Drug absorption aspirin

G. Levy, J. R. Leonards, and J. A. Procknal, Development of in vitro dissolution tests which correlate quantitatively with dissolution rate-limited drug absorption in man, J. Pharm. Sci., 54, 1719-1722 (1966). K. A. Javaid and D. E. Cadwallader, Dissolution of aspirin from tablets containing various buffering agents, J. Pharm. Sci., 61, 1370-1373 (1972). 

In an experimental study of the possible effects of laxatives on drug absorption, healthy subjects were given 10 to 20 g of oral sodium sulfate and 20 g of castor oil (doses sufficient to provoke diarrhoea). Absorption, measured by the amount of drug excreted in the urine, was decreased at 4 hours. The reduction was 21% for castor oil and aspirin, and 27% for sodium sulfate and aspirin. However, serum levels of aspirin were relatively unchanged. The overall picture was that while these laxatives can alter the pattern of absorption, they do not seriously impair the total amount of drug absorbed. ... 

The answer is c. (Hardman, pp 887, 889.) Bile acid-binding resins bind more than just bile acids, and binding of simvastatin to cholestyramine is the most likely mechanism for decreased Gl absorption. Cholestyramine may also bind to several other drugs, including digoxin, benzothiadiazides (thiazides), warfarin, vancomycin, thyroxine (T4), and aspirin. Medications should be given one hour before or four hours after cholestyramine. 

For a drug to interact with a target, it has to be present in sufficient concentration in the fluid medium surrounding the cells with receptors. Pharmacokinetics (PK) is the study of the kinetics of absorption, distribution, metabolism, and excretion (ADME) of drugs. It analyzes the way the human body deals with a drug after it has been administered, and the transportation of the drug to the specihc site for drug-receptor interaction. For example, a person has a headache and takes an aspirin to abate the pain. How does the aspirin travel from our mouth to reach the site in the brain where the headache is and act to reduce the pain ... 

Conversely, certain drugs modify the effectiveness or side effects of aspirin. Phenobarbital, occasionally used for seizures, induces liver enzymes that increase the metabolism and excretion of aspirin, (3-adrenoceptorblocking drugs, such as propranolol, and decrease the antiinflammatory effects of aspirin, whereas reserpine decreases its analgesic effects. Antacids decrease the absorption of aspirin. Alcohol consumption in combination with aspirin increases the latter s ulcerogenic effects. 

Although aspirin itself is pharmacologically active, it is rapidly hydrolyzed to salicylic acid after its absorption, and it is the salicylate anion that accounts for most of the anti-inflammatory activity of the drug. The superior analgesic activity of aspirin compared with sodium salicylate implies that aspirin has an intrinsic activity that is not totally explainable by its conversion to salicylic acid. Aspirin inhibits COX-1 to a much greater extent than COX-2 sodium salicylate is more selective for COX-1. This, combined with the ability of aspirin to acetylate proteins, might account for some of the therapeutic and toxicological differences between aspirin and the other salicylates. 

Theabsorptionof orally administered drug is altered e.g. achlorhydria reduces aspirin absorption. 

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