(Last Updated: 08/22/2018) Created by: Socco, Samantha Therapeutics of Diuretics Thambi, M. (2017). The Clinical Use of Diuretics. Lecture presented at PHAR 503 Lecture in UIC College of Pharmacy, Chicago. KIDNEY ANATOMY OVERVIEW Filters out red blood cells and proteins but otherwise non-selective o Anything filtered goes into tubules of the nephron The cortex consists of the glomerulus as well as proximal, and distal parts of the tubule The medulla consists of the loop of Henle of the tubule and the collecting duct Afferent artery brings blood TO THE KIDNEY Efferent artery brings blood AWAY FROM THE KIDNEY ( E for exit ) Podocytes wrap around the capillaries of the glomerulus to provide a filter, otherwise stuff leaks out too easy o Additionally the basement membrane of the capillary is fenestrated, which helps filter o Only plasma gets filtered Osmolarity increases going from the cortex to the medulla Kidneys are very vascularized so must be careful when doing a biopsy Average glomerular filtration rate is 120 ml/min Average urine output is 1mL/min or 1500 ml/day Majority of sodium is reabsorbed in the proximal tubule Descending loop of Henle is freely permeable to solutes and water water reabsorbed, solutes excreted o Bottom of the loop of Henle (in the medulla) highly concentrated Ascending loop is NOT PERMEABLE to water. Sodium is reabsorbed and this dilutes the urine Collecting duct is permeable to water when ADH is present o ADH causes more aquaporins to be made and will be produced depending ho much water your body needs to reabsorb (when tissues are hyperosmolar) Nephrons made up of epithelial cells o Basolateral side (closer to blood vessels) have 3Na-2K-ATPase pumps o Luminal side (closer to tubule lumen, or inside the tubule) have diff types of pumps depending on where in the nephron
PROXIMAL TUBULE Luminal side of the epithelial cells on the tubule have a Na + /H + symporter o Na + leaves the lumen and goes into the cell. H + comes into the tubule Carbonic anhydrase is an enzyme found in the epithelial cell and in the tubule lumen o In lumen: converts carbonic acid to CO2 and water o CO2 leaves lumen passively and goes into epithelial cell o In epithelial cell: converts CO2 and water to bicarbonate and H + o This H + can be used by the symporter to bring sodium from the lumen, to the epithelial cell, out into the bloodstream 2
CARBONIC ANHYDRASE INHIBITORS Acetazolamide, Methazolamide o Secreted into the proximal tubule o Used more for glaucoma rather than as a diuretic If carbonic acid is blocked, less H + produced and less Na + can be reabsorbed o Water follows Na + into the tubule diuresis HOWEVER these are considered weak diuretics b/c the rest of the nephron can compensate for the Na + reabsorption ASCENDING LOOP OF HENLE Basolateral side has 3Na-2K-ATPase pumps which use ATP to pump K + into the tubule and Na + out Na-K-2Cl symporter on luminal side, which pumps Na +, K + and 2Cl - out of the tubule while also pumping K + into the tubule o Tubule becomes electropositive, so Ca and Mag are repelled into the intercalated spaces 3
LOOP DIURETICS Furosemide, ethacrynic acid, bumetanide, torsemide o Uses a transporter to get into proximal tubule o Uric acid also uses this transporter, so these drugs can cause higher levels of uric acid in the blood gout o Uses: main use is edema Used as an alternative treatment to severe hypercalcemia Not really used for hypertension (thiazides used for that) Inhibit Na-K-2Cl symporter on luminal side of ascending loop of Henle o Less Na + is pumped out of the lumen. No Na + reabsorption causes the diuresis o Less K + in the lumen causes Ca and Mag to stay in the lumen (less electropositive), so they won t be reabsorbed and patient can get hypocalcemia and hypomagnesemia Most potent class of diuretics Have a ceiling dose where going any higher than this dose won t produce any more effective of a diuresis Furosemide Bumetanide Torsemide 50% bioavailable 80-100% bioavailable 80-100% bioavailable 20-160 mg/d 0.5-4 mg/d 10-80 mg/d Has short term lowering of blood pressure Need higher doses in renal insufficiency, cirrhosis, heart failure, nephrotic syndrome Side effects: o Lower BP o Raise HR o Orthostasis (standing up, you get dizzy) o Renal insufficiency o Hypokalemia (need to supplement if K <3.5) o Hypocalcemia o Hypomagnesemia o Ototoxicity o Hyperuricemia gout o Alkalosis 4
DISTAL TUBULE Basolateral side has 3Na-2K-ATPase pumps which use ATP to pump K + into the tubule and Na + out o Also has Cl - channel, which pumps Cl - out of the epithelial cell o Has Ca 2+ and Na + antiporter, which pumps Na + into the epithelial cell and Ca 2+ out of the cell Luminal side has Na + and Cl - symporter, which pumps both ions out of the lumen o Also has Ca 2+ channel which pumps Ca 2+ out of the lumen THIAZIDE DIURETICS Hydrochlorothiazide, chlorthalidone, metolazone, indapamide Uses: o Hypertension o With loop diuretics for potent diuresis Don t use in renal insufficiency (CrCl < 30 ml/min) Actively transported into proximal tubule o Transporter also for uric acid can get uricemia and gout Block the Na + and Cl - symporter o Less Na + can get into the epithelial cell, so more will come in from the blood through the Ca 2+ and Na + antiporter o More Na 2+ diuresis o More Ca 2+ reabsorbed hypercalcemia Side effects: 5
o Hypotension o Hypokalemia More Na + in tubule causes increased excretion of K + at the collecting duct Collecting duct has transporter for both K + and Na + o Hypercalcemia o Hyponatremia o Hypomagnesemia o Hyperuricemia COLLECTING DUCT Basolateral side has 3Na-2K-ATPase pumps which use ATP to pump K + into the tubule and Na + out Luminal side has transporter for both K + and Na + o More Na + leaves the lumen than K + that comes in, so there is a net negative charge in the lumen (also chloride ions add to this) POTASSIUM SPARING DIURETICS Amiloride, triamterene Block the Na + transporter on the luminal side of the epithelial cell in the collecting duct o Tubule has less of a negative charge, so less K + will come into the tubule 6
ALDOSTERONE ANTAGONISTS AND SODIUM CHANNEL BLOCKERS Aldosterone: Enters epithelial cells of collecting duct and causes increased production of Na + channels, so more Na + is reabsorbed and more K + is excreted Aldosterone antagonists: Spironolactone and eplerenone o Works in epithelial cells of the collecting duct (doesn t need to go into lumen o Inhibits Na + channels and decreases Na + reabsorption o Uses: Weak diuretic not much Na + reabsorbed at collecting duct Used with hydrochlorothiazide (HCTZ) to prevent hypokalemia Heart failure with reduced ejection fraction Hepatic cirrhosis with ascites Resistant hypertension Sodium channel blockers o Used in combo with HCTZ to prevent hypokalemia Side effects: o Hyperkalemia (worse if renal insufficiency) o Spironolactone gynecomastia OSMOTIC DIURETICS Mannitol pulls water into the nephron tubule o IV only o Can t be reabsorbed o Increases excretion of Na + and water follows COUNSELING Sodium restricted diet (<1 gm/day) o Loop diuretics first line to treat edema, but patient must follow low sodium diet Patient should weigh themselves daily indirect measurement of edema For furosemide, start with daily dosing. Can increase dose or change to BID o can reach the ceiling dose twice a day (duration of action around 6 hours) o Would give second dose at 4-5 pm not at bedtime 7