Amoxicillin 500mg treats a wide range of bacterial infections, including strep throat, ear infections, sinus infections, urinary tract infections, certain skin infections, and some lower respiratory infections like bronchitis and pneumonia. It’s one of the most commonly prescribed antibiotics in the world, and the 500mg capsule or tablet is the standard adult strength for most of these conditions.
Ear, Nose, and Throat Infections
Strep throat is one of the most common reasons doctors prescribe amoxicillin. The CDC lists it as the antibiotic of choice for group A streptococcal pharyngitis, the bacterial infection behind strep throat. For adults, the typical course is 500mg taken twice daily for 10 days. Finishing the full course matters even if you feel better after a few days, because stopping early increases the risk of the infection returning or developing complications like rheumatic fever.
Amoxicillin also works well for bacterial sinus infections and middle ear infections (otitis media). These are frequently caused by the same types of bacteria: streptococcus, staphylococcus, and a common respiratory bacterium called H. influenzae. Not every sinus infection or ear infection needs antibiotics, since many are viral, but when a doctor determines bacteria are the likely cause, amoxicillin 500mg is often the first choice.
Lower Respiratory Infections
Amoxicillin is approved for bacterial infections of the lower respiratory tract, which includes bronchitis and community-acquired pneumonia. For mild pneumonia in otherwise healthy adults, amoxicillin can be effective against the most common bacterial culprit, Streptococcus pneumoniae. More severe cases or those involving drug-resistant bacteria typically require a different antibiotic or a combination approach. Your doctor will consider how sick you are and whether you have other health conditions before deciding if amoxicillin alone is sufficient.
Urinary Tract Infections
Amoxicillin is approved for urinary tract infections caused by E. coli, Proteus mirabilis, and Enterococcus faecalis. In practice, though, it’s no longer a first-line choice for most simple UTIs because resistance among urinary bacteria has become common. Doctors now tend to prescribe other antibiotics for straightforward bladder infections and reserve amoxicillin for UTIs where lab testing confirms the bacteria are susceptible to it.
Skin and Soft Tissue Infections
Bacterial skin infections caused by streptococcus, staphylococcus, or E. coli can respond to amoxicillin. This includes conditions like cellulitis (a spreading skin infection that causes redness, warmth, and swelling) and infected wounds. It does not work against MRSA, a resistant form of staph that requires different treatment. If you have a skin infection that isn’t improving on amoxicillin, resistance is one possible explanation.
H. Pylori and Stomach Ulcers
Amoxicillin plays a key role in treating Helicobacter pylori, the bacterium responsible for most stomach and duodenal ulcers. It isn’t used alone for this purpose. The standard approach is triple therapy: amoxicillin combined with another antibiotic and a proton pump inhibitor (a type of acid-reducing medication). A typical regimen involves 1,000mg of amoxicillin, essentially two 500mg capsules, taken twice daily for 10 days alongside the other two medications. Eradicating H. pylori significantly reduces the risk of ulcer recurrence.
Dental Infection Prevention
Amoxicillin is the go-to antibiotic for preventing heart valve infections before dental procedures in people at high risk, such as those with artificial heart valves or a history of endocarditis. The American Heart Association recommends a single 2g dose (four 500mg capsules) taken 30 to 60 minutes before the procedure. This is a one-time preventive dose, not a full course of treatment.
How Amoxicillin Works
Amoxicillin kills bacteria by blocking their ability to build and maintain their cell walls. Bacteria depend on a rigid outer wall to survive, and amoxicillin interferes with the proteins responsible for assembling that wall. Without it, bacteria can’t hold their structure together and they die. This mechanism is why amoxicillin works only on bacteria and has no effect on viruses, which lack cell walls entirely. Taking amoxicillin for a cold, flu, or COVID will not help.
Common Side Effects
Amoxicillin is generally well tolerated. A large meta-analysis of placebo-controlled trials found that diarrhea, nausea, rashes, and vomiting were not significantly more common with amoxicillin alone compared to placebo. The one notable exception is yeast infections (candidiasis), which occurred roughly seven times more often in people taking amoxicillin. This happens because the antibiotic disrupts normal bacterial populations, giving yeast an opportunity to overgrow.
Diarrhea becomes a much bigger concern with amoxicillin-clavulanate, a combination form. In that formulation, about 1 in 10 courses of antibiotics leads to diarrhea. If you’ve been prescribed plain amoxicillin 500mg, your risk of digestive side effects is considerably lower.
Allergic reactions are the main safety concern. True penicillin allergy affects a small percentage of people and can range from a mild rash to a serious reaction. If you’ve had a confirmed allergic reaction to penicillin or amoxicillin in the past, your doctor will choose a different antibiotic.
Important Drug Interactions
Amoxicillin interacts with a few medications worth knowing about. It can slow the body’s ability to clear methotrexate, a drug used for autoimmune conditions and certain cancers, through the kidneys. This raises the risk of methotrexate building up to harmful levels. If you take methotrexate and need a short course of amoxicillin, your doctor will likely monitor you for signs of toxicity like unusual bruising, sore throat, or mouth sores.
Probenecid, a gout medication, can raise amoxicillin levels in the blood by reducing how quickly the kidneys excrete it. And while older sources warned that amoxicillin might reduce the effectiveness of birth control pills, current evidence suggests this interaction is not clinically significant for most oral contraceptives.
Why the Full Course Matters
Bacterial resistance to amoxicillin has been rising for years, particularly among certain strains of respiratory and urinary bacteria. Resistance is already the reason amoxicillin has become less reliable for UTIs than it once was. Taking the full prescribed course at the correct dose helps ensure the infection is fully cleared and reduces the chance of contributing to resistance. If you skip doses or stop early because you feel better, surviving bacteria are more likely to develop the ability to resist amoxicillin in the future.