Facts you need to know about Antibiotics (part 1): General Principles

Antibiotic. One of the most important group of medicine that ever discovered, remarked the decreasing of infectious disease drastically in 20th century. With more if its power, comes more fear that antibiotic era will end some day. To prevent that from happening, we should know several facts about antibiotic. This serial article will describe anything about antibiotics and their principles of usage.

Fact # 1
Anti-infective Therapy Principles
These are principles in anti-infective therapy, specifically antibiotics; to maximize balance between safety and effectivity against infectious diseases.

1. Too often, antibiotics are prescribed to fulfill the patient’s expectations, rather than to treat a true bacterial infection. Patients often believe that antibiotic can cure their disease and relieve their illnesses.
2. A single antibiotic cannot meet all infectious disease needs. Infections in the ear and in the stomach may have different cause, thus needs different antibiotics.
3. Physicians ignore the remarkable adaptability of bacteria, fungi, and viruses at their patient’s peril.
4. Anti-infective therapy is dynamic and requires a basic understanding of microbiology. Some bacteria are susceptible against an antibiotic, but some others are not.
5. The “shotgun” approach to infectious diseases must end, or we may truly experience the end of the antibiotic era. This kind of approach just got us near to the most feared problem about antibiotic: resistance problem.



Fact # 2
Classification of antibiotics by its spectrum of activity
Why do we need to know about this? This classification is important in choosing antibiotics in several diseases. In a severe infectious disease, as soon as infectious disease is diagnosed (ideally) specimen is collected and sequential cultures are examined. Broad-spectrum antibiotic is administered as soon as possible then. This is why broad coverage of bacteria is reasonable as initial empiric therapy. But this therapy should not be given for a long time; soon after culture result is available (usually in 3 days); change the therapy into narrower spectrum antibiotics.

Narrow
Penicillin, oxacillin, cephalexin, cephradine, aztreonam, vancomycin, aminoglycosides, erithromycin, roxithromycin, linezolid, daptomycin, metronidazole, clindamycin, quinupristin-dalfopristin (QD).

Moderately Broad
Ampicillin, ticarcillin, cefaclor, ciprofloxacin, clarithromycin, azithromycin, trimethoprim-sulfamethoxazole, cefoxitin, cefaclor, cefuroxime-axetil

Broad
Ampicillin-sulbactam, amoxicillin-clavulanate, ceftriaxone, cefotaxime, ceftazidime, cefixime, ceftizoxime, tetracycline, doxycycline, chloramphenicol, levofloxacin

Very Broad
Ticarcillin-clavulanate, piperacillin-tazobactam, cefepime, imipenem-cilastatin, meropenem, ertapenem, moxifloxacin, tigecycline


Fact # 3

Which antibiotic for which bacteria?

This factor is also very important in determining the correct antibiotic to cure an infectious disease. This picture depicts "which antibiotic for which bacteria" concept. Here, fluoroquinolones and several new antibiotics are not included, but consider that they may have broader spectrum. Some other antibiotics are narrow-spectrum: Vancomycin and linezolid are specifically effective only against several Gram-positive bacteria (methicillin-resistant Staphylococcus aureus, MRSA); metronidazole and clindamycin are only effective against anaerobic bacteria; and aztreonam which is only effective against some Gram-negative bacteria and Pseudomonas.

What's Next in part 2:
We will discuss about antibiotics mechanism of actions; each class of antibiotics, how they work, and what bacteria are susceptible to them. Also discussed about how each class of antibiotics behave, how much are their doses, how about their safety, etc.



References:
Southwick F. Anti-infective Therapy; in Southwick F (eds). Infectious Diseases: A Clinical Short Course, 2nd ed. McGraw-Hill: 2007; 1: 1-8.