Amoxicillin and Flagyl: Uses, Dosages, Side Effects, More

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Flagyl is known by its generic name, Metronidazole. It is an antibiotic medication that treats bacterial infections in various body parts. Similarly, Amoxicillin is an antibiotic in the penicillin class that treats infections caused by bacteria. This article discusses Amoxicillin and Flagyl, their similarities, differences, uses, and more.

What is Flagyl?

Flagyl is a potent antibiotic medication used to treat infections caused by bacteria or parasites. Flagyl treats bacterial infections in different parts of the body, including the vagina, stomach, liver, skin, joints, brain, spinal cord, lungs, heart, and bloodstream. Known as

Metronidazole also treats trichomoniasis, a sexually transmitted infection caused by a parasite. Both sexual partners are usually treated simultaneously, even if one partner is asymptomatic.

Flagyl is in the nitroimidazole antibiotic class and is highly effective against bacteria in anaerobic environments.

What is Amoxicillin?

Amoxicillin is in the class of antibiotics called penicillin. This medication is used to combat various bacterial diseases, including bronchitis, tonsilitis, pneumonia, and urinary tract infections. Amoxicillin also treats ear, nose, throat, and skin infections caused by bacteria or parasitic organisms.

While Amoxicillin is highly effective against bacterial infections, it does not treat conditions like the flu or the common cold. This medication is a prescription drug, so it’s essential to inform your doctor before using any antibiotic.

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Amoxicillin and Flagyl: What are their uses?

Amoxicillin and Flagyl are antibiotics in the penicillin and nitroimidazole classes, respectively. Both drugs are prescribed to treat various bacterial infections and have varying levels of effectiveness depending on the bacteria causing the infection.

For instance, Metronidazole is prescribed to treat bacterial infections in the liver, stomach, bloodstream, skin, joints, brain, spinal cord, lungs, and heart. Flagyl is not typically recommended to treat urinary tract infections or viral infections like the common cold and flu.

Flagyl comes in different forms, including oral, suppository, liquid, gel, and tablet or capsule. Suppositories are capsules that can be inserted into the vagina, usually with an applicator provided with the drug packaging.

Amoxicillin is a potent antibiotic in the penicillin class that treats many bacterial infections, including tonsilitis, bronchitis, pneumonia, urinary tract infections, and nose, throat, ear, and skin infections.

Amoxicillin is combined with other antibiotics like clarithromycin to cure stomach ulcers caused by Helicobacter pylori bacteria. Sometimes, doctors recommend a stomach acid reducer called lansoprazole (Prevacid) with this combination.

Flagyl can treat the following conditions:

  • BV
  • Trichomoniasis
  • Pelvic inflammatory disease
  • Amebiasis
  • Clostridium difficile
  • Anaerobic bacterial infections in the stomach, liver, skin, joints, brain, spinal cord, lungs, heart, and bloodstream

Warnings before using Flagyl

Flagyl is a potent antibiotic that rarely causes severe side effects or complications. However, there are specific warnings and precautions to be aware of before using this antibiotic medication.

Flagyl is a prescription medication. This means you must speak to your doctor before using Flagyl in any form. Do not use Flagyl to treat any condition your healthcare professional has not examined.

Your healthcare expert will advise you to avoid alcohol while taking Metronidazole altogether. In addition, you should stay away from drinking for a further 3 days after you complete your dosage.

Flagyl can cause adverse reactions and neurological symptoms such as seizures, headaches, visual changes, weakness, numbness, or tingling.

If you experience these symptoms, stop using Flagyl immediately. Flagyl does not treat the common cold or flu. Flagyl (Metronidazole) is not effective against infections caused by viruses.

According to some studies, the use of Flagyl in some animals seemed to cause certain types of cancer. However, it is unclear if these occur in human patients.


Do not use Flagyl if you are allergic to metronidazole, secnidazole, or tinidazole.

It may harm an unborn baby, so avoid this drug during the first trimester of pregnancy.

Metronidazole is not approved for treating vaginal infections in girls who have not started seeing their periods.

Inform your doctor about any liver disease, kidney disease, heart rhythm disorder, or other health conditions before taking Flagyl.

Remember to consult your healthcare expert before using any medication, and follow their guidance closely.

