Amoxicillin (formerly amoxycillin in the British Pharmacopoeia) is a moderate-spectrum β-lactam antibiotic used to treat bacterial infections caused by susceptible microorganisms. It is usually the drug of choice within the class because it is better absorbed, following oral administration, than other beta-lactam antibiotics. Amoxicillin is susceptible to degradation by β-lactamase-producing bacteria, and so is often given clavulanic acid (see below). It is currently marketed by GlaxoSmithKline under the trade name Amoxil®.

Mode of action

Amoxicillin 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 wall of Gram-positive bacteria.

Main article: beta-lactam antibiotic

Microbiology

Amoxicillin is a moderate-spectrum antibiotic active against a wide range of Gram-positive, and a limited range of Gram-negative organisms. Some examples of susceptible and resistant organisms, from the Amoxil® Approved Product Information (GSK, 2003), are listed below.

Susceptible Gram-positive organisms

Streptococcus spp., Diplococcus pneumoniae, non β-lactamase-producing Staphylococcus spp., and Streptococcus faecalis.

Susceptible Gram-negative organisms

Haemophilus influenzae, Neisseria gonorrhoeae, Neisseria meningitidis, Escherichia coli, Proteus mirabilis and Salmonella spp.

Resistant organisms

Penicillinase producing organisms, particularly penicillinase producing Staphylococcus spp. Penicillinase-producing N. gonorrhoeae and H. influenzae are also resistant

All strains of Pseudomonas spp., Klebsiella spp., Enterobacter spp., indole-positive Proteus spp., Serratia marcescens, and Citrobacter spp. are resistant.

The incidence of β-lactamase-producing resistant organisms, including E. coli, appears to be increasing.

Amoxicillin and Clavulanic acid

Amoxicillin is sometimes combined with clavulanic acid, a β-lactamase inhibitor, to increase the spectrum of action against Gram-negative organisms, and to overcome bacterial antibiotic resistance mediated through β-lactamase production. This formulation is referred to as co-amoxiclav (British Approved Name), but more commonly by proprietary names such as Augmentin® and Clamoxyl®.

Main article: co-amoxiclav

Proprietary Preparations

The patent for amoxicillin has expired. Thus amoxicillin is marketed under many trade names including: Actimoxi®, Amoxibiotic®, Amoxicilina®, Pamoxicillin®, Lamoxy®, Polymox®, Trimox®, Tolodina® and Zimox®.

References

• GlaxoSmithKline Australia Pty Ltd (2003). Amoxil® Approved Product Information. Boronia: GlaxoSmithKline.
• Neal, MJ (2002). Medical Pharmacology at a Glance (4 ed.). Oxford: Blackwell Science. ISBN 0-632-05244-9