Infection is the general term describing invasion of the body by microorganisms, including bacteria, viruses, parasites and fungi/spores. Antibiotic is the general term for drugs used to treat infections (anti-biotic literally means anti-life). Antibiotics include drugs with antibacterial, antiviral, antifungal and antiparasitic properties.
Treatment modalities for infections may involve surgical or other interventions (for example treatment with hyperbaric oxygen), usually in conjunction with antibiotic medication. In some cases, infection is treated primarily (or solely) by medication(s).
Bacterial, viral and fungal infections are different conditions because the microorganisms causing the infections are different, and the ways in which the different types of infection affect the host are, therefore, different too. Accordingly, the strategies to treat these infections with medication(s) vary but all have one aspect in common: the drugs used to treat infections have to be considerably more toxic to the infectious microorganism(s) than to the host.
Bacterial infections are characterised by a large number of different types of bacteria which can (and do) cause infections in humans requiring treatment. Since the original accidental discovery of antibacterial agents (penicillin; A. Fleming), ca. 150 different antibacterial drugs have been introduced to treat a wide variety of bacterial infections. Worldwide, antibacterial drugs are the second most widely used medications, second only to analgesics (drugs for treating pain). Not all antibacterial drugs are relevant for the treatment of oral and maxillofacial bacterial infections, but some from each type of antibacterial agent are in use in this specialty.
Types of antibacterial drugs are classified according to the mechanisms by which they target bacteria; the four main targets are:
- bacterial DNA
- bacterial metabolic processes (synthesis of folic acid (vitamin B9))
- bacterial protein synthesis
- bacterial cell wall synthesis
Most antibacterial drugs are effective in treating infections by a range of bacteria of similar types. Most antibacterial agents aim to destroy their target pathogen, some mainly inhibit its growth. Unfortunately, in 2017 many infectious and harmful bacteria have developed resistance to the effects of a number of mainstream antibacterial drugs, with drug resistance becoming increasingly problematic.
Viral infections are more difficult to treat by medication: there are far fewer drugs with antiviral properties than there are antibacterial drugs (mainly drugs to treat HIV, some forms of hepatitis, influenza (flu) and herpes). It is much more difficult to develop antiviral drugs that are harmful to the pathogenic virus but not to the host: This is the case because a virus critically depends on the host’s metabolism for survival and propagation. Other than most antibacterial drugs, most antiviral drugs are highly specific and only affect one particular (type of) virus. While most antibacterial drugs kill their target pathogen(s), most antiviral drugs just inhibit the development of their target (type of) virus. Similar to antibacterial drugs, there are resistance issues also with antiviral drugs. Substances called monoclonal antibodies (substances that trigger the host immune system in some manner) may have some antiviral properties; these are niche applications and not yet fully established.
The best antiviral ‘drug’ in 2017 still is the body’s immune system, both with regard to preventing and fighting viral infections.
Fungal infections are very common generally (think of athlete’s foot). Relevant fungal infections in an oral and maxillofacial context are all kinds of thrush (candidiasis), affecting the soft tissue in the mouth and the skin. Some rare types of fungal infections can cause meningitis (cryptococcal meningitis). Most antifungal agents harm or destroy fungi by attacking their cell walls. This is a common mechanism also of many antibacterial drugs. However, fungi and bacteria feature rather different cell walls and thus tend to be vulnerable to different chemicals, with some overlap. Antifungal substances can be applied systemically or topically (locally); whenever possible the latter is the preferred mode in order to avoid systemic unwanted side effects (in contrast, systemic application is appropriate for antibacterial drugs).
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