Antibiotics and Infection 2

Question 1

Name and describe the mechanisms of action of an antibiotic that can be used to target the bacterial cytoplasm and state a common S/E?

Answer 1

Metronidazole - BACTERICIDAL to ANAEROBES
Good against PROTOZOA
Forms O2 radicals after activation inside the bacteria
Can be given PR (IBD) and crosses the BBB (brain abscess penetration)
Disulferam interaction with alcohol

Question 2

Name four types of antibiotics that target the bacterial ribosome?

Answer 2

1. Macrolides (X-mycin) (except clindamycin and gentamycin)
2. Lincosamides - clindamycin
3. Tetracyclines
4. Aminoglycosides - gentamycin

Question 3

Describe the mechanism of action of macrolides and give examples and describe how they are excreted and name common S/E?

Answer 3

Inhibit protein synthesis by binding to 50s ribosome
Good against ATYPICALs and both grams
Excreted in bile and urine
Examples: Erythromycin, azithromycin, clarythromycin
S/E - Prolonged QT and Hepatic enzyme inhibitor (phenytoin and warfarin)

Question 4

Describe the mechanism of action of lincosamides?

Answer 4

Clindamycin
Inhibits protein synthesis the same as macrolides - 50s ribosome
Good against Toxic-shock causing staph aureus

Question 5

Describe the mechanism of action of tetracylines and give examples and describe how they are excreted?

Answer 5

Doxycycline
Inhibit protein synthesis by binding to tRNA 30s ribosome = BACTERIOSTATIC and good ANTI-PROTAZOALS
Absorption reduced by milk and antacids
Excreted in bile

Question 6

Describe both the contraindications of using tetracyclines (3) and their S/E?

Answer 6

1. Pregnancy
2. Children under 12
3. Breastfeeding
   - Deposited in growing bones and teeth
   S/E - photo sensitivity and GI disturbance

Question 7

Describe the mechanism of action of aminoglycosides and give examples and describe how they are excreted and name three C/I?

Answer 7

Gentamycin
Inhibits ribosome at 50s and 30s subunits
Concentration dependant killing (OD)
Renally excreted - 99% unchanged in urine
C/I - Renal failure, myasthenia gravis, ototoxicity with furosimide

Question 8

Name three types of antibiotics that target the bacteria at the chromosome?

Answer 8

1. Quinilone - Ciprofloxacin
   2 Trimethoprim
2. Nitrofurentoin

Question 9

Describe the mechanism of action of quinalones and give examples and describe three C/I?

Answer 9

Ciproflaxacin
Inhibits DNA gyrase
100% bioavailable with increased cell penetration
C/I - 1. Epilepsy (reduces seizure threshold)
2. Arthropathy (tendon rupture)
3. C.diff association

Question 10

Describe the mechanism of action of Trimethoprim and describe a combination therapy that is useful and name four C/I?

Answer 10

Dihydro-reductase inhibitor (folate antagonist)
With sulfamethoxazole - SEPTRIN (PCP and malaria)
Used for UTI
1. BM suppression
2. Pregnancy
3. Renal failure
4. Methotrexate

Question 11

Describe the mechanism of action of Nitrofurentoin and name two contraindications?

Answer 11

BACTERICIDAL - active concentration only found in urine (UTI)

1. Renal impairment
2. Pregnancy

Question 12

Name the two organisms that commonly cause cellulitis?

Answer 12

Staph aureus

B-haemolytic strep (group A and B)

Question 13

Describe the TYPICAL treatment for cellulitis?

Answer 13

Flucoxacillin - PO/2wks
If moderate/severe - high dose IV
Outpatients (IV ceftrioxone (3rd))
Clindamycin (lincosamide) - alternative although S/E c.diff

Question 14

Name antibiotics effective against MRSA?

Answer 14

Vancomycin (S/E tinnitis)

Teicoplanin

Question 15

Describe management of meningitis in the community?

Answer 15

Benzylpenicillin IM

Question 16

What are the main causative agents for meningitis?

Answer 16

1. Neisseria meningitidis
2. Strep pneumoniae
3. H. Influenza
   - Group B step - neonates
   - E.coli - neonates
   - Listeria = neonates and older
   - Staph Aureus - older

Question 17

Describe the management of meningitis in a hospital setting?

Answer 17

Ceftrioxone/cefotaxime IV

Give dexamethasone as well

Question 18

How should household contacts of meningitis patients be managed?

Answer 18

Rifampacin or ciprofloxacin

Ceftrioxone in pregnancy

Question 19

What are the most likely causative organisms for bacterial endocarditis?

Answer 19

Native valve - strep viridens
Prosthetic valve - staph aureus
Always suspect SBE in pts with a NEW ONSET murmer

Question 20

Describe the management of bacterial endocarditits?

Answer 20

Strep viridens = benzylpenicillin and gentamycin
Staph aureus = flucoxacillin and rifampacin
Enteroccocus = Amoxicillin and gentamycin
If allergy = vancomycin and gentamycin