How antibiotics work depends on the type of antibiotic, but these medications generally fight bacteria by stopping their growth or killing them. Antibiotics are commonly used to treat bacterial infections such as pneumonia, ear infections, sinus infections, and urinary tract infections.
The type of antibiotic prescribed depends on the infection being treated. A healthcare provider may recommend antibiotics from different classes, such as penicillins, macrolides, fluoroquinolones, cephalosporins, or tetracyclines.
Antibiotics should only be used as prescribed and should be taken at the correct times and for the recommended length of treatment. Using antibiotics incorrectly can contribute to antibiotic resistance, which can make infections more difficult and take longer to treat.
Common antibiotics
Some of the most commonly used antibiotics for treating infections include:
1. Penicillins
The main antibiotics in the penicillin class include
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Oxacillin
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Ampicillin + sulbactam
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Piperacillin + tazobactam
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Nafcillin
These penicillins may be prescribed as tablets, oral liquids, or injections, depending on the specific medication, the type of infection, and the person's age.
Main uses: penicillins may be prescribed to treat infections such as pneumonia, bronchitis, tonsillitis, sinus infections, urinary or vaginal infections, and infections of the skin and mucous membranes.
Side effects: penicillins can cause side effects such as headache, nausea, vomiting, diarrhea, oral or genital yeast infections, and, in rare cases, a severe allergic reaction or anaphylactic shock.
2. Tetracyclines
The main tetracyclines that may be prescribed by a doctor include:
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Minocycline
Some tetracyclines should not be taken at the same time as milk or dairy products because this can reduce how much of the medication is absorbed. The recommended interval between the antibiotic and dairy products depends on the specific medication.
Tetracyclines should also not be taken at the same time as antacids or medications or supplements containing calcium, magnesium, aluminum, or iron. These substances can reduce antibiotic absorption, so the doses generally need to be separated according to the medication instructions.
Main uses: tetracyclines may be prescribed for infections caused by susceptible organisms, including brucellosis, some gum infections, Lyme disease, and certain sexually transmitted infections (STIs).
Side effects: the most common side effects of tetracyclines include inflammation of the esophagus, diarrhea, nausea, vomiting, indigestion, stomach pain, headache, and sensitivity to sunlight.
3. Sulfonamides
The main sulfonamide and sulfonamide-containing medications include:
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Sulfamethoxazole
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Sulfamethoxazole + trimethoprim
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Sulfasalazine
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Silver sulfadiazine
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Sulfacetamide
These medications are available in different forms, including tablets, oral liquids, creams, ointments, and eye preparations. The formulation used depends on the medication and the condition being treated.
Main uses: sulfonamide-containing medications may be used for conditions such as urinary tract infections (UTIs), certain respiratory infections, burns and wounds, inflammatory bowel disease, and rheumatic diseases, depending on the specific medication.
Side effects: sulfonamides can cause side effects such as headache, loss of appetite, nausea, vomiting, stomach pain or discomfort, yeast infections, and, in some cases, jaundice.
4. Fluoroquinolones
The main antibiotics in the fluoroquinolone class include
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Ofloxacin
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Delafloxacin
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Gatifloxacin, for ophthalmic use
These antibiotics are available in different forms, including tablets, injectable solutions, eye drops, and ear preparations, depending on the specific medication.
Main uses: fluoroquinolones may be prescribed for certain infections affecting the respiratory tract, ears, eyes, kidneys, urinary tract, skin, bones, or reproductive organs, as well as some serious systemic infections.
Side effects: fluoroquinolones can cause side effects such as tendinitis, tendon rupture, and nervous system symptoms. According to the FDA, systemic fluoroquinolones carry safety warnings about serious side effects involving the tendons, muscles, joints, nerves, and central nervous system. Their use during pregnancy or breastfeeding should be discussed with a doctor.
5. Macrolides
The main antibiotics in the macrolide class include:
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Erythromycin
Macrolides are available as tablets, oral liquids, topical preparations, or injections, depending on the specific medication. People with liver, kidney, or cardiovascular conditions may need additional medical evaluation before using certain macrolides because of their potential side effects and the way these medications are processed by the body.
Main uses: macrolides are generally prescribed to treat infections such as sinus infections, pneumonia, skin infections, and certain STIs, including chlamydia.
Side effects: the most common side effects include loss of appetite, nausea, vomiting, abdominal pain, gas, general discomfort, cramps, loose stools, and diarrhea.
6. Cephalosporins
The main antibiotics in the cephalosporin class include:
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Cefaclor
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Cefadroxil
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Cefuroxime
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Cefotaxime
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Ceftazidime
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Cefepime
The use of cephalosporins during pregnancy or breastfeeding should be discussed with a healthcare provider, as recommendations may vary depending on the specific antibiotic and the infection being treated.
Main uses: cephalosporins are generally prescribed to treat respiratory tract infections, middle ear infections (otitis media), skin and soft tissue infections, UTIs, and bone infections.
Side effects: the most common side effects include nausea, vomiting, diarrhea, abdominal pain, and hives. Some cephalosporins can also cause anal or genital itching.
