Amoxicillin is a beta-lactam antibiotic drug used to treat a wide range of bacterial infections. It is among the most commonly used antibiotics in the primary care setting.
Amoxicillin begins working within a few hours after a dose, an important feature of the drug. You may start to feel better within 48 to 72 hours after starting the antibiotic. However, you should always finish taking all your prescribed medication, even if you feel better before it runs out.
This article will explain the factors determining how quickly amoxicillin begins to work inside the body, why that matters, and other information regarding the drug's specific uses, potential side effects, storage requirements, and more.
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How Long Does Amoxicillin Take to Start Working?
Amoxicillin begins working immediately after the first dose and reaches full effectiveness about an hour or two later.
However, when amoxicillin is given via an extended-release (ER, a form of administration where a drug is slowly released into the body over an extended time) tablet, the medicine may take longer to begin fully working, likely around three hours.
Amoxicillin becomes less effective after the first few hours. Approximately 60% of the amoxicillin dose is expelled from the body within six to eight hours.
Because of this, amoxicillin is prescribed in multiple daily doses. Continuous dosing at regular intervals maintains healthy levels of amoxicillin, allowing it to fight infection around the clock.
Amoxicillin does not relieve symptoms of infection immediately. Instead, it takes around 72 hours to relieve the symptoms in most people, though some people notice improvements within 24 to 48 hours.
Finish taking all doses of amoxicillin, even if you feel better before it runs out. If you stop taking amoxicillin too early, your infection won't be treated completely and the bacteria could become resistant to antibiotics.
A person’s antibiotic resistance may also affect how long amoxicillin takes to work. Taking antibiotics frequently can also cause bacteria in your body to develop antibiotic resistance.
Always inform your healthcare provider if your antibiotics do not work as expected.
Severe bacterial infections can pose a grave risk to a person's life. Therefore, the rate at which medication stops an infection is crucial to ensuring a complete recovery with no long-term, lasting effects.
Taking Amoxicillin for a Sinus Infection: What to Expect
Amoxicillin Dosing
Amoxicillin is available in different oral formulations and strengths, including a capsule, a tablet, a chewable tablet, and a liquid suspension.
It is prescribed every eight or 12 hours at equal intervals with or without food.
The table below lists common forms of amoxicillin and their respective strengths:
| Common Dosage Forms/Strengths | |
|---|---|
| Dosage Form: | Strength: |
| • Amoxicillin/Amoxil oral tablet (chewable) | • 125 milligrams (mg) • 250 mg |
| • Amoxicillin/Amoxil oral tablet | • 500 mg • 875 mg |
| • Amoxicillin/Amoxil/Moxilin/Sumox/Trimox oral capsule | • 250 mg • 500 mg |
| • Amoxicillin/Amoxil/Moxilin/Sumox/Trimox powder | • 5 mL (milliliters) • 125 mg • 200 mg • 250 mg • 400 mg |
Shake the liquid suspension well before using it every time. Do not chew, crush or break amoxicillin if taking the ER tablets.
If you have phenylketonuria (PKU, an inherited condition that is caused by eating certain foods and artificial sweeteners leading to brain damage), ask your healthcare provider before taking amoxicillin chewable tablets.
Dosing Regimens
The table below outlines typical dosing regimens associated with the use of amoxicillin, concerning a person's age and body weight:
| Common Dosing Regimens/Schedules | ||
|---|---|---|
| Type of Bacterial Infection: | Age and Body Weight: | Maximum Daily Dose: |
| • Bacterial infections | • Adults, teenagers, and children weighing 88 lbs or more | • 250 to 500 mg every eight hours or 500 to 875 mg every 12 hours |
| • Bacterial infections | • Children and infants older than 3 months weighing less than 88 lbs | • Standard dose: 20 to 40 mg per kilogram (kg) of body weight per day, divided and given every eight hours, or 25 to 45 mg per kg of body weight per day, divided and given every 12 hours |
| • Bacterial infections | • Infants 3 months and younger | • Standard dose: 30 mg per kg of body weight per day, divided and given every 12 hours |
| • H. pylori infection | • Adults | • Dual therapy: 1000 mg of amoxicillin and 30 mg of lansoprazole, three times daily for 14 days • Triple therapy: 1000 mg of amoxicillin, 500 mg of clarithromycin, and 30 mg of lansoprazole, twice a day for 14 days |
| • H. pylori infection | • Children | • The healthcare provider will determine the use and dose |
The duration of your treatment and dose adjustment will depend on the type and severity of the infection you have.
Your healthcare provider may alter the dose for people with severe impaired renal (kidney) function to avoid adverse effects.
What to Do If You Miss a Dose
If you miss a dose of your medication, take it as soon as you remember. If it's almost time for the next dose, skip the missed dose and continue taking it on your regular schedule. Do not take two doses at once.
How Safe Is Amoxicillin?
Amoxicillin has been deemed relatively safe and effective when prescribed by your healthcare provider.
However, it may cause some side effects of varying severity.
Common Side Effects
Some of the more common, less severe side effects associated with the use of amoxicillin include:
- Changes in taste
- Diarrhea
- Headache
- Nausea
- Vomiting
If you experience any of these side effects, monitor your symptoms carefully. If your symptoms worsen, contact your healthcare provider immediately.
Severe Side Effects
More rare, severe side effects associated with the use of amoxicillin include:
- Hypersensitivity reaction
- Severe diarrhea
- Liver problems
If you experience severe side effects, immediately contact your healthcare provider. And in the case of a medical emergency, directly call 911.
Warnings and Precautions
The use of amoxicillin in some cases may cause some severe reactions and may need medical attention.
