Electrolytes Lecture Notes PDF

Electrolytes RGR Pharmaceutical Chemistry Department UP College of Pharmacy Outline Extracellular and Intracellular Ions Acid-Base Balance Blood Electrolyte Imbalances Electrolyte Replacement Therapy Electrolytes used in Acid-Base Therapy Electrolyte Combination Th...

Electrolytes RGR Pharmaceutical Chemistry Department UP College of Pharmacy Outline Extracellular and Intracellular Ions Acid-Base Balance Blood Electrolyte Imbalances Electrolyte Replacement Therapy Electrolytes used in Acid-Base Therapy Electrolyte Combination Therapy Fluid Compartments and Fluid Balance Fluid Compartments and Fluid Balance Fluid Compartments and Fluid Balance Fluid Compartments and Fluid Balance Fluid Compartments and Fluid Balance Extracellular and Intracellular Ions Sodium Ion Na+ most abundant extracellular ion Accounts for half of the osmolarity of ECF Generation and conduction of action potentials in neurons and muscle fibers Levels controlled by aldosterone, antidiuretic hormone and atrial natriuretic peptide Hyponatremia, Hypernatremia Chloride Ion Cl- Major extracellular anion Moves relatively easy between extracellular and intracellular compartments because of Cl- leakage channels and antiporters Helps balance anion levels in different fluid compartments Chloride shift Hydrochloric acid Regulated by ADH Na+-Cl- symporters Chloride Ion Chloride shift Chloride Ion Na+-Cl- symporters Potassium Ions K+ Major intracellular ions Establish membrane potential Repolarization phase of action potentials in neurons and muscle fibers Helps regulate pH of body fluids Often exchanged for H+ when it moves into or out of the cell Controlled mainly by aldosterone Increases secretion in the kidneys, lost in urine Hyperkalemia, hypokalemia Bicarbonate Ions HCO3- Second most prevalent extracellular anion Mainly regulated by the kidneys Bicarbonate Ions Calcium Ions Ca2+ Most abundant mineral (as calcium compounds in bones) One of the main extracellular cation Bone and teeth development Blood clotting Neurotransmitter release Excitability of nervous and muscle tissue Regulated mainly by the parathyroid hormone Secreted when Ca2+ are low in blood Enhances reabsorption in kidneys Increases calcitriol production, which increases Ca2+ food absorption Phosphate Ions H2PO4-, HPO42-, PO43- Principal ICF anion (as HPO42-) H2PO4- is the only form absorbed by the intestines HPO42- - poorly absorbed in the intestines, making its salts as useful saline cathartics Phosphate Ions Controlled by PTH and calcitriol PTH stimulates bone resorption, releasing both Ca2+ and PO43- in the blood PTH inhibits reabsorption of PO43- while stimulating Ca2+ reabsorption in kidneys NET effect: decreased blood phosphate levels Calcitriol promotes absorption of both Ca2+ and PO43- from GIT Fibroblast growth factor 23 Decreases HPO42- by promoting its renal excretion and decreasing its GI absorption Magnesium Ion Mg2+ Second most abundant intracellular ion Cofactor for enzymes– carbohydrate and protein metabolism and for the sodium-potassium pump Essential for neuromuscular activity, synaptic transmission, and myocardial functioning PTH secretion is dependent on Mg2+ Magnesium Ion Increased renal excretion in response to: Hypercalcemia Hypermagnesemia Increases in ECF volume Decreases in PTH Acidosis Acid-Base Balance Acid-Base Balance pH 7.35-7.45 pH homeostasis depends on: Buffer systems Fastest, temporarily bind H+ Raise blood pH but not remove H+ from the body Exhalation of carbon dioxide Within minutes, reduce levels of blood carbonic acid Kidney excretion of H+ Slowest mechanism Only way to remove acids other than carbonic acid Acid-Base Balance Buffer systems Protein-buffer system Most abundant buffer system in intracellular fluid and blood plasma E.g. Hgb in RBC, albumin in blood plasma Acid-Base Balance Buffer systems Protein-buffer system Acid-Base Balance Buffer systems Carbonic Acid- Bicarbonate Buffer System Not lost in the urine since there is renal reabsorption and synthesis of HCO3- Cannot protect against pH changes due to respiratory problems Acid-Base Balance Buffer systems Phosphate buffer system Important regulator of cytosolic pH Acid-Base Balance Exhalation of CO2 Acid-Base Balance Kidney excretion of H+ Acid-Base Balance Acid-Base Balance Blood Electrolyte Imbalances Blood Electrolyte Imbalances Blood Electrolyte Imbalances Blood Electrolyte Imbalances Electrolyte Replacement Therapy Sodium Replacement Potassium Replacement Calcium Replacement Magnesium Replacement Sodium replacement Sodium chloride Isotonic solutions (? w/v) Used as wet dressings, irrigation solutions and as injections when electrolytes are depleted Hypotonic solutions Administered for maintenance therapy when patients are unable to take fluid and nutrients orally for 1-3 days Hypertonic solutions Used when there is excessive loss of sodium Should be administered slowly in small volumes (200-400mL) Also used to induce vomiting for household poisoning accidents Sodium replacement Sodium chloride official preparations Preparation Category Sodium chloride injection, USP Fluid and electrolyte replenisher, irrigation solution Bacteriostatic sodium chloride injection, USP Sterile vehicle Sodium chloride solution, USP Isotonic vehicle