Anti-Ribosomal Antibiotics

Question 0

What are the 5 major antibiotics that inhibit the function of the bacterial ribosome?

Answer 0

1. Chloramphenicol and Clindamycin (50S)
2. Linezolid (50S)
3. Erythromycin (50S)
4. Tetracycline and Tigecycline (30S)
5. Aminoglycosides (30S)

Question 1

What is the stucture of the bacterial ribosome?

Answer 1

Consists of a 70S particle that has two subunits (50s and 30s). We have a 80S ribosome.

Question 2

What is the only anti-ribosomal drugs that cannot be absorbed orally?

Answer 2

The aminoglycosides. Must be given IM or IV for systemic treatment of infections.

Question 3

Is chloramphenicol a powerful drug?

Answer 3

Yes - like Imipenem, it is one of the few drugs that kills most clinically important bacteria (gram positives, gram negatives, anaerobes)

Question 4

What is the clinical use of chloramphenicol?

Answer 4

Because of its rare but severe side effects, it is used only when there is no alternate antibiotic.

1. For bacterial meningitis : when the organism is not yet known and the patient has severe allergies to penicillins.
2. For young children and pregnant women who have Rocky Mountain spotted fever and cannot be treated with tetracycline due to the side effects of tetracycline.
3. In underdeveloped countries this drug is widely used.

Question 5

What are the adverse effects of Chloramphenicol?

Answer 5

1. Famous for two types of bone marrow depression : the first is dose related and reversible, often only causes an anemia. The second is aplastic anemia (extremely rare occuring 1/24.000 to 1/40.000).
2. Gray baby syndrome : the neonates are unable to fully conjugate chloramphenicol in the liver or excrete it through the kidney, resulting in very high blood levels.

Question 6

What are the clinical uses of clindamycin?

Answer 6

1. Use for anaerobic infections.
2. Also used for infections of the female genital tract.
3. Combined with a beta lactam or vancomycin is used for the treatment of toxic shock syndrome associated with group A Streptococcus or S.aureus.
4. Also becoming the go-to drug in uncomplicated skin and soft tissue infections where there is a high suspicion for S.aureus or group A steptococcal infection.
5. Often given orally for months to out-patients who develop an anaerobic aspiration pneumonia.
   + The lung is the only organ that can contain an abscess that does not need surgical drainage. Chronic treatment with clindamycin (that covers anaerobic bacteria) will do the trick.

Question 7

What are the main adverse effects of clindamycin?

Answer 7

It can cause pseudomembranous colitis!!!!! (although most cases now are caused by the penicillin family drugs because they are prescribed more frequently).

Question 8

What do we give to treat pseudomembranous colitis?

Answer 8

Oral vancomycin or metronidazole (the latter is preferred due to inexpensiveness and because vancomycin can contribute to VRE).

Question 9

What is the clinical use of Linezolid?

Answer 9

For gram positives.
Frequently used in combination with a broad spectrum beta lactam for empiric coverage of hospital acquired pneumonia and in documented S.aureus infections (including MRSA).
Also active against VRE.

Question 10

How is linezolid administered?

Answer 10

Both IV and oral forms are available - in contrast to vancomycin which is only IV.

Question 11

What are the adverse effects of linezolid?

Answer 11

Can cause :

1. Bone marrow suppresion (thrombocytopenia, anemia, neutropenia).
2. Headaches and GI irritation.
3. Can precipitate symptoms of serotonin syndrome if used with SSRI antidepressants or MAO inhibitors. (avoid in patients on antidepressants).

Question 12

What drugs are included in the macrolides?

Answer 12

1. Erythromycin
2. Azithromycin
3. Clarithromycin
4. Telithromycin