Amoxicillin: Uses, Dosage & Side Effects

What Is Amoxicillin and What Is It Used For?

Amoxicillin is a broad-spectrum, semi-synthetic aminopenicillin antibiotic that has been in clinical use since the early 1970s. Developed as an improvement over the earlier aminopenicillin ampicillin, amoxicillin offers superior oral bioavailability (approximately 70–80% compared to 40–50% for ampicillin), which means a greater proportion of each oral dose reaches the bloodstream. This improvement in absorption also means that food does not significantly affect its uptake, making it convenient to take with or without meals.

The medication works by a bactericidal mechanism: it inhibits the synthesis of bacterial cell walls by binding to penicillin-binding proteins (PBPs). These enzymes are essential for the cross-linking of peptidoglycan chains, which provide structural integrity to bacterial cell walls. When amoxicillin blocks these enzymes, the bacterial cell wall becomes weakened, leading to osmotic instability, cell lysis, and ultimately bacterial death. Because human cells do not have peptidoglycan cell walls, amoxicillin is selectively toxic to bacteria with relatively few effects on human tissues.

Amoxicillin has activity against a broad range of both Gram-positive and Gram-negative bacteria. It is particularly effective against Streptococcus pneumoniae, Streptococcus pyogenes (Group A streptococcus), Enterococcus faecalis, Haemophilus influenzae (non-beta-lactamase producing), Escherichia coli (non-beta-lactamase producing), Proteus mirabilis, and Helicobacter pylori. However, many bacteria produce beta-lactamase enzymes that can break down amoxicillin, rendering it ineffective. For this reason, amoxicillin is sometimes combined with clavulanic acid (a beta-lactamase inhibitor) in a formulation known as co-amoxiclav or amoxicillin/clavulanate.

Amoxicillin is indicated for the treatment of a wide range of bacterial infections. Common clinical uses include:

• Upper respiratory tract infections: Acute otitis media (middle ear infection), acute bacterial sinusitis, and acute streptococcal pharyngitis and tonsillitis (sore throat caused by Group A streptococcus).
• Lower respiratory tract infections: Acute bacterial bronchitis, community-acquired pneumonia (mild to moderate), and acute exacerbations of chronic obstructive pulmonary disease (COPD).
• Urinary tract infections: Uncomplicated lower urinary tract infections (cystitis), particularly in pregnant women where other antibiotics may be contraindicated.
• Skin and soft tissue infections: Cellulitis, impetigo, wound infections, and infected animal or human bites (usually in combination with clavulanic acid).
• Dental infections: Dental abscesses and odontogenic infections, often as first-line treatment.
• Helicobacter pylori eradication: As part of a triple therapy regimen (with a proton pump inhibitor and clarithromycin or metronidazole) for the treatment of peptic ulcer disease caused by H. pylori.
• Endocarditis prophylaxis: Prevention of infective endocarditis before certain dental or surgical procedures in patients at high risk.
• Lyme disease: Early-stage Lyme disease (erythema migrans) in adults and children.

Amoxicillin is included on the World Health Organization (WHO) Model List of Essential Medicines, reflecting its importance in global healthcare. It is classified as an Access antibiotic under the WHO AWaRe (Access, Watch, Reserve) classification system, meaning it should be widely available as a first-line treatment while being used responsibly to minimize the development of antibiotic resistance. Amoxicillin is available in multiple formulations including capsules, tablets, dispersible tablets (which can be dissolved in water), and powder for oral suspension, making it suitable for patients of all ages.

What Should You Know Before Taking Amoxicillin?

Contraindications

There are specific situations where amoxicillin must not be used. Understanding these absolute contraindications is essential for safe medication use.

• Penicillin allergy: Do not take amoxicillin if you have a confirmed allergy (hypersensitivity) to amoxicillin, any other penicillin-type antibiotic, or any of the inactive ingredients in the specific product. Patients with a history of severe allergic reactions (anaphylaxis, angioedema, or severe skin reactions) to any penicillin must avoid all penicillin antibiotics.
• Severe previous reaction to beta-lactams: Patients with a history of a severe immediate hypersensitivity reaction (e.g., anaphylaxis) to another beta-lactam agent (such as a cephalosporin or carbapenem) should generally avoid amoxicillin due to possible cross-reactivity, though the actual cross-reactivity rate is low (approximately 1–2% with cephalosporins).

