Sulfonamides and cotrimoxazole - drdhriti

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Sulfonamides and cotrimoxazole - drdhriti

  1. 1. SULFONAMIDES & COTRIMOXAZOLE Dr. D. K. Brahma Associate Professor, Pharmacology NEIGRIHMS, Shillong
  2. 2. Sulfonamides • The first antimicrobials effective against Pyogenic Bacterial infections. • Derivatives of Sulfanilamide containing a “sufonamido “ring (SO2NH2). • Structurally and chemically related to p-aminobenzoic acid (PABA). • Structurally similar to many drugs – thiazides, acetazolamide, dapsone and sulfonylureas etc. • Physically – available as white powder, mildly acidic and form water soluble salts with bases. • However, indications and practical uses are very few these days.
  3. 3. History – Sulfonamides • Screening of “Dyes” for their antibacterial properties in 1920s. • Sulfonamido-chrysidine – commonly known as “Prontosil red” was the first one effective in streptococcal infection in mice by Domagk. – Cured his daughter • 1937: Prontosil was broken down to release “sulfanilamide” – many sulfonamides were produced. Para-amino-benzene-sulfonamide (sulfanilamide) Prontosil
  4. 4. Sulfonamides - Classification • Short acting: Sulfadiazine, Sulfadimidine, Sulfacetamide • Intermediate acting: Sulfamethoxazole • Long acting: Sulfadoxine, Sulfamethoxypyrazine, Sulfadimethoxine etc. • Topically used: Mafenide, Silver sulfadiazine and Sulfacetamide • Ulcerative colitis: Sulfasalazine
  5. 5. Sulfonamides – Antibacterial Property • Bacteriostatic against gm +ve and gm –ve bacteria • Bactericidal in urine • Susceptible organisms: Str. pyogens, H. influenzae, H. ducreyi, Callymatobacterium grannulomatosis, V. cholerae, Chlamydia, Actinomyces etc. – Few strains of Staph aureus, gonococci, meningococci, pneumococci, E. coli and Shigella • Chlamydiae: trachoma, lymphogrnuloma venereum., inclusion conjunctivitis. Also Actinomyces and Nocardia • Protozoa: – Plasmodium (Sulfadoxine + Pyrimethamine) – Toxoplasmosis (Sulfadiazine + Pyrimethamine) – PCP (Sulfamethoxazole + Trimethoprim = SXT)
  6. 6. Sulfonamides - MOA Woods and Fielde`s Theory:  Bacteriae normally picks up PABA from surroundings to synthesize folic acid  Inhibition of bacterial folic acid synthesis from PABA (enzyme folate synthase) – competitive  Essential metabolic reactions suffer Why no human affect?? Preformed folic acid by human. Evidence of MOA: PABA antagonizes Sulfonamides, only the organisms synthesizing FA Dihydropteroic acid Dihydrofolic acid Enzymes: Pteridine synthetase and Dihydrofolate synthetase
  7. 7. Sulfonamides – MOA image
  8. 8. Sulfonamides - Resistance • Many strains – S. aureaus, pneumococci, gonococci, meningococci, Strep. Pyogens, E. coli and Shigella • Mechanism: 1. Production of increased amounts of PABA (Staph, Neisseria) 2. Folate synthase enzyme has low affinity to sulfonamides 3. Adopt alternative pathway of folate synthesis – structural changes in folate synthase (E coli) – encoded chromosomally and plasmid mediated • Resistant to one sulfonamide – resistant to all • No cross resistance
  9. 9. Sulfonamides – Kinetics • Rapidly and completely absorbed from GIT • Extend of plasma protein binding differs (10 – 95%) – Longer acting ones are highly plasma protein bound – Widely distributed – enters in serous cavity easily • Metabolized by non microsomal acetyl transferase in liver – slow and fast acetylators • Acetylated product – inactive excreted in urine (but, more toxic than parent) – crystalluria • Acetylated form accumulates in blood – toxic in renal faiure • Reabsorbed in tubule
  10. 10. Sulfonamides - ADRs • Nausea, vomiting and epigastric pain • Crystalluria – alkanization of urine • Hypersensitivity (2 – 5%) – rashes, urticaria, drug fever. Exfoliative dermatitis, SJ syndrome (long acting ones) • Hepatitis • Haemolysis – G-6-PD deficiency • Kernicterus – displacement of bilirubin
  11. 11. Individual Sulfonamides • Sulfadiazine: General purpose use – absorbed orally and rapidly excreted. More crystalluria. Preferred in meningitis. • Sulfamethoxazole: slower absorption and lower excretion. 10 Hrs. half life. Combination with Trimethop • Sulfadoxine:Ultra-long acting >1 week. High protein bound – long excretion. Not suitable for Pyogenic infections – low plasma conc.. Used in Malaria, Pneumocystis jiroveci and toxoplasmosis • Sulfacetamide: Ophthalmic use – infections by bacteria, chlamydia, ophthalmia neonatorum etc • Mafendie: Atypical sulfonamide. Local application – inhibits variety of bacteria – active in presence of pus – pseudomonas and clostridia • Silver sulfadiazine: Bacteria, fungi, Pseudomonas. In burn cases
