COTRIMOXAZOLE

MECHANISM:
                    Cotrimoxazole is a combination of sulfamethaoxazole + trimethoprim in a ratio of 5:1 .
Sulfamethaoxazole and trimethoprim separately are bacteriostatic drugs but when combined together they become bacteriocidal .
Cotrimoxazole is a bacteriocidal drug.
Bacteriocidal activity is due to sequential blockade .
Sulfamethoxazole inhibit folate synthase and trimethoprim inhibits
folate reductase.  

PHARMACOKINETICS:

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

USE:

1. UTI
2. RTI
3. MRSA
4. Drug of choice for Pneumocystitis jirovecii and nocardiosis .

ADVERSE EFFECTS:

It has adverse effects of both sulphonamides and trimethoprim .

SULPHONAMIDE 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 SIDE EFFECTS 

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