Description
Amoxil (amoxicillin)
The most common mistake with amoxicillin isn’t a dosing error. It’s taking it for the wrong kind of infection entirely.
Amoxicillin kills bacteria. It does nothing to viruses — not slow them, not weaken them, not shorten how long you feel sick. Colds, flu, most sore throats, COVID-19: amoxicillin prescribed for any of these is a course of treatment that treats nothing while selecting for resistant organisms in your gut. That’s the background worth having before anything else.
For the infections it does cover, it covers them well: tonsillitis, sinusitis, otitis media, bronchitis, community-acquired pneumonia, urinary tract infections at any severity level, dental infections, skin infections, strep throat. Also H. pylori eradication — though not alone; the standard approach pairs amoxicillin with clarithromycin and lansoprazole, twice daily for 14 days.
Available in 250 mg, 500 mg, and 1000 mg tablets.
Dosing
For most moderate infections in adults: 500–750 mg twice daily, or 375–500 mg three times daily. Severe infections move up to 750–1000 mg three times daily.
“Three times daily” means evenly spaced — roughly every 8 hours, not three times during waking hours. The goal is to keep blood concentration consistently above the threshold that inhibits bacterial growth. Drop below it repeatedly and the bacteria that survive are the ones worth worrying about on the next course.
⚠️ Children between 3 and 10 typically receive 250 mg three times daily. Over 10, adult dosing applies. Kidney impairment requires dose adjustment — the kidneys handle clearance, and reduced function changes how long the drug stays active.
Before you start
Penicillin allergy comes first. Amoxicillin is a penicillin, and if you’ve had a serious reaction to any penicillin — hives, throat swelling, breathing difficulty — this needs to be on your prescriber’s radar before the prescription is written. Cross-reactivity with cephalosporins exists, though at a lower rate. A history of stomach upset with penicillin is a different thing from anaphylaxis; knowing which category you’re in changes the conversation.
Infectious mononucleosis is the other contraindication most people don’t know about. If the illness might be mono rather than a straightforward bacterial infection, amoxicillin causes a widespread maculopapular rash in a meaningful proportion of mono patients. The mechanism is immune-mediated rather than a classical allergy — the rash isn’t dangerous, but it’s unpleasant and avoidable. Ruling out mono before starting is worth the extra step when there’s any diagnostic doubt.
Side effects
Diarrhea, nausea, vomiting — common, affect a real proportion of people, manageable for most.
The more serious concern is allergic reaction, ranging from urticaria to anaphylaxis. Facial swelling, throat tightness, or difficulty breathing during a course are same-day emergency situations. Mild rash needs same-day evaluation too — distinguishing drug allergy from the mono reaction requires a clinician, not a search.
With courses of several weeks or longer, the risk profile expands: pseudomembranous colitis (Clostridioides difficile overgrowth presenting as severe persistent diarrhea), liver enzyme elevation, peripheral neuropathy, interstitial nephritis. Not everyday concerns for a 10-day course. Relevant for anyone on extended treatment.
Contraindications
Hypersensitivity to penicillins or cephalosporins. Infectious mononucleosis. Lymphocytic leukemia. Hematopoietic disorders. Pregnancy and breastfeeding require a prescriber conversation — amoxicillin passes into breast milk, and the clinical relevance depends on the infant.
Finishing the course
Symptoms ease before the infection is cleared. The bacteria that survive a shortened course are, by definition, the ones best adapted to partial drug exposure. Complete the course.
