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Pharmacokinetics: Routes of Drug Administration & Absorption Patterns

Learn about common drug administration routes, absorption patterns, dosage forms, and novel delivery systems in pharmacokinetics. Understand drug movement, absorption, distribution, metabolism, and excretion processes. Explore factors affecting drug absorption and bioavailability.

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Pharmacokinetics: Routes of Drug Administration & Absorption Patterns

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  1. Pharmacokinetics Prof. Mazen Qato

  2. Objectives At the end of this sessions students should be able to: • List and discuss common routes of drug administration • Explain the absorption pattern of common routes of drug administration. • Describe various dosage forms and their absorption pattern • Discuss noveldrugdelivery systems like transdermal drug delivery etc…

  3. PHARMACOKINETICS • The quantitative study of drug movement in, through and out of the body(Effect of Body on Drug, fate of drug). • Pharmacokinetic processes include • Absorption of drug • Distribution of drug • Metabolism of drug • Excretion of drug

  4. Prof. Mazen Qato

  5. Pharmacokinetics is significant for • Route of drug administration • Dose of drug • Latency of onset • Time of peak action • Duration of action • Frequency of drug administration

  6. Prof. Mazen Qato

  7. Prof. Mazen Qato

  8. Routes of drug administration Factors governing choice of route • Physical and chemical properties of drug • Site of desired action • Rate and extent of absorption of drug from different routes • Effect of digestive juices and first pass metabolism. • Rapidity with which the response is desired • Condition of the patient

  9. PHARMACOKINETICS IIDRUG ABSORPTION Prof. Mazen Qato

  10. Objectives • Discuss factors affecting drug absorption • Emphasize factors influencing bioavailability and bioequivalence • Explain the concept of Henderson Hasselbach equation.

  11. DRUG ABSORPTION Absorption is the movement of drug from its site of administration into the blood stream. Factors affecting drug absorption: • Aqueous solubility(transport across membrane) • Effect of pH • Area of absorbing surface • Vascularity of the absorbing surface • Route of administration

  12. Prof. Mazen Qato

  13. Prof. Mazen Qato

  14. Prof. Mazen Qato

  15. Prof. Mazen Qato

  16. Pharmacological implications of Henderson Hasselbach’s equation: Most drugs are weak electrolytes, that is, their ionization is pH dependant. • Weakly acidic drugs which form salts with cations ( example: sodium phenobarbitone, sodium sulphadiazine ,potassium penicillin V) ionise more at alkaline pH.

  17. Weakly basic drugs which form salts with anions(example: atropine sulphate, ephedrine hydrochloride, chloroquine phosphate) ionize more at acidic ph. • Ions being lipid insoluble do not diffuse across a biological membrane. • Acidic drug example aspirin(pKa =3.5) are largely unionized at acidic gastric pH and are absorbed from the stomach.

  18. Basic drugs like atropine(pKa =10) are largely unionized and absorbed only when they reach small intestine. • Acidic drug are ionized more in alkaline urine – do not diffuse in the kidney and are excreted faster. Accordingly, basic drugs are excreted faster if urine is acidified. This principle is used in treatment of drug overdose.

  19. Bioavailability • It is a measure of the fraction of administered dose of a drug that reaches the systemic circulation in the unchanged form. • Bioavailability of a drug injected intravenously(IV) is 100%. • Calculated from comparing plasma level of a drug after a particular route of administration with plasma drug level achieved by IV injection.

  20. Prof. Mazen Qato

  21. Factors that influence bioavailability of a drug • First pass hepatic metabolism • Solubility of a drug • Chemical stability • Nature of drug formulation. Bioavailibility variation assumes practical significance for drugs with low safety margin (digoxin) or where dosage needs precise control.

  22. Prof. Mazen Qato

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