Amoxicillin is an antibiotic from the group of semi-synthetic penicillins with a wide spectrum of action. It is one of the most widely used antibiotics today, which is included in the list of medicines recommended by WHO as vital. Amoxicillin (amoxicillin trihydrate) was released in 1972. At the time of release, it favorably differed from its direct competitor – ampicillin, first of all, by its high bioavailability. It was one of the first antibiotics, the bioavailability of which was about 90% when taken orally and did not depend on food intake, while other antibiotics could not boast of such indicators – they were almost two times lower, and most of them had to be taken. on an empty stomach Amoxicillin gained great popularity due to the fact that it didn’t t cause a large number of severe side effects.

Today, despite the discovery of new classes of antibacterial drugs, Amoxicillin retains its position in the global pharmaceutical market due to its good tolerance, high safety profile, convenient method of administration, as well as the possibility of implementing stepwise therapy and low cost. Amoxicillin was developed by one of the oldest British pharmaceutical companies Beecham in 1972 and began to be sold by GlaxoSmithKline (the assignee of Beecham) under the name Amoxil. However, the patent protection of the branded drug has long expired, and many other manufacturers sell the antibiotic with the active ingredient Amoxicillin under other names.

Chemical structure and properties

From a chemical point of view, Amoxicillin is a semi-synthetic antibacterial drug, an analogue of ampicillin, which has a wide spectrum of bactericidal activity against many gram-positive and gram-negative microorganisms. The molecular weight is 419.45 Da. Cross-resistance exists between amoxicillin and ampicillin. The spectrum of antibacterial action is expanded with the simultaneous use of Amoxicillin and the beta-lactamase inhibitor clavulanic acid.

Amoxicillin has significant pharmacokinetic advantages compared to a number of other penicillins. The bioavailability of amoxicillin reaches 70 – 80%, while for phenoxymethylpenicillin this most important pharmacokinetic indicator is 50%, and for ampicillin it is only 40%. The degree of binding to plasma proteins for amoxicillin, on the contrary, is minimal and is 17% (phenoxymethylpenicillin – 80%, ampicillin – 22%). High bioavailability and low degree of binding to plasma proteins provide a high concentration of amoxicillin in tissues when taken orally, which makes it possible to achieve eradication of the pathogen and at the same time avoid the development of adverse events. An important advantage of Amoxicillin is the independence of absorption from the gastrointestinal tract from food intake, in contrast to phenoxymethylpenicillin and ampicillin, the bioavailability of which is significantly reduced when taken with food. In pediatric practice, it is important to have a soluble oral form. Favorable organoleptic properties of the soluble form of amoxicillin can improve patient compliance and tolerability of antibiotic therapy.

Mechanism of Action

Amoxicillin is similar to penicillin in its bactericidal action against sensitive bacteria that are at the stage of active reproduction. It acts by inhibiting the biosynthesis of the cell wall, which leads to the death of bacteria. Amoxicillin inhibits transpeptidase, disrupting the synthesis of peptidoglycan (the supporting protein of the cell wall) during cell division and growth.

The spectrum of action of amoxicillin is much wider than that of natural penicillins. Despite the fact that this medicine could not destroy Pseudomonas aeruginosa and did not act very effectively on some streptococci and staphylococci, its broad spectrum of action made it possible to use it for infections caused by gram-negative bacteria. High activity against pneumococcus has become one of the basic advantages, thanks to which Amoxicillin quickly took a leading position among penicillins.

Medical Applications

Amoxicillin is used in the practice of a pediatrician (primarily as a starting therapy for children with purulent bronchitis, pneumonia, otitis media, sinusitis, urinary tract infections), and in adults for the eradication of Haemophilus influenzae, in the treatment of chronic bronchitis and chronic obstructive pulmonary disease, in therapy of exacerbations associated with viral and bacterial pathogens, and in the treatment of community-acquired pneumonia. Amoxicillin is also effective in the treatment of gastrointestinal pathology. This antibiotic is used in the form of sequential therapy to eliminate the carriage of Helicobacter pylori.

Amoxicillin is most effective in the treatment of those infectious diseases that are caused by the development of streptococci. Among them, it is worth noting especially intestinal infections (such as enteritis, colitis), infectious lesions of soft tissues (phlegmon, abscess).

The most common dosage of Amoxicillin is 500 mg in one tablet or capsule. Adults are advised to take 500 mg three times a day. For the treatment of adolescent children, a dosage of 250 mg per tablet or capsule may be used. However, 500mg tablets are conveniently divided into two parts and are cheaper than those containing 250mg of the active ingredient, so buyers usually give preference to the 500mg dosage.

It should be noted that in order for the patient to receive the correct treatment according to the most suitable scheme for him, it is imperative to consult a doctor and get a prescription. It may even be necessary to check the body for the sensitivity of bacteria to Amoxicillin. Self-medication with antibiotics can lead to very detrimental consequences for the patient’s body.

Amoxicillin, like many other antibiotics, must be taken for at least three days after the symptoms of the underlying disease have completely disappeared. Otherwise, the remnants of the surviving bacteria may become active, and it will take a very long time to undergo treatment. You should not rely on self-recovery of the body. Due to the need to destroy all pathogenic bacteria in severe forms of some diseases, it may be necessary to take Amoxicillin for 14-20 days, although generally 7-10 days of therapy are sufficient.

Side Effects and Contraindications

Side effects experienced by patients taking Amoxicillin can be divided into common and rare.

Among the common side effects from the digestive system are diarrhea, nausea; from the nervous system, the body may react with drowsiness, headache; from the cardiovascular system – tachycardia, phlebitis; on the part of the liver and biliary tract – an increase in the concentration of bilirubin in the blood serum; from the skin and subcutaneous tissues – skin rash, urticaria.

