Antibiotics: Uses, Side-Effects and Safety Information

You’ve most likely taken an antibiotic or anti-infective at least once in your lifetime. From treatments for painful strep throat or ear infections as a child, to burning urinary tract infections or itchy skin infections as an adult, antibiotics are one of the most highly utilized and important medication classes we have in medicine.

When Should I Use an Antibiotic?

Antibiotics are specific for the type of bacteria being treated and, in general, cannot be interchanged from one infection to another. When antibiotics are used correctly, they are usually safe with few side effects. Health care providers can diagnose your infection individually to determine the correct antibiotic, dose and length of treatment.

However, as with most drugs, antibiotics can lead to side effects that may range from being a nuisance to serious or life-threatening. In infants and the elderly, in patients with kidney or liver disease, in pregnant or breastfeeding women, and in many other people antibiotic doses may need to be adjusted based upon the individual patient.

Drug interactions can also be common with antibiotics, so tell your pharmacist and doctor what other prescription, over-the-counter (OTC) or herbal supplements you take.

When should I Avoid Antibiotics?

Antibiotics are not the correct choice for all infections. For example, most sore throats, cough and colds, flu, COVID or acute sinusitis are viral in origin (not bacterial) and do not need an antibiotic. These viral infections are “self-limiting”, meaning that your own immune system will usually kick in and fight the virus off. You may need to treat symptoms like a nagging cough, stuffy nose or body aches with OTC medicines.

Using antibiotics for viral infections can increase the risk for antibiotic resistance. When this happens, antibiotic-resistant bacteria cannot be fully inhibited or killed by an antibiotic, even though the antibiotic may have worked effectively before the resistance occurred. This can also lower your options for effective treatments if an antibiotic is needed eventually due to a secondary infection. Using unnecessary antibiotics also puts you at risk for side effects and adds extra cost.

It's important that you do not share your antibiotic with anyone, or take medicine that was prescribed for someone else. It may be harmful or ineffective. Also, don't save an antibiotic in your medicine chest to use the next time you get sick. It may not be the right drug for your illness, and could expire.

List of Common Infections Treated with Antibiotics

• Acne
• Bronchitis
• Conjunctivitis (Pink Eye)
• Otitis Media (Ear Infection)
• STDs
• Skin Infections
• UTI

List of Top Generic Antibiotics

• Amoxicillin
• Doxycycline
• Cephalexin
• Ciprofloxacin
• Clindamycin

List of Top Brand Name Antibiotics

• Augmentin
• Flagyl
• Amoxil
• Cipro
• Keflex
• Keflex
• Fleming

List of Common Antibiotic Classes

• Penicillins
• Cephalosporins
• Macrolides
• Fluoroquinolones
• Sulfonamides

Tables of Antibiotic Classes and Drug Names

Most antibiotics fall into their individual antibiotic classes. An antibiotic class is a grouping of different drugs that have similar chemical and pharmacologic properties. Their chemical structures may look comparable and drugs within the same class may kill the same or related bacteria.

However, it is important not to use an antibiotic for an infection unless your doctor specifically prescribes it, even if it's in the same class as another drug you were previously prescribed. Antibiotics are specific for the kind of bacteria they kill. Plus, you would need a full treatment regimen to effectively cure your infection, so don't use or give away leftover antibiotics.
Note: Tables are not all-inclusive, and other brand or generic products are available.

1. Penicillins

Another name for the penicillin class is the "beta-lactam" antibiotics, referring to their structural formula. The penicillin class contains five groups of antibiotics: aminopenicillins, antipseudomonal penicillins, beta-lactamase inhibitors, natural penicillins and the penicillinase resistant penicillins.

