Amoxicillin

Amoxicillin (INN, BAN), or amoxycillin (AAN), and abbreviated amox, is an antibiotic useful for the treatment of a number of bacterial infections.

It is a moderate-spectrum, bacteriolytic, β-Lactam antibiotic in the aminopenicillin family used to treat susceptible Gram-positive and Gram-negative bacteria. It is usually the drug of choice within the class because it is better-absorbed, following oral administration, than other β-lactam antibiotics. Amoxicillin is susceptible to degradation by β-lactamase-producing bacteria, which are resistant to a narrow spectrum of β-lactam antibiotics, such as penicillin. For this reason, it is often combined with clavulanic acid, a β-lactamase inhibitor. This drug combination is commonly called co-amoxiclav. Combining the drugs increases effectiveness by reducing susceptibility to β-lactamase resistance.

Side effects include an increased risk of yeast infections and, when used in combination with clavulanic acid, diarrhea.

Amoxicillin is one of the most common antibiotics prescribed for children. The drug first became available in 1972. It is on the World Health Organization's List of Essential Medicines, a list of the most important medications needed in a basic health system.

§Medical uses

Amoxicillin is used in the treatment of a number of infections, including acute otitis media, streptococcal pharyngitis, pneumonia, skin infections, urinary tract infections, Salmonella infections, Lyme disease, and chlamydia infections. It is also used to prevent bacterial endocarditis in high-risk people having dental work done, to prevent Streptococcus pneumoniae and other encapsulated bacterial infections in those without spleens, such as people with sickle-cell disease, and for both the prevention and the treatment of anthrax. The United Kingdom recommends against its use for infectious endocarditis prophylaxis. These recommendations have not appeared to have changed the rates of infection for infectious endocarditis.

Amoxicillin and amoxicillin-clavulanate are recommended by guidelines as the first-choice drug for bacterial sinusitis, but most sinusitis is caused by viruses, for which amoxicillin and amoxicillin-clavulanate are ineffective. Amoxicillin is occasionally used for the treatment of skin infections, such as acne vulgaris. It is often an effective treatment for cases of acne vulgaris that have responded poorly to other antibiotics, such as doxycycline and minocycline.

§Adverse effects

Side effects are similar to those for other β-lactam antibiotics, including nausea, vomiting, rashes, and antibiotic-associated colitis. Loose bowel movements (diarrhea) may also occur. Rarer side effects include mental changes, lightheadedness, insomnia, confusion, anxiety, sensitivity to lights and sounds, and unclear thinking. Immediate medical care is required upon the first signs of these side effects.

The onset of an allergic reaction to amoxicillin can be very sudden and intense; emergency medical attention must be sought as quickly as possible. The initial phase of such a reaction often starts with a change in mental state, skin rash with intense itching (often beginning in fingertips and around groin area and rapidly spreading), and sensations of fever, nausea, and vomiting. Any other symptoms that seem even remotely suspicious must be taken very seriously. However, more mild allergy symptoms, such as a rash, can occur at any time during treatment, even up to a week after treatment has ceased. For some people allergic to amoxicillin, the side effects can be fatal due to anaphylaxis.

Use of the amoxicillin/clavulanic acid combination for more than one week has caused mild hepatitis in some patients. Young children having ingested acute overdoses of amoxicillin manifested lethargy, vomiting, and renal dysfunction.

§Nonallergic amoxicillin rash

Between 3 and 10% of children taking amoxicillin (or ampicillin) show a late-developing (>72 hours after beginning medication and having never taken penicillin-like medication previously) rash, which is sometimes referred to as the "amoxicillin rash". The rash can also occur in adults.

The rash is described as maculopapular or morbilliform (measles-like; therefore, in medical literature, it is called "amoxicillin-induced morbilliform rash".) It starts on the trunk and can spread from there. This rash is unlikely to be a true allergic reaction, and is not a contraindication for future amoxicillin usage, nor should the current regimen necessarily be stopped. However, this common amoxicillin rash and a dangerous allergic reaction cannot easily be distinguished by inexperienced persons, so a healthcare professional is often required to distinguish between the two.

A nonallergic amoxicillin rash may also be an indicator of infectious mononucleosis. Some studies indicate about 80-90% of patients with acute Epstein Barr virus infection treated with amoxicillin or ampicillin develop such a rash.

§Interaction

Amoxicillin may interact with these drugs:

• Anticoagulants (e.g., warfarin, dabigatran)
• Allopurinol (gout treatment)
• Certain antibiotics
• Cancer treatment (methotrexate)
• Uricosuric drugs
• Typhoid vaccine

§Mechanism of actions

This drug acts by inhibiting the synthesis of bacterial cell walls. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the cell walls of both Gram-positive and Gram-negative bacteria.

It has two ionizable groups in the physiological range (the amino group in alpha-position to the amide carbonyl group and the carboxyl group).

§Spectrum of microorganism susceptibility and resistance

In general, Streptococcus, Bacillus subtilis, Enterococcus, Haemophilus, Helicobacter, and Moraxella are susceptible to amoxicillin, whereas Citrobacter, Klebsiella and Pseudomonas aeruginosa are resistant to it. Some E. coli and most clinical isolates of Staphylococcus aureus have developed resistance to amoxicillin to varying degrees.

§History

Amoxicillin was one of several semisynthetic derivatives of 6-aminopenicillanic acid (6-APA) developed at Beecham, England in the 1960s. It became available in 1972, and was the second aminopenicillin to reach the market (after ampicillin in 1961). Co-amoxiclav became available in 1981.

§Formulations

§Modes of delivery

Pharmaceutical manufacturers make amoxicillin in trihydrate form, available as capsules, chewable and dispersible tablets, syrup and pediatric suspension for oral use, and as the sodium salt for intravenous administration. Amoxicillin is most commonly taken orally. The liquid forms are helpful where the patient might find it difficult to take tablets or capsules.

Research with mice indicated successful delivery using intraperitoneally injected amoxicillin-bearing microparticles.

§Brand names

Amoxicillin is one of the semisynthetic penicillins discovered by Beecham scientists. The patent for amoxicillin has expired, thus amoxicillin and co-amoxiclav preparations are marketed under many trade names and/or have several synonyms across the world, such as:

Names without individual reference are referenced on the drugs.com website.

§References

§Further reading

• Neal, M. J. (2002). Medical pharmacology at a glance (4th ed.). Oxford: Blackwell Science. ISBN 0-632-05244-9. 

• British National Formulary 45 March 2003

§External links

• U.S. National Library of Medicine: Drug Information Portal - Amoxicillin

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