What are Antibiotics and How do they Work?

Antibiotics also called antibacterials or antimicrobials are types of medications that impede the growth of bacteria. Bacteria are microscopic organisms, some of which may cause various types of illnesses. Before bacteria can multiply and cause symptoms, the body’s immune system can destroy them. The body’s white blood cells attack harmful bacteria and kill them. Even if symptoms reoccur, the body’s immune system can usually fight off the infection. However, on occasion, antibiotics are the savior to decrease the burden.

Alexander Fleming discovered the first antibiotic penicillin. Today, over 100 different antibiotics are available to cure minor, and life-threatening infections. Although antibiotics are useful to treat a range of infections, their effectiveness is confined to only bacterial infections. They are not effective against viral infections (for example, the common cold) and fungal infections (such as ringworm).

If afflicted by an infection, it is vital to know whether the infection is caused by bacteria or a virus. Most upper respiratory tract infections, such as the common cold, flu, sore throats, bronchitis, and many sinuses and ear infections are viral diseases – antibiotics do not work against these viruses. Symptom relief is the best treatment option for viral infections. Rest, fluids, and over-the-counter products may be the best treatment option against viral infections.

Types of Antibiotics

Antibiotics are usually grouped together based on how they work. A bactericidal antibiotic kills the bacteria. Penicillin is bactericidal. A bactericidal usually either interferes with the formation of the bacterium’s cell wall or its cell contents. A bacteriostatic stops bacteria from multiplying.

A broad-spectrum antibiotic is effective against a wide range of infections. A narrow-spectrum antibiotic on the other hand is effective only against a few types of bacteriome antibiotics that attack ack aerobic bacteria, while others work against anaerobic bacteria. Aerobic bacteria need oxygen, while anaerobic bacteria do not.

Antibiotics may be given beforehand, to prevent infection, as might be the case before surgery. This is called the ‘prophylactic’ use of antibiotics. They are commonly used before bowel and orthopedic surgery. Each type of antibiotic only works against certain types of bacteria or parasites. This is why different antibiotics are used to treat different types of infections.

The main types of antibiotics include:

1) Penicillins- for example, phenoxymethylpenicillin, flucloxacillin, and amoxicillin
2) Cephalosporins- for example, cefaclor, cefadroxil, and cefalexin
3) Tetracyclines- for example, tetracycline, doxycycline, and lymecycline
4) Aminoglycosides- for example, gentamicin and tobramycin
5) Macrolides- for example, erythromycin, azithromycin, and clarithromycin
6) Sulfonamides and trimethoprim- for example, co-trimoxazole
7) Metronidazole and tinidazole
8) Quinolones- for example, ciprofloxacin, levofloxacin, and norfloxacin

As well as the above main types of antibiotics, there are several other antibiotics that specialist doctors or hospital doctors may prescribe for more uncommon infections such as tuberculosis (TB). Each antibiotic is effective only against certain bacteria and parasites. You need antibiotics if you have certain serious infections caused by bacteria such as meningitis or pneumonia. In these situations, antibiotics are often life-saving. Antibiotics can also be prescribed to treat acne – a less serious condition. For acne, take antibiotics through the mouth or apply them directly to the skin

Antibiotic Resistance

One of the main concerns of modern medicine is a condition term as “antibiotic resistance”. If an antibiotic is overused, bacteria will emerge with a new form and structure (mutation) which becomes resistant to that antibiotic.

One of the reasons for the development of antibiotic-resistant bacteria includes the common practice of prescribing antibiotics for the common cold or flu. If your sickness is because of a virus, taking antibiotics may not help the cause and can on the other hand cause harm. Also using antibiotics frequently, even when you don’t need them can add to antibiotic resistance.

There is a growing concern globally regarding the overuse of antibiotics. This has led to a growing number of bacterial infections that are becoming resistant to antibacterial medications. The ECDC (European Centre for Disease Prevention and Control) has come out with a report which says antibiotic resistance continues to be a serious public health threat globally. In a statement issued on 19th November 2012, the ECDC informed that about 25,000 people die each year in the European Union from antibiotic-resistant bacterial infections.

We are at a critical juncture where antibiotic resistance is seen as a global threat to public health.
However, efforts are on to distinguish clearly between a bacterial and viral infection through various screening tests thus helping in a more accurate antibiotic prescription.

