Antimicrobials V

Question 1

what are the sulfonamides

Answer 1

Sulfadiazine
Sulfamethoxazole
Sulfasalazine

Question 2

mechanism of sulfonamides (name them)

Answer 2

sulfadiazine, sulfamethoxazole, sulfasalazine

structural analogues of PABA so competes with PABA for dihydropterote synthase and folic acid production

competitive inhibitors of PABA

Question 3

what synergistic effect does the combination of sulfonamides and dihydrofolate reductase (trimethoprim) cause

Answer 3

synergistic activity that leads to sequential inhibition of folate synthesis

Question 4

clinical application of sulfonamides (name them)

Answer 4

sulfadiazine, sulfamethoxazole, sulfasalazine

• topical treatment to treat ocular and burn infections
• UTI
• Orally for ulcerative colitis, enteritis, and IBD

Question 5

what group of sulfonamides must be reduced in renal failure

Answer 5

oral absorbable

oral non absorbable and topical not affected

Question 6

adverse effects of sulfonamides (name them)

Answer 6

sulfadiazine, sulfamethoxazole, sulfasalazine

common: fever, skin rash, photosensitivity, urticaria nausea, vomiting, diarrhea

Crystalluria/nephrotoxicity
Hematopoietic effects esp in G6PD
Kernicterus: competes with bilirubin for binding site on albumin

Question 7

what other drugs does sulfonamides compete with for binding site hence increasing the levels

Answer 7

phenytoin, warfarin, methotrexate

Question 8

contraindications of sulfonamides (name them)

Answer 8

sulfadiazine, sulfamethoxazole, sulfasalazine

newborns and infants less than two months due to risk of kernicterus

Question 9

mechanism of trimethoprim

Answer 9

selectively inhibits dihydrofolate acid reductase that converts dihydrofolic acid to tetrahydrofolic acid –> inhibition of purine, pyrimidines, and AA synthesis

Question 10

clinical application of trimethoprim

Answer 10

• UTI
• Bacterial prostatitis
• Vaginitis

same activity as sulfonamides except it is more potent

Question 11

adverse effects of trimethoprim

Answer 11

Anti-folate effects (hence can treat withe folic acid):

Megaloblastic anemia
Leucopenia
Granulocytosis

skin rash and pruritus

Question 12

contraindications of trimethoprim

Answer 12

pregnancy due to its antifolic effects

Question 13

what is co-trimoxazole and its mechanism

Answer 13

combination of trimethoprim and sulfamethaxole –> sequential blockade of folate synthesis

Question 14

clinical application of co-trimoxazole

Answer 14

• uncomplicated UTI
• prevention and treatment of pneumocystis jiroveci
• alternative treatment for toxo

Question 15

adverse effects of co-trimoxazole

Answer 15

same as sulfonamides with AIDs pts experiencing them at a higher level

• Kernicterus
• Crystalluria/Nephrotoxicity
• Hematopoeitic effects esp in G6PD
• fever, rash, leucopenia, diarrhea
• Antifolate effects as well

Question 16

contraindication of co-trimoxazole

Answer 16

pregnancy due to anti-folate effects

Question 17

mechanism of metronidazole

Answer 17

forms cytotoxic products that interfere with nucleic acid synthesis – activity against protozoa and bacteria

Question 18

clinical applications of metronidazole

Answer 18

GET GAP

Giardiasis
Entamoeba Histolytica
Trichomonas (vaginitis)
Gardnerella vaginalis
Anaerobes like bacteroides and clostridium
Pylori Helicobacter

Question 19

adverse effects of metronidazole

Answer 19

Disulfiram like effects: avoid alcohol
Opportunistic Fungal infection
Dark discoloration of urine

Question 20

contraindication of metronidazole

Answer 20

pregnancy esp 1st trimester: no data for its safety

Question 21

mechanism of Nitrofurantoin

Answer 21

urinary antiseptic that is quickly excreted in the urine –> bacteria reduces nitrofurantoin in urine to reactive intermediates –> damage bacterial DNA –> suppresses bacteriuria

Question 22

use of nitrofurantoin

Answer 22

uncomplicated UTI

Question 23

adverse effects of nitrofurantoin

Answer 23

anorexia, nausea, and vomiting

neuropathies and hemolytic anemia in G6PD

Question 24

contraindication of nitrofurantoin

Answer 24

pregnancy at 38-42 weeks and infants less than one month due to hemolytic anemia in newborn

significant renal insufficiency due to accumulation of drug