Some of these reactions include:
- Clostridioides difficile-associated diarrhea (CDAD): CDAD has been reported when using amoxicillin and may range in severity from mild diarrhea to fatal colitis (inflammation of the inner lining of the colon). Treatment with antibacterial agents changes the normal flora of the colon (bacteria present in the colon), causing overgrowth of C. difficile.
- Development of drug-resistant bacteria: Amoxicillin may encounter drug resistance if prescribed without a proven or suspected bacterial infection. In such cases, the drug is unlikely to benefit a person in the future.
- Anaphylactic reactions: Severehypersensitivity (anaphylactic) reactions have been reported in people on penicillin therapy, including amoxicillin. Anaphylaxis is a serious, potentially life-threatening reaction that can cause hives, swelling, and trouble breathing. Call 911 if you experience any signs of anaphylaxis.
Call your healthcare provider immediately if you experience any reactions to amoxicillin.
Who Shouldn't Take Amoxicillin?
Amoxicillin is discouraged in people with the following conditions:
- Hypersensitivity to amoxicillin or other beta-lactam drugs, including cephalosporins and penicillins. It may cause severe hypersensitivity reactions, such as anaphylaxis or Stevens-Johnson syndrome (SJS).
- Mononucleosis (an infection caused by a herpes virus called Epstein-Barr). Taking amoxicillin may cause an erythematous skin rash (a skin reaction caused by medicine).
- Phenylketonuria (PKU, an inherited condition in which certain foods and artificial sweeteners could result in brain damage and severe intellectual disability). Chewable amoxicillin tablets are sweetened with aspartame, which forms phenylalanine that can aggravate the condition.
- Pregnancy. Amoxicillin is safe for pregnant people, but it is advisable to ask your healthcare provider before taking it.
- Breastfeeding. No studies have determined the safety of amoxicillin in breastfeeding people. The benefit-to-risk ratio should evaluate the use of amoxicillin in nursing people.
Amoxicillin Interactions
Amoxicillin may interact with the following drugs:
Probalan (probenecid): It decreases the renal tubular secretion (one of several steps in filtering blood to produce urine) of amoxicillin. The simultaneous use of amoxicillin and probenecid may increase the blood levels of amoxicillin.
Anticoagulant agents: The simultaneous use of amoxicillin with oral anticoagulant (blood thinning) drugs, such as Jantoven (warfarin), may prolong blood clotting time. If you're currently taking a blood thinning medication, your healthcare provider may need to change the dose of your drugs.
Zyloprim (allopurinol): The simultaneous administration of Zyloprim (allopurinol) and amoxicillin increases the number of rashes in people receiving these drugs compared to people receiving amoxicillin alone.
Oral contraceptives: Amoxicillin may affect the bacteria in your intestines, leading to lower estrogen hormone reabsorption and reduced efficacy of combined oral hormonal (estrogen/progesterone) contraceptives.
Antibacterial drugs: The medicines belonging to different classes of antibiotic drugs, such as chloramphenicol, macrolides, sulfonamides, and tetracyclines, may interfere with the bactericidal effects of amoxicillin.
Some of these drugs include:
- Cefaclor
- Cefadroxil
- Ceftriaxone
- Cephalexin
Tell your healthcare provider about all the drugs you take before starting treatment with amoxicillin to avoid any adverse drug interaction.
Summary
Amoxicillin is a beta-lactam antibiotic that treats various skin, respiratory tract, urinary tract, ear, nose, and throat infections caused by bacteria.
Amoxicillin starts working within a few hours of taking it. You may begin to feel better within two to three days of starting amoxicillin. However, you should always finish taking your medication to ensure you treat the infection completely. If you stop too early, you may increase the risk of getting an infection later and may cause bacterial resistance.
Amoxicillin is safe for adults, teenagers, children under 12, and infants 3 months and older when used as prescribed by your healthcare provider.
Frequently Asked Questions
How can I safely store amoxicillin?
Store amoxicillin tablets and capsules at room temperature. Keep the medicines away from excess heat and moisture. Do not store it in the bathroom.
Store the liquid dosage form of amoxicillin in the refrigerator, but do not freeze. Dispose of any reconstituted and unused liquid medication after 14 days.
Keep all medication out of sight and reach of children and pets. Always keep the safety locks.
Dispose of unwanted medications. Ask your pharmacist or local garbage/recycling department about medicine take-back programs in your community.
Can I drink or smoke while taking amoxicillin?
Smoking and drinking do not directly affect the effectiveness of amoxicillin. It is better to do it in moderation as they harm overall physical and mental health.
According to a study, tobacco use during an infection treated with antibiotics may require an increased prescription.
It may also cause antibiotic resistance development (the ability of bacteria to resist antibiotics).
What common conditions are not treatable with antibiotics?
Antibiotics are ineffective for viral infections, such as colds and runny noses, sore throats (except strep throat), flu, and chest colds (bronchitis).
Taking antibiotics when unnecessary can cause side effects and may develop bacterial resistance.
6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
DailyMed. Label: amoxicillin- amoxicillin capsule.
Prescriber's Digital Reference. Amoxicillin - drug summary.
MedlinePlus. Amoxicillin.
U.S Food and Drug Administration. Amoxil (amoxicillin) capsules, tablets, or powder for oral suspension). label.
Steinberg MB, Akincigil A, Kim EJ, Shallis R, Delnevo CD. Tobacco smoking as a risk factor for increased antibiotic prescription. Am J Prev Med. 2016;50(6):692-698. doi:10.1016/j.amepre.2015.11.009.
Centers for Disease Control and Prevention. Antibiotic use questions and answers.
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By Ayesha Gulzar, PharmD
Ayesha Gulzar is a clinical pharmacist interested in medical research, pharmacy practice, and medication therapy management. Dr. Gulzar has been working in medical communications, writing medical and clinical research for patients and health professionals in the United Kingdom.
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