What are the side effects of antibiotics?

Common side effects of antibiotics include:
i) Feeling and being sick
ii) Fungal infections of the mouth, digestive tract, and vagina

Some of the rare side effects include:

iii) Formation of kidney stones (when taking sulphonamides)
iv) Abnormal blood clotting (when taking some cephalosporins)
v) Sensitivity to the sun (when taking tetracyclines)
vi) Blood disorders (when taking trimethoprim)
vii) Deafness (when taking erythromycin and aminoglycosides)

Allergic reactions to antibiotics some patients may develop allergic reactions to antibiotics, particularly penicillins. Side effects may be developing a rash, swelling of the tongue and face, and difficulty breathing.

Use antibiotics with extreme caution and consult your doctor if:
i) You have reduced liver or kidney function.
ii) You are breastfeeding
iii) You are pregnant

Penicillins, cephalosporins, and other antibiotics may reduce the impact of oral contraceptives. If the antibiotic has caused diarrhea/vomiting the absorption of contraceptives may also be disrupted. If you are taking any of these drugs you should consider taking additional contraceptive precautions.

A blood test can help find out the patient’s need for antibiotics. It would be difficult for you to take a course of antibiotics in the case of a prior history of antibiotic allergy. However, doctors choose a different type of antibiotic if you have had an allergic reaction to one antibiotic. Some people are allergic to penicillin. If you have a query about a possible allergic reaction, ask your doctor or pharmacist before taking the medicine.

Allergic reactions commonly have the following symptoms:

i) Shortness of breath
ii) Rash
iii) Hives
iv) Itching
v) Swelling of the lips, face, or tongue
vi) Fainting

How to use Antibiotics?

One should take the complete course of antibiotics prescribed. Even though one may feel better before completing the course in medicine, one must follow through and take the entire course. If an antibiotic is stopped in midcourse, the bacteria may be partially treated and not completely killed, causing the bacteria to be resistant to the antibiotic. This can cause a serious problem if those now-resistant bacteria grow enough to cause a re-infection.

How to take the medication?

Antibiotics are usually taken orally( by mouth); however, they can also be administered by injection or applied directly to the affected part of the body( topical ). Some antibiotics should not be taken along with certain foods and drinks. Others should not be taken with food in your stomach – these would normally be taken about an hour before meals, or two hours after. If you are taking metronidazole do not consume alcohol. Dairy products should not be consumed if you are taking tetracyclines, as they might affect the absorption of the medication.

Some medications are taken along with a glass of milk while others only with water. Taking your antibiotics incorrectly affects their absorption, reducing or eliminating their effectiveness. Even if you are pregnant or breastfeeding there are several antibiotics that are safe to take. Antibiotics (other than one called rifampicin) do not interfere with the effectiveness of the birth control pill. You should continue taking your pill as normal if you also need to take any antibiotics.

Some antibiotics may interact with other medicines that you might take. This may cause reactions, or reduce the effectiveness of one or other of the treatments. So, when you have been prescribed an antibiotic you should tell a doctor if you take other medicines. All this goes to prove that the mode and method of administering the drug should be meticulously followed for proper results.

Most side effects of antibiotics are not serious. Common side effects include soft stools (feces), diarrhea, or mild stomach upset such as feeling sick (nausea).

Notify your doctor if you have any of the following side effects:

i) Vomiting
ii) Severe watery diarrhea and abdominal cramps
iii) Allergic reaction (shortness of breath, hives, swelling of lips, face, or tongue, fainting)
iv) Rash
v) Vaginal itching or discharge
vi) White patches on the tongue

Other factors that influence Antibiotics choice. These include:

i) How severe the infection is?
ii) How well your kidneys and liver are working.
iii) Dosing schedule.
iv) Other medications you may be taking.
v) Common side-effects.
vi) A history of having an allergy to a certain type of antibiotic.
vii) If you are pregnant or breastfeeding.

Q) Can I buy Antibiotics OTC (Over-the-counter)?
No, to buy antibiotics one must need a prescription.


It is also vital that you store your medication appropriately. Many antibiotics must keep out of reach of children. Store them in the refrigerator and the remaining you can store them at room temperature.

Written by MedPlus