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Comprehensive Analysis of Factors Affecting Drug Absorption Through the Gastrointestinal Tract

Explores pharmaceutical, physicochemical, physiological, and patient-related factors influencing drug absorption in the GI tract, essential for pharmacology and nursing studies.

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Pharmacology Bachelor of Science in Nursing Here is where your presentation begins GONDIA COLLEGE OF PHARMACY, CHULOD
Name : Yuganti Toplal Hemne PRN : 2146601823109 Class : B Pharm (VIth Semester) Topic : Factors Affecting Drug Absorption Trough GI tract. ( Biopharmaceutics and Pharmacokinetics) Guided By : Mr. V. R. Garg Sir Introduction of Student
Factors Affecting The Absorption of Drugs 💊 Pharmaceutical Factors 💊 Physicochemical Factors 💊 Physiological Factors 💊 Patient Related Factors
Table of contents Pharmaceutical Factors • Particle size of drug • Nature of the drug • Formulation Excipients • Physical state • Dosage form • Chemical Nature of drugs • Product age and storage condition Physicochemical Factor • Lipid solubility • Particle size / Surface area • pH of the drug • Ionization of drug • Partition Coefficient • Protonated and Unprecedented Form Physiological Factors • Membrane Thickness • Membrane Surface Area • pH of GIT fluid • Functional integrity of GIT • Gastric emptying time • Blood Flow Patient Related Factors • Gastric Emptying • Intestinal Transit • Gastrointestinal pH • Gases State • Gastrointestinal Contents • Blood Flow
I) Particle Size :- Small water soluble molecules diffuse more efficiently across cell membrane through pores, small particles faster the rate of diffusion. II) Nature of Drug :- The drug administration in different rate of disintegration and dissolution and these are limiting factor in absorption of drug particles. III) Concentration of Drug :- Drug ingested or injected in solution of high concentration are absorbed more rapidly than drug in low concentration. IV) Formulation Excipients :- Substances like sucrose, lactose, starch are commonly used as Excipients in formulating the drug. These substances may affect the absorption. V) Physical state :- Liquids are better absorbed than solids and crystalloids are absorbed than collides. Pharmaceutical Factors
VI) Chemical nature of Drug :- Inorganic iron preparation is better from GIT than organic preparation ferrous sulphate are better than ferric salt. VII) Products Age and Storage Condition :- • Due to aging these may be number of changes in physicochemical properties of drug in dosage form that can affect bioavailability. • Change in particle size distribution can be observed with number of suspension dosage forms that further result in decreased rate of drug dissolution and absorption. • In case of solid dosage forms (eg.tablets) disintegration and dissolution rates are greatly affected due to aging and storage condition. • Change that occur during shelf life of a dosage forms are affected by large variation in temperature and humidity. Eg. Prednisolone tablets that contain lactose as filter, at high humidity form harder tabs that result in slow dissolution.
Physicochemical Factors I) Lipid Solubility :- Drugs those are lipid soluble diffuse through the cell membrane more rapidly than the lipid insoluble drugs because the compatibility of the drug with structure of lipid bilayer. • For hydrophobic drugs like griseofulvin/ spironolactone, absorption of such drug is dissolution rate limited. • If hydrophile is rapid and RDS is absorption of such drugs is rate of permeation through biomembrane II) Particle Size / Surface area :- Particle size plays an important role in drug absorption. Dissolution rate is directly proportional to surface area, smaller particle size or drug molecule provide larger surface area which results in higher rate of dissolution.
