Metronidazole and amoxicillin

Can You Take Metronidazole and Amoxicillin Together?

By Nicholas White

Treatment of various infectious diseases is nowadays an easily solved issue. After the introduction of the first antibiotic penicillin, numerous synthetic analogs were created. They are active against different microorganisms and can be utilized in combinations. One such possible option is amoxicillin and metronidazole combination. How do they work and why are they useful? Let’s unveil more interesting details.

What are Antibiotics

Originally, antibiotics were the natural compounds that were able to kill bacteria. The first in this group was penicillin. However, after its introduction into the medical practice, microorganisms started to develop protection from it and became resistant.

That is why modern scientists all over the world are studying various substances to find new active molecules and create novel antibiotics. Even if they are half or fully synthetic, they still preserve this name. Thus, we got used to the fact that all infectious diseases can be treated with some of the group of antibiotics.

What is Metronidazole

This medicine belongs to the group of nitroimidazoles. Its reduced form interacts with the DNA of the cells of microorganisms and inhibits the synthesis of their nucleic acids. This causes their death.

The medicine is active against protozoa like Trichomonas vaginalis, Gardnerella vaginalis, Giardia intestinalis, Entamoeba histolytica, anaerobic bacteria (Bacteroides, Fusobacterium, Veillonela), some gram-positive bacteria (Eubacterium, Clostridium, Peptococcus, Peptostreptococcus) and Helicobacter pylori.

What is Amoxicillin

This medicine is semisynthetic broad-spectrum antibiotic of the penicillin group. It is utilized for the treatment of various types of infections including middle ear infections, sore throat, pneumonia and skin and urinary tract infections.

It inhibits certain ferments and prevents the creation of the bacterial cell wall, their division and growth, which causes the death of microorganisms. Amoxicillin is active against aerobic gram-positive bacteria (Staphylococcus and Streptococcus species) and aerobic gram-negative bacteria (Neisseria gonorrhoeae, Neisseria meningitidis, Escherichia coli, Shigella, Salmonella, Klebsiella).

Comparison between Metronidazole and Amoxicillin

Metronidazole and amoxicillin are quite different in terms of their nature and mechanism of action. That is why their combination may be beneficial. Before we proceed with it, let’s discover more about their differences.


Amoxicillin works better against various aerobic gram-positive and gram-negative bacteria. Actually, they cause the majority of the infectious diseases that are the most common in our population nowadays.

As for metronidazole, it works against anaerobic infections and protozoa. Thus, it is more specific and can be applied only under certain conditions.

Spectrum of Activity

According to the activity spectrum, amoxicillin belongs to broad-spectrum antibiotics, while metronidazole is a well-known narrow-spectrum option.

Dosage & Duration

Amoxicillin is usually prescribed in the dose from 250 to 500 mg three times per day or from 500 to 1000 mg two times per day. The treatment lasts from 5 to 7 days.

The dosage of metronidazole varies from 250 to 500 mg. The medicine is prescribed from 5 to 10 days according to the type of infection and the condition of the patient.


Both these medicines increase the effectiveness of indirect anticoagulants and may lead to bleeding during combined use with this group.

Furthermore, there are numerous possible interactions for each of these antibiotics separately. Thus, amoxicillin reduces the effectiveness of estrogen-containing oral contraceptives and increases the toxicity of certain medicines. As for metronidazole, it disturbs the efficiency of many medicines that influence the central nervous system and this may lead to life-threatening situations.

Therefore, the prescription of antibiotics must be made by the doctor, who takes into account other medicines that the patient should take.

Side Effects

Adverse effects of amoxicillin include:

  • various allergic reactions up to anaphylactic shock in rare cases;
  • digestive system issues, such as dysbacteriosis, vomiting, nausea, diarrhea and liver issues;
  • nervous system changes, including agitation, anxiety, insomnia, confusion, behavior changes, depression, headache and dizziness;
  • anemia, leukopenia and neutropenia;
  • difficulty breathing and tachycardia;
  • candidiasis.

As for metronidazole, it has almost the same list of side effects that include issues from the digestive and nervous system, allergic reactions and changes in laboratory indicators for blood. This antibiotic is not associated only with candidiasis as a result of the treatment.

Metronidazole and Amoxicillin Combination

As far as we can see, these two antibiotics are quite different in terms of their nature and mechanism of action, as well as in the spectrum of activity and microorganisms they can destroy. This leads us to the idea of the potential efficacy of their combination, especially for complex infections.

Dental Infections

Several scientific investigations now suggest that the combination of amoxicillin and metronidazole is beneficial for the treatment of various dental infections. They are often caused by mixed pathogens and require a sophisticated approach.

At the same time, such a combination did not lead to severe adverse effects even with the high dosage of metronidazole up to 500 mg. Thus, a positive short-term effect allows considering this approach as an effective one.

Complex Infections

The combination of broad and narrow-spectrum antibiotics is a good choice for various complex infections. While the doctor needs some time for analysis, he can at once start from this option and observe the reaction of the patient.

In such a combination, amoxicillin is active against almost all common infections, while metronidazole is more specific and kills only anaerobic bacteria and protozoa. These two medicines do not hinder each other. On the contrary, they make the activity even stronger and contribute to faster recovery.


The discussed combination also has a positive impact on the treatment of periodontal disease. Together amoxicillin and metronidazole provide a synergic effect and help to cope with anaerobic microorganisms that live inside the tissues and often become resistant to other antibiotics or their combinations.

The selected regimen is 500/500 mg or 500/400 mg of amoxicillin/metronidazole. This provides enough efficacy and is not associated with side effects.


The basic prescription of this combination is made for one week with 500/500 mg or 500/400 mg of amoxicillin/metronidazole. The following actions are taken according to the condition of the patient.

Sometimes, lower initial doses are prescribed. Thus, the doctor may start from 250 mg of amoxicillin but the dose of metronidazole is usually taken a bit higher. The duration of treatment is around one week.


All antibiotics and their combinations must be prescribed by the doctor. Usually, the analysis is required first to determine the cause of the disease, namely the microorganism, and then select the appropriate option for treatment.

Such a combination as amoxicillin with metronidazole works well due to the different mechanisms of action and spectrum of activity, which allows getting the maximum efficiency with the lowest possible side effects. These two medicines work in one direction and make the effects of each other stonger.


Can amoxicillin and metronidazole be taken together?

Yes, this combination is used, especially in the stomatology practice for the treatment of various dental infections.

How long does it take for metronidazole and amoxicillin to work?

The course of the intake lasts from several days up to 1 week, 10 days or more. This depends on the severity of the condition and must be determined by the doctor.

Recommended dosage of metronidazole and amoxicillin when taken together?

The most common option is a 7-day regimen of 500/500 mg or 500/400 mg amoxicillin and metronidazole.