Types of Antibiotics
Bacteria are tiny single-celled microbes with a simple internal structure. They exist absolutely everywhere excepting sterilized places. They are a natural part of life. Most bacteria are of great help to humans, but some, when gaining access to vulnerable parts of the body, cause inflectional disease.
To inhibit the growth of bacteria or even to kill them special drugs called antibiotics (or antibacterials) are used. These drugs are intended to target bacteria, fungi and parasites, but are absolutely ineffective against viruses.
An Overview of Antibiotics
How can one sort out antibiotics, because there are so many of them? These drugs can be classified by bacterial spectrum (broad vs. narrow), type of activity (bactericidal vs. bacteriostatic), but the most popular classification criteria are based on chemical structure. Each structural class tend to have antibacterials with consimilar effectiveness, toxicity, and allergic potential.
Commonly act as bactericidal agents, causing bacterial cell death:
- β-Lactams (penicillins such as amoxicillin and flucloxacillin, cephalosporins such as cephalexin).
- Aminoglycosides (streptomycin, neomycin, kanamycin, paromomycin).
- Glycopeptides (vancomycin, teicoplanin).
- Quinolones (ciprofloxacin, levofloxacin, trovafloxacin).
- Ansamycins (geldanamycin, rifamycin, naphthomycin).
- Streptogramins (pristinamycin IIA, pristinamycin IA).
- Lipopeptides (daptomycin, surfactin).
Commonly act as bacteriostatic agents, restricting growth and reproduction:
- Oxazolidinones (linezolid, posizolid, tedizolid, cycloserine).
- Sulfonamides (prontosil, sulfanilamide, sulfadiazine, sulfisoxazole).
- Tetracyclines (tetracycline, doxycycline, lymecycline, oxytetracycline).
- Macrolides (erythromycin, clarithromycin, azithromycin)
All bacteria split into two main classes - Gram-positive and Gram-negative. Those names derive from the special test, so called Gram test. It means that a special violet dye is added to bacteria. Gram-positive bacteria retain the color of the dye. Gram-negative bacteria do not, and get instead red or pink color. Some bacteria can also be gram-variable, they stain unevenly either negative or positive.
Gram-negative bacteria have a largely impenetrable cell wall that is the reason they are more resistant to antibiotic medication than Gram-positive bacteria.
β-lactams include a wide range of antibacterials. Among them are penicillins, such as amoxicillin, and cephalosporins. They inhibit bacteria cell wall biosynthesis, and are mostly used against Gram-positive bacteria. However, bacteria can develop resistance to β-lactams.
Aminoglycosides suppress protein synthesis in bacteria and lead to cell death. They are very good against aerobic Gram-negative bacteria and some anaerobic, though there can resistance arise, but on the whole ineffective against Gram-positive and anaerobic Gram-negative bacteria. Aminoglycosides must be injected, because are not absorbed during digestion.
Antibiotics of this class inhibit bacteria wall biosynthesis rather than killing it directly and are usually used as ‘drugs of last resort’, when other antibacterial treatment has failed. Due to their toxicity, use of those antibiotics is restrained to patients who are critically ill, who are hypersensitive to the β-lactams, or infected with β-lactam-resistant species. They are effective mostly against Gram-positive cocci.
Quinolones are bactericidal compounds that interfere with bacteria DNA replication and transcription. They are broad-spectrum antibiotics. Quinolones administered orally or intravenously for treating a number of infectious diseases where resistance to older classes of antibiotics is suspected. Resistance to quinolones can progress especially rapid. One of the top contributors is their prescription for unrecommended conditions.
This class of antibiotics inhibits the synthesis of RNA in bacteria, leading to cell death. They are effective against Gram-positive bacteria and some Gram-negative bacteria. Uncommonly, they can also demonstrate antiviral activity.
This is quite a unique class of antibacterials that are capable of direct killing bacteria cells, by inhibiting the synthesis of proteins. Each antibacterial of the class has at least 2 molecules that are structurally unrelated: streptogramins A and streptogramins B. On their own, they only suppress bacteria growth, but combined they act synergistically and kill bacteria. They are often used to treat resistant infections. But resistance to the streptogramins themselves can still occur.
They are the most recent class of antibiotics. Lipopeptides are bactericidal against Gram-positive bacteria. Antibacterials of this group disrupt cell membrane functions that leads to cell death. Incidences of resistance to lipopeptides seem to be occasional. Given via injection.
Chloramphenicol, a broad spectrum antibiotic, inhibits synthesis of proteins, preventing bacteria from growth. Though there exists a possibility of serious toxic effects. Due to that reason it is only used if infections are considered to be life-threatening. Despite this, it is occasionally used in the treatment of eye infections.
Potent antibiotics commonly used as “drugs of last resort”. This class of antibiotics act against a large range of Gram-positive bacteria. Oxazolidinones inhibit the synthesis of proteins in bacteria, preventing their growth. These antibacterials can act both bacteriostatic and bactericidal depending on bacteria being treated. They are relatively safe antibiotics, serious adverse effects appear if administered for a long period of time.
Sulfonamides are broad-spectrum antibiotics. They act on both Gram-positive and Gram-negative bacteria. The antibacterials of this class do not kill bacteria, but prevent their growth and multiplication. Sulfonamides are rarely used recently, partially due to the development of bacterial resistance, but also due to concern about unwanted effects (e.g., they cause allergic reaction in some patients).
These antibiotics act against a wide variety of pathogens, including both Gram-positive and Gram-negative bacteria. Tetracyclines inhibit the synthesis of proteins in bacteria, preventing bacteria growth. Due to increasing incidences of bacterial resistance, their use is decreasing. However, they are still used in treatment of some infectious diseases (e.g., acne, urinary tract, chlamydia infections).
They are mostly effective against Gram-positive bacteria. Macrolides inhibit synthesis of protein in bacteria, occasionally leading to cell death. Their effectiveness is insignificantly broader than that of penicillins, besides macrolides are effective against several species of bacteria that penicillins are not. Though some bacteria developed resistance to these antibiotics, they are still among the most commonly prescribed antibiotics.
Pros and Cons of Antibiotics
Antibacterials have been widely used in medicine for more than fifty years, with immense benefits to human health - countless lives were saved with their help. Treating a wide variety of infections was and still is possible because of their high efficiency.
Most antibiotics are quite easy to administer either orally or intravenously via injection.
Short-term use has few adverse effects, which makes them the perfect option when you feel extremely sick. Besides most older antibiotics—especially those with generic alternatives—are very affordable on any budget, even if you lack health insurance.
To cons belongs a possibility of an allergic reaction. Some people are extremely allergic to some types of antibiotics (e.g., those containing sulfa).
Another serious health threat is the development of resistance to antibiotics that commonly results in loss of their effectiveness against certain bacterial species. It appears as a result of misuse and overuse of antibacterials, so these drugs must be used appropriately and responsible to slow the development of resistance.
Though many antibiotics have few side effects, long-term administration can still trigger serious adverse effects, particularly when used for more than two weeks.
When deciding whether to administer antibacterials for an illness, consider both their advantages and disadvantages. Always consult your doctor to determine what he or she feels is the best for you.