Question

Please answer all parts of these questions by using the topic !!

Selective toxicity Prompt:

Explain the concept of selective toxicity. Explain the ways that antimicrobial drugs affect pathogens. Identify which categories of drugs are most selectively toxic and why.

USING THE TOPIC: Inhibition of Protein Synthesis

Answer 1

Ans) Selective toxicity is the property of the drug to targets or affect sites that are relatively specific to the microorganism responsible for infection and against whom we intend to use the drug . These sites may either be unique to the microorganism or may be present in both the host and microbe but simply more important for  the survival of the microorganism than to the host.It is used to express a drug's therapeutic index (TI) - ratio of the toxic dose (which is toxic to the patient) to the therapeutic dose (to eliminate the infection).

Most of the drugs work by selective toxicity.

Ans)Antimicrobials may affect the pathogen by  either being bactericidal, that is killing the target bacteria or being bacteriostatic, that is inhibiting its growth.

The mode of action of antibiotics may be as follows-

• Inhibition of Cell Wall Synthesis-By either prevention of new glycosidic bond formation inhibiting cell wall synthesis-eg) beta lactams
• Inhibition of Protein Synthesis-Tetracyclines by inhibit protein synthesis by binding to the 30S subunit of the ribosome or inhibit the binding of amino-acyl tRNA to the A site of the ribosome.
• Alteration of Cell Membranes.
• Inhibition of Nucleic Acid Synthesis eg flouroquinolones or rifamycin
• Antimetabolite Activity by inhibiting folic acid synthesis eg sulfones

The drugs that inhibit cell wall synthesis eg) Penicillins,cephalosporins,monobactams are most selectively toxic. This is because they inhibit cell wall synthesis and cell wall is absent in human cells, so no effect on humans hence they are most selectively toxic.