Warnings before using Amoxicillin

Amoxicillin is a prescription antibiotic, so you must discuss this with a qualified healthcare expert before using this medication for your condition. In addition, discuss your medical history with your healthcare provider before using this medication.

Your medical expert will advise you to stay away from Amoxicillin if you’re allergic to Amoxicillin or any other penicillin antibiotics (such as ampicillin, dicloxacillin, oxacillin, penicillin, or ticarcillin).

Additionally, inform your doctor if you are allergic to cephalosporins (such as Omnicef, Cefzil, Ceftin, Keflex, and others).

Discuss your condition with your doctor if you have kidney disease, mononucleosis (mono), diarrhea caused by antibiotics, or food and drug allergies.

Amoxicillin can cause birth control pills to become less effective. You should consider talking to your doctor about non-hormone methods of birth control (such as a condom, diaphragm, or spermicide) while taking this medicine.

You must take Amoxicillin for the full prescribed length, even if your symptoms improve, before completely clearing the infection.

Like some antibiotics, Amoxicillin can cause severe diarrhea. If you experience diarrhea while taking antibiotics, notify your doctor.

Antibiotic side effects

It’s not unusual for antibiotics to cause side effects with varying degrees of severity in patients. For instance, Flagyl can cause some side effects to occur, including nausea, dizziness, and vomiting.

Flagyl side effects

The following are common side effects of Flagyl:

  • Nausea
  • Dizziness
  • Headache
  • Stomach upset
  • Vomiting
  • Loss of appetite
  • Diarrhea
  • Constipation
  • Metallic taste in your mouth
  • Darkening of urine

Severe side effects include the following:

  • Agitation
  • Blurred vision
  • Confusion
  • Depression
  • Seizures
  • Unsteadiness
  • Fever
  • Eye pain
  • Hearing or seeing things that are not there
  • Slurred speech
  • Unusual tiredness or weakness
  • Vomiting
  • Weakness in the arms, hands, legs, or feet
  • Loss of voice
  • Blood in the urine
  • Irregular heartbeat
  • Skin rash or hives
  • Stomach and back pain (severe)
  • Yellowing of eyes or skin

The following are rare side effects of Flagyl:

  • Bleeding gums
  • Chest pain
  • Fast heartbeat
  • Indigestion
  • Loss of appetite
  • Painful or difficult urination
  • Sore throat
  • Swollen glands
  • Joint or muscle pain
  • Red skin lesions
  • Purple center on the skin

7 common side effects of amoxicillin

Amoxicillin side effects

The following are common side effects of Amoxicillin:

  • Nausea
  • Vomiting
  • Diarrhea
  • Stomach upset
  • Headache
  • Skin rash
  • Abnormal taste sensation
  • Vaginal yeast infection

Serious Side Effects:

  • Allergic reactions
  • Liver or kidney problems
  • Blood disorders
  • Seizures
  • Chest pain
  • Irregular heartbeat
  • Difficulty with swallowing
  • Joint or muscle pain
  • Unusual weight loss
  • Changes in behavior
  • Sleeplessness
  • White patches in the mouth or throat
  • Agitation
  • Dizziness
  • Trouble sleeping
  • Discoloration of teeth
  • Convulsions

Less common side effects:

  • Bad, unusual, or unpleasant taste
  • White patches with diaper rash
  • Black, hairy tongue
  • Changes in behavior
  • Confusion
  • Sleeplessness
  • Trouble sleeping

Read also: Flagyl Food Interactions and What to Avoid

Frequently Asked Questions

Amoxicillin and Flagyl (Metronidazole) can be taken together under certain circumstances. However, it’s essential to consult your healthcare expert before combining these medications. Here are some considerations:

Infection Type: Both drugs treat different types of infections. Amoxicillin is a broad-spectrum antibiotic effective against various bacteria, while Flagyl is primarily used for anaerobic bacterial infections and certain parasitic infections.

Interaction: When taken together, there is a potential for drug interactions. Flagyl can increase the blood levels of Amoxicillin, leading to a higher probability of adverse reactions. Your doctor will assess the benefits versus risks and adjust the dosages if needed.

