What happens if you take antibiotics for a viral infection

Antibiotics are strong medicines that can kill bacteria. They have saved many lives and prevented bad outcomes. These drugs do not kill viruses. They only work on bacteria. Every day, doctors must decide if a child's infection is viral or bacterial. Here's how they do it:

Table of Contents Show

Bacterial Infections
Viral Infections
Cold Symptoms that are Normal
Side Effects of Antibiotics
Giving Antibiotics for Viral Infections: What Happens?
What You Can Do
When antibiotics are needed
How to take antibiotics?
Missing a dose of antibiotics
Accidentally taking an extra dose
Side effects of antibiotics
Considerations and interactions
Types of antibiotics
What happens if antibiotic are given for viral infection?
Why do doctors give antibiotics for viral infections?
What happens if you take antibiotics without infection?
Why can't you take antibiotics for a viral infection?

Bacterial Infections

Much less common than viral infections. Antibiotics can help. Bacteria cause:

Some ear infections
Some sinus infections (not sinus congestion)
20% of sore throats which are Strep throats
10% of pneumonia (a lung infection)

Viral Infections

Most infections in children are caused by a virus. Antibiotics do not help. Viruses cause:

100% of colds. (Note: unless they turn into an ear or sinus infection. This happens with 5 to 10% of colds.)
95% of new coughs. (Note: asthma can also start with a cough.)
95% of fevers
80% of sore throats
90% of pneumonia. (Note: most cases in children are caused by a virus.)
99% of diarrhea and vomiting
Note: There are a few anti-viral drugs that can treat viral infections. An example is Tamiflu used for severe influenza.

Cold Symptoms that are Normal

Parents sometimes are worried about common cold symptoms. The symptoms below are not signs of bacterial infections. Nor, are they a reason to start antibiotics.

Green or yellow nose discharge. This is a normal part of getting over a cold. It is not a clue to a sinus infection.
Green or yellow coughed up phlegm. This is a normal part of getting over viral bronchitis. It is not a sign of pneumonia.
High fevers. High fevers (more than 104° F or 40° C) can be caused by a virus or bacteria.

Side Effects of Antibiotics

All antibiotics have side effects. Some children taking these drugs can get side effects. Examples are diarrhea, nausea, vomiting, or a rash. Loose stools occur because the drug kills off the good bacteria in the gut. If your child gets a rash, it can be from the drug. Your doctor has to decide if the rash is an allergy or not. The biggest side effect of overuse is called antibiotic resistance. This is when the germs are no longer killed by the drug. That's why we only use antibiotics if your child really needs one.

Giving Antibiotics for Viral Infections: What Happens?

If your child has a virus, an antibiotic won't get rid of the fever. It will not help the other symptoms. The drug will not get your child back to school sooner. It will not get you back to work any faster. If your child has side effects from the drug, he will feel worse.

What You Can Do

Save antibiotics for bacterial infections when your child really needs them
Don't pressure your child's doctor for an antibiotic
Treat your child's cold and cough symptoms with home treatment that works
Keep in mind that fever is fighting the infection. It also boosts the immune system to prevent future infections.

Last Reviewed: 11/16/2022

Last Revised: 09/18/2022

Antibiotics are used to treat or prevent some types of bacterial infection. They work by killing bacteria or preventing them from spreading. But they do not work for everything.

Many mild bacterial infections get better on their own without using antibiotics.

Antibiotics do not work for viral infections such as colds and flu, and most coughs and sore throats.

Antibiotics are no longer routinely used to treat:

chest infections
ear infections in children
sore throats

When it comes to antibiotics, take your doctor's advice on whether you need them or not. Antibiotic resistance is a big problem – taking antibiotics when you do not need them can mean they will not work for you in the future.

When antibiotics are needed

Antibiotics may be used to treat bacterial infections that:

are unlikely to clear up without antibiotics
could infect others
could take too long to clear without treatment
carry a risk of more serious complications

People at a high risk of infection may also be given antibiotics as a precaution, known as antibiotic prophylaxis.

Read more about when antibiotics are used and why they are not routinely used to treat infections.

How to take antibiotics?

Take antibiotics as directed on the packet or the patient information leaflet that comes with the medicine, or as instructed by your GP or pharmacist.

