What are Antibiotics?

Antibiotics are powerful medications that treat certain infections and can save lives when used properly. They either stop bacteria from reproducing or destroy them.

Before bacteria can multiply and cause symptoms, the immune system can typically kill them. White blood cells (WBCs) attack harmful bacteria — even if symptoms occur, the immune system can usually cope and fend off the infection.

However, sometimes the number of harmful bacteria is excessive, and the immune system cannot clear them all. Antibiotics are useful in this scenario.

The first antibiotic was penicillin. Penicillin-based antibiotics, such as ampicillin, amoxicillin, and penicillin G, are still available to treat a variety of infections and have been in use for many years.

Several types of modern antibiotics are available, and they are usually only available with a prescription in the United States. Topical antibiotics are available in over-the-counter (OTC) creams and ointments.

How do Antibiotics work?

There are different types of antibiotics, which work in their unique way. However, the two main they work include:

• A bactericidal antibiotic, such as penicillin, kills the bacteria. These drugs usually interfere with either the formation of the bacterial cell wall or its cell contents.
• A bacteriostatic stops bacteria from multiplying.

It may take a few hours or days after taking the first dose before people feel better or their symptoms improve.

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, check the patient information leaflet that came with your medicine to find out what to do. If you’re not sure, speak to a pharmacist or a GP.

In most cases, you can take the dose you missed 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.

Types of antibiotics

There are various classes or groups of antibiotics, which depend on their chemical structure. Some classes of antibiotics include the following:

Class	Examples
Penicillins	amoxicillin (Amoxil)
Macrolides	azithromycin (Zithromax) and erythromycin (Ery-Tab)
Cephalosporins	cephalexin (Keflex) and cefdinir (Omnicef)
Fluoroquinolones	ciprofloxacin (Cipro) and levofloxacin (Levaquin)
Beta-lactams with increased activity	amoxicillin/clavulanate (Augmentin)
Urinary anti-infectives	nitrofurantoin (Macrobid)
Lincosamides	clindamycin (Cleocin)

This list is not inclusive — other classes and brand names exist. In addition, penicillins, cephalosporins, and other antibiotics may be regarded as subclasses of beta-lactam drugs.

Why is it important to take antibiotics when needed?

Experts advise using antibiotics only when they are needed. This is to ensure that the bacteria is killed and is unable to multiply and spread to other parts of the body.

Also, antibiotic use can sometimes be associated with side effects and antibiotic resistance.

Resistance

Antibiotic resistance occurs when germs no longer respond to the antibiotic designed to kill them. Inappropriate prescription of antibiotics is driving up the incidence of antibiotic resistance.

Sometimes prescriptions of the wrong medication — or the wrong dosage — can lead to antibiotic misuse. Misuse can also occur when people do not take antibiotics as their doctor prescribes. Some measures people can take include finishing the treatment course and not sharing antibiotic medications with others— even if they have the same symptoms.

The Centers for Disease Control and Prevention (CDC)Trusted Source state that in the United States, around 47 million antibiotic courses are inappropriately prescribed to people, meaning their illness did not require antibiotics.

Some bacteria — such as Enterobacterales — can become resistant to carbapenems, a major class of last-line antibiotics. Enterobacterales are an order of bacteria that can cause pneumonia, meningitis, and other diseases. Escherichia coli (E.coli) is an example of an Enterobacterale.

What do antibiotics treat?

A doctor prescribes antibiotics for the treatment of a bacterial infection. It is not effective against viruses.

Knowing whether an infection is bacterial or viral helps to treat it effectively.

Viruses cause most upper respiratory tract infections, such as the common cold and flu. Antibiotics do not work against these viruses.

If people overuse antibiotics or use them incorrectly, the bacteria might become resistant. This means that the antibiotic becomes less effective against that type of bacterium, as the bacterium has been able to improve its defenses.

A doctor can prescribe a broad-spectrum antibiotic to treat a wide range of infections. A narrow-spectrum antibiotic is only effective against a few types of bacteria.

Some antibiotics attack aerobic bacteria, while others work against anaerobic bacteria. Aerobic bacteria need oxygen, and anaerobic bacteria do not.

In some cases, a healthcare professional may provide antibiotics to prevent — rather than treat — infection, as might be the case before surgery. This is the “prophylactic” use of antibiotics. People commonly use these antibiotics before bowel and orthopedic surgery.

