What are antibiotics? Know about Types and Uses

Manoj Kumar - B.Pharmacy

Published : Aug 19, 2024

Last Updated : Nov 14, 2025

What Are Antibiotics?

Antibiotics are medicines that help your body fight bacterial infections and protect your health.

They work by either killing bacteria or stopping them from multiplying, so your immune system can clear the infection more easily.

The word antibiotic literally means “against life” – in this case, the “life” of harmful germs. Technically, any drug that kills microorganisms in the body could be called an antibiotic, but in practice, the term usually refers to medicines that target bacteria, not viruses.

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What Do Antibiotics Treat?

Antibiotics are designed to treat infections caused by harmful bacteria, such as:

• Strep throat

• Urinary tract infections (UTIs)

• Certain chest and skin infections

• Some stomach or intestinal infections, like E. coli

However, antibiotics do not work against:

• Common cold

• Flu

• Most sore throats

• Viral fevers

Some bacterial infections, like mild sinus infections or some ear infections, may improve on their own without antibiotics. Using antibiotics when they are not needed:

• Doesn’t speed up recovery

• Can cause side effects

• Increases the risk of antibiotic resistance

Always talk to your doctor before taking antibiotics. Never use them on your own or reuse old prescriptions.

How Do Antibiotics Work?

Antibiotics usually work in one of two main ways:

1. Killing bacteria (bactericidal):
   Medicines like Penicillins damage the bacterial cell wall or internal structures, causing the bacteria to break apart and die.

2. Stopping bacteria from growing (bacteriostatic):
   Some antibiotics don’t kill bacteria directly but stop them from multiplying. This gives your immune system time to fight and clear the infection.

You might not feel better immediately after starting antibiotics.
It can take a few hours to a couple of days before symptoms start improving.

Why Is It Important to Take Antibiotics When Needed?

During a bacterial infection, harmful bacteria multiply in your body and overwhelm your immune system.

If not treated when necessary, bacterial infections can:

• Spread to other parts of the body

• Cause serious complications

• Sometimes become life-threatening

Doctors examine your symptoms, medical history, and sometimes lab tests to confirm if the infection is bacterial. If needed, they prescribe the right antibiotic, dose, and duration.

However, because antibiotics can also cause side effects and antibiotic resistance, they should only be used:

• When clearly indicated

• At the prescribed dose

• For the full advised course

Types of Antibiotics

Antibiotics are grouped into different classes, each working in slightly different ways and used for specific infections.

1. Penicillins

Penicillins are commonly used to treat:

• Urinary tract infections(UTIs)

• Chest infections

• Skin infections

Examples include: Amoxicillin capsules, Co-amoxiclav, Flucloxacillin, and Phenoxymethylpenicillin.

2. Cephalosporins

Cephalosporins are often used for moderate to severe bacterial infections, such as:

• Meningitis

• Septicaemia (blood infections)

• Severe respiratory infections 

Examples: Cefaclor, Cefadroxil, Cefalexin.

3. Aminoglycosides

These antibiotics are typically used in serious infections, usually in hospitals, such as:

• Septicaemia

• Complicated abdominal or urinary infections

Examples: Gentamicin, Tobramycin.

They are often given by injection and require close monitoring due to side effect risks.

4. Tetracyclines

Tetracyclines are widely used for:

• Acne

• Rosacea

• Certain respiratory or genital infections

Examples: Doxycycline, Lymecycline, Tetracycline.

They can make your skin more sensitive to sunlight, so sun protection is important.

5. Macrolides

Macrolides are often prescribed as an alternative to penicillins, especially in people allergic to penicillin. They help treat:

• Chest infections

• Lung infections

• Throat infections

Examples: Azithromycin, Clarithromycin, Erythromycin are among the antibiotics good for throat infections, lung infections and chest infections..

6. Fluoroquinolones

Fluoroquinolones are powerful antibiotics used for certain serious infections, such as:

• Complicated UTIs

• Some intestinal infections

• Specific respiratory infections

Examples: Ciprofloxacin tablets, Levofloxacin, Norfloxacin.