Antibiotics can come as:

tablets, capsules or a liquid that you drink – these can be used to treat most types of mild to moderate infections in the body
creams, lotions, sprays and drops – these are often used to treat skin infections and eye or ear infections
injections – these can be given as an injection or through a drip directly into the blood or muscle, and are used for more serious infections

Missing a dose of antibiotics

If you forget to take a dose of your antibiotics, take that dose as soon as you remember and then continue to take your course of antibiotics as normal.

But if it's almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

Accidentally taking an extra dose

There's an increased risk of side effects if you take 2 doses closer together than recommended.

Accidentally taking 1 extra dose of your antibiotic is unlikely to cause you any serious harm.

But it will increase your chances of getting side effects, such as pain in your stomach, diarrhoea, and feeling or being sick.

If you accidentally take more than 1 extra dose of your antibiotic, are worried or you get severe side effects, speak to your GP or call NHS 111 as soon as possible.

Side effects of antibiotics

As with any medicine, antibiotics can cause side effects. Most antibiotics do not cause problems if they're used properly and serious side effects are rare.

The common side effects include:

being sick
feeling sick
bloating and indigestion
diarrhoea

Some people may have an allergic reaction to antibiotics, especially penicillin and a type called cephalosporins. In very rare cases, this can lead to a serious allergic reaction (anaphylaxis), which is a medical emergency.

Read more about the side effects of antibiotics.

Considerations and interactions

Some antibiotics are not suitable for people with certain medical problems, or women who are pregnant or breastfeeding. Only ever take antibiotics prescribed for you – never "borrow" them from a friend or family member.

Some antibiotics do not mix well with other medicines, such as the contraceptive pill and alcohol.

Read the information leaflet that comes with your medicine carefully and discuss any concerns with your pharmacist or GP.

Types of antibiotics

There are hundreds of different types of antibiotics, but most of them can be classified into 6 groups.

Penicillins (such as penicillin, amoxicillin, co-amoxiclav, flucloxacillin and phenoxymethylpenicillin) – widely used to treat a variety of infections, including skin infections, chest infections and urinary tract infections
Cephalosporins (such as cefalexin) – used to treat a wide range of infections, but some are also effective for treating more serious infections, such as septicaemia and meningitis
Aminoglycosides (such as gentamicin and tobramycin) – tend to only be used in hospital to treat very serious illnesses such as septicaemia, as they can cause serious side effects, including hearing loss and kidney damage; they're usually given by injection, but may be given as drops for some ear or eye infections
Tetracyclines (such as tetracycline, doxycycline and lymecycline) – can be used to treat a wide range of infections, but are commonly used to treat acne and a skin condition called rosacea
Macrolides (such as azithromycin, erythromycin and clarithromycin) – can be particularly useful for treating lung and chest infections, or as an alternative for people with a penicillin allergy, or to treat penicillin-resistant strains of bacteria
Fluoroquinolones (such as ciprofloxacin and levofloxacin) – are broad-spectrum antibiotics that were once used to treat a wide range of infections, especially respiratory and urinary tract infections. These antibiotics are no longer used routinely because of the risk of serious side effects

Other antibiotics include chloramphenicol (used for eye and ear infections), fusidic acid (used for skin and eye infections), and nitrofurantoin and trimethoprim (used for urinary tract infections).

Page last reviewed: 23 May 2019
Next review due: 23 May 2022

What happens if antibiotic are given for viral infection?

If you take an antibiotic when you have a viral infection, the antibiotic attacks bacteria in your body. These are bacteria that are helpful or are not causing disease. This incorrect treatment can then promote antibiotic-resistant properties in harmless bacteria that can be shared with other bacteria.

Why do doctors give antibiotics for viral infections?

In complicated or prolonged viral infections, bacteria may invade as well, and cause what is known as a “secondary bacterial infection”, such as bacterial pneumonia. In these cases, your doctor may prescribe an antibiotic, if one is needed, to kill the specific invading bacteria.

What happens if you take antibiotics without infection?

Antibiotic resistance is not a distant threat, but is in fact one of the most dangerous global crises facing the modern world today. Taking antibiotics when you don't need them puts you and your family at risk of developing infections which in turn cannot be easily treated with antibiotics.

Why can't you take antibiotics for a viral infection?

Viruses are surrounded by a protective protein coating; they don't have cell walls that can be attacked by antibiotics like bacteria does. It is because of this that antibiotics don't work on viruses.