1. Principles of Drug Action
Practicum of Health Science Technology

2. General Properties of Drugs
Drugs do not confer any new functions on a tissue or organ in the body, they only modify existing functions
Drugs in general exert multiple actions rather than a single effect
Drug action results from a physiochemical interaction between the drug and a functionally important molecule in the body

3. Mechanisms of Drug Action
To produce its optimal effect, a drug must reach appropriate concentrations at its site of action

4. Pharmacokinetics
The study of the concentration of a drug during the process of absorption, distribution, biotransformation, and excretion.

5. Pharmacokinetic Activities
Absorption
Distribution
Biovailibility
Excretion

6. Absorption
The process involving the movement of drug molecules from the site of entry into the body to the circulation
The rate of absorption depends on the route of administration

7. Routes of Drug Administration
Enteral – oral
Parenteral – injection
- Subcutaneous
- Intramuscular
- Intravenous
- Intrathecal
- Epidural

8. Routes of Drug Administration
Pulmonary – inhalation; nebulilzers
Topical – skin and mucous membranes
- Skin - transdermal
- Eyes
- Ears
- Nasal mucosa

9. Bioavailability
The percentage of active drug substance absorbed and available to target tissues, following administration

10. Distribution
The transport of a drug in body fluids from the bloodstream to various tissues of the body and ultimately to its site of action

11. Drug Reservoirs
Allow a drug to accumulate by binding to specific tissues in the body
Sustains the pharmacologic effect of the drug at its point of action
Involve two general types of drug pooling:
- Plasma Protein Binding
- Tissue Binding

12. Plasma Protein Binding
On entry into the circulatory system drugs may become attached to proteins, mainly albumin contained in the blood
Protein binding decreases the amount of free drug in circulation, which limits the amount of drug that travels to the site of action

13. Tissue Binding
Fat tissue – Lipid soluble drugs have a high affinity for adipose tissue, which is where these drugs are stored
Relatively low blood flow in fat tissue makes it a stable reservoir
Bone – Some drugs have an unusual affinity for bone;

14. Barriers to Drug Distribution
Specialized structures made up of biologic membranes can serve as barriers to the passage of drugs at certain sites in the body
- Blood Brain Barrier
- Placental Barrier

15. Blood - Brain Barrier
Special anatomic arrangement that allows distribution of only lipid – soluble drugs into the brain and cerebrospinal fluid;
Compounds that are strongly ionized and poorly soluble in fat cannot enter the brain

16. Placental Barrier
The membrane layers that separate the blood vessels of the mother and the fetus
Does not completely protect the fetus
The barrier is permeable to lipid soluble and insoluble drugs
Many drugs intended to produce a therapeutic response in the mother also my affect the developing baby

17. Biotransformation or Metabolism
Chemical inactivation of a drug by converting it into a more water-soluble compound, or metabolite, that can be excreted from the body
Liver is the primary site of metabolism of drugs

18. Excretion
The process where drugs and pharmacologically active or inactive metabolites are eliminated from the body;
- Kidneys
- Intestine
- Lungs
- Sweat and salivary glands
- Mammary glands

19. Kidneys Most important route of drug elimination
The availability of a drug for kidney filtration depends on its concentration in unbound form in the plasma
Lipid soluble drugs are not excreted by the kidneys
Water-soluble drugs are excreted by the kidneys

20. Intestines
Some of the medications are eliminated through the intestines through biliary excretion
After metabolism by the liver, the metabolite is secreted into the bile, passed into the duodenum and is eliminated with the feces

21. Lungs
Most drugs removed by the pulmonary route are intact, and not metabolites
Agents such as gases and volatile liquids that are administered through the respiratory system usually are eliminated by the same route.

22. Sweat and Salivary Glands
Relatively unimportant because excretion of a drug through this route requires diffusion of lipid-soluble drugs through the epithelial cells of the glands.
May result in dermatitis or other skin reactions.

23. Mammary Glands
Many drugs or their metabolites cross the epithelium of the mammary glands and are excreted in breast milk
Breast milk is acidic, and therefore basic compounds such as narcotics achieve high concentrations in this fluid
Major concern is transference of drugs from mother to child