These medicines are usually reserved for selected cases because of potential side effects.

What Is Antibiotic Resistance?

As you learned, antibiotics kill bacteria or stop them from growing.

However, over time, some bacteria can change and adapt so that antibiotics no longer work against them. This is called antibiotic resistance.

In antibiotic resistance:

• Bacteria survive even after antibiotic treatment

• Infections become harder to treat

• Stronger or multiple antibiotics may be needed

This is a major global health concern.
Key reasons for antibiotic resistance include:

• Using antibiotics when not needed (for viral infections)

• Not completing the full antibiotic course

• Taking leftover medicines or someone else’s prescription

Using antibiotics wisely helps keep them effective for future patients.

Side Effects of Antibiotics

Each antibiotic class has its own side effect profile, but some common side effects of antibiotic drugs include:

Common Side Effects

• Nausea

• Vomiting

• Diarrhoea

• Stomach discomfort or stomach pain due to certain antibioitcs

• Skin rash

• Sensitivity to sunlight (especially with Tetracyclines)

Long-term use or repeated courses may also:

• Disturb the normal balance of good bacteria

• Lead to fungal infections of the mouth, gut, or vagina

Less Common or Serious Side Effects

• Fluoroquinolones: Can sometimes cause severe muscle or joint pain

• Cephalosporins and Penicillins: May reduce platelet count in rare cases

• Sulfonamides: May contribute to kidney stone formation

• Penicillins: Occasionally affect white blood cell types like granulocytes

• Macrolides and Aminoglycosides: High doses or prolonged use may affect hearing

In older adults, some antibiotics can trigger C. difficile infection, causing severe, bloody diarrhoea and bowel inflammation. Any severe or unusual symptoms should be reported to a doctor immediately.

How to Use Antibiotic Medications

Antibiotics are available in several forms:

• Tablets or capsules (most common)

• Liquids (for children or those who can’t swallow tablets)

• Injections (used in hospitals for severe infections)

• Topical creams or ointments (for skin infections)

General guidelines:

• Take your antibiotic exactly as prescribed (dose, timing, and duration)

• Some can be taken with food, others on an empty stomach — follow your doctor’s or pharmacist’s advice

• Do not skip doses or stop early, even if you feel better

Stopping treatment too soon can:

• Leave some bacteria alive

• Increase the risk of infection coming back

• Promote antibiotic resistance

Tips While Taking Antibiotics

• Avoid alcohol with certain antibiotics (especially Metronidazole)

• Avoid dairy close to doses of Tetracyclines, as they can affect absorption

• Take doses at regular intervals to maintain steady levels in the body

• Take a diet that supports antibiotics working and supports fast recovery.

• Always talk to your doctor before taking any antibiotic during pregnancy or breastfeeding; consider its safe use.

Antibiotic Interactions

Antibiotics can interact with:

• Other prescription medicines

• Over-the-counter (OTC) drugs

• Herbal supplements

That’s why you should always inform your doctor and pharmacist about all medicines you are using.

Some important points:

• A few antibiotics may temporarily affect the way hormonal contraceptives work, so extra protection might sometimes be advised

• Alcohol can increase side effects with certain antibiotics

• Some combinations can strain the liver or kidneys

Using antibiotics exactly as prescribed and avoiding self-medication greatly reduces interaction risks.

Final Lines

Antibiotics are essential medicines for treating bacterial infections. They work by killing bacteria or stopping them from multiplying, allowing your immune system to clear the infection.

However, they are not needed for every illness and should never be used casually. Misuse or overuse can cause:

• Unwanted side effects

• Imbalance in normal flora

• Antibiotic resistance is making future infections much harder to treat

Always use antibiotics only when prescribed by a healthcare professional, follow the full course, and be aware of possible interactions with other medicines or alcohol. This way, antibiotics remain effective, safe, and protective for you and others in the long term.