Side Effects: Combining these medications may increase the likelihood of side effects. These adverse reactions include nausea, vomiting, and diarrhea. Severe side effects are rare.

Medical History: Inform your doctor about any existing medical conditions, allergies, or other medications you’re taking. Certain conditions (such as liver disease) may affect how your body processes these drugs.

Monitoring: Regular monitoring by your healthcare expert provider is crucial. They will assess your response to treatment and adjust dosages if necessary.

Flagyl (Metronidazole) typically starts to work within 1 to 2 hours after you take it. It is quickly absorbed, and its maximum concentration is reached between 20 minutes to 3 hours.

However, it may take a couple of days before you notice an improvement in your symptoms or feel better. The usual duration of therapy with Flagyl varies depending on the specific condition being treated.

Anaerobic Bacterial Infections: Loading dose of 15 mg/kg IV, followed by 7.5 mg/kg PO/IV every 6 hours for 7-10 days (or 2-3 weeks if severe).

Bacterial Vaginosis:

Nonpregnant women: 500 mg PO BID for 7 days, or 2 g PO qDay as a single dose, or 750 mg extended-release PO qDay for 7 days.

Pregnant women: 500 mg PO BID for 7 days, or 250 mg PO TID for 7 days.

Trichomoniasis: 250 mg PO q8hr for 7 days, or 2 g PO qDay as a single dose, or 1g PO q12hr for 2 doses.


Acute intestinal amebiasis (acute amebic dysentery): 750 mg PO TID for 5-10 days.

Amebic liver abscess: 500-750 mg PO TID for 5-10 days.

Amoxicillin, a fast-acting antibiotic, begins to work within one hour after ingestion. Its strength is bolstered by the consistent use of multiple doses per day.

Most notably, Amoxicillin often alleviates symptoms in less than 72 hours and remains active in your system for 24 hours1. The duration of action depends on the specific type of Amoxicillin and the infection being treated.

Mechanism of Action: It inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins. This action prevents cell wall biosynthesis, leading to bacterial lysis.


Immediate-release: Approximately 61.3 minutes.

Extended-release: Around 90 minutes.

Distribution: It readily enters various tissues, including the liver, lungs, prostate, muscle, middle ear effusions, and bone.

Excretion: Primarily through urine (about 60% as unchanged drug).

Flagyl is an antibiotic that can effectively treat infections caused by bacterial organisms, including dental infections. Antibiotics are not the first-line treatment for dental infections but may be necessary in certain situations.

However, Amoxicillin is recommended for treating dental infections caused by bacteria. It’s often one of the first antibiotics advised by dentists.

Amoxicillin works relatively quickly to treat tooth infections and alleviate discomfort. If you follow your healthcare provider’s advice, it should take effect within a few days.

However, even if the pain and swelling subside, completing the entire course of antibiotics as your dentist prescribes is crucial.

Flagyl (Metronidazole) is generally considered safe during pregnancy, especially when medically necessary. It would help if you spoke to your healthcare expert before using Flagyl during pregnancy to avoid unwanted complications.

Amoxicillin is considered safe for use during pregnancy. The U.S. Food and Drug Administration (FDA) classifies Amoxicillin as a pregnancy category B drug, indicating its safety during pregnancy.

Amoxicillin works against a wide range of bacteria, including both Gram-positive and Gram-negative strains.

It is commonly prescribed for ear infections, sinusitis, bronchitis, urinary tract infections, and skin infections. While potent against many bacteria, it is not necessarily the strongest antibiotic available.

The term “strong” can be subjective and depends on the infection and the susceptibility of the bacteria causing it.

Flagyl is considered a broad-spectrum antibiotic. It is effective against a wide range of bacteria and certain parasites. Flagyl is used to treat infections in various parts of the body, including the vagina, stomach, liver, skin, joints, brain, spinal cord, lungs, heart, and bloodstream.

It is also used to treat trichomoniasis. Following statistical analysis and clinical trials, Flagyl is considered a potent antibiotic against bacteria in anaerobic environments.

The content on Doctor Alexa’s blog is reviewed by Advanced practice registered nurses or pharmacist and is intended for educational purposes only. This information should not be relied upon as professional medical counsel. Be sure to always consult with your physician about the dangers and benefits of any medication, treatment or procedure.

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