Common antibiotics in the penicillin class include:

Generic	Brand Name Examples
amoxicillin	Amoxil
amoxicillin and clavulanate	Augmentin
ampicillin	Unasyn
dicloxacillin	Not available
oxacillin	Bactocill injection
penicillin V potassium	Penicillin VK
piperacillin and tazobactam	Zosyn

Certain penicillinase-resistant penicillins (such as oxacillin or dicloxacillin) are inherently resistant to certain beta-lactamase enzymes by themselves. Others, for example, amoxicillin or ampicillin, have greater antibacterial activity when they are combined with a beta-lactamase inhibitor like clavulanate, sulbactam, or tazobactam.

2. Tetracyclines

Tetracyclines are broad-spectrum against many bacteria and treat conditions such as acne, urinary tract infections (UTIs), intestinal tract infections, eye infections, sexually transmitted infections, periodontitis (gum disease), and other bacterial infections. The tetracycline class contains drugs such as:

Generic	Brand Name Examples
demeclocycline	Not available
doxycycline	Doryx, Doxy 100, Monodox, Oracea, Vibramycin
eravacycline	Xerava
minocycline	Dynacin, Minocin, Minolira, Solodyn, Ximino, Zilxi Foam
omadacycline	Nuzyra
sarecycline	Seysara
tetracycline	Ala-Tet, Achromycin V, Brodspec

3. Cephalosporins

There are five generations of cephalosporins, with increasing expanded coverage across the class to include gram-negative infections. Newer generations with updated structures are developed to allow wider coverage of certain bacteria. Cephalosporins are bactericidal (kill bacteria) and work in a similar way as the penicillins.

Cephalosporins treat many types of infections including strep throat (streptococcal pharyngitis), ear infections, urinary tract infections (UTIs), skin infections, lung infections, and meningitis (infection that leads to swelling of the brain and spinal cord). Common medications in this class include:

Generic	Brand Name Examples	Generation
cefaclor	Not available	2nd generation
cefadroxil	Duricef	1st generation
cefdinir	Not available	3rd generation
cephalexin	Keflex	1st generation
cefprozil	Cefzil	2nd generation
cefepime	Maxipime	4th generation
cefepime and enmetazobactam	Exblifep	4th gen + beta-lactamase inhibitor
cefiderocol	Fetroja	4th generation
cefotaxime	Not available	3rd generation
cefotetan	Cefotan	2nd generation
ceftobiprole medocaril	Zevtera	5th generation
ceftolozane and tazobactam	Zerbaxa	5th gen / beta-lactamase inhibitor
ceftaroline	Teflaro	5th generation
ceftazidime	Avycaz, Fortaz, Tazicef	3rd generation
ceftriaxone	Not available	3rd generation
cefuroxime	Ceftin, Zinacef	2nd generation

4. Fluoroquinolones

The fluoroquinolones, commonly referred to as "quinolones", are a synthetic, bactericidal antibacterial class with a broad-spectrum of activity used in adults (not children).

Due to risk of multiple serious side effects, the FDA has advised that they are not suitable for common infections such as sinusitis, bronchitis, and uncomplicated urinary tract infections. They may affect the muscles, tendons, joints, heart, and metabolic or nervous system. They should only be considered when treatment with other, less toxic antibiotics has failed. Ask your doctor about the warnings associated with this class of drug before you take it.

The FDA has issued several strong warnings about this class due to potential disabling side effects.

Learn More: FDA Drug Safety Communication: FDA updates warnings for oral and injectable fluoroquinolone antibiotics due to disabling side effects

Generic	Brand Name Examples
ciprofloxacin	Cipro, Cipro XR
delafloxacin	Baxdela
levofloxacin	Levaquin (discontinued)
moxifloxacin	Avelox
gemifloxacin	Factive

5. Lincomycins

This class has activity against gram-positive aerobes and anaerobes (bacteria that can live without oxygen), as well as some gram-negative anaerobes.

