The 10 Most Used Antibiotics

Antibiotics are essential medicines, as fighting infections is vital for the survival of human beings as an individual and as a species. Here we present the 10 most used in the field of human medicine.

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 12 July, 2023

Antibiotics are drugs that fight bacterial infections in humans and other animals and are the most widely used antibacterial agents in the medical field worldwide. They kill harmful bacteria or inhibit their growth, preventing the symptoms and clinical signs of infections, both localized and systemic, from appearing or worsening. We’ll look at the most used antibiotics today.

These drugs act as lines of defense against mild and serious bacterial diseases, but they also prevent fatal clinical conditions, such as septicemia and bacteremia.

What is an antibiotic?

According to the National Cancer Institute (NIH), an antibiotic is a drug used to treat infections caused by bacteria and other microorganisms – such as protozoa, in some cases. These drugs must stop the growth of pathogenic bacterial colonies that have settled in the body.

To do this, they adopt one of these strategies:

• Inhibition of cell wall synthesis: The cell wall protects bacteria from all environmental elements, both within the host organism and in the external environment. If the synthesis of this protective barrier is inhibited, the bacteria die.
• Inhibitors of protein synthesis: Proteins are the basis of all living tissues. Its synthesis is encoded in the DNA of the microorganism, but it’s the ribosomes of the cytoplasm that carry out its formation and assembly. If either of the two subunits of the bacterium’s ribosomes are inhibited, protein production stops.
• Inhibitors of nucleic acid synthesis: These antibiotics prevent vital processes essential for bacterial division, such as replication and transcription. Thanks to this, the bacteria cannot multiply in number and it’s easier for the immune system to fight the infection.
• Folic acid antagonists: Inhibit dihydrofolate reductase and the action of folic acid.

These are some of the methods most used by antibiotics to kill bacteria or prevent their growth, but not the only ones. In any case, the aim in all cases is to prevent or cure a bacterial infection.

The 10 most used antibiotics

As indicated by the Centers for Disease Control and Prevention (CDC), each year more than 266 million antibiotics are dispensed to treat infectious diseases in outpatients in the United States. This equates to more than 5 prescriptions per year for every 6 people in the country.

In any case, it’s estimated that 30% of antibiotic prescriptions outside the hospital environment are unnecessary, since the patient’s picture is mistaken for a viral infection or other diagnostic errors are committed. If you add to over-prescribing, too long treatment durations, or the use of the wrong antibiotics, 50% of the antibiotics could be being used wrongly.

With these lines, we want to emphasize, before immersing ourselves in the most famous antibiotics, that their prescription must be carried out with the utmost caution. Now, we’ll show you the 10 most used antibiotics in the world and their mechanism of action.

1. Amoxicillin

Amoxicillin is a semi-synthetic antibiotic derived from penicillin. This drug acts against a wide spectrum of bacteria, both Gram-positive and Gram-negative. Like the other drugs in the penicillin group, it’s part of those that inhibit bacterial synthesis of the cell wall.

This pharmacological option was discovered in 1958 and didn’t begin to be used in the clinical field until 1972. As indicated by the ClinCalc portal, it’s the 17th drug in terms of prescriptions in the United States. More than 31 million prescriptions are made each year in this country and it’s one of the antibiotics most used in young children.

Amoxicillin is mainly used to treat acute otitis media, respiratory infections, gastric infection with Helicobacter pylori, skin infections, and as prevention of endocarditis. As side effects, it usually causes nausea, colitis, and vomiting.

2. Doxycycline

Doxycycline is a broad-spectrum antibiotic from the group of tetracyclines. It’s used to treat bacterial infections, but it’s also a useful drug against certain parasitic infections. For example, it can be given to prevent malaria in conjunction with quinine. It comes as a pill to take orally or as an intravenous injection.

This drug was discovered in 1957 and began to be distributed to the general population 10 years later. It comes in the form of a generic drug and has reached number 80 in terms of prescriptions in the United States, with more than 10 million prescriptions annually.

Doxycycline is useful for fighting bacterial infections such as cholera, tularemia, respiratory tract infections, psittacosis, bartonellosis, and Lyme disease, among others. In addition to being an anti-malaria drug, it can also be useful in some parasitic diseases due to its anthelmintic action.

3. Cephalexin

Cephalexin is an antibiotic from the group of beta-lactams, which in turn belong to the first-generation cephalosporins. Like many other drugs in this block, it acts by inhibiting the synthesis of the bacterial cell wall. It isn’t only used to treat conditions in humans, as it’s one of the many drugs that have been approved in veterinary medicine.

Cephalexin is another of the most widely used antibiotics worldwide and ranks 85th on the US list, with more than 8 million prescriptions annually. It was first synthesized in 1967 and pioneering commercial versions were released in 1969 and 1970, under the names Keflex ® and Ceporex ®.

It’s used as a treatment for otitis media, strep throat, skeletal and joint infections, pneumonia, bacterial cellulitis, and urinary tract infections. It can also act as a preventive against heart infections.

4. Ciprofloxacin

Ciprofloxacin is an antibiotic that is classified within the group of fluoroquinolones. Unlike other drugs already mentioned, this paralyzes the replication of bacterial DNA, by blocking the enzyme DNA gyrase. After binding to the target complex, the bacterium is incapacitated, cannot divide, and ends up dying.

This drug was patented in 1980 and was released on the market in 1987. It’s still one of the most widely used antibiotics in the world, but it falls somewhat lower on the list that we have taken as a reference so far. It’s drug 109, with about 6 million prescriptions each year in the United States.