Warnings and Precautions

You should inform your doctor before taking amoxicillin if any of the following conditions apply to you:

• Infectious mononucleosis (glandular fever): Amoxicillin causes a characteristic widespread maculopapular rash in the majority (70–100%) of patients with infectious mononucleosis. This is not a true allergic reaction but can be confused with one. Amoxicillin should be avoided if mononucleosis is suspected or confirmed.
• Impaired kidney function: The kidneys are the primary route of elimination for amoxicillin. In patients with severe renal impairment (creatinine clearance < 30 ml/min), the dose should be reduced or the dosing interval extended to prevent drug accumulation.
• Liver disease: While hepatic events are uncommon with amoxicillin alone, liver function should be monitored during prolonged treatment courses. The combination of amoxicillin with clavulanic acid carries a higher risk of cholestatic jaundice.
• History of antibiotic-associated colitis: Broad-spectrum antibiotics including amoxicillin can cause Clostridioides difficile-associated diarrhea (CDAD), ranging from mild diarrhea to fatal colitis. Contact your doctor immediately if you develop severe, persistent, or bloody diarrhea during or after treatment.
• Phenylketonuria (PKU): Some amoxicillin formulations, particularly certain chewable tablets and oral suspensions, may contain aspartame, which is a source of phenylalanine. Check the product labeling if you have PKU.
• Prolonged treatment: If amoxicillin is used for an extended period, periodic assessment of organ system functions including renal, hepatic, and hematopoietic function is advisable. Overgrowth of non-susceptible organisms (including fungi) may also occur with prolonged use.

Pregnancy and Breastfeeding

Amoxicillin is generally considered safe for use during pregnancy and is one of the most commonly prescribed antibiotics for pregnant women. Extensive clinical experience spanning decades, combined with animal reproductive studies, has not demonstrated evidence of teratogenicity (harm to the developing fetus). Major medical guidelines, including those from NICE, the American College of Obstetricians and Gynecologists (ACOG), and the European Medicines Agency (EMA), support the use of amoxicillin during pregnancy when clinically indicated.

However, as with all medications during pregnancy, amoxicillin should only be used when the potential benefit justifies the potential risk to the fetus. If you are pregnant or planning to become pregnant, inform your doctor so they can make an appropriate treatment decision. There is a theoretical risk that broad-spectrum antibiotics may reduce the efficacy of oral hormonal contraceptives, although the clinical significance of this interaction with amoxicillin is debated.

Amoxicillin is excreted in breast milk in small amounts. At standard therapeutic doses, the amount transferred to the nursing infant is considered too small to have a harmful effect. However, the infant may experience sensitization (development of allergy) or alterations in bowel flora, which could manifest as diarrhea or thrush (candidiasis). If your breastfed infant develops diarrhea, skin rash, or thrush while you are taking amoxicillin, consult your doctor or pediatrician.

Driving and Operating Machinery

Amoxicillin has no known effect on the ability to drive or operate machinery. Unlike some antibiotics (such as fluoroquinolones), amoxicillin does not typically cause dizziness, drowsiness, or visual disturbances. However, adverse reactions such as allergic reactions, dizziness, or seizures (very rare) should be taken into account before driving or using machines. If you experience any symptoms that could impair your concentration, refrain from driving until the symptoms have resolved.

How Does Amoxicillin Interact with Other Drugs?

While amoxicillin has fewer drug interactions than many other antibiotics, several clinically significant interactions exist. Understanding these is essential for safe use, particularly in patients taking multiple medications. Always inform your doctor, pharmacist, or nurse about all prescription and over-the-counter medications, vitamins, herbal remedies, and dietary supplements you are taking.

Major Interactions

Minor Interactions

What Is the Correct Dosage of Amoxicillin?

Amoxicillin dosing varies according to the type and severity of infection, patient age, body weight, and kidney function. The following recommendations are based on international guidelines including the BNF, EMA SmPC, and FDA-approved labeling. Always follow your doctor's specific instructions, as doses may be adjusted based on your individual clinical situation.

Adults and Adolescents (Over 40 kg Body Weight)

TDS = three times daily; BD = twice daily; PPI = proton pump inhibitor

Children (Under 40 kg Body Weight)

Pediatric dosing of amoxicillin is always based on body weight to ensure safe and effective therapy. Higher doses (80–90 mg/kg/day) are recommended by many international guidelines, including those from the American Academy of Pediatrics (AAP), for the treatment of acute otitis media and community-acquired pneumonia in children, particularly in regions with high rates of penicillin-resistant Streptococcus pneumoniae. Dispersible tablets approved by the WHO are available in resource-limited settings and can be dissolved in a small amount of water for easy administration to infants and young children.

Elderly Patients

No specific dose adjustment is routinely required for elderly patients with normal kidney function. However, older adults are more likely to have reduced renal function, which may require dose adjustment. Assess kidney function (estimated glomerular filtration rate, eGFR) before initiating treatment and adjust the dose accordingly if significant impairment is found. Elderly patients may also be more susceptible to certain adverse effects, including Clostridioides difficile-associated diarrhea.

Renal Impairment

Missed Dose

If you miss a dose of amoxicillin, take it as soon as you remember. However, if it is nearly time for your next scheduled dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. Maintaining consistent antibiotic levels in your blood is important for effective treatment, so try to take doses at evenly spaced intervals throughout the day. If you frequently forget doses, speak to your pharmacist about strategies such as setting alarms or using a pill organizer.

