How Antibiotics Work for Urinary Tract Infections

Antibiotics are used to treat urinary tract infections because the causative agents are typically bacteria. We’ll tell you about the various therapeutic options in this article.
How Antibiotics Work for Urinary Tract Infections
Leonardo Biolatto

Written and verified by the doctor Leonardo Biolatto.

Last update: 11 June, 2022

It’s common for doctors to prescribe antibiotics for urinary tract infections, as antibiotics work to cure them. After a medical consultation and diagnosis that certifies bacterial colonization, the professional prescribes antibiotics the patient must take for some days. Most of the time, that protocol is correct and works.

In fact, UTI’s are one of the most common ailments in general outpatient practice around the world. That said, antibiotics have historically been the most effective way to control this condition and prevent complications.

Urinary tract infections

This condition is very common, especially among women. It’s estimated that 20% of the female population will suffer from a urinary tract infection that requires antibiotics at least once in her life.

Although it’s less common in men, a complication that results from not treating it is chronic prostatitis. Many men start with urinary symptoms that they don’t pay much attention to. Consequently, the colonizing bacteria migrate to the prostate and settles there, causing severe inflammation.

Overall, statistics show that lower urinary tract infections are the most common. A lower urinary tract infection occurs in the bladder and urethra, while an upper one in the kidneys and ureters.

In addition, aging seems to be a risk factor. Postmenopausal women and elderly men admitted to nursing homes have a high probability of becoming infected.

A man with a UTI.
Although urinary infections are less common in men, they can be the trigger for chronic prostatitis.

Keep reading: Urinary Sepsis: Causes and Treatments

How antibiotics work for urinary tract infections

As we mentioned above, bacteria are the microorganisms that are most related to urinary infections. They cause more cases than viruses and fungi.

Among bacteria, Escherichia coli causes up to 80% of cystitis and urethritis. This bacterium regularly inhabits the digestive system, particularly in the last intestinal section. Therefore, the same person transmits it to themselves.

In women, it’s associated with their shorter urethra and how close their urinary and digestive systems are. This favors the passage of Escherichia coli between the anus and the urethral opening, where it ascends to colonize.

To a lesser extent, other microorganisms can cause urinary infections, among which we can mention the following:

  • Proteus mirabilis
  • Klebsiella pneumoniae
  • Enterococcus faecalis

All these bacteria are sensitive to some type of antibiotic. Therefore, an antibiogram may be required before starting treatment. This test measures pathogen sensitivity to drugs to prescribe the correct one that’s capable of killing the microorganism.

The most common antibiotics for urinary tract infections

Once the medical professional identifies the causative agent and the antibiogram determined the most appropriate antibiotic for that urinary infection, the treatment protocol begins. No drug is ideal. Instead, the prescription must be adapted to each particular case.

In this sense, it’s important to take the patient’s age, possible diseases, allergies, and the type of disorder caused in the renal system into account.

So what are the most commonly used antibiotics?

Below, we’ll explain this in detail.

Penicillins and derivatives

As it’s of the oldest groups in the fight against bacteria, penicillins have evolved. Amoxicillin and ampicillin belong to this family and are effective against many different microorganisms. Similarly, there are cephalosporins, such as cephalexin, cephalothin, and ceftriaxone.

Most Escherichia coli and Proteus are sensitive to these antibiotics. They’re a great option for pregnant women since studies haven’t recorded effects on the fetus. Thus, they’re quite safe during pregnancy.


Different types of antibiotics.
Penicillin and its derivatives are the most widely used drugs in cases of bacterial urinary tract infections.


This family, whose representative is gentamicin, can fight gram-negative bacteria. This means that they don’t stop bacterial growth but rather kill gram-negative microorganisms. For this reason, doctors prescribe them for enterococci.

However, they have many adverse effects, which limit their use. They shouldn’t be prescribed to pregnant women and infants who are still developing their tissues due to the possibility of interfering with the cellular formation processes.


