Amoxicillin is an antibiotic of the penicillin class, widely used to treat common bacterial infections: otitis media, tonsillitis, sinusitis, bronchitis, urinary and dental infections. It works by preventing bacteria from building their cell wall, killing them. It is generally well tolerated; the allergic reaction (rash, urticaria; rarely anaphylaxis) is the main concern.
Also known as: Amoxil
Combining Amoxicillin and Allopurinol increases the incidence of skin rashes.
As with ampicillin, the allopurinol label lists "amoxicillin" among the drugs that "may increase the risk of serious skin reactions" (section 7.1) and recommends "discontinuing allopurinol immediately if a skin rash develops". The mechanism is shared with ampicillin — penicillins are believed to increase skin reactivity to allopurinol, possibly through alteration of the gut microbiota or accumulation of the oxypurinol metabolite. The combination is frequent in practice (gout prophylaxis during antibiotic therapy for respiratory or urinary infection). The rash is usually maculopapular and benign, but can progress to severe reactions (DRESS, Stevens-Johnson syndrome). Start allopurinol and the antibiotic at different times whenever possible; if the patient is already on allopurinol, advise them to watch their skin while taking amoxicillin; if a rash appears, stop both and use an alternative antibiotic (macrolide, doxycycline) or reintroduce allopurinol after resolution, with vigilance.
Allopurinol + amoxicillin: increased risk of severe skin reaction. Watch for skin rash and stop if it appears.
Increased cutaneous hypersensitivity reactivity when coadministered; mechanism not fully established.
Skin status, signs of hypersensitivity.
Generalized rash, fever, mucosal involvement.
Watch for a rash; consider an antibiotic alternative or adjust allopurinol if the eruption is significant.
DailyMed/FDA (NIH/NLM) — approved Amoxicillin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=57e56202-950b-10f6-e063-6394a90a4912 ; approved Allopurinol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b6c5b5c0-b1cb-44c0-a849-5d317e6fa300
Amoxicillin can be taken with or without food; absorption is not significantly affected.
May be taken with or without food, consistently.
DailyMed/FDA (NIH/NLM) — approved Amoxicillin label (capsules): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=afb4149a-0714-4a85-b9e8-2379a8e6a302
Alcohol does not interact directly with amoxicillin, but can reduce adherence and worsen gastrointestinal symptoms.
Moderate alcohol intake during treatment.
DailyMed/FDA (NIH/NLM) — approved Amoxicillin label (capsules): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=afb4149a-0714-4a85-b9e8-2379a8e6a302
Amoxicillin is contraindicated in patients with documented penicillin allergy (risk of anaphylaxis).
Confirm allergy history before prescribing; consider an alternative class.
DailyMed/FDA (NIH/NLM) — approved Amoxicillin label (capsules): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=afb4149a-0714-4a85-b9e8-2379a8e6a302
Amoxicillin in patients with infectious mononucleosis frequently causes a maculopapular rash.
Avoid amoxicillin/ampicillin in mononucleosis; consider an alternative.
DailyMed/FDA (NIH/NLM) — approved Amoxicillin label (capsules): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=afb4149a-0714-4a85-b9e8-2379a8e6a302
Penicillins are considered safe in pregnancy; amoxicillin is used in common infections in pregnancy.
May be used in any trimester when indicated.
Present in breast milk in small amounts; compatible with breastfeeding.
No specific contraception required.
DailyMed/FDA (NIH/NLM) — approved Amoxicillin label (capsules): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=afb4149a-0714-4a85-b9e8-2379a8e6a302
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Broad-spectrum semisynthetic penicillin (aminopenicillin, bactericidal), stable to gastric acid and well absorbed orally; active against streptococci, pneumococci, enterococci, Listeria, Haemophilus, E. coli, Proteus, Salmonella and H. pylori (in combination). Susceptible to beta-lactamases.
Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), blocking peptidoglycan transpeptidation — time-dependent bactericidal effect.
Stable to gastric acid, rapidly absorbed: peaks 1-2 h after dosing (3.5-7.5 mcg/mL for 250-500 mg); ~20% protein binding; diffuses well into most tissues and fluids (except CNS with uninflamed meninges).
Partial metabolism; ~60-80% excreted unchanged renally (glomerular filtration and tubular secretion); probenecid reduces excretion. Adjust in renal impairment.
Elimination half-life ~1 h with normal renal function; the half-life is prolonged in renal impairment (extended dosing interval).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
