From the Guidelines
Penicillin and amoxicillin are both beta-lactam antibiotics, but amoxicillin is a more potent and better-absorbed derivative of penicillin.
Key Differences
- Spectrum of activity: Amoxicillin has a broader spectrum of activity than penicillin, making it effective against a wider range of bacteria, including streptococci, pneumococci, and Haemophilus influenzae 1.
- Absorption: Amoxicillin is better absorbed than penicillin, resulting in higher serum levels and increased efficacy 1.
- Resistance: Amoxicillin is more effective against penicillin-resistant strains of bacteria, including Streptococcus pneumoniae 1.
- Dosage: Amoxicillin is often prescribed at higher doses than penicillin to overcome resistance and ensure efficacy 1.
Clinical Use
- Community-acquired pneumonia: Amoxicillin is recommended as a first-line treatment for community-acquired pneumonia, while penicillin is not due to increasing resistance 1.
- Streptococcal infections: Amoxicillin is preferred over penicillin for the treatment of streptococcal infections, including pharyngitis and skin infections 1.
Important Considerations
- Resistance patterns: The increasing prevalence of penicillin-resistant Streptococcus pneumoniae strains has led to a shift towards using amoxicillin and other beta-lactam antibiotics with broader spectra of activity 1.
- Dosing and administration: High-dose amoxicillin (4 g/day for adults and 90 mg/kg per day for children) may be necessary to overcome resistance and ensure efficacy in certain cases 1.
From the FDA Drug Label
Amoxicillin is similar to penicillin in its bactericidal action against susceptible bacteria during the stage of active multiplication. It acts through the inhibition of cell wall biosynthesis that leads to the death of the bacteria
The main difference between penicillin and amoxicillin is not explicitly stated in the provided drug label, but it can be inferred that they have a similar mechanism of action. However, the label does not provide a direct comparison of their differences. 2
From the Research
Overview of Penicillin and Amoxicillin
- Penicillin and amoxicillin are both antibiotics that belong to the penicillin class 3
- Amoxicillin is a semisynthetic penicillin, closely related to ampicillin, with a similar antibacterial spectrum and level of activity 4
Differences in Absorption and Efficacy
- Amoxicillin is better absorbed than ampicillin after oral administration, resulting in higher peak serum levels 4
- Amoxicillin has been shown to be more effective than ampicillin in treating certain infections, such as those caused by Escherichia coli 5
- The bacteriolytic activity of amoxicillin is greater than that of ampicillin, which may contribute to its superior therapeutic activity 5
Spectrum of Activity
- Amoxicillin has a broader spectrum of activity than penicillin, including gram-negative bacteria such as Escherichia coli, Proteus mirabilis, and Haemophilus influenzae 3
- Penicillin is more effective against streptococcal and staphylococcal infections, while amoxicillin is more effective against infections caused by gram-negative bacteria 3
Resistance and MICs
- The minimum inhibitory concentrations (MICs) of amoxicillin and co-amoxiclav are lower than those of penicillin for Streptococcus pneumoniae isolates 6
- Amoxicillin and co-amoxiclav MICs are also lower than penicillin MICs for penicillin-intermediate and -resistant isolates 6
Clinical Use
- Phenoxymethylpenicillin is the antibiotic of choice for respiratory tract infections in Scandinavian countries, while amoxicillin is used in most other European countries 7
- Studies have shown no significant differences in clinical effect between phenoxymethylpenicillin and amoxicillin for certain infections, such as acute sinusitis and GAS tonsillitis 7