Katzung 12th ed - Chapter 46 - Sulfonamides, Trimethoprim, Quinolones (2) Flashcards
What is the basic mechanism of action of sulfonamides?
Inhibition of DNA synthesis. Sulfonamides are structural analogues of PABA, and competitively inhibit folic acid synthesis.
It is interesting to note that sulfonamides do NOT inhibit growth of which microorganism?
Rickettsia. Sulfonamides actually STIMULATE the growth of rickettsia.
What are some clinical uses of sulfonamides?
Sulfonamides are rarely used as a single agent. They are used in combination with trimethoprim (sulfamethoxazole + trimethoprim = Bactrim) to treat UTI, Pneumocystis jiroveci pneumonia, toxoplasmosis…
What is the basic mechanism of action of trimethoprim?
Trimethoprim inhibits a step in the synthesis of folic acid (leading to DNA synthesis). This is a different step to the one inhibited by sulfonamides.
Sulfonamides and trimethoprim: are they bactericidal or bacteriostatic?
Sulfonamide alone is bacteriostatic. Trimethoprim alone is bacteriostatic. Sulfonamide in combination with trimethoprim is bactericidal.
Sulfonamides and trimethoprim: What are the routes of metabolism and excretion?
Both are metabolised in the liver and excreted in urine.
Sulfonamides and trimethoprim: Half-life?
10-12 hours. They have similar half-lives and are therefore suitable to use as a combination drug.
What are some adverse effects of sulfonamides?
Stevens-Johnson syndrome, vomiting and diarrhoea, photosensitivity, exfoliative dermatitis.
What would make a microorganism NOT susceptible to sulfonamides or trimethoprim?
If it could make use of exogenous folic acid rather than synthesizing its own.
What can you give safely to patients with a sulphonamide allergy and a UTI?
Trimethoprim.
Name two or three fluoroquinolones.
Norfloxacin, Ciprofloxacin, Moxifloxacin.
What is the basic mechanism of action of fluoroquinolones?
Inhibits DNA synthesis, by inhibiting bacterial topoisomerase II (DNA gyrase).
Ciprofloxacin can be used to treat UTIs by which bacteria? And diarrhoea by which bacteria?
UTIs: Pseudomonas, amongst many others
Diarrhoea: Shigella, Campylobacter, Salmonella, E.coli
Half-life of quinolones?
3-4 hours.
