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Antibiotics are a group of anti-infectives that come from bacterial sources and are useful in treating infections. These are the most frequently prescribed medication in modern medicine. The term is used interchangably with antibacterials, which may work against bacteria but are synthetically derived. They work exclusively against bacteria and does not kill viruses, fungi, or other parasites. They treat infections by killing bacteria directly, by stopping them from reproducing, or by allowing the body's natural defenses to eliminate them from the system.



Ancient history tells how some civilizations of mankind were exterminated by plagues of bacterial origin. People during that time used plants and molds to treat these unseen organisms. The term “antibiosis” was introduced by Jean Paul Vuillemin, a French microbiologist, to describe how certain drugs kill these microbes. These drugs were renamed “antibiotics” by Selman Waksan, an American microbiologist in 1942.

Infection is the most common cause of death before 1929. It was the time when Alexander Fleming discovered the first antibiotic, penicillin, from molds of Penicillum notatum. The antibacterial activity of penicillin against the deadly bacteria of that time had spurred drug manufacturers to research, develop and market drugs that can kill microorganisms of various types. Rene Dubois, a French microbiologist, reportedly discovered gramicidin from B. brevis, and was one of the first naturally derived antibiotic in 1939.


There are many varied classifications done by pharmacologists to distinguish one antibiotic from the other. This may be according to what types of bacteria can be killed (antimocrobial spectrum), how it is given to the patient (route of administration) or type of activity (bactericidal or bacteriostatic). However, the most commonly used especially in microbiology textbooks are according to chemical structures. These allow better understanding of their action, effectiveness, and corresponding toxic effects.


As it name suggests, this group contains sulfur contained in a sulfonamide group. These were the oldest antimicrobials and they paved the way for the discovery of antibiotics. All of them, except sulfasalazine and sulfacetamide, are used for treating urinary tract infections . Mafenide is used topically for burns. Common side effects are gastrointestinal upset, photosensitivity, and decrease in white blood cells.


This type of antibiotic is characterized by the beta-lactam ring in their chemical structure.

  • Penicillins. These are the oldest class of antibiotics and are somewhat similar to cephalosporins. They kill bacteria on the spot although they are quite prone to microbial resistance. They treat a wide range of infections such as syphilis, Lyme disease, and those caused by Streptococci bacteria. Common side effects are gastrointestinal upset or development of serious allergic reactions. Examples are amoxicillin, ampicillin, cloxacillin, penicillin G and V, and ticarcillin.
  • Cephalosporins. This is the most diverse type of beta-lactam antibiotic as they are classified according to generation. The newer the generation, the broader the spectrum. These drugs are derived from acremonium which was previously known as cephalosporium. Common side effects are gastrointestinal upsets and allergic reactions.
    • 1st Generation. Caters to infections of the skin and other soft tissues. Examples are cephalexin and cefazolin.
    • 2nd Generation. These are given mostly for some respiratory infections like cefaclor and cefuroxime. However, cefoxitin may also be given for abdominal infections.
    • 3rd Generation. When given by mouth, this class of cephalosporins have a broader coverage especially for mild to moderate skin and soft tissue infections. When given by injection, it may treat serious infections such as meningitis or infections that were acquired in the hospital. Examples are cefixime, cefotaxime, and ceftriaxone.
    • 4th Generation. Cefepime is given for serious infections of people with weak immune systems or for those infections that have developed a certain amount of resistance to other antibiotics.
    • 5th Generation. Ceftobiprole is prescribed for complicated skin infections such as foot infections caused by Escherichia, Pseudomonas, or methcillin-resistant Staphylococcus for diabetics.
  • Carbapenems. This class of antibiotics have the most highly-resistant chemical structure against beta-lactamases and were originally developed from thienamycin which is a naturally extracted product of Streptomyces cattleya. These are antibiotics of last resort for Escherichia and Klebsiella infections. Side effects are seizures and confusion. Examples of such drugs are impenem-cilastatin and meropenem.
  • Monobactams. This contain a beta-lactam ring that is not fused with another ring. It specializes in killing gram negative bacteria and as a substitute for people allergic to other beta-lactams. Aztreonam is the only commercially available form.


This antibiotic is made up of amino-modified sugars. It is derived from genus Streptomyces and often have the suffix -micin in their generic names. It is used for infections of gram-negative bacteria like Escherichia coli or species of Klebsiella. Common side effects are hearing loss, dizziness, and kidney damage. Examples of such drugs are gentamicin, streptomycin, and amikacin.


These are very toxic forms antibiotics that must never be used for systemic infections. Their chemical make up is very similar to aminoglycosides. They are often applied locally on the affected area which makes them effective agents for eye, ear, skin and bladder infections. When given by injection, there is a risk that they might cause kidney or nerve damage. Bacitracin and polymyxin B are popular examples.


Tetracycline antibiotics have four hydrocarbon rings. They were originally derived from Streptomyces aureofaciens. They can treat syphilis, and chlamydial, mycoplasmal and rickettsial infections. Staining of teeth in children under 8 years or in the fetus when used in the last trimester is a common side effect. Other side effects are photosensitivity and gastrointestinal upset. Examples of such antibiotics are doxycycline, minocycline, and tetracycline.