Side effects

Antibiotics commonly cause the following side effects:

• diarrhea
• nausea
• vomiting
• rash
• upset stomach
• sensitivity to sunlight, when taking tetracyclines
• with certain antibiotics or prolonged use, fungal infections of the mouth, digestive tract, and vagina

Some unusual side effects of antibiotics include:

• low platelet count, when taking cephalosporins, and penicillins, among others
• severe aches and pains, when taking fluoroquinolones
• hearing loss, when taking macrolides or aminoglycosides
• low granulocyte — a type of WBC — count, when taking penicillin
• formation of kidney stones, when taking sulfonamides

Allergy

Some people may develop an allergic reaction to antibiotics, especially penicillin. Side effects might include:

• a raised rash, or hives
• swelling of the tongue and face
• coughing
• wheezing
• difficulty breathing

Allergic reactions to antibiotics might be immediate or delayedTrusted Source. This means that a person may experience adverse effects of the drug within an hour or within weeks.

Anyone who has an allergic reaction to an antibiotic must tell their doctor or pharmacist. While rare, people may experience a serious and sometimes fatal reaction to an antibiotic. They are called anaphylactic reactions.

Anaphylaxis is a severe allergic reaction that can be life threatening. The symptoms develop suddenly and include:

• hives
• swelling of the face or mouth
• wheezing
• fast, shallow breathing
• a fast heart rate
• clammy skin
• anxiety or confusion
• dizziness
• vomiting
• blue or white lips
• fainting or loss of consciousness

If someone has these symptoms:

1. Check whether they are carrying an epinephrine pen. If they are, follow the instructions on the side of the pen to use it.
2. Dial 911 or the number of the nearest emergency department.
3. Lay the person down from a standing position. If they have vomited, turn them onto their side.
4. Stay with them until the emergency services arrive.

Some people may need more than one epinephrine injection. If the symptoms do not improve in 5–15 minutes, or they come back, use a second pen if the person has one.

Interactions

Individuals taking an antibiotic should not take other medicines or herbal remedies without speaking with a doctor first. Certain OTC medicines might also interact with antibiotics.

Some doctors suggest that antibiotics can reduce the effectiveness of oral contraceptives. However, research does not generally support this.

Nonetheless, people who experience diarrhea and vomiting or are not taking their oral contraceptive during illness due to an upset stomach might find that its effectiveness reduces.

In these circumstances, doctors may recommend people take additional contraceptive precautions.

Doctors may also advise avoiding alcohol for certain drugs, such as doxycycline. However, drinking alcohol in moderation is unlikely to cause problems with the most commonly used antibiotics.

How to use

People usually take antibiotics by mouth. However, doctors can administer them by injection or apply them directly to the part of the body with infection.

Most antibiotics can start working within a few hours. Doctors advise people to complete the whole course of medication to prevent the return of the infection.

Stopping the medication before the course has finished increases the risk that the bacteria will become resistant to future treatments. The ones that survive will have had some exposure to the antibiotic and may consequently develop resistance to it.

An individual needs to complete the course of antibiotic treatment even after they notice an improvement in symptoms.

Doctors and the leaflet provided with the drug provide specific instructions on how to take the medication correctly.

People can follow some tips for using antibioticsTrusted Source effectively, such as:

• Avoiding alcohol when using metronidazole.
• Avoiding dairy products when taking tetracyclines, as these might disrupt the absorption of the medication.
• Taking the medication at the same time, or at set times in the day — this depends on how many times a day a person needs to take the drug.

What causes antibiotic resistance?

Most of us will have taken antibiotics at some point in our lives. But what if nothing happens the next time you pop one of those little bug-busting pills? Your life could be in serious danger.

Bacteria are an integral part of our ecosystem and we share our bodies with many of these tiny creatures. However, they can be the root of serious health problems.

There are roughly as many human cells as bacterial cells in our bodies, and our microscopic passengers pay their way by helping our immune system and contributing to our metabolism.

But bacteria come in all manner of guises. Some can turn from friend to foe, while others are just plain nasty and will make us sick at any chance they get.

Since their discovery in the 1920s and their introduction into mainstream medicine after World War Two, we’ve been relying on antibiotics to keep pathogenic bacteria at bay.

Antibacterial resistance is on the rise, however. According to the Centers for Disease Control and Prevention (CDC), each yearTrusted Source in the United States, at least 2,049,442 illnesses are caused by resistance to medicines prescribed to treat bacterial or fungal infections. What is more, 23,000 people die each year when these drugs fail to work.

So, why have our once reliable antibacterials stopped working, and how do the pesky bugs manage to outfox us? It’s all about mutations.

Mutations, a ‘natural phenomenon’

Bacteria are prone to DNA mutations. This is part of their natural evolution and allows them to constantly adapt their genetic makeup. When one bug naturally becomes resistant to a drug, it survives when all others are killed.

Now it’s a race against the clock.

