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Sulfonamides and Cotrimoxazole

Sulfonamides

Mechanism of Action

Sulfonamides are competitive inhibitors of the bacterial enzyme Dihydropteroate synthetase.

Sulfonamides are structural analogs and competitive antagonists of para amino benzoic acid (PABA). They inhibit normal bacterial utilization of PABA for the synthesis of folic acid, an important metabolite in DNA synthesis. The effects seen are usually bacteriostatic in nature.

Indication

Sulfonamides are not used alone.

It is most often used as part of a synergistic combination with trimethoprim in a 5:1 ratio in co-trimpoxazole. Its primary activity is against susceptible forms of streptococcus, staphylococcus aureus, E.coli, H.influenzae and oral anaerobes.

They can be applied in suppressive therapy of chronic UTI, for streptococcal pharyngitis, gum infection.

Adverse effects

  • Allergies to sulfa-based medications typically cause skin rashes, hives or trouble breathing or swallowing and warrant immediate discontinuation of the medication.
  • Nausea, vomiting and epigastric pain.
  • Crystalluria is dose related.
  • Sulfonamides can cause heamolysis in a dose dependent manner in patients with G6PD deficiency.

Short acting sulfonamides (4-8 hrs)

Sulfadiazine

Brand Name: Sulfadiazine 0.5 g tab.

Intermediate acting sulfonamides( 8-12 hrs)

Sulfamethoxazole

Brand Name: Gantantol 0.5g tab

Sulfamoxole

Sulfonamides, Cotrimoxazole

Long Acting Sulfonamiodes

Sulfadoxine, Sulfamethopyrazine

These are ultra long acting compounds, their action lasting to about >1week. They are not suitable for treatment pyogenic infection.

Special purpose sulfonamides

Sulfacetamide

Brand Name: Locula, Albucid 10%, 20 % , 30% eye drops.

Sulfasalazine

Used in the treatment of ulcerative colitis and rheumatoid arthritis.

Mafenide

Brand Name: Sulfamylon 1% cream for surface application. It has been mainly applied to burn dressing to prevent infection. The biggest disadvantage is burning sensation when applied to raw surface.

Silver sulfadiazine

Used topically as 1% cream. It is used to prevent infection of burnt surface and chronic ulcers.

Cotrimoxazole

It is a fixed dose combination of trimethprin and sulfamethoxazole.

Mechanism of action

Synergistic antibacterial effect when compared to each of its components administered singly. This is because trimethoprim and sulfamethoxazole inhibit successive steps in the folate synthesis pathway.

Indications

  • Urinary tract infection.
  • Respiratory tract infection.
  • Bacterial diarrhoea an dysentry.
  • Chancroid and granuloma inguinale.

Adverse effects

Similar to sulfonamides.

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