Antibiotics

Question 1

What are the common B-lactams used?

Answer 1

Penicllins -
Benzyl Penicillin
Amoxicillin, ampicillin
Co-amoxiclav
Flucloxacillin
Piperacillin
Imipenem, meropenem

Cephalosporins

Question 2

Benzyl Penicillin

Answer 2

Inhibits cell wall synthesis
Largely acts against Gram positive organisms.
It is the best choice for intra-venous treatment of serious pneumococcal, meningococcal and strep pyogenes infection.
Phenoxymethylpenicillin is a derivative that has a slightly better absorption when taken orally.

Question 3

Amoxicillin, ampicillin

Answer 3

Better oral absorption than benzylpenicillin.
Covers streptococci (including enterococci) and some coliforms.

Question 4

Co-amoxiclav

Answer 4

combines amoxicillin with the B-lactamase enzyme inhibitor clavulanic acid, thus extending the spectrum to cover B-lactamase producing coliforms.

Question 5

Flucloxacillin

Answer 5

First choice of treatment for staphylococcal infections.
Methicillin is a similar agent which is used to represent flucloxacillin in laboratory testing - resistant strains are therefore termed methicillin resistant Staph aureus (MRSA)

Question 6

Piperacillin

Answer 6

Broad spectrum penicillin with extended gram negative cover. Useful against Enterococcus faecalis and unlike other B-lactams is active against Pseudomonas species.

Question 7

Imipenem, meropenem

Answer 7

Sub group of penicillins called carbapenems.

Widest spectrum of all and are active against most bacteria, including anaerobes.

Question 8

Cephalosporins

Answer 8

Divided into generations
Activity against gram negative organisms increases from first generation (cephradine) through second generation (cefuroxime) to third generation (cefriaxone) drugs.
Only ceftazidime is active against Pseudomonas species.
Gram positive activity decreases proportionally from first through to third generation drugs.
Use of cephalosporins has decreased markedly as they encourage Clostridium difficile infection (CDI).

Question 9

Aminoglycosides (Parental use only)

Answer 9

Noted for their action against gram negative organisms including pseudomonas.
Most staphylococci are also sensitive but not streptococci.
Gentamicin is the cheapest and most commonly used, but serum levels must be monitored because of potential toxicity.

Question 10

Glycopeptides (parenteral use only)

Answer 10

Vancomycin and teicoplanin
Activity only against gram positive organisms, both aerobic and anaerobic.
Vancomycin levels must be monitored because of potential toxicity.

Question 11

Macrolides

Answer 11

Clarithromycin or Erythromycin activity is mainly against gram positive organism and are often used as an alternative to penicillin in patients with penicillin hypersensitivity (allergy).
Macrolides are effective against organisms causing ‘atypical pneumonia’ (e.g. Chlamydia psittacci, Coxiella burnetti and Mycoplasma pneumoniae) and are first choice therapy against Legionella pneumophila.

Azithromycin is a newer macrolide which is useful for single dose treatment of Chlamydia infection

Question 12

Quinolones

Answer 12

Ciprofloxacin has a wide spectrum of action and is active against nearly all gram negative organisms including pseudomonas.
This group provides virtually the only possibility for oral therapy in the treatment of pseudomonas infection.

Question 13

Miscellaneous Antibiotics

Answer 13

Metronidazole
Fusidic acid
Trimethroprim
Tetracyclines
Clindamycin
Linezolid
Daptomycin

Question 14

Metronidazole

Answer 14

Effective against anaerobes, both gram positive and gram negative.
It is widely used in any situation which may involve anaerobic infection e.g. intra-abdominal sepsis.

Question 15

Fusidic acid

Answer 15

Used only as an anti-staphylococcal drug.
Staphylococcus aureus can develop resistance very readily and thus it should always be used in combination with other anti-staphylococcal drugs such as flucloxacillin.
Diffuses well into bone and tissues and so is useful in staphylococcal osteomyelitits and pneumonia.

Question 16

Trimethoprim

Answer 16

Used in treatment of urinary infections.
Trimethoprim and sulfamethoxazole are marketed together as co-trimoxazole.
Sometimes used for treatment of chest infections as it does not predispose to Clostridium difficile infection.

Question 17

Clindamycin

Answer 17

Only lincosamide antibiotic in common use.
Good activity against gram positive organisms such as staphylococci and streptococci. Also good activity against anaerobes.
Has very good tissue penetration - e.g. into bone - and can be taken orally.
The disadvantage is that it is a common cause of pseudo-membranous colitis.

Question 18

Linezolid

Answer 18

Active against MRSA.

Unlike glycopeptides it can be taken orally, but can cause bone marrow suppression.

Question 19

Daptomycin

Answer 19

Novel agent active against Gram positive organisms only and may be useful for the treatment of serious MRSA infections.

Question 20

Urinary Tract agents only

Answer 20

Nalidixic acid is a urinary antiseptic with activity against gram-negative aerobes (coliform) organisms.
Completely excreted in urine, the only indication for its use is coliform urinary tract infections.

Nitrofurantoin is a further urinary antiseptic agent.
Effective against most gram negative organisms with the exception of Proteus and Pseudomonas spp.
Unlike nalidixic acid, is effective against some gram positive organisms.