Anti-Metabolites

ANTI-METABOLITES

Q. 1

The ratio of concentration of drug in co-trimoxazole trimethoprim and sulfamethoxazole is:

 A

1 : 2

 B

1 : 3

 C

1 : 5

 D

3 : 1

Q. 1

The ratio of concentration of drug in co-trimoxazole trimethoprim and sulfamethoxazole is:

 A

1 : 2

 B

1 : 3

 C

1 : 5

 D

3 : 1

Ans. C

Explanation:

Trimethoprim is usually given orally, alone or in combination with sulfamethoxazole, which has a similar half-life.
Trimethoprim-sulfamethoxazole can also be given intravenously.
Trimethoprim is well absorbed from the gut and distributed widely in body fluids and tissues, including cerebrospinal fluid.
 
Because trimethoprim is more lipid-soluble than sulfamethoxazole, it has a larger volume of distribution than the latter drug.
 
Therefore, when 1 part of trimethoprim is given with 5 parts of sulfamethoxazole (the ratio in the formulation), the peak plasma concentrations are in the ratio of 1:20, which is optimal for the combined effects of these drugs in vitro. 
 
Ref: Deck D.H., Winston L.G. (2012). Chapter 46. Sulfonamides, Trimethoprim, & Quinolones. In B.G. Katzung, S.B. Masters, A.J. Trevor (Eds), Basic & Clinical Pharmacology, 12e.

Q. 2

Which of the following statements is not true regarding sulfonamides –

 A

Sulfasalazine is absorbed well from GIT

 B

Crystalluria can occur with sulfonamide administration

 C

Sulfonamide administration to Newborn may cause Kernicterus

 D

Sulfonamides are of value in treatment of infections due to Norcardia species

Q. 2

Which of the following statements is not true regarding sulfonamides –

 A

Sulfasalazine is absorbed well from GIT

 B

Crystalluria can occur with sulfonamide administration

 C

Sulfonamide administration to Newborn may cause Kernicterus

 D

Sulfonamides are of value in treatment of infections due to Norcardia species

Ans. A

Explanation:

Ans. is ‘a’ i.e., Sulfasalazine is absorbed well from GIT

o Sulfasalazine is poorly absorbed from the gastrointestinal tract.

  • Sulfasalazine is a compound of sulfapyridine and 5 – aminosalicylicacid.
  • Only 10-20% of orally administered sulfasalazine is absorbed.

o It is split up in the intestine to release sulfapyridine and 5 – ASA. Sulfapyridine is well absorbed while 5 – amino salicylic acid remains unabsorbed.

  • Sulfonamides can precipitate in urine specially at neutral or acid pH producing crystalluria, hematuria or even obstruction. Crystalluria is treated by administration of sodium bicarbonate to alkalinize the urine and fluids to maintain adequate hydration.
  • Crystalluria is minimum with soluble drugs like sulfisoxazole.

o Kernicterus may be precipitated in new born specially if premature by displacement of bilirubin from plasma protein bending sites and more permeable blood brain barrier.

  • Sulfonamides are primarily bacteriostatic. They inhibit both gram positive and gram negative bacteria, nocardia, chlamydia trachomatis and some protozoa.

o Sulfadoxine is longest acting whereas sulfacystine is shortest acting.


Q. 3

Trimethoprim acts by-

 A

Inhibiting DHFR

 B

Inhibiting protein

 C

Inhibiting cell wall

 D

Inhibiting cell membrance

Q. 3

Trimethoprim acts by-

 A

Inhibiting DHFR

 B

Inhibiting protein

 C

Inhibiting cell wall

 D

Inhibiting cell membrance

Ans. A

Explanation:

Ans is ‘a’ i.e., Inhibiting DHFR


Q. 4

Treatment of choice for chloroquine resistant malaria is –

 A

Mefloquine

 B

Sulfadoxine + Pyrimethamine

 C

Primaquine + Chloroquine

 D

Chloroquine + Pyrimethamine

Q. 4

Treatment of choice for chloroquine resistant malaria is –

 A

Mefloquine

 B

Sulfadoxine + Pyrimethamine

 C

Primaquine + Chloroquine

 D

Chloroquine + Pyrimethamine

Ans. B

Explanation:

Ans. is ‘b’ i.e., Sulphadoxine + Pyrimethamine 

o In chloroquine resistant cases of P. falciparum malaria, the first line of treatment is artesunate combination theraphy consisting of —> Artesunate + Sulphadoxine/Sulphalene + Pyrimethamine.

o In case of resistant to these drugs or to treat severe and complicated malaria, quinine is the drug of choice.

Quiz In Between



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