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What Is Amoxicillin and How Does It Work?

Brand Names: Amoxil, Moxatag, Trimox

Generic Name: Amoxicillin

Drug Class: Penicillins

What Is Amoxicillin and How Does It Work?

Amoxicillin is a prescription antibiotic used to treat a wide variety of bacterial infections. This medication is a penicillin-type antibiotic that works by stopping the growth of bacteria.

  • Amoxicillin treats only bacterial infections and is not effective for viral infections (e.g., common cold, flu). Unnecessary use or misuse of any antibiotic can lead to decreased effectiveness.
  • Amoxicillin is also used with other medications to treat stomach or intestinal ulcers caused by the bacteria H. pylori and to prevent the ulcers from returning.
  • Amoxicillin is available under the brand names Amoxil, Moxatag, and Trimox.

Dosages of Amoxicillin

Adult and Pediatric Dosages

Oral Solution

  • 50 mg/5 mL
  • 125 mg/5 mL
  • 200 mg/5 mL
  • 250 mg/5 mL
  • 400 mg/5 mL

Capsule

  • 250 mg
  • 500 mg

Tablet

  • 500 mg
  • 875 mg

Chewable Tablet

  • 125 mg
  • 250 mg

Extended-Release (Moxatag)

  • 775 mg

Dosage Considerations – Should Be Given as Follows:

Adult Dosage Considerations

Ear, Nose, and Throat Infections

Mild to moderate infections:

  • 500 mg orally every 12 hours or 250 mg orally every 8 hours for 10–14 days

Severe infections:

  • 875 mg orally every 12 hours or 500 mg orally every 8 hours for 10–14 days

Tonsillitis/Pharyngitis

  • Moxatag: 775 mg orally once daily for 10 days, taken within 1 hour after a meal

Genitourinary Tract Infections

Mild to moderate infections:

  • 500 mg orally every 12 hours or 250 mg orally every 8 hours

Severe infections:

  • 875 mg orally every 12 hours or 500 mg orally every 8 hours

Spectrum of action:

  • E. coli, P. mirabilis, or E. faecalis

Skin and Skin Structure Infections

Mild to moderate infections:

  • 500 mg orally every 12 hours or 250 mg orally every 8 hours

Severe infections:

  • 875 mg orally every 12 hours or 500 mg orally every 8 hours

Lower Respiratory Tract Infections

  • 875 mg orally every 12 hours or 500 mg orally every 8 hours for 10–14 days

Helicobacter pylori Infection

H. pylori infection with an active or 1-year history of duodenal ulcer:

Triple therapy:

Dual therapy:

  • 1 g orally every 8 hours for 14 days with lansoprazole (30 mg) in patients intolerant of or resistant to clarithromycin

Anthrax (Off-Label)

Post-exposure inhalational prophylaxis:

  • 500 mg orally every 8 hours

Infective Endocarditis Prophylaxis

  • 2 g orally 30–60 minutes before procedure

Dosing considerations: AHA guidelines recommend prophylaxis only in high-risk patients undergoing invasive procedures with a history of cardiac conditions that predispose them to infection.

Lyme Disease (Off-Label)

Chronic migrating rash and other symptoms of early dissemination:

  • 500 mg orally every 8 hours (depending on patient size) for 3–4 weeks

Chlamydial Infection in Pregnant Women (Off-Label)

  • First trimester: 500 mg orally every 8 hours for 7 days

Dosing considerations:

  • First trimester: Test to document chlamydial eradication and retest for infection 3 months after treatment.
  • Second or third trimester: Test to document chlamydial eradication.

Limitation of Use

  • For use when susceptibility test results show susceptibility to amoxicillin, indicating no beta-lactamase production.

Administration

  • Take without regard to meals.

