Amoxicillin (Amoxil)

What it's used for

Ear infections (otitis media), strep throat, sinus infections, urinary tract infections, skin infections, dental infections, and as part of combination therapy for H. pylori stomach ulcers. Also used for endocarditis prophylaxis before dental procedures in at-risk patients.

Typical dosing (adults)

• Mild to moderate infections: 250–500 mg every 8 hours, or 500–875 mg every 12 hours.
• Severe infections: 875 mg every 12 hours or 500 mg every 8 hours.
• Can be taken with or without food (food may reduce stomach upset).
• Always finish the entire prescribed course, even if you feel better.

Key interactions

• Warfarin: moderate — amoxicillin may increase bleeding risk; INR monitoring recommended.
• Methotrexate: major — amoxicillin can reduce methotrexate clearance, increasing toxicity risk.
• Allopurinol: minor — increased risk of skin rash when taken together.
• Oral contraceptives: minor — theoretical reduced efficacy; use backup contraception if concerned (evidence is limited).
• Probenecid: moderate — raises amoxicillin blood levels by slowing kidney excretion.

Common side effects

Diarrhea (most common), nausea, stomach upset, and skin rash. A non-allergic rash (flat, pink, widespread) is common with mononucleosis — this is not a true penicillin allergy. Vaginal yeast infections may occur. Rare but serious: severe allergic reaction (anaphylaxis), C. difficile colitis (severe watery diarrhea).

Who should be cautious

• True penicillin allergy (especially anaphylaxis history — do not take).
• Mononucleosis (high risk of rash).
• Kidney disease (dose adjustment may be needed).
• History of antibiotic-associated colitis.

What to ask your pharmacist

• I had a rash with penicillin as a child — is it safe to take amoxicillin?
• Do I need to take a probiotic while on this antibiotic?
• How should I store the liquid suspension, and how long is it good for?
• Can I drink alcohol while taking amoxicillin?