With the passage of time and the discovery of new drugs, some new drugs gained ground and became the antibiotics of choice against urinary tract infections. This is the case of quinolones, which displaced amoxicillin and penicillin.

Although this hasn’t always been based on scientific evidence, it possibly occurred due to the ease of use of these drugs, as they require fewer doses for fewer days.

A few of the members of this family are norfloxacin, ciprofloxacin, pefloxacin, and gatifloxacin. The first two are the most indicated for this condition due to their bactericidal action. An advantage of this group is that quinolones are strongly concentrated in the tissues where they must attack.

For example, in men, their power to penetrate the prostate makes them the first-line treatment to prevent the condition from becoming more chronic. Meanwhile, norfloxacin is found in high concentrations in the urine once it’s ingested.

Find out more here: Uses and Side Effects of Norfloxacin


This drug combination is considered an antibiotic on its own. However, it can’t always be used because its ability to act is limited to the bacteria that are most frequently detected in urinary tract infections. Nevertheless, if the antibiogram allows it, it isn’t a bad option.

This drug has a good effect on the prostate, which is why it’s the second line of choice for men after norfloxacin. Also, its low side effects give it a safety profile that’s suitable for almost any age and condition.

A person taking antibiotics.
A doctor’s choice between one type of antibiotic or another varies depending on the microorganism that causes the infection and its severity.

Safe use of antibiotics for urinary tract infections

Regardless of the type of infection, the safe use of antibiotics is essential. When taken and prescribed indiscriminately, bacterial strains become resistant and their treatment becomes increasingly difficult.

Therefore, it’s essential to consult a doctor and get an antibiogram if the urgency of the case allows it. Thus, the choice of the antibiotic is based on evidence of its effectiveness in killing bacteria and reducing the appearance of resistant strains.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Orrego-Marin, Claudia Patricia, Claudia Patricia Henao-Mejia, and Jaiberth Antonio Cardona-Arias. “Prevalencia de infección urinaria, uropatógenos y perfil de susceptibilidad antimicrobiana.” Acta Médica Colombiana 39.4 (2014): 352-358.
  • Tandogdu, Zafer, and Florian ME Wagenlehner. “Global epidemiology of urinary tract infections.” Current opinion in infectious diseases 29.1 (2016): 73-79.
  • Medina, Martha, and Edgardo Castillo-Pino. “An introduction to the epidemiology and burden of urinary tract infections.” Therapeutic advances in urology 11 (2019): 1756287219832172.
  • Barker, Charlotte I., Eva Germovsek, and Mike Sharland. “What do I need to know about penicillin antibiotics?.” Archives of Disease in Childhood-Education and Practice 102.1 (2017): 44-50.
  • Hanif, Shamayela. “Frequency and pattern of urinary complaints among pregnant women.” Journal of the College of Physicians and Surgeons–pakistan: Jcpsp 16.8 (2006): 514-517.
  • Alinejad, Saeed, et al. “Nephrotoxic effect of gentamicin and amikacin in neonates with infection.” Nephro-Urology Monthly 10.2 (2018).
  • Tayebi, Zahra, et al. “Comparison of quinolone and β-lactam resistance among Escherichia coli strains isolated from urinary tract infections.” Infezioni in Medicina 24.4 (2016): 326-330.
  • Talan, David A., et al. “Extended-release ciprofloxacin (Cipro XR) for treatment of urinary tract infections.” International journal of antimicrobial agents 23 (2004): 54-66.
  • Stamatiou, Konstantinos, and Nikolaos Pierris. “Mounting resistance of uropathogens to antimicrobial agents: A retrospective study in patients with chronic bacterial prostatitis relapse.” Investigative and clinical urology 58.4 (2017): 271-280.
  • NEMIROVSKY, CORINA, et al. “Consenso Argentino Intersociedades de Infección Urinaria 2018-2019-Parte I.” MEDICINA (Buenos Aires) 80.3 (2020): 229-240.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.