Dosing Modifications

  • Renal impairment: Patients with impaired renal function generally do not require dose reduction unless the impairment is severe; do not administer extended-release product in patients with creatinine clearance less than 30 mL/min.
  • GFR less than 30 mL/min: Do not administer 875 mg (immediate-release) or 775 mg (extended-release).
  • GFR 10–30 mL/min: 250–500 mg every 12 hours, depending on infection severity.
  • GFR less than 10 mL/min: 250–500 mg every 24 hours, depending on infection severity.
  • Hemodialysis patients: 250–500 mg every 24 hours, depending on infection severity; administer an additional dose during and at the completion of dialysis. Do not administer extended-release product or 875 mg immediate-release.

Pediatric Dosage Considerations

Ear, Nose, and Throat Infections

Mild to moderate infections:

  • Under 3 months: 30 mg/kg/day orally divided every 12 hours for 48–72 hours; for less than 10 days for S. pyogenes infections.
  • Older than 3 months and under 40 kg: 25 mg/kg/day orally divided every 12 hours or 20 mg/kg/day orally divided every 8 hours.
  • Over 40 kg: 500 mg orally every 12 hours or 250 mg orally every 8 hours for 10–14 days.

Severe infections:

  • Under 3 months: 30 mg/kg/day orally divided every 12 hours for 48–72 hours; for less than 10 days for S. pyogenes infections.
  • Older than 3 months and under 40 kg: 45 mg/kg/day orally divided every 12 hours or 40 mg/kg/day orally divided every 8 hours.
  • Over 40 kg: 875 mg orally every 12 hours or 500 mg orally every 8 hours for 10–14 days.

Tonsillitis/Streptococcal Pharyngitis

  • Under 3 months: Safety and efficacy not established.
  • Older than 3 months: 50 mg/kg/day orally every day for 10 days, not to exceed 1 g/day, or 25 mg/kg/day orally twice daily for 10 days, not to exceed 500 mg/dose.
  • Older than 12 years: 775 mg (Moxatag) orally once daily for 10 days, taken within 1 hour after a meal (swallow tablet whole; do not crush or chew).

Acute Otitis Media

  • Older than 3 months and under 40 kg: 80–90 mg/kg/day orally divided every 8–12 hours.
  • Over 40 kg: 500 mg orally every 12 hours or 250 mg orally every 8 hours for 10–14 days.

Lower Respiratory Tract Infections

Mild, moderate, or severe infections:

  • Under 3 months: 30 mg/kg/day or more orally divided every 12 hours for 48–72 hours; for less than 10 days for S. pyogenes infections.
  • Older than 3 months and under 40 kg: 45 mg/kg/day orally divided every 12 hours or 40 mg/kg/day orally divided every 8 hours.
  • Over 40 kg: 875 mg orally every 12 hours or 500 mg orally every 8 hours for 10–14 days.

Community-Acquired Pneumonia (Off-Label)

Since M. pneumoniae is the primary pathogen causing pneumonia in patients 5–15 years old, a macrolide antibiotic may be the first-choice treatment.

  • Under 3 months: Safety and efficacy not established.
  • Older than 3 months:
  • Empiric treatment: 90 mg/kg/day orally divided every 12 hours for 10 days; not to exceed 4,000 mg/day.
  • Group A Streptococcus: 50–75 mg/kg/day orally divided every 12 hours for 10 days; not to exceed 4,000 mg/day.
  • H. influenzae: 75–100 mg/kg/day orally divided every 8 hours for 10 days; not to exceed 4,000 mg/day.
  • S. pneumoniae (mild infection or step-down therapy or when MICs to penicillin are 2.0 mcg/mL or higher): 90 mg/kg/day orally divided every 12 hours or 45 mg/kg/day divided every 8 hours for 10 days; not to exceed 4,000 mg/day.

Anthrax (Off-Label)

Post-exposure inhalational prophylaxis:

  • Under 40 kg: 15 mg/kg orally every 8 hours; minimum recommended dose, not to exceed 45 mg/kg/day or given less than every 8 hours.
  • Over 40 kg: 500 mg orally every 8 hours.
  • 80 mg/kg/day orally divided every 8 hours for 4 weeks (with simultaneous vaccine) or for 60 days (without vaccine).

