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Sulfonamides & Cotrimoxazole:

Sulfonamides & Cotrimoxazole Dr Reena Verma M.D (Pharmacology)


Overview Introduction History Structure Classification Spectrum Mechanism of action Resistance Pharmacokinetics Uses Adverse effects Drug interactions

Introduction :

Introduction First chemotherapeutic agents Employed effectively for prevention and cure of bacterial infections in humans Status  small place in therapeutic armamentarium

History :

History 1932: Farben industries patented prontosil azo -dyes Domagk proved efficacy in mice  awarded Nobel prize in 1938 Pasteur institute: discovered sulfanilamide as the active component ( bioactivation ) Elixir – sulfanilamide disaster (1937) Federal Food, Drug, and Cosmetic Act - 1938



Classification :

Classification Short-acting (4-8 hours) Sulfadiazine Intermediate-acting (8-12 hours) Sulfamethoxazole (SMX) - a component of Co- trimoxazole Long-acting (7 days) Sulfadoxine Sulfamethopyrazine Special purpose Sulfacetamide Mafenide Silver sulfadiazine Sulfasalazine olsalazine


ANTIBACTERAL SPECTRUM Bacterio static Cover many gram positive &gram negative bacteria Sensitive strains are- Strepto.pyogenes , H.influenzae , H.ducreyi , C.granulomatis , V.cholerae , Chlamydae , Actinomyces , Nocardia & Toxoplasma Anaerobics are not susceptible Resistance & better options - use has declined


Cotrimoxazole Combination of sulfamethoxazole and trimethoprim Conc ratio: 20:1 Dose ratio : 5:1 (400mg + 80mg) Produces sequential block and synergism

Mechanism Of Action:

Mechanism Of Action Act on bacteria which synthesize their own folic acid Structural analogues +competitive antagonists of PABA Sequential block

Slide 10:

DHFRase Trimethoprim Dihydropteroate synthase Sulfonamides Glutamate In bacteria Nucleic acid, AA RNA, DNA & Proteins Folic acid DHFRase In humans DHFA THFA Dihydropteroic acid Pteridine + PABA


Resistance Random mutation & selection Conjugation Alterations Low affinity of folate synthetase Permeability or efflux of drug Alternative metabolic pathway Increased production of PABA Cross resistance

Pharmacokinetics :

Pharmacokinetics A  nearly complete absorption, never given s.c or i.m D  wide, PPB - 10-95%, cross placenta & BBB, CSF Conc = Plasma conc. M  acetylation, metabolite inactive but toxic E  less soluble in acidic urine, ppt - crystalluria

Uses :

Uses Rarely used as single agent Replaced by co-trimoxazole Sulfomethoxazole + trimethoprim Conc. Ratio 20:1 Dose ratio 5:1 (400mg+80mg) Reasons for combining similar half-life(10 hours) synergistic combination

Uses of sulfonamides :

Uses of sulfonamides Acute uncomplicated UTI by E.coli - sulfisoxazole Outmoded uses: Nocardiosis , Chancroid , LGV Sulfadiazine + pyrimethamine : Rx + prevention of recurrence of Toxoplasmosis Sulfadoxime + pyrimethamine : chloroquine resistant Falciparum malaria Sulfasalazine : ulcerative colitis & Rheumatoid arthritits Topical: Sulfacetamide - trachoma & bacterial conjuntivitis Silver sulfadiazine: burns Mafenide : active in pus against pseudomonas & clostridium

Uses of Cotrimoxazole:

Uses of Cotrimoxazole UTI : 5-10 days DS b.d Acute cystitis : single dose therapy 4 tabs DS Prostatits : Trimethoprim alone RTI : one DS bd Bacterial diarrhea & dysentry Nocardiosis STD’s – Chancroid , LGV, NSU, gonorrhea Meliodosis Drug of choice : infections caused by pneumocystis jeroveci , immunocompromised pts Typhoid: resistance

Adverse effects :

Adverse effects Crystalluria & renal toxicity Hypersensitivity  rashes, stevens -johnson syndrome, drug fever Hemolytic anemia (in G6PD def) Topical use  contact sensitisation ( not permitted ) Cotrimoxazole Megaloblastic anemia in folate deficient people


Stevens – Johnson Syndrome

Drug interactions :

Drug interactions Displacing from PPB sites  increased activity of OAC, SFU, MTX Diuretics with cotrimoxazole : thrombocytopenia Sulfonamides displaced by aspirin & NSAIDs


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