Katzung 12th ed - Chapter 44 - Tetracyclines, Macrolides, Chloramphenicol (2)

Question 1

Name a couple of tetracyclines.

Answer 1

Doxycycline. Minocycline.

Question 2

What is the mechanism of action of tetracyclines?

Answer 2

Bind to the 30S ribosomal subunit, inhibiting protein synthesis.

Question 3

Name some clinical uses of tetracyclines.

Answer 3

Mycoplasma, Chlamydia, Rickettsia, Acne, Malaria prophylaxis.

Question 4

Name some resistance mechanisms against tetracyclines.

Answer 4

1) Impaired active transport of the drug into the microorganism
2) Decreased binding to ribosome due to production of inhibitory proteins
3) Enzymatic inactivation
Note that resistance is common

Question 5

Describe the absorption and distribution of doxycycline.

Answer 5

95-100% is absorbed orally. Widely distributed, 40-80% protein-bound, does not cross BBB.

Question 6

Name some of the toxic effects of tetracyclines.

Answer 6

GIT: Vomiting, diarrhoea.
Bones and teeth: Discoloration, impaired bone growth
Skin: Photosensitivity

Question 7

What are the routes of metabolism and excretion of tetracyclines?

Answer 7

Metabolised by the liver, excreted in urine and bile.

Question 8

Name a few macrolides

Answer 8

Erythromycin, Roxithromycin, Clarithromycin, Azithromycin.

Question 9

Mechanism of action of macrolides?

Answer 9

Binds reversibly to the 50S subunit of the bacterial ribosome, inhibiting protein synthesis.

Question 10

Name some clinical uses for macrolides.

Answer 10

Atypical pneumonia (mycoplasma, legionella), Skin and soft tissue infections (Strep, staph), STI (Chlamydia, Neisseria gonorrhoea), Campylobacter. Useful in penicillin allergy.

Question 11

Routes of metabolism and excretion for macrolides? Half-life?

Answer 11

Metabolised by liver, excreted in bile. Half-life 1.5hrs.

Question 12

Chloramphenicol: Mechanism of action?

Answer 12

Binds to the 50S subunit of bacterial ribosome, inhibiting protein synthesis.

Question 13

Why is chloramphenicol used mostly for eye infections, and rarely for anything else?

Answer 13

Chloramphenicol has greater toxic effects and greater bacterial resistance than many other available agents. It is good for eye infections because of its broad spectrum and good penetration of ocular tissues.

Question 14

What are some toxicities of chloramphenicol?

Answer 14

Bone marrow: suppression of RBC production
GIT: vomiting, diarrhoea
Neonates: Grey baby syndrome