The lincomycin derivatives may be used to treat serious infections like pelvic inflammatory disease, intra-abdominal infections, lower respiratory tract infections, and bone and joint infections. Some forms are also used topically on the skin to treat acne. A single-dose vaginal cream is available to treat some bacterial vaginal infections (bacterial vaginosis). These drugs include:

Generic	Brand Name Examples
clindamycin	Cleocin, Cleocin T, Clindets, Clindesse, Evoclin
lincomycin	Lincocin

6. Sulfonamides

Sulfonamides are effective against some gram-positive and many gram-negative bacteria, but resistance is widespread. Uses for sulfonamides include urinary tract infections (UTIs), treatment or prevention of pneumocystis pneumonia, or ear infections (otitis media). Familiar names include:

Generic	Brand Name Examples
sulfamethoxazole and trimethoprim	Bactrim, Bactrim DS, Septra, Septra DS
sulfasalazine	Azulfidine

Are There Any Over-the-Counter (OTC) Antibiotics?

Over-the-counter (OTC) oral antibiotics are not approved in the U.S. A bacterial infection is best treated with a prescription antibiotic that is specific for the type of bacteria causing the infection. Using a specific antibiotic will increase the chances that the infection is cured and help to prevent antibiotic resistance.

In addition, a lab culture may be needed to pinpoint the bacteria and to help select the best antibiotic. Taking the wrong antibiotic -- or not enough -- may worsen the infection and prevent the antibiotic from working the next time.

Frequently Asked Questions

What happens if antibiotics don’t work for UTI?

If antibiotics don’t work for a urinary tract infection (UTI), it may be due to antibiotic resistance or an incorrect choice of antibiotic. In such cases, your doctor might order urine cultures to identify the bacteria and recommend a more effective antibiotic. It’s important to complete the full course of prescribed antibiotics to help prevent resistance.

What are the common side effects of antibiotics?

Common side effects of antibiotics can include upset stomach, diarrhea, nausea, and allergic reactions. Some classes, like fluoroquinolones, carry more serious risks including tendon damage and nervous system effects. Always consult your healthcare provider about potential side effects of your specific antibiotic.

Should you take probiotics with antibiotics?

Probiotics can help restore the natural balance of bacteria in your gut, which antibiotics may disrupt. Taking probiotics during or after antibiotic treatment may reduce the risk of diarrhea and yeast infections, but you should discuss this with your doctor for personalized advice.

What are the best antibiotics for a tooth infection?

Penicillins, like amoxicillin, are commonly used to treat tooth infections due to their effectiveness against many bacteria that cause oral infections. If allergic to penicillin, alternatives like clindamycin or certain cephalosporins may be used. Always follow your dentist’s prescription.

Can antibiotics cause yeast infections?

Yes, antibiotics can disrupt the natural balance of bacteria and yeast in the body, sometimes leading to yeast infections, especially in women. This is because antibiotics kill beneficial bacteria that normally keep yeast growth in check.

Allergic to Penicillin? Which antibiotics can you take?

If you are allergic to penicillin, doctors may prescribe antibiotics from other classes such as cephalosporins (if the allergy is mild), clindamycin, or macrolides. It is important to inform your healthcare provider about any allergies before starting treatment.

Can antibiotics cause diarrhea?

Antibiotic-associated diarrhea is common because antibiotics can disrupt the gut’s natural bacterial balance. This can range from mild to severe and sometimes may indicate an overgrowth of harmful bacteria like Clostridioides difficile. Contact your doctor if diarrhea is severe or persistent.

Can antibiotics cause constipation?

While less common than diarrhea, some people may experience constipation when taking antibiotics. This can be due to changes in gut bacteria or side effects of the medication. Staying hydrated and eating fiber-rich foods may help.

How do antibiotics work to kill bacteria?

Antibiotics work by targeting essential functions or structures in bacteria. For example, penicillins and cephalosporins disrupt bacterial cell wall synthesis, leading to bacterial death. Others inhibit protein synthesis or DNA replication. These actions stop bacteria from growing or kill them outright.