Infections, Penicillins

Question 1

Although benzylpenicillin sodium is effective in the treatment of tetanus, what is the preferred agent? How does this preferred agent work?

Answer 1

Metronidazole is the preferred agent (think alcohol contraindication) which works by entering bacterial and protozal cells and interfering with their genetic material.

Question 2

Why must benzylpenicllin be given by injection?

Answer 2

It is inactivated by gastric acid and absorption from the GI tract is low.

Question 3

Which penicllin is used for the treatment of early syphilis and late latent syphilis; it is given by intramuscular injection?

Answer 3

Benzathine benzylpenicillin

Question 4

Phenoxymethylpenicillin (Pen V) has similar spectrum of activity to benzylpenicillin but is less active. It is orally administered due to higher stability but should not be used for what?

Answer 4

Pen V should not be used for serious infections because absorption can be unpredictable and plasma concentrations variable.

Question 5

What is Pen V/Phenoxymethylpenicillin used primarily for? (treatment not prophylaxis) [2]

Answer 5

1. RTI in children.
2. Steptococal tonsillitus.]

Prophylaxis against streptococcal infections following rheumatic fever and against pneumococcal infections following splenectomy or in sickle-cell disease.

Question 6

Pen V/Phenoxymethylpenicllin is used for the prophylaxis of what? [2]

Answer 6

1. Streptococcal infections following rheumatic fever.

2. Pneumoccocal infections following splenectomy or in sickle-cell disease.

Question 7

Most __________ are now resistant to benzylpenicllin because they produce what?

Answer 7

Most staphylococci are now resistant to benzylpenicillin because they produce penicllinases.

Flucloxacillin, however, is not inactivated by these enzymes and is thus effective in infections caused by penicillin-resistant staphylococci, which is the sole indication for its use.

Question 8

What is the sole indication for the use of flucloxacillin?

Answer 8

Treatment of penicillin-resistant staphylocci as it is not inactivated by penicillinases.

Question 9

Temocillin is active against Gram-negative bacteria and is stable against a wide-range of beta-lactamases. It should be reserved for the treatment of what?

Answer 9

Temocillin should be reserved for the treatment of infections caused by beta-lactamase-producing strains of Gram-negative bacteria, including those resistant to third gen cephalosporins.

Note: Temocillin is not active against pseudomonas aeruginosa or acinetobacter spp.

Question 10

Temocillin is active against Gram-negative bacteria and is stable against a wide-rande of beta-lactamases.

What is it not active against? (2)

Answer 10

P. aeruginosa or acinetobacter spp.

Question 11

Which of the following IS active against P.aeruginosa?

Temocillin
Piperacillin with tazobactam
Pivmecillinam

Answer 11

Piperacillin with tazobactam has activity against a wider range of Gram-negative organisms than ticarcillin with clavulanic acid and it is more active against Pseudomonas aeruginosa.

Question 12

Which of the following IS active against MRSA?

Piperacillin with tazobactam.
Ticarcillin with clavulanic acid.
Doxycycline
Clindamycin.

Answer 12

A tetracycline or clindamycin can be used for bronchiectasis caused by MRSA.

Question 13

Why should ampicillin not be used for blind treatment or in hospital patients without first checking sensitivity of causative organisms?

Answer 13

Almost all staphylococci, approx. 60% of E. coli strains and approx. 20% of Haemophilus influenzae strains are now resistant. The likelihood of resistance should therefore be considered before using ampicillin for the ‘blind’ treatment of infections; in particular, it should not be used for hospital patients without checking sensitivity.

Question 14

Ampicillin is well excreted in the bile and urine. It is principally indicated for the treatment of exacerbations of chronic bronchitis and middle ear infections, both of which may be due to what?

Answer 14

Streptococcus pneumoniae
OR
H. Influenzae

Question 15

What is the effect of food in the gut on the absorption of ampicillin?

Answer 15

Ampicillin can be given by mouth but less than half the dose is absorbed, and absorption is further decreased by the presence of food in the gut.

Question 16

What can occur when broad-spectrum penicillins such as ampicillin are used for blind treatment of a sore throat?

Answer 16

Maculopapular rashes commonly occur with ampicillin (and amoxicillin) but are not usually related to true penicillin allergy. They almost always occur in patients with glandular fever; broad-spectrum penicillins should not therefore be used for ‘blind’ treatment of a sore throat. The risk of rash is also increased in patients with acute or chronic lymphocytic leukaemia or in cytomegalovirus infection.

NB: glandular fever is caused by epstein barr

Question 17

Unlike ampicillin, amoxicllin is unaffected by what?

Answer 17

The presence of food in the gut.

NB: amoxicillin may also be used for the treatment of lyme disease.

Question 18

What is co-amoxiclav?

Answer 18

Amoxicllin with the betalactamase inhibitor clavulanic acid.

Question 19

What is co-fluampacil? What is it used to treat?

Answer 19

A combination of ampicillin with flucloxacillin (as co-fluampicil is available to treat infections involving either streptococci or staphylococci (e.g. cellulitis).

Question 20

How do piperacillin with tazobactam and ticarcillin with clavulanic acid compare in terms of spectrum of activity and activity against P. aeruginosa in particular?

Answer 20

Piptaz has activity against a wider range of Gram-negative organisms than ticarcillin with clavulanic acid and it is more active against pseudomonas aeruginosa.

Question 21

For severe pseudomonas infections, Piptaz and ticarcillin with clavulanic acid can be given with what other class of antibiotics due to a synergistic effect?

Answer 21

For severe pseudomonas infections these antipseudomonal penicillins can be given with an aminoglycoside (e.g. gentamicin) since they have a synergistic effect.

Question 22

What antibacterial drugs have a mechanism of action which involves disrupting cell wall synthesis? (5)

Answer 22

1. Carbapenems (imipenem etc)
2. Cephalosporins
3. Glycopeptides (vanco)
4. Monobactams (Aztreonam)
5. Penicillins

Question 23

How do the generations of cephalosporin differ in terms of activity?

Answer 23

The 1st Gen are predominantly active against Gram+ve organisms with succeeding generations more active against Gram-ve organisms.

Question 24

What class of antibacterial is clindamycin? How does it work?

Answer 24

Clindamycin is a lincosamide which inhibits protein synthesis via 50S binding.

Question 25

What class of antibacterial is daptomycin? How does it work?

Answer 25

Daptomycin is a lipopeptide which inhibits protein, DNA and RNA synthesis.

Question 26

What class of antibacterial is linezolid? How does it work?

Answer 26

Linezolid is an oxalidinone protein synthesis inhibitor (initiation step)

Question 27

Why is the marketing slogan of ertapenem ‘The Power of One’?

Answer 27

Its dose is 1g once daily.

Question 28

Imipenem and meropenem are associated with dose-related what?

Answer 28

Seizures

Question 29

Dapsone, Clofazimine and Rifampicin all have a place in the treatment of what?

Answer 29

Leprosy - caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis.

Clofazimine can induce pink-brown skin pigmentation within a few weeks of its use.