Overdose

Amoxicillin overdose is generally less dangerous than overdoses of many other medications, but it can still cause significant symptoms and complications. Reported symptoms of amoxicillin overdose include nausea, vomiting, diarrhea, and abdominal pain. In cases of significant overdose, crystalluria (formation of amoxicillin crystals in the urine) may occur, which can lead to renal impairment or failure. Neurological symptoms including confusion, agitation, and, very rarely, seizures may occur, particularly in patients with pre-existing renal impairment. Treatment is primarily supportive, with attention to maintaining adequate hydration and urine output. Hemodialysis can effectively remove amoxicillin from the bloodstream in severe cases.

What Are the Side Effects of Amoxicillin?

Like all antibiotics, amoxicillin can cause side effects, although not everyone experiences them. Most side effects are mild, transient, and resolve without specific treatment after the course is completed or the medication is stopped. The following section classifies potential side effects by frequency, based on data from regulatory authorities, clinical trials, and post-marketing surveillance.

It is important to distinguish between a true penicillin allergy and non-allergic side effects. A maculopapular (flat, widespread) rash that appears gradually over several days is usually non-allergic, particularly in the context of infectious mononucleosis or concurrent allopurinol use. In contrast, urticaria (hives), angioedema, or anaphylaxis developing within minutes to hours of taking amoxicillin suggests a true IgE-mediated allergic reaction and requires medical evaluation. If you are uncertain whether a reaction is allergic, consult your doctor, as this distinction has important implications for future antibiotic prescribing.

If you experience any adverse effects while taking amoxicillin, even if they are not listed here, you can report them directly to your national pharmacovigilance authority (e.g., the MHRA Yellow Card scheme in the UK, the FDA MedWatch program in the US, or the EMA EudraVigilance system in Europe). Reporting helps monitor the ongoing safety of medicines.

How Should You Store Amoxicillin?

Proper storage of amoxicillin is important to ensure the medication remains effective and safe throughout its use. Different formulations have different storage requirements:

• Capsules and tablets: Store at room temperature, below 25°C (77°F), in the original packaging. Protect from moisture and direct sunlight. Do not remove capsules from their blister pack until you are ready to take them.
• Dispersible tablets: Store in a cool, dry place below 25°C. Keep in the original container with the lid tightly closed. Dispersible tablets are particularly sensitive to moisture.
• Powder for oral suspension (before reconstitution): Store at room temperature, below 25°C. Keep the powder in the original sealed container until ready to prepare the suspension.
• Oral suspension (after reconstitution): Once prepared, the oral suspension must be stored in the refrigerator (2–8°C / 36–46°F). Shake well before each use. Use within 7 to 14 days depending on the manufacturer's instructions. Mark the date of preparation on the bottle and discard any remaining suspension after the recommended period.
• Child safety: Keep all medicines securely out of the sight and reach of children. Amoxicillin oral suspension is often flavored (strawberry, banana) and may be attractive to children. Store in a locked cabinet or out of reach.
• Disposal: Do not dispose of medications via household waste or down drains. Return unused or expired amoxicillin to your local pharmacy for safe disposal.

Do not use amoxicillin after the expiry date stated on the packaging. The expiry date refers to the last day of the stated month. If the capsules appear discolored, crumbled, or the oral suspension has changed color, developed an unusual odor, or contains visible particles, do not use it and consult your pharmacist.

What Does Amoxicillin Contain?

All amoxicillin formulations contain amoxicillin as the active pharmaceutical ingredient, typically in the form of amoxicillin trihydrate. The inactive ingredients (excipients) vary depending on the dosage form and manufacturer. These excipients are pharmacologically inactive and serve various functions including binding, filling, flavoring, coloring, and preserving the formulation.

Common Formulations

Capsules (250 mg, 500 mg): Typically contain magnesium stearate, titanium dioxide, gelatin (capsule shell), and may contain coloring agents such as iron oxide (yellow/red) and indigo carmine. Some capsule brands contain starch, talc, and microcrystalline cellulose.

Dispersible tablets (125 mg, 250 mg, 500 mg, 1 g): Contain excipients designed to allow rapid dissolution in water, including microcrystalline cellulose, crospovidone (disintegrant), magnesium stearate, and flavorings. Some brands may contain aspartame as a sweetener.

Powder for oral suspension (125 mg/5 ml, 250 mg/5 ml): Contains amoxicillin trihydrate along with excipients such as sodium benzoate (preservative), sodium citrate, sucrose or artificial sweeteners, xanthan gum (thickener), citric acid, and flavoring agents (commonly strawberry, banana, or bubble gum flavor). Some sugar-free formulations are available.

Standard tablets (500 mg, 750 mg, 1 g): Typically contain microcrystalline cellulose, magnesium stearate, sodium starch glycolate (disintegrant), and may have a film coating composed of hypromellose, titanium dioxide, and talc.

If you have known allergies to any excipients (such as gelatin, certain food colorings, or aspartame), always check the specific product's patient information leaflet or consult your pharmacist before taking any amoxicillin product. Different brands may contain different inactive ingredients.