These are synthetic broad-spectrum antibiotics. Its parent molecule is nalidixic acid, which was produced during chloroquine manufacture. This group treats blood infections, urinary tract infections, inflammation of the prostate, bacterial diarrhea, and gonorrhea. Common side effects are tremors, seizures, abnormal heart rhythms, rupture of the tendons, and inflammation of the colon. Examples of such drugs are ciprofloxacin, levofloxacin, ofloxacin and norfloxacin.


This group is made up of a large macrocyclic lactone ring where a DNA-related sugars may be attached. They treats infections caused by streptococci, syphilis, respiratory infections, infections caused by mycoplasma and Lyme disease. Treatment with this group may result in gastrointestinal disturbance, jaundice and abnormal heart rhythms. Examples are azithromycin, clarithromycin, and erythromycin.

Miscellaneous antibiotics

Antibiotics of varied chemical structures are also included in antibiotics and may treat a variety of infections. Some examples of these are chloramphenicol, drugs against mycobacteria, metronidazole, and nitrofurantoin.

General use

Antibiotics are used against all types of bacteria. They may be prescribed for a certain period of time (which range from 3 to 10 days). Deadly infections may require longer treatment of several months. Lower doses may be given to certain people for a long period of time to prevent being infected.

Standard protocol is initially prescribing an empirical antibiotic when certain symptoms appear. However, they will get a sample for susceptibility testing. This test is used for determining which is the best antibiotic that will kill the offending organism. After the empirical treatment is over and the patient has not yet recovered, the antibiotic that gave the best result will be prescribed for a certain period of time. But sometimes, antibiotics that work in the laboratory might not work when given to a person. Factors vary but health care professionals will consider the nature and gravity of the infection, the possible side effects of the antibiotic, possibility of developing allergies as well as its cost to the patient.


Antibiotics must be taken correctly in order to benefit from it. Every patient must check their antibiotics after it is dispensed in the pharmacy. Ask for the package insert, especially if the medication is being used for the first time. Read the labels if it is the correct drug dispensed and its expiration date. Ask the pharmacist in-charge for information about the medication.

Patients must understand the instructions in their prescriptions. It will indicate how many pills to take and how often it should be taken. Remembering how to take it is very important. Some antibiotics need to taken with something to prevent stomach upsets. Others need nothing at all, as it might affect their absorption and effectiveness.

Storage is an important factor in retaining the effectiveness of antibiotics. Tablets, capsules and other solid forms of the antibiotics must be protected from extreme humidity. All antibiotics must not be subjected to extremes in temperature. Freezing or heating them will inactivate the components or destroy the drug completely.


Bacteria may develop resistance to antibiotics over a period of time. They evolve and produce characteristics necessary for survival which they might pass on to other strains. Medical research continually battles drug resistance by developing new antimicrobials. Doctors and patients may help prevent this resistance by:

  • Taking antibiotics only when necessary. This means avoiding antibiotic use for infections caused by other microorganisms like viruses, fungi, or protozoa. Antibiotics are effective only against bacteria.
  • Allowing the body's immune system to fight bacteria. Not all infective conditions must be treated by antibiotics. The body has natural defenses that can fight them, although at a much gradual rate.
  • Using the correct antibiotic for the correct bacteria. Although doctors follow certain protocols for prescribing antibiotics,these must match the condition it is supposed to treat.
  • Taking antibiotics for the complete time prescribed. Antibiotics work best when taken at full course of treatment. Patients must not stop midway when their conditions improve.

Current issues

The problem with antibiotic abuse is prevalent in the Philippines as studies conducted by the Philippine Society for Microbiology and Infectious Diseases (PSMID) reveals. It is a collective problem involving the patients, the drugstores, and the prescribers. Filipinos in the rural areas assume that antibiotics are the cure all for all ailments. Many prefer to self-medicate as this will save them money from consultations. Others who are wary of antibiotic side effects would ask people who they think have similar symptoms that they have and buy the antibiotic the latter had used and cured their condition. Moreover, they would consult a doctor but would stop taking the antibiotic once their disturbing symptoms clear up. Small, neighborhood drugstores sell these antibiotics to their patrons in the absence of prescription. Large chain drugstores would forego the prescription provided that the buyer shows a used foil of the tablet or capsule or at least the carton of the suspension. Prescribers would prescribe the antibiotic even when it is not needed. Worse, some physicians prescribe expensive broad spectrum antibiotics when there are cheaper narrow spectrum antibiotics that will work as well. It is not surprising, therefore, that there are emerging resistant strains against beta-lactam and aminoglycoside antibiotics.

In another study conducted, almost half of the drugstores in rural areas in the Philippines sell antibiotics without prescription. More surprising is that, on the average, people from these areas buy mostly 7 to 10 tablets mostly of sulfonamides (i.e. cotrimoxazole) and natural penicillins. They use these medications to treat upper respiratory tract infections and for skin or soft tissue infections. Others stock up on antibiotics for their homes, sari-sari stores, or clinics. Researchers point out that the lack of pharmacies in the area and inadequate health professionals are partly to blame for the community's tendency to self-medicate with antibiotics.