  12. 12. Sulfonamides - Uses • Rarely used now a days systemically • UTI: caused by E. coli and P. mirabilis: Sulfisoxazole – 1 gm 4 times daily • Malaria: sulfadoxine and pyrimethamine combination • Toxoplasmosis: sulfadiazine + pyrimethamine • In Combination with Trimethoprim: Cotrimoxazole • Ulcerative colitis: Sulfasalazine – 1-4 gm initially and 500 mg 6 Hrly. • Locally: – Sodium sulfacetamide: 10-30% ophthalmic solution in bacterial conjunctivitis, trachoma etc. – Mafenide acetate (1% cream) and Silver sulfadiazine 1% cream): Burn dressing and chronic ulcers
  13. 13. Cotrimoxazole – In 1969 Fixed drug combination of Sulfamethoxazole and Trimethoprim SYNERGISM
  14. 14. Trimethoprim • Trimethoprim (trimethyl benzyl pyrimidine) is a diaminopyrimidine, chemically related to Pyrimethamine • Do not confuse: Clotrimazole (antiungal) - Cotrimoxazole is TMP –SMZ, but Sulfadoxine + Pyrimethamine is antimalarial • MOA: Sequential block of folate metabolism • Trimethoprim is 50,000 or more times more active against bacterial DHFRase enzyme than mammalian • So, no harm to human folate metabolism
  15. 15. Tetrahydropteroic acid synthetase Dihydrofolic acid Dihyrofolate reductase Tetrahydrofolic acid Purine synthesis DNA synthesis Sulfonamides Trimethoprim MOA OF TRIMETHOPRIM-SULFAMETHOXAZOLE 1.Sulfamethoxazole inhibits dihydrofolate synthase. 2.Trimethoprim inhibits dihydrofolate reductase. PABA
  16. 16. Cotrimoxazole – general points • Individually, both are bacteriostatic, but combination is – bactericidal • Both drugs have almost similar half lives (10 Hrs) • Maximum synergism if the organism is sensitive to both the agents • Optimal synergism is obtained at 20 (S) : 1 (T) concentration (MIC of both is reduced by 3 - 6 times) – This ratio is obtained at 5:1 dose ratio ( e.g. 800 mg:160 mg) – Because TMP has large Vd and enters many tissues – plasma conc. is low • But, TMP crosses BBB and placenta and SMZ not • TMP is more rapidly absorbed than SMZ • TMP is 45% plasma protein bound but SMZ is 65% bound • TMP is partly metabolized in liver
  17. 17. Cotrimoxazole – antibacterial spectrum • Similar to sulfonamides • Additional benefits: Salmonella typhi, Serratia, Klebsiella Enterobacter, Yersinia and Pneumocystis jiroveci – Sulfonamides resistance strains of S. aureus, E. coli, gonococci, meningococci and H influenzae • RESISTANCE: Slow to develop – By mutational changes or plasmid mediated acquisition of a DHFRase enzyme having lower affinity for the inhibitior.
  18. 18. Cotrimoxazole - ADRs • All adverse effects of sulfonamides – nausea, vomiting, stomatitis, rash etc • Folate deficiency (megaloblastic anaemia) – patients with marginal folate levels • Blood dyscrasias • Pregnancy: teratogenic risk, Neonatal haemolysis and methaemoglobinaemia • Patients with renal disease may develop uremia • Fever, rash and bone marrow hyperplasia • Elderly – risk of bone marrow toxicity from cotrimoxazole • Diuretics given with cotrimoxazole have produced a higher incidence of thrombocytopenia • Bone marrow hypoplasia among AIDS patients with Pneumocystis jiroveci infection
  19. 19. Cotrimoxazole - Uses • Uncomplicated infection of the lower urinary tract infection – Cystitis (5 tablet dose) – chronic and recurrent urinary tract infections (including enterobacteriaceae) – 3-10 days • Respiratory tract infection – lower and upper, chronic bronchitis, facio-maxillary infections, otitis media due to gm+ve cocci and H influenzae etc • Typhoid • Bacterial diarrhoeas & dysentery: due to campylobacter, E coli, Shigella etc. • Pneumocystis jiroveci: Severe pneumonia - Prophylactic use in AIDS patients with neutropenia. Dose – DS tablet 4-6 times 2-3 weeks • Chancroid – H. ducreyi • Alternative to penicillin in agrannulocytosis patients, scepticaemia etc.
  20. 20. Must Know • Classification of Sulfonamides – examples of some Sulfonamides • Uses of some selected Sulfonamides • Cotrimoxazole – as a whole • Rationale of combinations – Cotrimoxazole and Sulfadoxine + pyrimethmine
  21. 21. Take Home ……. Students (Sulfonamides) + Teachers (Trimethoprim) • Similar half lives (10 Hrs) – human being • Both are bacteriostatic – combination is bactericidal - alone nothing - together can make difference • Synergism is obtained at 20 (S) : 1 (T) concentration (MIC of both is reduced by 3 - 6 times) – This ratio is obtained at 5:1 dose ratio ( e.g. 800 mg:160 mg) – Because TMP has large Vd and enters many tissues – plasma conc. is low – teachers effort • Optimal synergism if the organism is sensitive to both the agents – have to reciprocate each other • Combination - Lesser toxic (trimethoprim) - have to monitor • Alone (trimethoprim) - sometimes have to act
  22. 22. Thank you

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