Infective Endocarditis Prophylaxis (Off-Label)

  • 50 mg/kg orally 30–60 minutes before procedure.

Dosing considerations: AHA guidelines recommend prophylaxis only in high-risk patients undergoing invasive procedures with a history of cardiac conditions that predispose them to infection.

Lyme Disease (Off-Label)

Chronic migrating rash and other symptoms of early dissemination:

  • Under 3 months: Safety and efficacy not established.
  • Over 3 months and under 40 kg: 25–50 mg/kg/day orally divided every 8 hours; not to exceed 500 mg/dose.

Administration

  • Take without regard to meals.
  • For oral suspension: Tap bottle until all powder flows freely; add approximately one-third of the total amount of water for reconstitution and shake vigorously to wet powder; add remainder of water and shake vigorously again.
  • After reconstitution, place the required amount of suspension directly on the child’s tongue for swallowing. If the taste is unacceptable, add the suspension to formula, milk, fruit juice, water, ginger ale, or other cold drinks; preparation must be taken immediately.
  • Shake the suspension well before using; discard any unused portion after 14 days.

What Are Side Effects Associated with Using Amoxicillin?

Common Side Effects of Amoxicillin:

Post-Marketing Side Effects of Amoxicillin:

This is not a complete list of possible side effects. Consult your physician for additional information about side effects.

What Other Drugs Interact with Amoxicillin?

If your doctor has prescribed this medication for diabetes, your doctor or pharmacist may already be aware of possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine without consulting your doctor, health care provider, or pharmacist.

Severe Interactions: None

Moderate Interactions: Amoxicillin has moderate interactions with at least 27 different drugs.

Mild Interactions:

This is not a complete list of possible interactions. Inform your doctor or pharmacist of all products you use. Keep a list of all your medications and share it with your doctor and pharmacist. Consult your physician if you have health questions or concerns.

Warnings and Precautions for Amoxicillin

Warnings:

  • Documented hypersensitivity to penicillins, cephalosporins, or imipenem.
  • This medication contains amoxicillin. Do not take Amoxil, Moxatag, or Trimox if you are allergic to amoxicillin or any ingredients contained in this drug.
  • Keep out of reach of children. In case of overdose, seek medical help or contact a Poison Control Center immediately.

Contraindications: None

Effects of Drug Abuse: None

Short-Term Effects: See "What Are Side Effects Associated with Using Amoxicillin?"

Long-Term Effects: See "What Are Side Effects Associated with Using Amoxicillin?"

Cautions:

  • Severe allergic reactions have been reported rarely but are more likely following parenteral therapy with penicillins.
  • Clostridium difficile-associated diarrhea (CDAD) has been reported with nearly all antibacterial agents; severity may range from mild diarrhea to fatal colitis. CDAD may occur over 2 months after discontinuation of therapy. If suspected or confirmed, discontinue immediately and begin appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation.
  • Do not administer in patients with infectious mononucleosis due to the risk of developing a red skin rash.
  • Do not administer to patients without a proven or suspected bacterial infection, as this may lead to the development of drug-resistant bacteria.
  • Superinfections with bacterial or fungal pathogens may occur during therapy. If suspected, discontinue immediately and begin appropriate treatment.
  • Chewable tablets contain aspartame, which contains phenylalanine.
  • Use caution in patients with allergies to cephalosporins or carbapenems.
  • Endocarditis prophylaxis: Use only for high-risk patients, per recent AHA guidelines.
  • High doses may cause false urine glucose test results with some methods.

Pregnancy and Lactation:

  • Use of amoxicillin during pregnancy may be acceptable. Animal studies show no risk, or human studies show no risk despite minor risks in animal studies.
  • Amoxicillin is excreted in breast milk. Use with caution during lactation. Consult your doctor before breastfeeding.
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