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DRUG EXCRETION

DRUG EXCRETION. Dr. Megha Rani N. Dept of Pharmacology Yenepoya Medical College. EXCRETION D efined as the process wherein drugs or metabolites are irreversibly transferred from internal to external environment. Most drugs are excreted unchanged / water soluble drug

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DRUG EXCRETION

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  1. DRUGEXCRETION Dr. MeghaRani N • Dept of Pharmacology • Yenepoya Medical College

  2. EXCRETION • Defined as the process wherein drugs or metabolites are irreversibly transferred from internal to external environment. • Most drugs are excreted • unchanged / water soluble drug • metabolites. • Principal organ - kidneys.

  3. ROUTES OF EXCRETION

  4. Renal Excretion Processes: • Glomerularfiltration (GF) • Active tubular secretion (TS) • Tubular reabsorption (TR) Net renal excretion = (GF + TS) - TR

  5. Weakly Acidic drugs – (Barbiturates, Salicylates) ionised & excreted in alkaline urine. Forced alkaline diuresis • Weakly Alkaline drugs – (Morphine, Amphetamine) ionised & excreted in acidic urine. Forced acid diuresis • Strongly acidic or basic drugs remain ionized at all pHs, hence cannot be reabsorbed.

  6. FACTORS AFFECTING RENAL EXCRETION Physicochemical properties of drug Urine pH Blood flow to the kidney Biological factor - Age, gender, species, strain difference alter the excretion of the drug. Drug interaction Disease state

  7. BIOLOGICAL FACTORS Age – The renal excretion in newborn is 30-40 % less in comparison to adults. Old age – The GFR is reduced and tubular function is altered which results in slow excretion of drugs and prolonged half lives.

  8. DRUG INTERACTION Eg : Penicillin, Probenecid – compete for transporter in proximal tubule

  9. DISEASE STATE RENAL DYSFUNCTION Greatly impairs the elimination of drugs especially those that are primarily excreted by kidney. UREMIA Characterized by Impaired GFR. Half life of the drug is increased resulting in drug accumulation & increased toxicity.

  10. BILIARY EXCRETION Bile juice is secreted by hepatic cells of the liver. ENTEROHEPATIC CIRCULATION-90% of bile acid is reabsorbed from intestine and transported back to the liver for re-secretion. Drugs – Quinine, Colchicine, DTC, Corticosteroids, Erythromycin, Digoxin.

  11. Alveolar Excretion • Gases and volatile liquids e.g. GA, Alcohol are eliminated through breath. • Pulmonary blood flow, rate of respiration, solubility & partial pressure of substance in the blood effect this.

  12. Breast Milk • Unwanted pharmacological effects in the nursing infant. • Basic Drugs - chloramphenicol, tetracyclines, ergotamine, morphine, diazepam, antihistamines • Acidic drugs – less secreted can cause serious side effects in infants. E.g sulfonamides, penicillins, phenobarbitone, theophylline.

  13. Minor Routes • Skin – griseofulvin • Hair follicles – arsenic, mercury salts • Saliva – lithium, phenytoin, Rifampicin • Sweat – amines, urea derivatives

  14. Clearance (CL) – is a theoretical volume of plasma from which the drug is completely removed in unit time.

  15. THANK YOU

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