SULPHONAMIDE , TRIMETHOPRIM

SULPHONAMIDE:

MECHANISM:

                         Sulphonamide inhibits folate synthase enzyme . Thus bacteria cannot synthesize the folic acid required for its growth . 

This drug does not affect the folic acid level in humans , because humans acquire folic acid directly from food and it's not synthesized.

DRUGS:
Short acting : Sulfisoxazole
Intermediate acting : Sulfadiazine , Sulfamethaoxazole
Long acting : Sulfadoxime
For use in GIT : Sulfasalazine
For topical use : Sulfacetamide, Silver Sulfadiazine

Pharmacokinetics:

1. Taken orally 
2. Metabolized in liver by acetylation
3. Crosses placenta and Blood Brain Barrier
4. Excreted in urine

Use: 

1. Sulfisoxazole used in UTI
2. Sulfadiazine used in nocardiasis 
3. Sulfadiazine + Pyrimethamine used for Toxoplasmosis and as prophylaxis of Pneumocystitis jiroveci
4. Sulfadoxime + Pyrimethamine used in malaria .
5. Sulfasalazine is used in Ulcerative colitis .
6. Sulfacetamide is used for Ocular infections
7. Silver sulfadiazine is used in burns patients .

Adverse Effects:

1. Aplastic Anemia 
2. Bilirubin displacement from plasma protein leading to Kernicterus
3. Crystalluria
4. Rash 
5. SLE
6. Hemolysis in patients with G-6PD deficiency 

                      mnemonic : ABC RAsH


TRIMETHOPRIM:
MECHANISM:
                         These drugs inhibit Folate reductase enzyme , thus inhibiting the synthesis of THFA required for survival of bacteria . 
It is specific for bacterial folate reductase enzyme and has no effects on humans .

PHARMACOKINETICS:

1. Given orally
2. Metabolized in liver
3. Excreted in urine

USE:

1. It is combined with sulphnomides and used widely.
2. Used alone in UTI and Prostitis .

Adverse Effects:

1. Megaloblastic Anemia
2. Leukopenia
3. Pancytopenia
4. Hyperkalemia ( due to amiloride like action , amiloride is a Potassium sparing diuretic ).