2.4 - Absorption Flashcards
Movement of drug form site of administration to the central compartment (blood)
Absorption
Rate & Extent of disappearance of a drug from the site of administration
Physiologic
Rate & extent of drug entry into systemic circulation
Pharmacokinetic
Factors Affecting Absorption
- Dose Size
- Surface Area of the Absorption Environment
- pH of the Absorption Environment
- Degree of Perfusion
- Gastric Emotying Time
Dose Size
⬆️dose = ⬆️absorption
Absorption Environment
- Stomach
* Small Intestine
Surface Area of the Absorption Environment
⬆️Surface Area = ⬆️Absorption
Main site of drug absorption
Small Intestine
– SA = 120 m2 (villi& microvilli)
pH of the Absorption Environment
- Stomach — Acidic (⬇️pH)
* SI — Basic (⬆️pH)
Weak Acid
- Stomach: Non-ionized (absorbed)
* SI: ionized (excreted)
Weak Base
- Stomach: Ionized (excreted)
* SI: Non-ionized (absorbed)
Degree of Perfusion — Blood Supply
⬆️Perfusion = ⬆️Absorption
– For PO drugs
– Time it takes for the stomach to empty its contents
Gastric Emptying Time (GET)
Stomach
– Small Surface Area
– Small perfusion
— POOR ABSORPTION Environment except ASA & Ethanol
Gastric Emptying Time (GET)
⬆️GET = ⬇️Absorption
Normal Gastric Emptying Time
2-3 hours
Factors that ⬆️ GET
- Stress
- Gastric ulcer
- Heavy exercise
- Heavy meal
- Lying on the left side
- Antimotility/ Anticholinergics
Factors that ⬇️ GET
- Extremes in food temp
- Lying on the RIGHT side
- Mild exercise
- Promotility Drugs
Pharmacokinetic Parameters
- Bioavailability
* Bioequivalence
Measurement of RATE AND EXTENT of drug absorption
Bioavailability
Methods
- Cumulative Urinary Excretion Data
* Plasma Concentration vs Time Graph
Parameters
- Cmax
- tmax
- AUC
– Maximum drug plasma concentration
– Measure BOTH rate and extent
– Most variable
Cmax
– Time to reach Cmax
– Measures the RATE
Tmax
– Area Under the Curve
– Measures the EXTENT
AUC
Bioavailability Studies
- Absolute Bioavailability
* Relative Bioavailability
– Measurement in the similarity of the bioavailability of the generic drug product and the BA of the innovator
Bioequivalence
Minimum number of subjects
12
Acceptable
(90% Confidence Interval) 0.8 (80%) - 1.25 (125%)
– Same API, salt/ ester/ complex-
– Same dosage form, strength
– Differ in excipient, brand name
Pharmaceutical Equivalents
– Same API – May differ in: - salt/ ester/ complex - dosage form - dosage strength
Pharmaceutical Alternatives
– Pharmaceutical Equivalents
– Bioequivalent
Therapeutic Equivalence
– Differ in API
– Same drug class
Therapeutic Alternatives
