PENICILLINS

 

Objectives of the topic; By the end of this topic, the medical student/reader/ will be able to;

1.  Explain the mechanism of action and drug class of penicillins

2.  Briefly describe the sub classes of penicillins

3.  Mention some of the most common side effects of penicillins

Introduction:  The penicillins share features of chemical properties, mechanism of action, pharmacological aspects, and immunologic characteristics such as reactions and hypersensitivity with cephalosporins, monobactams, carbapenems, and β-lactamase inhibitors.  

Classification:  These group of drugs are named β-lactam antibiotics basing on their chemical structure.  

Penicillins can be assigned to one of three groups as described in the following discussion.  Within each of these groups are compounds that are relatively stable to gastric acid and suitable for oral administration because that means they will not be deactivated in the stomach.  These include drugs such as penicillin V, dicloxacillin, and amoxicillin.

Penicillins such as, penicillin G:  These have greatest activity against gram-positive organisms, gram-negative cocci, and non-β-lactamase producing anaerobes.  However, they have little activity against gram-negative rods, and they are susceptible to hydrolysis by β-lactamases.

Antistaphylococcal penicillins such as, nafcillin:  These penicillins are resistant to staphylococcal β-lactamases. They are active against staphylococci and streptococci but not against enterococci, anaerobic bacteria, and gram-negative cocci and rods.

Extended-spectrum penicillins:  These include ampicillin and the antipseudomonal penicillins.  These drugs retain the antibacterial spectrum of penicillin and have improved activity against gram-negative organisms.  Like penicillin, however, they are relatively susceptible to hydrolysis by β-lactamases.

Microbial Resistance to penicillins: Resistance to penicillins and other β-lactams is due to one of four general mechanisms:  

(1) Inactivation of antibiotic by β-lactamase.  

(2) Modification of target PBPs.  

(3) Impaired penetration of drug to target PBPs, and  

(4) Efflux.  

Beta-lactamase production is the most common mechanism of resistance. Hundreds of different β-lactamases have been identified.

RELATED;

1.  CEPHALOSPORINS

2.  PHARMACOLOGY AND THERAPEUTICS

REFERENCES