based on their chemical composition (Becker, 2013; Purdue Research Foundation, 1996). Understanding the chemical composition of the antimicrobial helps the physician to treat the infection with the most efficacious, evidence-based intervention.

Mechanism of Action Classifying antimicrobial agents according to their mechanism of action can also help narrow down which drugs to prescribe under which conditions. However, using a mechanism of action classification scheme is more common in cancer chemotherapy than for treating acute infectious agents (Purdue Research Foundation, 1996). Understanding mechanisms of action may be helpful in situations in which the cause of the infection remains unknown.

Some mechanisms of action for antimicrobials may include antimetabolic agents, agents that work via cell wall synthesis, and those that work on protein synthesis (Puedue Research Foundation, 1996). Viral vs. Bacterial Infections Viruses and bacteria can sometimes cause similar symptoms in the human patient, but their modes of action are totally different, and most importantly, the antimicrobial agents they respond to will also be different. A bacterial infection cannot be effectively treated with an antiviral medication and vice-versa.

To correctly determine whether an infection is viral, bacterial, or otherwise, healthcare workers need to take into account multiple variables including site of infection, patient characteristics, demographics, and geographical factors that might implicate exposure issues, and symptoms. The only unequivocal method of distinguishing the source of the infection would be through blood, urine, and other biological tests enabling seriological analysis. As Leekha, Terrell & Edson (2011) also point out, non-microbial causes should also be ruled out before prescribing antimicrobials unnecessarily due to the potential for unwanted side effects.

A less effective method of distinguishing between viral and bacterial infections would be to issue a general agent and monitor for patient response, but this method is not recommended except in extreme circumstances such as if the symptoms are severe and immediate treatment is warranted. Selecting The Proper Antimicrobial Agent Proper identification of the infection is the key to selecting the appropriate antimicrobial agent. Ideally, the agent with the narrowest spectrum of likely pathogens should be selected (Becker, 2013).

For example, antibacterial agents can be further broken down into sub-categories like broad-spectrum, narrow spectrum, or limited spectrum. Broad.