First Pass Metabolism

912 WordsApr 9, 20134 Pages
First pass metabolism. Pharmacology is the study of the effects drugs have and how they exert them. Drugs can be administered enteral or parenteral. [1] Enteral refers to any form of administration that involves the alimentary tract. The four enteral routes of administration include the mouth, sublingual, buccal and rectal. Parenteral refers to routes of administration outside of or beside of the alimentary tract. The parenteral route includes intravascular (IV), Intramuscular (IM) and subcutaneous (SC) routes of administration. The parenteral routes are used for drugs that are poorly absorbed or that are unstable in the GI tract. The parenteral routes are used in unconscious patients or when a fast response is needed as it provides the…show more content…
The passage of the drugs is not affected by lipid solubility or pH. [2] Proximal tubular secretion: The drug that do not enter the glomerular filtrate leaves the glomeruli though efferent arterioles. The arterioles divide to form a capillary plexus surrounding the nephric lumen in the proximal tubule. The occurrence of secretions mainly occurs in the proximal tubule. This happens by active transport, one for anions and one for cations. Active transport requires energy. The two systems have low specificity and can transport many compounds. [2] Distal tubular reabsorption: The concentration of the drug will exceed that of the perivascular space due to the increase in concentration as the drug moves toward the distal convoluted tubule. The drug may diffuse back into the circulation if it is uncharged. In attempt to minimize the diffusing back into circulation, the pH of the urine may be manipulated to increase the ionised from of the drug. [2] Below is a diagram to show renal elimination. [4] People with kidney problems/disease must have the dosage of drugs administered adjusted as they have a lower glomerular filtration rate than those without kidney problems/disease. People with renal dysfunction and those on dialysis are often given opioids for pain relief. Adjusting the dosage for a therapeutic effect without overdosing is difficult for patient with renal dysfunction and those on dialysis. Giving opioids to the patient

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