Antimicrobial Chemotherapy 3

Question 1

Describe the factors to be considered in the choice of Benzyl-Penicillin as an antimicrobial.

Answer 1

Benzyl-penicillin was the first known antibiotic and is largely used against gram positive organisms (NOTE: meningococci, which are gram negative but still important).
It is the best choice for intravenous treatment of serious pneumococcal, meningococcal and Strep. pyogenes (group A) infections.
Phenoxymethylpenicillin is a derivative that has slightly better absorption when taken orally.

Question 2

Describe the factors to be considered in the choice of aminoglycosides as an antibiotic.

Answer 2

Parental use ONLY.
Action again Gram negative organisms.
(Most staphylococci are sensitive but not streptococci)
Gentamycin is the cheapest and most commonly used.
Serum levels must be monitored due to potential toxicity.

Question 3

Describe the factors to be considered in the choice of glycopeptides in treatment of infection.

Answer 3

Parental use only
Activity against only Gram positive organisms (both aerobic and anaerobic)
Vancomycin (more toxic) and Teicoplanin (less toxic).

Question 4

Describe the factors to be considered in the choice of macrolides to treat infection.

Answer 4

Clarithromycin or Erythromycin activity is mainly against Gram positive organisms.
These are used as an alternative in patients that are allergic to penicillin.
(Azithromycin used for a single dose treatment of chlamydia).

Question 5

Describe the factors to be considered in the choice of quinolones to treat infection.

Answer 5

They have a wide spectrum of action, and are active against all gram negative organisms (including pseudomonas).
These are the only possible oral therapy of pneumonia.

Question 6

Describe the factors to be considered in the choice of metronidazole to treat infection.

Answer 6

It is effective against anaerobes, gram positive and gram negative.
Any resistance is virtually unknown.
Has no useful activity against aerobes.
Widely used in any situation that may involve anaerobic infection (e.g. intra-abdominal sepsis).

Question 7

Describe the factors to be considered in the choice of trimethoprim to treat infection.

Answer 7

Used in the treatment of UTIs.
Can be used in combination with Sulphamethoxazole = co-trimoxazole.
This is used for chest infections on the grounds that it doesn’t pre-dispose to C.difficile.

Question 8

Describe the factors to be considered in the choice of fusidic acid in the treatment of infection.

Answer 8

Used as an anti-staphylococcal drugs.
Always used in combination with other anti-staphylococcal drugs (e.g. flucloxacillin).
Diffuses well in tissue.

Question 9

Describe the factors to be considered in the choice of tetracyclines to treat infection.

Answer 9

Should not be given to pregnant women or children under the ages of 12 as they are deposited in teeth and bone.

Question 10

Describe the factors to be considered in the choice of clindamycin to treat infection.

Answer 10

Clindamycin is the only lincosamide antibiotic in common use.
Has good activity against gram positive organisms. (e.g. staphylococci and streptococci).
Good activity against anaerobes.
Good tissue penetration.
However,
It is a common cause of pseudo-membranous colitis.

Question 11

Describe the factors to be considered in the choice of linezolid to treat infection/

Answer 11

Activity against MRSA.
Unlike glycopeptides it can be given orally.
However, can cause bone marrow suppression and lower platelet counts.

Question 12

Name two agents only used in treatment of lower UTIs.

Answer 12

Nalidixic acid (quinolone) = urinary antiseptic active only against gram negative aerobes (coliforms). Is completely excreted in urine.
Nitrofurantoin (quinolone) = effective against most gram negative organisms, unlike *above, it is also active against gram positives.

Question 13

Describe allergic reactions in relation to antimicrobial drugs e,.g. penicillin.

Answer 13

Allergic reactions could occur from any antimicrobial drug but are most commonly associated with Beta-Lactams.
True penicillin hypersensitivity is rare.
(approx 10% of truly penicillin allergic patients are also allergic to cephalosporins.

Question 14

Describe anaphylactic shock as an example of immediate hypersensitivity.

Answer 14

Anaphylactic shock usually follows parental administration of the antibiotic.
It is IgE mediated and occurs within MINUTES of administration.
It is characterised by itching, urticaria, nausea, vomiting, wheezing and shock.

Question 15

Describe delayed hypersensitivity to an allergic reaction

Answer 15

This takes hours or days to develop.
It can have an immune complex or a cell-mediated mechanism.
Drug rashes are the most common, but there is also;
drug fever, serum sickness and erythema nodosum.

Question 16

Describe gastrointestinal side effects from usage of antibiotics.

Answer 16

E.g. nausea, vomiting, diahorrea, which is associated with toxin production from C.difficile.

Question 17

Describe the problems in healthcare, caused by C.difficile.

Question 18

Describe thrush as a side effect of antibiotics.

Answer 18

Broad spectrum antimicrobials suppress normal flora in other parts of the body, resulting in overgrowth of resistant organisms.
Therapy with penicillin or cephalosporins may be complicated by overgrowth of the yeast , Candida albicans, resulting in oral/vaginal thrush.

Question 19

Describe liver toxicity as a side effect of antibiotics.

Answer 19

The liver is susceptible to side effects (as it is an important mechanism of secretion).
Side effects are more common in patients with pre-existing liver disease and pregnancy.

Tetracycline and the anti-tuberculous drugs, isoniazid and rifampicin are associated with such toxicity.

Question 20

Describe renal toxicity as a side effect of antibiotics.

Answer 20

The kidney is the most important route of drug excretion.
Nephrotoxicity is dose related and more common in patients with pre-existing renal disease.
Most common with aminoglycosides or vancomycin.

Question 21

List the possible toxic neurological side effects of antibiotics.

Answer 21

Ototoxicity (vancomycin/aminoglycosides)
Optic neuropathy (Ethambutol)
Peripheral neuropathy (Metronidazole and nitrofurantoin)
Encephalopathy and convulsions (Penicillin and cephalosporins - high dose).

Question 22

Describe haematological toxicity as a side effect of antibiotics.

Answer 22

Antimicrobials have a toxic effect on bone marrow, resulting in selective depression of one cell line (e.g. neutropenia) or unselective depression of all bone marrow elements (e.g. pancytopenia).

Question 23

Describe the resulting haematological toxicity of Co-trimoxazole.

Answer 23

The components of co-trimoxazole (sulphonamide and trimethoprim) act by competitive inhibition of folic acid synthesis in both bacterial and mammalian cells.
The resulting folate deficiency leads to megaloblastic anaemia after prolonged therapy.