How Quickly Does Amoxicillin Work?

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.

Specifically, amoxicillin is an amino-penicillin (a group of antibiotics in the penicillin family) that contains what is known as an extra "amino group" (a nitrogen atom bonded to two hydrogen atoms) used to fight antimicrobial resistance.

Amoxicillin is available in the United States under many brand names, such as Amoxil, Larotid, and Talicia (a combination of amoxicillin, omeprazole, and rifabutin).

Amoxicillin is an effective antibiotic that works within a few hours after a dose, an important feature of the drug. Nonetheless, why is the rate at which amoxicillin starts working important for treating bacterial infections?

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.

What Is Amoxicillin?

Amoxicillin is an antibiotic with many uses to treat infections caused by different bacteria.

Approved Uses

Amoxicillin is Food and Drug Administration (FDA)-approved to treat the following:

• Infections of the ear, nose, and throat 
• Urinary tract infections (UTIs)
• Infections of the skin and skin structure
• Infections of the lower respiratory tract
• Dual therapy: Amoxicillin/lansoprazole for treating people with Helicobacter pylori (H. pylori) infection and peptic ulcer disease
• Triple therapy: Amoxicillin/clarithromycin/lansoprazole for H. pylori bacteria treatment to reduce the risk of peptic ulcer disease

Amoxicillin is also used off-label (a non-FDA-approved use) to treat Lyme disease and to treat and prevent anthrax infection of the skin.

How It Works

Amoxicillin belongs to the class of beta-lactam antimicrobials (enzymes made by bacteria).

It attaches to penicillin-binding proteins that hinder transpeptidation (moving peptic residue throughout the body) to fight bacterial infections.

Through this process, amoxicillin initiates the breakdown of the bacterial cell wall, subsequently destroying the bacterial cell. This is known as bactericidal killing.

Amoxicillin is often used with other beta-lactamase inhibitors, such as clavulanic or sulbactam. However, these drugs do not have bactericidal activity.

Instead, they may broaden amoxicillin's ability to fight infections that produce the beta-lactamase enzyme; this is helpful, as beta-lactamase enzyme infections are otherwise immune to the effects of penicillin, for example.

Amoxicillin is approved for use in adults, teenagers, children under 12, and infants 3 months and older.

Furthermore, it's important to know that a person's weight may affect whether or not a healthcare provider will prescribe amoxicillin, as amoxicillin dosage is determined by body weight.

How Quickly Does Amoxicillin Start to Work?

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.

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.

A person’s antibiotic resistance (taking antibiotics frequently may cause bacteria in your body to develop resistance to the medications) may also affect how long amoxicillin takes to work.

Always inform your healthcare provider if your antibiotics do not work as expected.

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:

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:

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.

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 conditions may cause some severe reactions and may need medical attention.

Some of these conditions include:

Anaphylactic reactions: Severe hypersensitivity (anaphylactic) reactions have been reported in people on penicillin therapy, including amoxicillin. If an anaphylactic reaction occurs, amoxicillin should be discontinued.

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.

People with mononucleosis: A high percentage of people with mononucleosis (an infection caused by a herpes virus called Epstein-Barr) taking amoxicillin may develop an erythematous skin rash (a skin reaction caused by medicine).

Therefore, amoxicillin should not be administered to people with mononucleosis.

Phenylketonuria: If you have phenylketonuria (PKU, an inherited condition caused by eating certain foods and artificial sweeteners resulting in brain damage and can cause severe intellectual disability).

Chewable amoxicillin tablets are sweetened with aspartame, which forms phenylalanine which may aggravate the condition.

Call your healthcare provider immediately if you experience any of these symptoms.

Who Shouldn't Take Amoxicillin?

Amoxicillin is discouraged in people with the following conditions:

• Hypersensitive 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).
• Amoxicillin is safe for pregnant people, but it is advisable to ask your healthcare provider before taking it.
• 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.m

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. It is also available in multiple combination drugs to treat stomach ulcers.

Amoxicillin belongs to penicillin-like antibiotics that work by stopping the growth of bacteria. Amoxicillin will not work for colds, flu, and other viral infections.

Taking antibiotics when not needed can increases the risk of getting an infection later and may cause bacterial resistance. 

It works quickly after an initial dose and helps eradicate the infection. It is given in repeated doses and helps to alleviate the symptoms within two to three days.

Amoxicillin is safe for adults, teenagers, children under 12, and infants 3 months and older when used as prescribed by your healthcare provider.