Sodium chloride tablets, USP Electrolyte replenisher Dextrose and sodium chloride injection, USP Fluid, nutrient, and electrolyte replenisher Sodium chloride and dextrose tablets, NF Electrolyte and nutrient replenisher Mannitol and sodium chloride injection, USP Diuretic Fructose and sodium chloride, USP Fluid, nutrient, and electrolyte replenisher Ringer’s Injection, USP Fluid and electrolyte replenisher Lactated Ringer’s Injection, USP Systemic alkalizer; fluid and electrolyte replenisher Potassium replacement Potassium chloride Potassium gluconate Potassium replacement Potassium chloride Preferably as a solution (usually mixed with fruit or vegetable juice) Solutions must be well diluted since it is irritating to the GI tract IV injections for severe hypokalemia and if patient is unable to swallow Electrocardiograms and urine output is monitored Potassium replacement Potassium chloride Other indications: Periodic paralysis Adjunct drug in myasthenia gravis (progressive, severe muscle weakness) Potassium replacement Potassium chloride official preparations Preparation Category Potassium chloride injection, USP Electrolyte replenisher Potassium chloride tablets, USP Electrolyte replenisher Ringer’s injection USP Fluid and electrolyte replenisher Lactated Ringer’s injection, USP Systemic alkalizer; fluid and electrolyte replenisher Potassium replacement Potassium gluconate Less irritating than potassium chloride Official Preparations Potassium gluconate tablets, USP Potassium gluconate oral solution, USP Calcium replacement Calcium chloride Calcium gluconate Calcium lactate Dibasic calcium phosphate Tribasic calcium phosphate Calcium replacement Calcium chloride Calcium source in many commercially available electrolyte replacement and maintenance solutions Should be injected slowly because it is irritating to the veins Rapid injection may cause burning sensation, peripheral vasodilation, and fall in blood pressure Official preparations: Calcium chloride injection, USP Ringer’s injection, USP Lactated ringer’s injection, USP Calcium replacement Calcium gluconate Non-irritating alternative to calcium chloride Has risk of abscess formation when administered muscularly Official preparations: Calcium gluconate injection, USP Calcium gluconate tablets, USP Calcium replacement Calcium lactate Non-irritating calcium salt for oral calcium replacement therapy Official preparations: Calcium lactate tablets, USP Calcium replacement Dibasic calcium phosphate (CaHPO4) Source of calcium and phosphorus in pregnancy and in lactation and calcium deficiency states Converted to the soluble monobasic calcium phosphate (Ca(H2PO4)2) and CaCl2 in the stomach Absorbed in the intestine Tribasic calcium phosphate (Ca3(PO4)2) Also forms soluble salts in stomach acid Also used as an antacid Magnesium replacement Magnesium sulfate Anticonvulsant, cathartic CNS depressant in treatment of eclampsia For severe cases of hypomagnesemia For magnesium-deficient alcoholics Overdose can cause respiratory paralysis and cardiac depression Treatment: Calcium salt injection Official preparation: Magnesium sulfate injection, USP Electrolytes Used in Acid-Base Therapy Electrolytes for Acid-Base Therapy Bicarbonates Increase HCO3-/H2CO3 ratio Lactates, acetates, citrates Converted to CO2 and water through Krebs cycle Doesn’t cause as much alkalosis as bicarbonates, and can be sterilized Sodium biphosphate Ammonium chloride Electrolytes for Acid-Base Therapy Bicarbonates Drug of choice for systemic acidosis H+ + NaHCO3 → H2CO3 + Na+ Electrolytes for Acid-Base Therapy Bicarbonates Other uses: Antacid If taken orally, lessens acidity of urine Component of effervescent tablets Treatment of methanol intoxication Electrolytes for Acid-Base Therapy Bicarbonates Sodium bicarbonate injection, USP Sodium bicarbonate tablets, USP Sodium bicarbonate oral powder, USP Potassium bicarbonate, USP Electrolytes for Acid-Base Therapy Citrates Sodium citrate Official use is an anticoagulant Potassium citrate Electrolytes for Acid-Base Therapy Lactates Sodium lactate Acetates Sodium acetate Potassium acetate Sodium Biphosphate (dihydrogen phosphate) Urinary acidifier since dihydrogen phosphate is readily excreted in kidneys Electrolytes for Acid-Base Therapy Ammonium chloride Mainly used as systemic acidifier by conversion of ammonium ion to urea with consequent formation of H+ and Cl- Other uses: Diuretic Expectorant: probably due to irritation of throat Electrolyte Combination Therapy Electrolyte Combination Therapy Infusions Ringer’s Injection Lactated Ringer’s Injection Oral Rehydration Salts, USP Oral electrolyte solutions Pedialyte® Gatorade® END OF LECTURE References Block, J.H., Roche, E.B., Soine, T.O. and Wilson, C.O. (1974). Inorganic Medicinal and Pharmaceutical Chemistry. Philadelphia: Lea and Febiger. Discher, C.A., and Medwick, T. (2006). Inorganic Pharmaceutical Chemistry. 2013. In: Gennaro, A.R. (Ed.), Remington: The science and practice of pharmacy (20th ed). Philadephia, PA: Lippincott, Williams & Wilkins. Tortora, G.J. and Derrickson, B. (2009). Principles of Anatomy and Physiology 12th edition. New Jersey: John Wiley & Sons, Inc. United States Pharmacopeial Convention. United States Pharmacopeia and National Formulary. MD: USPCI.