It’s used in endocarditis, bacterial gastroenteritis, malignant external otitis, respiratory and urinary tract infections, prostatitis, and anthrax. Although it treats conditions with catarrhal and flu-like symptoms, it should be noted that it doesn’t report any antiviral action.

5. Clindamycin

Clindamycin is a semisynthetic antibiotic derived from lincomycin, a natural compound from the group of lincosamides. These types of drugs bind to the 50S subunit of bacterial ribosomes, an action by which they prevent protein synthesis. If the bacterium is unable to make polypeptide chains to repair its tissues and grow, it ends up dying.

This drug was isolated and produced from lincomycin for the first time in 1966. It is found in generic forms worldwide and is the 130th drug on ClinCalc’s list, with more than 5 million prescriptions annually.

Clindamycin is used to fight infections caused by anaerobic bacteria, meaning that they don’t require oxygen to grow and survive. Within this group are pathologies such as dental infections, peritonitis, respiratory tract, and skin infections. Sometimes it can also be used as a substitute for penicillin in patients who are hypersensitive to it.

 6. Metronidazole

Metronidazole is one of the most widely used antibiotics in the world, it belongs to the group of nitroimidazoles and inhibits the synthesis of nucleic acids in various microorganisms. Apart from its bactericidal action, this drug shines in the treatment of parasitic infections.

The drug began to be marketed in France in 1960. It’s the 119th drug on the list of the most used in the United States, with more than 5 million prescriptions a year. It isn’t only used in humans, it’s also useful in veterinary medicine to treat gastrointestinal tract infections in pets.

Beyond its uses as an antibiotic, metronidazole is especially effective in treating infections by the protozoan Entamoeba histolytica, one of the major causes of gastrointestinal symptoms in the world, especially in low-income regions. It also effectively treats giardiasis and vaginal trichomoniasis.

7. Azithromycin

Azithromycin is a broad-spectrum antibiotic within the group of macrolides. It is useful for treating infections caused by Gram-positive and Gram-negative bacteria. Like clindamycin, it binds to the 50S subunit of the bacterial ribosome, preventing protein synthesis from occurring in the bacterial cytoplasm.

This drug was discovered in 1980 and marketed in 1988. It is found in generic drug form throughout the world and is far ahead of the other named antibiotics on the cited list. It ranks 46th, with more than 17 million prescriptions in the United States each year.

According to studies, it’s especially useful for the treatment of infectious pictures caused by C. pneumoniae, H. influenzae, M. pneumoniae and S. pneumoniae. It’s also prescribed for the approach of male genital chancre, acute bacterial sinusitis, acute otitis media, and bacterial tonsillitis, among other infectious pathologies.

8. Trimethoprim and sulfamethoxazole

This case is a bit special, since we find an antibiotic composed of two active principles: trimethoprim and sulfamethoxazole. Its method of action can be explained very simply:

1. Trimethoprim prevents the reduction of dihydrofolate to tetrahydrofolate.
2. On the other hand, sulfamethoxazole inhibits the conversion of p-aminobenzoic acid to dihydropteroate.

Both synergistic effects act as bactericides and cause the death of both Gram-positive and Gram-negative bacteria. In addition, this antibiotic tandem is also useful to treat infections caused by the protozoa of the species Cystoisospora and Cyclospora, and to kill the fungus Pneumocystis jirovecii.

This compound is ineffective against anaerobic bacteria, Pseudomonas aeruginosa, and species of the genus Mycoplasma.

9. Amoxicillin / clavulanic acid

We go back to the first item on this list, because in this position we have the pharmacological combination of amoxicillin + clavulanic acid (potassium clavulanate). We recall that amoxicillin is one of the most widely used antibiotics, belonging to the group of beta-lactams, but together with clavulanic acid it’s more effective and remains active for longer in the body.

This drug was approved in 1984, is in the form of a generic drug, and is the 95th drug on the ClinCalc list, with more than 7 million prescriptions annually in the United States. In addition to its use in humans, it’s also prescribed in dogs, cats, cattle, and pigs to treat a wide spectrum of bacterial infections.

10. Levofloxacin

Levofloxacin is an antibiotic from the group of quinolones. Like the rest of the drugs included in this block, it’s responsible for inhibiting the action of the enzyme DNA gyrase and the synthesis of nucleic acids. Beyond the common uses in other areas, it stands out in the treatment of tuberculosis, meningitis and pelvic inflammatory disease.

Levofloxacin was patented in 1985, but it didn’t begin to be marketed until 11 years later. It ranks 160th when it comes to prescriptions in the United States, with more than 3 million prescriptions annually in the country. Although it is the least prescribed on this list, it’s still considered one of the most used antibiotics in the world.

An essential group of drugs, but with certain considerations

In this list we have the 10 most widely used antibiotics in general, but it should be noted that today there are more than 100 and new ones continue to be patented year after year. The fight against bacteria is constant, because just as we create drugs against these microorganisms, they evolve to become resistant over time.

According to the CDC, more than 2.8 million infections due to antibiotic-resistant microorganisms occur in the United States each year, of which 35,000 end in death. The improper administration of these drugs and the lack of awareness on the part of the general population are the main triggers of this worrisome global panorama.

If you’re prescribed an antibiotic, take it for the exact time prescribed, even if you feel fine before the end of the treatment. On the other hand, remember not to consume any of these drugs if they have not been prescribed by a doctor.