Pharmacology Lecture 1

Study Notes

Pharmacology is the study of substances that interact with living systems through chemical processes, especially by binding to regulatory molecules and activating or inhibiting normal body processes.

Pharmacodynamic processes refer to the actions of the drug on the body, which determine the group in which the drug is classified and decide whether that group is appropriate therapy for a particular symptom or disease.

Pharmacokinetic processes refer to the actions of the body on the drug, governing the absorption, distribution, and elimination of drugs, which are of great practical importance in the choice and administration of a particular drug for a particular patient.

Absorption: the entry of the drug into plasma from the site of administration.
Distribution: the reversible movement of the drug from the bloodstream into interstitial and intracellular fluids.
Metabolism: the biotransformation of the drug by the liver or other tissues.
Elimination: the removal of the drug and its metabolites from the body in urine, bile, or feces.

Enteral route:
- Administering a drug by mouth, which is the safest, most common, convenient, and economical method of drug administration.
- Oral administration provides many advantages, such as easy self-administration and the ability to overcome toxicities and overdoses with antidotes.
- however, the pathways involved in oral drug absorption are the most complicated, and the low gastric pH inactivates some drugs.
Parenteral route:
- Introduces drugs directly into the body by injection, used for drugs that are poorly absorbed from the GI tract or unstable in the GI tract.
- Provides the highest bioavailability and is not subject to first-pass metabolism or the harsh GI environment.
- However, parenteral routes have disadvantages, such as pain, fear, local tissue damage, and infections.

Intravenous (IV) route:
- The most common parenteral route, useful for drugs that are not absorbed orally.
- IV delivery permits a rapid effect and a maximum degree of control over the amount of drug delivered.
- Can be administered as a bolus or infusion, but may cause irritation when administered via other routes.
Intramuscular (IM) route:
- Administered IM can be in aqueous solutions or specialized depot preparations.
- Depot preparations often consist of a suspension of the drug in a nonaqueous vehicle.
Subcutaneous (SC) route:
- Provides absorption via simple diffusion and is slower than the IV route.
- Minimizes the risks of hemolysis or thrombosis associated with IV injection and may provide constant, slow, and sustained effects.

pH of the environment:
- The ratio between the charged and uncharged forms of a drug at its absorption site is determined by the pH at the site and the ionization constant (pKa) of the drug.
Blood flow to the absorption site:
- The intestines receive much more blood flow than the stomach, making absorption from the intestine more favored.
Total surface area available for absorption:
- The intestine has a surface area about 1000-fold that of the stomach, making absorption of the drug across the intestine more efficient.

Bioavailability is the rate and extent to which an administered drug reaches the systemic circulation.
Determining bioavailability is important for calculating drug dosages for non-intravenous routes of administration.
Orally administered drugs often undergo first-pass metabolism, which determines the rate and extent to which the agent reaches the systemic circulation.