Antimicrobial Chemotherapy 4

Question 1

Describe susceptible groups that have extra care exercised when administering antimicrobials.

Answer 1

Susceptible groups:
Extremes of age
Pregnant women
Patients with liver or renal deficiency.

Question 2

Describe antimicrobials with a low therapeutic margin.

Answer 2

Should be monitored to ensure maximum efficacy and minimal toxicity.

Question 3

Name some drugs that are contraindicated in children.

Answer 3

Ciprofloxacin as it is thought to affect developing cartilage.

Question 4

Name some drugs that are contraindicated according to the degree of renal insufficiency.

Answer 4

Aminoglycosides, acyclovir.

Question 5

Describe why some drugs are contraindicated according to the degree of hepatic insufficiency.

Answer 5

Antimicrobials may be metabolised by the liver and excreted in bile.
Doses should be decreased in hepatic insufficiency or an alternative drug should be chosen if possible.

Question 6

Name some drugs that are contraindicated when patient is pregnant.

Answer 6

Mutagenic - induce mutation in foetal chromosomes.
Teratogenic - associated with congenital abnormalities.

Question 7

Name the known safe drugs in pregnancy.

Answer 7

Penicillin, Cephalosporins and the urinary antiseptic nitrofurantoin.

Question 8

Define “prophylaxis”.

Answer 8

Prophylaxis is the administration of antimicrobials to prevent the future occurance of infection.

Question 9

Describe how prophylaxis is indicated.

Answer 9

Prophylaxis is indicated in cases where the patient has been exposed to other patients with highly communicable diseases,
OR
If they are shortly about to be subjected to surgical procedures with high post-operative infection rates.

Question 10

Describe empirical antimicrobial therapy.

Answer 10

Empirical antimicrobial therapy is used in targeting infections where the organisms causing it are unknown.
It takes into account the site and type of infection as well as the likely causative organisms and their common antimicrobial susceptibility patterns.

Question 11

Describe the importance of the consideration of the spectrum of the antimicrobial agent.

Answer 11

The antimicrobial chosen should normally be effective against the known or likely causative organism(s).
The choice should be based on results of sensitivity tests after the infecting organism has been isolated.

Question 12

Describe monotherapy.

Answer 12

Monotherapy of antimicrobials is the simplest and generally the best approach.
However it is sometimes insufficient when trying to treat mixed infections by more than one organism.

Question 13

Describe combination therapy.

Answer 13

Combination therapy is useful, as 2 antimicrobials can have an enhanced effect together.
This can minimise the development of resistant strains to any one agent.
To cover mixed infection of more than one organism.

Question 14

Describe the three possible outcomes of antimicrobials in combination.

Answer 14

The effects are additive.
The effects are antagonistic and their combined effect is less than the sum of their individual contributions.
The effects are synergistic and their combined effect is greater than the sum of their individual contributions.

Question 15

Describe the most common combination therapy of antimicrobials.

Answer 15

Combination of penicillin and gentamycin.
Penicillin breaks down the streptococcal cell wall, which allows gentamycin to access the ribosome.
(used in streptococcal infective endocarditis).

Question 16

Describe the synergistic effect of combined antimicrobials.

Answer 16

Two cidal drugs combined or two static drugs is additive or synergistic.

Question 17

Describe the antagonistic effect of the combination of antimicrobials.

Answer 17

One static and one cidal drugs may result in antagonism.

Question 18

Describe the significance of considering the antimicrobials ability to penetrate to the site of infection.

Answer 18

An antimicrobial with high serum concentrations, appropriate spectrum and excellent safety profile, but with the INABILITY to penetrate to the site of infection is of little use in clinical practice.

Question 19

Explain the importance of monitoring gentamycin and vancomycin when prescribed.

Answer 19

These must be monitored carefully as they have a low therapeutic index.
i.e. they have a low toxic dose.

Question 20

State the duration of a standard course of antimicrobial therapy.

Answer 20

7 days

Question 21

State the duration of the course of therapy for osteomyelitis or endocarditis.

Answer 21

Several weeks.

Question 22

State the recommended course of therapy when treating staph. aureus.

Answer 22

Recommended at least 14 days of IV.

Question 23

State the recommended course of therapy for a simple UTI.

Answer 23

Treated with 3 days course of trimethoprim.

Question 24

State the 2 main reasons for monitoring serum levels.

Answer 24

1) to ensure that therapeutic levels have been achieved.
2) to ensure that levels are not so high as to be toxic.

Question 25

State the simplest method of susceptibility testing.

Answer 25

MIC - Minimum inhibitory concentration.
The simplest way to measure it is E-test.

Question 26

State some automated methods of susceptibility testing

Answer 26

There are nationally agreed “cut offs” for MIC values.
If an organism is below these they are considered “sensitive”, and if they are above they are considered “resistant”.

Question 27

List the factors affecting the outcome of susceptibility testing

Answer 27

Route of administration
Dosing schedule
Penetration of antibiotic to the target site
Interactions with other drugs
E-test