Excretion (drugs)

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Excretion Overview What is drug excretion? Drug excretion is defined as the removal of drugs from the body. How are drugs excreted from the body? Drugs and their metabolites can leave the body in urine, bile, sweat, saliva, breast milk, and expired air. Which is the most important organ used in excretion? The most important organ for drug excretion is the kidney.

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Excretion Overview What are some non-renal routes that a drug can be excreted from the body? Breast milk Bile Lungs Sweat Saliva

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Excretion Overview What is the consequence of drug metabolism? Renal drug excretion The kidney, which is the major organ of drug excretion, is unable to excrete drugs that are highly lipid soluble. By converting lipid-soluble drugs into more polar (less lipid-soluble) compounds, drug metabolism makes it possible for the kidney to excrete many drugs.

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GLOMERULAR FILTRATION This is where blood is filtered and is where urine formation begins. Hydrostatic pressure pushes a portion of blood to be filtered across a semi-permeable membrane into the Bowman’s Capsule. Porosity of Glomerular membrane allows only small molecular weight particles to be filtered. Blood cells, platelets, and plasma proteins are retained in the blood and not filtered..

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The nephron is the basic functional unit of the kidney.

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GLOMERULAR FILTRATION RATE (GFR)? The amount of blood filtered by the glomeruli in a given time. The clearance of any filtered substance can be calculated. If the clearance is more than the GFR then the substance is filtered and then added to by tubular secretion. Only 1ml/min is excreted as urine and the rest is reabsorbed by the peritubular capillary network. The body can speed up GFR by increasing blood flow to the glomerular capillaries. The body can slow down GFR by decreasing blood flow to the glomerular capillaries.

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Indivials in which GFR is not an appropriate measure (Because of altered creatinine levels) . People with muscle wasting conditions. People who have had an amputation of an arm or leg. Malnourished people. Pregnancy. People with acute kidney failure. People with a lot of edema (fluid retention). Children.

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Why is GFR important? GFR - glomerular filtration rate is the best test to measure your level of kidney function. Your doctor can calculate it from the results of your blood creatinine test, your age, race, gender and other factors. The earlier kidney disease is detected, the better the chance of slowing or stopping its progression. Diseases like Diabetes and hypertension can affect GFR and give us an indication of Renal impairment. If GFR is impaired too much, toxic levels of drugs can remain in the body.

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How are drugs passively reabsorbed? 1. Think of your kidneys as filters such as which filter out things like…… Sodium Potassium Drug Toxins 2. Think of the inside the filter as in side the kidney and outside the filter is the blood vessel. Since the kidneys filter out water and waste - anything that fits through the filter will go through.

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How are drugs passively reabsorbed cont... Problem - during this filtration process the kidneys absorb a lot of things so they get full. So this means the blood vessels around the kidneys are free of debris so what happens? 3. The particles that can pass the filter wall and move back into the open space of the blood vessel will do just that. 4. End result. Instead of having all the particles in the kidney be excreted in the urine, some particles, like lipid soluble drugs, are passively reabsorbed back into the blood.

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Active Tubular Secretion Occurs mostly in the proximal tubule Requires Energy Active process A few substances which are present in great excess, or are natural poisons are secreted Secretion of K+, H+, ammonia; penicillin & other drugs, excess amino acids Secretion of ionized drugs into the lumen

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Active secretion of some weak electrolyte, especially weak acids Significant pathway for some compounds such as penicillins Competitive inhibition of the secretion of one compound by another Drugs which are protein-bound are excreted Transports organic acids and organic bases through tubular pumps. Active Tubular Secretion

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Active Tubular Secretion The rapid transfer of drug metabolites into urine is by active transport. Many drugs are eliminated by tubular secretion. Drugs can compete for secretion due to saturation Example: inhibition of penicillin excretion by competition with probenecid Probenecid alters the distribution of penicillins to various tissues causing more drug to distribute out of plasma, causing even less to be eliminated.

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Excretion Review Excretion is necessary in order for the body to rid itself of drugs, toxins, etc. What are 3 functions of the kidney which assist in renal excretion? Glomerular Filtration Passive Tubular Reabsorption Active Tubular Secretion

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Excretion Overview What conditions can affect drug excretion? Hypertension Severe dehydration Diabetes (all types)? Cardiac problems (ie. CHF)? Renal disease It is necessary to understand that if one system of the body is not working properly it affects other systems also.

Why is Excretion important to nurses? : 

Why is Excretion important to nurses? It is the primary mechanism that humans use to get rid of drugs and other waste products. Many disease processes (Diabetes, Hypertension, etc.) can interfere with kidney function and inhibit waste removal. When excretion is inhibited, accumulations of drugs and waste products can become toxic. Recognizing signs/symptoms of renal impairment can help identify renal disease early and can potentially be life-saving.

Nursing Interventions : 

Nursing Interventions Encourage adequate fluid consumption of 2000-3000 ml a day. Monitor fluid I/O (consumption vs. excretion) Assess color changes of urine since it can indicate hydration levels. Monitor lab values periodically (GFR, Creatinine Clearance, and BUN).

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References Lehne, Richard A.. Pharmacology for Nursing Care, 6th Edition. 062006: Saunders Book Company, 062006. 69. Lewis, Sharon Mantik. Medical-Surgical Nursing (Single Volume): Assessment and Management of Clinical Problems, 7th Edition. 032007: Mosby, 032007. Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall.

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References National Kidney Foundation Web Team (2009). Glomerular Filtration Rate. Retrieved February 9, 2009, Web site: http://www.kidney.org/kidneydisease/ckd/knowGFR.cfm Forcon Forensic Consulting (2004). Excretion. Retrieved February 9, 2009, Web site: http://www.forcon.ca/learning/excretion.html The Encyclopedia of Earth (1999). Excretion of toxicants. Retrieved February 9, 2009, Web site: http://www.eoearth.org/article/Excretionoftoxicants.html