Differences between Amoxicillin and Penicillin

Differences between Amoxicillin and Penicillin

Amoxicillin and penicillin are both beta-lactam antibiotics used to treat bacterial infections. Amoxicillin is a derivative of penicillin and belongs to the aminopenicillin family of antibiotics. It was developed by chemically modifying the original penicillin structure to improve its effectiveness. Both drugs function by inhibiting the synthesis of bacterial cell walls, which leads to the death of the bacteria. While they share a common mechanism, their structural differences result in distinct properties affecting their range of activity and clinical use.

Comparison table

Category	Amoxicillin	Penicillin (Penicillin V/G)
Antibiotic Spectrum	Broad-spectrum. Effective against many gram-positive and some gram-negative bacteria such as H. influenzae and E. coli.	Narrow-spectrum. Primarily effective against gram-positive bacteria like Streptococcus.
Chemical Structure	A penicillin core with an added amino group and a hydroxyl group on its side chain.	A natural or semi-synthetic antibiotic with a core penicillin structure.
Oral Absorption	Well-absorbed when taken orally, with bioavailability between 74% and 92%. Absorption is not significantly affected by food.	Penicillin V is acid-stable for oral use, but has variable bioavailability (25% to 60%). Penicillin G is largely destroyed by stomach acid and is typically given by injection.
Common Uses	Respiratory tract infections, ear infections, urinary tract infections (UTIs), and H. pylori eradication.	Strep throat, dental infections, and rheumatic fever prophylaxis.
Year of Medical Use	1972.	Widespread use began during World War II, following its discovery in 1928.
Resistance	Can be rendered ineffective by beta-lactamase enzymes produced by some bacteria; often combined with clavulanic acid to overcome this.	Susceptible to beta-lactamase enzymes.

Venn diagram comparing Differences between Amoxicillin and Penicillin

Chemical structure

Amoxicillin is a semi-synthetic aminopenicillin. Its structure is different from that of penicillin G due to the addition of a hydroxyl group on the phenyl side chain. This modification increases the drug's ability to penetrate the outer membrane of some gram-negative bacteria, which expands its spectrum of activity.

Spectrum of activity

The structural differences between the two antibiotics directly impact the range of bacteria they can treat. Penicillin is considered a narrow-spectrum antibiotic, mainly targeting gram-positive bacteria. Amoxicillin is a broad-spectrum antibiotic because it is effective against a wider range of bacteria, including gram-positive bacteria and some gram-negative bacteria such as Haemophilus influenzae, Neisseria gonorrhoeae, and certain strains of Escherichia coli.

Pharmacokinetics

A significant difference between the two drugs is their behavior in the body. Amoxicillin is more stable in stomach acid and is absorbed more efficiently and consistently than penicillin V when taken orally. This results in higher concentrations of the drug in the blood. Penicillin V has much more variable oral absorption. Penicillin G is not acid-stable and is usually administered via injection to be effective.