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Lesson A.5.docx

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Queen's University
Pharmacology and Toxicology
PHAR 100
Bill Racz

Lesson A. 5 - Drug Absorption, distribution, metabolism and excretion Drug Absorption 1. By Inhalation • Drugs in gaseous form can be inhaled and enter bloodstream through lungs • Ex. general anesthetics • Drugs used to target respiratory diseases are administrated by inhalation to minimize effect of drugs on other organs 2. Rectal administration • Sometimes used when patient is nauseous or vomiting and can’t take it by mouth 3. Oral administration • Most convenient route of administration • Over 90% of drugs administrated this way Tablet drugs • How a tablet drug works: o Disintegrate into small particles, then dissolved from fluids of stomach and/or small intestine o May be absorbed through stomach walls into blood vessels (faster on empty stomach) • To ensure it is properly made: o Tablet must be shown to contain adequate amounts of the chemical responsible for the activity of drug o Must disintegrate in a test-tube test However, these do not ensure the effectiveness of the drug, because: • Disintegration time in test tube and in body fluids are different • Made by different companies and ways and contain different additives, but they must produce the same blood level s of the active ingredient Lesson A. 5 - Drug Absorption, distribution, metabolism and excretion Blood level of a drug indicates how much drug gets into the blood and is available to exert a therapeutic effect . Bioavailability – percentage of a drug contained in a drug product that enters the systemic/general circulation in an unchanged form after administration of the product. Also includes the rate at which this entry occurs Generic and Brand Names • Can be very confusing, especially for practitioners, since a drug is usually manufactured by many different companies, all with different brand names • Different versions of drug can have varying blood levels in them, risking fatal consequences • By 1990, all drug products marketed in Canada have been examined for their bioavailability so differences between manufacturer’s products no longer exist The Therapeutic Jungle • So many drug and drug combinations: situation named the “Therapeutic Jungle” • Problems: o Although there is only 1 generic name for a drug, companies selling it can use many different names o Overwhelming number of drugs introduced (companies feel they need to capture a share of the market in many types of drugs, though rarely they any better than original) o Large amount of marketing directed towards new drugs difficult to compare quality in comparison to older drug.  Read unbiased assessments ex. “Medical Letter on Drugs and Therapeutics” Drug Absorption • Must be able to cross biological membrane (lipid bi-layer) to exert a response • Administration of drugs is an attempt to maintain drug concentration at a certain level/range Termination of Drug Action • Redistribution/distribution Lesson A. 5 - Drug Absorption, distribution, metabolism and excretion o Changing distribution of drug in body, without removing it • Excretion o Drug is filtered through kidney and eliminated in urine • Conversion to water soluble inactive products in the liver o In the liver, there are enzymes available for converting drugs to more water soluble products which may be excreted by the kidney o Main series of enzymes, called cytochromes P450
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