Pharmacology 2060A/B Lecture Notes - Lecture 2: Lipophilicity, Drug Metabolism, Rugae

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Module 2 Pharmcokinetics Absorption
Pharmacokinetics
- Is defined the study of drug movement in the body
- Is what the body does to the drug
- Pharmacokinetics is composed of four basic processes (ADME)
o Absorption
o Distribution
o Metabolism
o Excretion
Absorption
- Drug absorption is the movement of the drug from the site of administration into the blood.
- The rate of absorption determines how quickly the drug effect will occur
- The amount of drug absorption determines how intense the effect of the drug will be
2.1 - Factors affecting absorption
1) Rate of dissolution
2) Surface area
3) Blood flow
4) Lipid solubility
5) pH partitioning
6) Activity of drug transport proteins
1) Rate of dissolution
- Dissolution means dissolving in solution
- Drugs must dissolve before they can be absorbed
o Must disintegrate and dissolve in our gastric fluid before it can be absorbed
- Drugs with a fast rate of dissolution will have a faster onset of action than drugs with slow
dissolution
- E.g. drugs placed in a liquid
o Over time dissolution occurs and the drug molecules are dissolved in the liquid
o The same thing happens when we swallow a medication, the tablet undergoes
disintegration and the medication dissolves in our stomach contents
2) Surface area
- Surface area is a major determinant of drug absorption
- The larger the surface area, the faster drug absorption is
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- Which has the greater surface, the stomach or the small intestine? SMALL INTESTINE
o Stomach has folds called rugae (small SA)
o Intestine has thousands of finger like projections called villi. The villi that line the
intestine make the surface area very large
3) Blood flow
- Drug absorption is fastest in areas with high blood flow
- Areas with a high blood flow maintain a concentration gradient which drives absorption
o High blood flow = takes blood into systemic circulation maintaining a concentration
gradient to follow and be absorbed
- Areas with low blood flow do not maintain as great of a concentration gradient
- Conditions can change blood flow and influence drug absorption
- Exercise increases blood flow to certain tissues (such as muscle) and can increase drug
absorption
- Blood flow is decreased in heart failure, severe hypotension, hypothermia and circulatory shock
o = absorption may be decreased
4) Lipid solubility
- Drugs with high lipid solubility (i.e. lipophilic drugs) are absorbed more rapidly than water
soluble (i.e. hydrophilic) drugs
- Lipophili drugs are ale to ross the ell erae hereas hydrophili drugs at
5) pH partitioning
- Drug asorptio is greater he theres a difference between the pH at the site of
administration and the blood such that the drug is ionized in the blood
- Drug will be trapped in the blood
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- E.g. a drug is non-ionized in the stomach and when it reaches the blood, it becomes ionized and
is trapped in the blood = cannot return to the stomach
o This increases absorption because the drug is taken away by the blood and creates a
concentration gradient
6) Activity of drug transport proteins
- The rate and extent of drug absorption can be significantly impacted by drug transporters
- Uptake drug transporters increase the absorption of drugs
o Bring hydrophilic drugs from outside to inside and facilitate the absorption of drugs
- Efflux drug transporters decrease the absorption of drugs
o Lipophilic drug can diffuse through the membrane but efflux transporter pumps drug
from inside to the outside
2.2 - Routes of administration
1) Oral (PO = per os (by mouth)) most common route
2) Sublingual
3) Transdermal
4) Rectal
5) Intravenous (IV)
6) Subcutaneous (subQ or SC)
7) Intramuscular (IM)
8) Pulmonary
- Routes of administration are often referred to as enteral or parenteral
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Document Summary

Is defined the study of drug movement in the body. Is what the body does to the drug. Pharmacokinetics is composed of four basic processes (adme: absorption, distribution, metabolism, excretion. Drug absorption is the movement of the drug from the site of administration into the blood. The rate of absorption determines how quickly the drug effect will occur. The amount of drug absorption determines how intense the effect of the drug will be. 2. 1 - factors affecting absorption: rate of dissolution, surface area, blood flow, lipid solubility, ph partitioning, activity of drug transport proteins, rate of dissolution. Drugs must dissolve before they can be absorbed: must disintegrate and dissolve in our gastric fluid before it can be absorbed. Drugs with a fast rate of dissolution will have a faster onset of action than drugs with slow dissolution. Surface area is a major determinant of drug absorption. The larger the surface area, the faster drug absorption is.

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