7. Aminoglycosides
The main examples of aminoglycoside antibiotics include:
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Gentamicin
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Streptomycin
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Amikacin
Aminoglycosides may be prescribed as eye drops, ophthalmic ointments, topical preparations, or injections, depending on the specific antibiotic and the type of infection.
Main uses: aminoglycosides may be used to treat certain skin infections and serious bacterial infections, including peritonitis, meningitis, and systemic infections, depending on the specific antibiotic and the susceptibility of the bacteria.
Side effects: important side effects can include decreased kidney function, hearing loss, vertigo, ringing in the ears, loss of balance, headache, and changes in blood test results.
8. Nitroimidazoles
The main nitroimidazole antimicrobial medications include:
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Tinidazole
These medications are available in forms such as tablets, vaginal preparations, and topical gels.
Main uses: nitroimidazoles may be used to treat rosacea, giardiasis, amebiasis, trichomoniasis, bacterial vaginosis, and other infections caused by susceptible bacteria or protozoa, depending on the specific medication.
Side effects: the most common side effects include nausea, vomiting, diarrhea, stomach pain, a metallic taste in the mouth, loss of appetite, headache, excessive tiredness, and dizziness. Vaginal or topical formulations may also cause local burning or itching.
9. Nitrofurans
Nitrofurantoin is the main nitrofuran antibiotic used in the United States and is available as capsules or an oral suspension.
Main uses: nitrofurantoin is mainly prescribed to treat certain uncomplicated UTIs caused by susceptible bacteria.
Side effects: the most common side effects include nausea, vomiting, loss of appetite, diarrhea, and stomach discomfort.
10. Phosphonic acid derivatives
Fosfomycin tromethamine is the main antibiotic in the phosphonic acid derivative class. It comes as granules that are dissolved in water and is typically taken as a single oral dose for its FDA-approved use.
Main uses: fosfomycin tromethamine is mainly used to treat uncomplicated bladder infections, also known as acute cystitis.
Side effects: the most common side effects include headache, dizziness, vaginal symptoms, nausea, stomach pain, diarrhea, and skin reactions such as itching and redness.
11. Carbapenems
The main carbapenem antibiotics used in the United States include:
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Meropenem
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Ertapenem
These antibiotics are given by injection because they are not adequately absorbed when taken by mouth. They are generally used in hospitals or other healthcare settings.
Main uses: carbapenems may be prescribed for serious bacterial infections, including certain cases of meningitis, sepsis, lung infections, UTIs, and intra-abdominal infections, depending on the specific medication.
Side effects: the most common side effects include diarrhea, nausea, vomiting, abdominal pain, headache, and oral or vaginal yeast infections.
12. Glycopeptides
Vancomycin is a commonly used glycopeptide antibiotic in the United States. It may be given intravenously to treat serious infections throughout the body. Oral vancomycin is also used for certain intestinal infections.
Main uses: intravenous (IV) vancomycin may be prescribed for serious susceptible bacterial infections involving the bones, lungs, skin, muscles, or heart, including conditions such as bacterial endocarditis and osteomyelitis.
Side effects: possible side effects include infusion-related reactions, itching, skin redness, kidney problems, ringing in the ears, hearing changes, and, rarely, severe allergic or skin reactions.
Frequently asked questions
Some commonly asked questions about antibiotics include:
1. Do antibiotics cause weight gain?
Antibiotics do not typically cause weight gain or increased appetite. However, some can cause indigestion, gas, or bloating, which may temporarily feel like weight gain.
2. Do antibiotics make birth control less effective?
According to the CDC, most broad-spectrum antibiotics do not reduce the effectiveness of combined hormonal contraceptives. However, rifampin and rifabutin can make some hormonal contraceptives less effective.
Griseofulvin, which is an antifungal medication rather than an antibiotic, may also interact with some hormonal contraceptives.
Vomiting or severe diarrhea may interfere with the absorption of oral birth control pills if it occurs soon after a dose.
In these situations, a backup contraceptive method may be needed. Follow the instructions provided with the contraceptive and ask a healthcare professional if you are unsure.
3. Do I need to finish the entire course of antibiotics?
Antibiotics should be taken exactly as prescribed by a healthcare provider, including for the recommended length of time, even if symptoms improve before treatment is complete.
People should not stop taking an antibiotic early on their own because they feel better. The appropriate treatment duration depends on the infection, the antibiotic being used, and the person's response to treatment.
4. Why do antibiotics cause diarrhea?
Diarrhea is a common side effect of antibiotics because these medications can affect the bacteria that normally live in the intestines.
Antibiotics target susceptible bacteria and can affect both disease-causing bacteria and beneficial gut bacteria. These changes in the intestinal microbiome can lead to diarrhea and other digestive symptoms.
5. Does alcohol stop antibiotics from working?
Alcohol does not automatically stop antibiotics from working. However, drinking alcohol while sick can worsen side effects such as nausea, dizziness, or stomach discomfort and may make recovery more difficult.
Alcohol should also be avoided with certain antimicrobial medications because important interactions can occur. This includes medications such as metronidazole and tinidazole.
For this reason, patients should follow the instructions from their doctor, pharmacist, and medication label regarding alcohol use during treatment.