How quickly can this one bacterium adapt to the new mutation, and how quickly can it replicate in the face of species eradication? If the bug comes on out top, it’s bad news for the infected individual and bad news for society at large: the drug-resistant bacterium will likely spread.

Not only has it evaded the grim reaper, but it can also now spread the love by passing the resistance to its numerous offspring, who will soon be the dominant species on the block.

Bacteria are also able to pass genes to other bacteria. This is known as horizontal gene transfer, or “bacterial sex.” While this process is actually quite rare, bacteria are highly mobile creatures, which gives them plenty of opportunity to come into contact with other microbes and pass on their mutated genes.

But how do genetic mutations equip bacteria with the skills to outsmart anti-biotics?

Combating antibiotics

A studyTrusted Source recently published in Nature Communications sheds new light on how Echerichia coli and other members of the Enterobacteria family fight off commonly used anti-biotics.

A gene called mar is commonly shared by family members. Some of the proteins encoded in this gene can switch on other genes, explain researchers from the University of Birmingham’s Institute of Microbiology and Infection in the United Kingdom.

“We found two completely unexpected mechanisms,” says senior study author Prof. David Grainger, “that bacteria use to protect themselves from anti-biotics. One protected their DNA from the harmful effects of fluoroquinolone anti-biotics, and the other prevented doxycyline getting inside bacteria.”

But finding out how Enterobacteria combat anti-biotics is only the first step in this decade-long research project.

First study author Prateek Sharma, Ph.D., says that “the resistance mechanisms that we identified are found in many different species of bacteria therefore, our research could lead to the discovery of molecules that could be developed into new drugs that can treat bacterial infections.”

The World Health Organization (WHO) call antibiotic resistanceTrusted Source “one of the biggest threats to global health, food security, and development today.” The need for new drugs is great.

Antibiotic Use Questions and Answers

What is an antibiotic?

Antibiotics are medicines that fight infections caused by bacteria in humans and animals by either killing the bacteria or making it difficult for the bacteria to grow and multiply.

Bacteria are germs. They live in the environment and all over the inside and outside of our bodies. Most bacteria are harmless and even helpful to people, but some can cause infections, like strep throat.

What DO antibiotics treat?

Antibiotics ONLY treat certain infections caused by bacteria, such as:

• Strep throat
• Whooping cough
• Urinary tract infection (UTI)

Antibiotics are also needed to treat life-threatening conditions caused by bacteria, such as sepsis, which is the body’s extreme response to infection.

What DON’T antibiotics treat?

Antibiotics DO NOT work on viruses, such as those that cause:

• Colds and runny noses, even if the mucus is thick, yellow, or green
• Most sore throats (except strep throat)
• Flu
• Most cases of chest colds (bronchitis)

Antibiotics also ARE NOT needed for some common bacterial infections, including:

• Many sinus infections
• Some ear infections

This is because these illnesses will usually get better on their own, without anti-biotics.

Taking antibiotics when they’re not needed won’t help you, and their side effects can still cause harm.

Viruses are germs different from bacteria. They cause infections, such as colds and flu. However, anti-biotics do not treat infections caused by viruses.

For more information on common illnesses and when anti-biotics are and aren’t needed, visit Common Illnesses.

What are the side effects of Antibiotics?

Anytime antibiotics are used, they can cause side effects. Common side effects range from minor to very severe health problems and can include:

• Rash
• Nausea
• Diarrhea
• Yeast infections

Why is it important to take Antibiotics only when they’re needed?

Antibiotics are important to treat infections and have saved countless lives. However, anytime anti-biotics are used, they can cause side effects and contribute to antibiotic resistance, one of the most urgent threats to the public’s health.

When anti-biotics are needed, the benefits usually outweigh the risks of side effects or antibiotic resistance. However, too many anti-biotics are prescribed unnecessarily and misused, which threatens the usefulness of these important drugs.

This is why it’s important that we all use anti-biotics ONLY when we need them to protect us from harms caused by unnecessary antibiotic use and to combat antibiotic resistance.

What is unnecessary antibiotic use?

Unnecessary antibiotic use happens when a person is prescribed anti-biotics when they’re not needed, such as for colds and flu.

Unnecessary use also happens when a person is prescribed anti-biotics for infections that are sometimes caused by bacteria that do not always need anti-biotics, like many sinus infections and some ear infections.

Antibiotics aren’t always the answer when you’re sick. It’s important to use anti-biotics only when they are needed to protect yourself from harms caused by unnecessary antibiotic use and combat antibiotic resistance.

What is misuse of antibiotics?

Misuse of anti-biotics happens when a person is prescribed

• the wrong antibiotic,
• the wrong dose of an antibiotic, or
• an antibiotic for the wrong length of time.

Talk with your doctor about the best treatment for your illness.