Question

Describe the major categories of antibiotics and their strengths and weaknesses?

Answer 1

Classification of Antibiotics according to the mechanism of action

1. Drugs that inhibit cell wall synthesis

a) Penicillins

b) Cephalosporins

c) Carbepenems

2. Drugs that affect cell membrane function

a) Amphoteracin B (AMB)

b) Polymyxin

3. Drugs that inhibit protein synthesis

a) Tetracyclins

b) Chloramphenicol

c) Erythromycin

4. Drugs that alter protein synthesis by misreading of mRNA code and premature termination of mRNA translation

a) Aminoglycosides

5. Drugs that affect DNA function

a) Rifampicin

b) Rifabutin

6. Drugs that inhibit DNA gyrase

a) Fluroquinolones

7. Antimetabolites

a) Sulphonamides

The antibiotics which used widely are:

1. Penicillin antibiotics

They are the antibiotics having beta-lactam ring in their structure.

Eg: Penicillin, Amoxicillin, Ampicillin etc.

Mechanism of Action: Beta lactam antibiotics produce bactericidal effect by inbibiting the cell wall synthesis in susceptible bacteria.

Strengths

They can be administered orally as well as parenterally.

They are having broad spectrum activity.

Weaknesses

Greater likelihood of adverse reactions.

Antibiotic antagonism.

Chance of microbial resistance is more.

2. Sulphonamides

They are the synthetic derivatives of para-amino benzene sulphonamide. Sulphonamides are bacteriostatic in nature.

Eg: Sulphadiazine, Sulphamethoxazole, Sulphacetamide

Mechanism of action: Sulphonamides inhibit the enzyme folate synthetase which is essential for the synthesis of folic acid in bacteria and produce bacteriostatic effect.

Strengths

Broad spectrum activity.

They can be administered orally as well as parenterally.

Weaknesses

Bacteriostatic

Occurrence of bacterial resistance

3. Quinolones and Fluoroquinolones

The first quinolone, nalidixic acid is a urinary antiseptic. It is effective against gram negative vacteria includine E. coli, Klebsiella, Enterobacter, Salmonella, Shigella..

Fluoroquinolones are synthetic fluorinated analogues of nalidixic acid.

Eg: Norfloxacin, Ciprofloxacin Levofloxacin

Mechanism of action: They inhibit DNA topoisomerase II in gram-negative and topoisomerase IV in gram-positive bacteria and prevent the bacterial replication.

Strengths

Broad spectrum activity.

Weaknesses

Multiple drug interactions.

Tendonitis or tendon rupture.

4. Cephalosporins

Cephalosporins are beta-lactam antibiotics with 7-aminocephalosporanic acid nucleus. The mechanism of action and development of resistance are similar to the penicillin antibiotics. They are the cell wall synthesis inhibitors.

Eg: Cephalexin, Cefaclor, Cefixime.

Strengths

Bactericidal action

Broad spectrum activity.

Weaknesses

Occurrence of bacterial resistance

Hypersensitivity

Nephrotoxicity