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Genital excretion. 3 Slide 4: LONGITUDNAL SECTION OF KIDNEY 4 Slide 5: ANATOMY OF NEPHRON 5 GLOMERULAR FILTRATION : 6 GLOMERULAR FILTRATION It Is non selective , unidirectional process Ionized or unionized drugs are filtered, except those that are bound to plasma proteins. Driving force for GF is hydrostatic pressure of blood flowing in capillaries. GLOMERULAR FILTRATION RATE: Out of 25% of cardiac out put or 1.2 liters of blood/min that goes to the kidney via renal artery only 10% or 120 to 130ml/min is filtered through glomeruli. The rate being called as glomerular filtration rate (GFR).e.g. creatinine, insulin. ACTIVE TUBULAR SECRETION : ACTIVE TUBULAR SECRETION This mainly occurs in proximal tubule. It is carrier mediated process which requires energy for transportation of compounds against conc. gradient Two secretion mechanisms are identified. System for secretion of organic acids/anions E.g. Penicillin, salicylates etc uric acid secreted System for organic base / cations E.g. morphine, mecamylamine hexamethonium Active secretion is Unaffected by change in pH and protein binding. Drug undergoes active secretion have excretion rate values greater than normal GFR e.g. Penicillin. TUBULAR REABSORPTION : 8 TUBULAR REABSORPTION It occurs after the glomerular filtration of drugs. It takes place all along the renal tubules. Reabsorption of drugs indicated when the excretion rate value are less than the GFR 130ml/min.e.g. Glucose TR can be active or passive processes. Reabsorption results in increase in the half life of the drug. Slide 9: 9 Active Tubular Reabsorption: Its commonly seen with endogenous substances or nutrients that the body needs to conserve e.g. electrolytes, glucose, vitamins. Passive Tubular Reabsorption: It is common for many exogenous substances including drugs. The driving force is Conc. Gradient which is due to re-absorption of water, sodium and inorganic ions. If a drug is neither excreted or re-absorbed its conc. In urine will be 100 times that of free drug in plasma. FACTORS AFFECTING RENAL EXCRETION : 10 FACTORS AFFECTING RENAL EXCRETION Physicochemical properties of drug. Urine PH. Blood flow to the kidney . Biological factor . Drug interaction. Disease state. PHYSICOCHEMICAL PROPERTIES OF DRUG : 11 PHYSICOCHEMICAL PROPERTIES OF DRUG Molecular size . Binding characteristics of the drugs. BIOLOGICAL FACTORS Age, sex, species, strain difference etc alter the excretion of the drug. Sex – Renal excretion is 10% lower in female than in males. 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. DRUG INTERACTION : 12 DRUG INTERACTION Any drug interaction that result in alteration of binding characteristics, renal blood flow, active secretion, urine pH, intrinsic clearance and forced diuresis would alter renal clearance of drug. Renal clearance of a drug highly bound to plasma proteins is increased after it is displaced with other drug e.g. Gentamicin induced nephrotoxicity by furosemide. Alkalinization of urine with citrates and bicarbonates promote excretion of acidic drugs. DISEASE STATE : 13 DISEASE STATE RENAL DYSFUNCTION Greatly impairs the elimination of drugs especially those that are primarily excreted by kidney. Some of the causes of renal failure are B.P, Diabetes, Pyelonephritis. UREMIA Characterized by Impaired GFR , accumulation of fluids & protein metabolites, also impairs the excretion of the drugs. Half life is increased resulting in drug accumulation and increased toxicity. NON-RENAL ROUTE OF DRUG EXCRETION : 14 NON-RENAL ROUTE OF DRUG EXCRETION Various routes are Biliary Excretion Pulmonary Excretion Salivary Excretion Mammary Excretion Skin/dermal Excretion Gastrointestinal Excretion Genital Excretion Slide 15: CONCEPT OF CLEARANCE 15 CLEARANCE:- Is defined as the hypothetical volume of body fluids containing drug from which the drug is removed/ cleared completely in a specific period of time. Expressed in ml/min. Slide 16: TOTAL BODY CLEARANCE:- Is defined as the sum of individual clearances by all eliminating organs is called total body clearance/ total systemic clearance. Total Body Clearance = CLliver + CLkidney + CLlungs +CLx 16 Slide 17: RENAL CLEARANCE Major organ for elimination of almost all drugs & their metabolites. Water soluble, Nonvolatile, Low molecular weight/ slowly metabolized drugs by liver are eliminated by kidneys. Drugs like Gentamycin- exclusively eliminated by kidneys. Basic functional unit of kidney involved in excretion is NEPHRON. 17 Slide 18: The principle processes that determine the urinary excretion of drugs are:- Glomerular filtration Active tubular secretion Active/ passive tubular reabsorption RE = RF + RS - RRA 18 Slide 19: RENAL CLEARANCE:- is defined as the volume of blood/ plasma which is completely cleared of the unchanged drug by the kidney/unit time ClR = rate of urinary excretion ÷ plasma drug concentration 19 REFERENCES : REFERENCES 20 Shargel L.,Susanna W., Applied Biopharmaceutics and Pharmacokinetics. Brahmankar MD,Jaiswal S.,Biopharmaceutics & Pharmacokinetics- A teratise; Biopharmaceutics and clinical pharmacokinetics by Milo Gibaldi, 4th ed.; 1991. You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.