Antimicrobial Chemotherapy

Question 1

Antimicrobial drug definition:

Answer 1

A substance that kills or inhibits the growth of the bacteria
The substance can be chemical — chemotheraputic or natural – antibiotic
Drugs that kill are called bacteriocidal and the drugs that inhibit the growth are called bacteriostatic

Question 2

Broad spectrum antibiotics definition and examples:

Answer 2

Acts on both gram +ve and gram -ve

Chlorampenicol and tetracycline

Question 3

Narrow spectrum antibiotics examples and definition

Answer 3

Only choses to act on either gram +ve bacteria or gram -ve bacteria
like: Nialidixic acid, polypeptide, macrolides
Polymexin B (acts of gram -ve)

Question 4

Factors in the drug that determine the effectiveness of the antimicrobial agent

Answer 4

The drug should be able to:
1- Reach the site of infection
2- Low in toxicity to the host cell but high in toxicity to the organism

Question 5

Factors in the host that determine the effectiveness of the antimicrobial agent

Answer 5

The host should not be:
1- Allergic or hypersensitive to the drug
2- destroied, neutralised or excreted rapidly

Question 6

Factors in the organisim that determine the effectiveness of the antimicrobial agent

Answer 6

The organisim should not redily become resistant to the drug

Question 7

Mechanisim of antimicrobial drug resistance:

Answer 7

1- Inactivation of the antibiotic by production of bacterial enzymes
2- Change in the permiablity to the drug
3- Modification of the receptor
4- Alteration to the metabolic pathway inhibited by the drug

Question 8

1- Inactivation of the antibiotic by production of bacterial enzymes
HOW

Answer 8

• Production of B-lactamase to destroy B-lactame drugs
• Production of adenylating, phosphorylating or acetylating drugs to destroy aminoglycosides
• Production of chloramphenicol acetyl transferase to destroy chloramphenicol

Question 9

2- Change in the permiablity to the drug

EXAMPLES

Answer 9

Tetracycline is concentrated less in resistant bacteia or efflux pump as pseudomonas

Question 10

3- Modification of the receptor

EXAMPLES

Answer 10

Chromosomal mutation changes the receptor shape so:
30s ribosomal subunit becomes resistant to Tetracycline and aminoglycosides
50s ribosomal subunit becomes resistant to Chloramphencol and erythromycin
Penicillin binding protein changes its shape

Question 11

4- Alteration to the metabolic pathway inhibited by the drug

EXAMPLE:

Answer 11

Bacteria that depend on folic acid to synthesis purine bases other than PABA are resistant to sulphonamides

Question 12

Limitations of drug resistance:

Answer 12

1- Avoid using the drug without sensitivity test
2- Restrict usage of last stage antibiotics like vancomycin
3- Maintain high level of the drug in the body
4- Simultaneous admistration of more than one drug

Question 13

Complications of antimicrobial chemotherapy:

Answer 13

1- Development of drug resistance
2- Overdose may lead to drug toxicity
3- Allergy in hypersensitive people
4- Prolonged use of drug supresses normal bacterial flora leading to superinfection
5- Early use of drug leads to complications

Question 14

Overdose may lead to drug toxicity

EXAMPLES

Answer 14

• Chloramphenicol attacks the bone marrow causing Aplastic anemia and Agranulocytosis
• Streptomycin causes nephrotoxicity and is ototoxic

Question 15

Complications of superinfection

Answer 15

• Overgrowth of Candidda in vagina leading to vaginitis and in mouth causing oral thrush
• Overgrowth of Clostrodium difficile causing pseudomembranous colitis

Question 16

Early use of the drug complications:

Answer 16

• Suppress formation of antibodies

- Masks clinical signs and symptoms