Incomparably less common are such side effects as antibiotic-associated colitis, the appearance of black coloration of the tongue, pain in the epigastric region, nervousness, irritability, ataxia, peripheral neuropathy, dizziness, convulsions, visual impairment, lowering blood pressure, jaundice, hepatitis, increased activity of liver enzymes , acute liver failure, edema of the skin and mucous membranes, toxic epidermal necrosis (mainly in patients with chronic diseases and reduced immune status), candidiasis of the skin and mucous membranes, reversible leukopenia, reversible thrombocytopenia, hemolytic anemia, angioedema, anaphylactic shock, anorexia, hypoglycemia, bronchospasm, tendinitis, increased serum creatinine concentration, general weakness and fever. Their frequency is statistically insignificant, and the likelihood of encountering them is minimal.

The main contraindication to taking Amoxicillin is a serious hypersensitivity reaction (e.g., anaphylaxis or Stevens-Johnson syndrome) to amoxicillin or other beta-lactam antibacterial drugs (e.g., penicillins and cephalosporins). It is also not recommended to take Amoxicillin for diseases such as infectious mononucleosis, lymphocytic leukemia, severe gastrointestinal infections accompanied by diarrhea or vomiting, respiratory viral infections, allergic diathesis, bronchial asthma.

Drug Interaction

In combination with metronidazole, Amoxil is effective in the treatment of chronic gastritis, as well as gastric and duodenal ulcers caused by the presence of Helicobacter pylori.

Amoxicillin may reduce the effectiveness of oral contraceptives, as it may affect the intestinal microflora, resulting in a decrease in estrogen reabsorption.

With the simultaneous use of Amoxicillin with bactericidal antibiotics (including aminoglycosides, cephalosporins, cycloserine, vancomycin, rifampicin), synergism appears. When using Amoxicillin with bacteriostatic antibiotics (including macrolides, chloramphenicol, lincosamides, tetracyclines, sulfonamides), antagonism is observed.

Amoxicillin enhances the effect of indirect anticoagulants by suppressing the intestinal microflora, reduces the synthesis of vitamin K and the prothrombin index.

Probenecid, diuretics, allopurinol, phenylbutazone, NSAIDs reduce the tubular secretion of Amoxicillin, which may be accompanied by an increase in its concentration in the blood plasma.

Antacids, glucosamine, laxatives, aminoglycosides slow down and reduce, and ascorbic acid increases the absorption of Amoxicillin.

With the combined use of amoxicillin and clavulanic acid, the pharmacokinetics of both components does not change.

Chloramphenicol, macrolides, sulfonamides and tetracyclines may interfere with the bactericidal action of Amoxicillin, which is why it is not recommended to use them together.

Amoxicillin and Bacterial Resistance

Bacterial resistance to Amoxicillin is mediated primarily by beta-lactamases, which cleave the beta-lactam ring of amoxicillin, rendering it inactive. Notably, Amoxicillin was the first antibiotic used to eradicate Helicobacter pylori infection due to the alleged lack of resistance to it by this microorganism. However, modern studies give reason to believe that the development of resistance of Helicobacter pylori to Amoxicillin is possible due to point mutations in the pbp1 genes and a deletion in hopC. They lead to a significant increase in the minimum inhibitory concentration of amoxicillin. Membrane permeability also depends on the omp25 and omp32 genes, point mutations in which are also included in the list of reasons for the development of H. pylori resistance to Amoxicillin. Meanwhile, proven cases of H. pylori resistance to amoxicillin are few in number against the background of high resistance to other antibiotics (except in Africa and Asia). As for the resistance of H. influenzae to antibacterial drugs, it is quite variable in different countries. In many countries, Haemophilus influenzae has acquired resistance to aminopenicillins by 30 – 50% or more. Already in the 1980s. there have been reports that the incidence of resistance to amoxicillin among untyped strains of Haemophilus influenzae in North America has reached 15-16%. In Europe, the frequency of amoxicillin-resistant strains of Haemophilus influenzae ranges from 13 to 32%.

The key point, thanks to which it is possible to restrain the development of resistance of various bacteria to Amoxicillin, is the use of this drug, like other antibiotics, strictly on the recommendation of a doctor and in case of serious need. It is also important not to take antibiotics from the same pharmacological group more than once every four months. The abuse of antibacterial agents does not help reduce the incidence of certain diseases in people, but only makes them more defenseless, because the bacteria get used to the fact that ever-increasing doses of antibiotics are constantly being applied to them. In response to this, they rapidly mutate and are no longer amenable to treatment with previously effective means. When considering antibiotic resistance by doctors, it is necessary to focus primarily on the level of regional pneumococcal penicillin resistance.

In patients over 60 years of age with COPD, as well as in those who have numerous comorbidities, the likelihood of the etiological role of gram-negative microorganisms (including those with some resistance mechanisms) increases. Because of this, the use of inhibitor-protected aminopenicillins (in particular, amoxicillin/clavulanate) is recommended as the drugs of choice.


Amoxicillin, despite a fifty-year history of its use in medicine, is still a popular antibacterial agent that is important for human health even in resource-limited settings. In particular, Amoxicillin is used in situations where adults and children cannot or do not want to be hospitalized. The World Health Organization recommends that the health authorities of all countries have this medicine in their assortment.

The correct use of Amoxicillin, which has a number of advantages over other penicillin antibiotics, can slow down the development of microbial resistance to this antibiotic. Therefore, it is necessary to strive to control the intake of Amoxicillin and increase the frequency of tests for the sensitivity of certain pathogens to various antibiotics so as not to provoke the development of bacterial resistance.