III) pH of The Medium :- In the stomach the phenobarbitone will be in the nonionized state hence these are lipid soluble and would be better absorbed than the alkaline medium of the intestine. On the other hand weak bases eg. Quinidine ephedrine would be highly ionized in the stomach while it would be better absorbed in the intestine with alkaline medium. IV) Ionization of Drug :- Most drugs are weak acids or bases and are present in the solution in both ionized and unionized form. The non ionized being the lipid soluble diffuse across the cell membrane while ionized form being the lipid insoluble unable to penetrate the lipid membrane. For Acid in acidic medium: HA –— A– + H + For base in acidic medium: BH+ —– B + H +
V) Ionization Coefficient :- The distribution of weak electrolyte is determined by its ionization Coefficients Pka value and pH gradient across the membrane when PKa of the drug is equal to the pH of the medium then 50% will be in the nonionized state. Dissociation of an acid : Ka = ____________ Dissociation of an basic :. Ka = _____________ VI) Partition Coefficient :- Partition Coefficient deal with motion ol² molecule across the cell membrane. Greater will be the diffusion. Relation between pH, PKa and ionized unionized fracion can be depicted from Henderson Hasselbalch equation. [ A– ] [ H+ ] HA [ B ] [ H+ ] [ BH+ ]
For Acid : PKa = pH + log __________________________________ For Base : PKa = pH + log __________________________________ VII) Protonated and Unprotonated Form :- Protonated form of acid is well absorbed and in unionized form while Protonated form of base is less absorbed because it is ionized form of base. The equation given for acid is as follows Pka = pH + log _________________ Protonated form of acid and base ( HA or BH+ ) form Unprotonated form of acid and base ( A or B ) Molecular conc. Of nonionized acid Molecular conc. Of ionized acid Molecular conc. Of ionized base Molecular conc. Of nonionized base Protonated form Unprotonated Form
I) Membrane Thickness :- Membrane thickness is inversly proportional to the absorption of drug across the membrane. As the thickness of the lipid in membrane increases the absorption of a drug decreases II) Membrane surface area :- Drugs are better absorbs from large surface area such as pulmonary elveolar epithelium, intestinal mucosa etc. The area of absorbing surface depends to agreater extent on the route of administration. III) pH of gastrointestinal fluids :- In the stomach the weak acids eg. Aspirin, phenobarbilone will be in the nonionized state hence these are lipids soluble and would be better absorbed in the alkaline medium of the intestine. On the other hand weak bases, eg. Quinidine, ephedrine, would be highly ionized in the stomach and poorly absorbed from the stomach while it would be better absorbed in the intestine with alkaline medium. Physiological Factors
IV) Functional Integrity of GIT :- Increased Peristaltic movement as in diarrheal reduces the drug absorption Gastro intestinal mucosal edema depress the absorption of drug. V) Gastric Emptying Time :- Enhance the gastro emptying time increased the rate of absorption in the GIT eg. Metoclopramides enhances the gastric emptying time. VI) Blood flow :- In shock , blood flow to intestine is decreased and absorption from the intestine is reduced.
1.) Age :- Infants — In Infants biological system is not developed well, therefore gastric pH is high and intestinal surface and blood flow is low which results in altered absorption pattern in comparison to adults. 2.) Elder Patient :- Where in elderly patient biological system is impaired altered gastric emptying is result in increased intestinal surface area GIT blood flow. Higher incidence of a chlorhydria and bacterial ever growth in small intestine. 3.) Gastric Emptying :- Passage of drug from starch to small intestine is called gastric emptying. It can also be a rate limiting step in drug absorption because the major site of drug absorption is intestine. Rapid gastric emptying may increases bioavailability of drug. Number of factors that influence gastric emptying: • Volume of meal :- larger bulk of meal leads to larger gastric emptying. • Composition of meal :- rate of gastric emptying for various food materials in the following orders • Carbohydrates > Proteins > Fats Patient Related Factors
• Physical state and viscosity of meal • Temperature of meal. • Gastrointestinal pH • Electrolyte and osmotic press • Body posture. • Emotional state • Exercise • Disease state 4.) Intestinal Transit :- For complete drug absorption small intestine can also be a site for absorption of most drugs for which long intestinal Transit time is desirable.
Delayed intestinal Transit is desirable . • During that formulated for sustained release. •Drugs that dissolves only in intestine. •Food - decreased digestive secretion. •Pregnancy – Retard intestinal transit etc. 5.) Gastrointestinal pH :- GI pH increases gradually as one pose through down the stomach to colon and erectum . GI fluid pH influence drug absorption in several ways.
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