Drug Absorption Process: Oral Dosage Form

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Questions and Answers

What is the initial phase in the process of drug absorption subsequent to administering an oral dosage form?

Disintegration of the dosage form

What is the pH of the stomach, as mentioned in the text?

1-3

Which part of the gastrointestinal tract has a notably basic pH?

Colon

What is the function of the bimolecular lipid layer in drug absorption?

To facilitate absorption through biological membranes Signup and view all the answers

In drug absorption, what is the final state that each molecule of the drug reaches before becoming fully dissolved and available?

Molecular state Signup and view all the answers

According to the pH-Partition Theory, what parameters are considered determinants affecting the extent of drug absorption across biological membranes?

Dissociation constant of the drug, lipid solubility, and pH of the fluid at the absorption site Signup and view all the answers

What pH conditions are preferable for optimal absorption of basic and acidic drugs according to the passive diffusion mechanism?

Higher pH for basic drugs and lower pH for acidic drugs Signup and view all the answers

What is the anticipated site of absorption for aspirin based on its pKa value of 3.5?

Stomach Signup and view all the answers

Why is it preferred to take aspirin after a meal?

Prolongs its stay in the stomach, optimizing its absorption at the intended site Signup and view all the answers

Which one of the following figures represents passive diffusion?

(A) Signup and view all the answers

What is the purpose of drug metabolism?

To convert lipid-soluble compounds into water-soluble forms Signup and view all the answers

Which reactions are involved in Phase I metabolism?

Oxidation, reduction, dealkylation, and hydroxylation Signup and view all the answers

What defines the Lipinski Rule of 5?

A guideline for differentiating drug-like and non-drug-like molecules Signup and view all the answers

How does enalapril convert into its active form?

By hydrolysis of its ester bond by esterase enzymes Signup and view all the answers

What is a prodrug?

An inactive derivative of a drug molecule that undergoes chemical changes to release the active parent drug Signup and view all the answers

Which of the following parameters is NOT a characteristic of a molecule suitable for bioisosterism?

More than 5 hydrogen bond donors Signup and view all the answers

What is the optimal isostere for the phenyl ring in drug design?

Pyridine ring Signup and view all the answers

Why do ester-containing drug molecules exhibit high in vivo lability and low metabolic stability?

Presence of cytochrome P450 oxidases Signup and view all the answers

What makes fluorine an ideal biostere for the replacement of a para-methyl group in drug molecules?

Resistance to attack by cytochrome P450 oxidases Signup and view all the answers

What is the primary objective behind using bioisosterism in drug design?

Crafting improved pharmacodynamic profiles Signup and view all the answers

Study Notes

Drug absorption from oral dosages involves disintegration, dissolution, and traversing biological membranes.
Gastrointestinal tract pH varies significantly, with stomach being acidic and small intestine alkaline.
Passive diffusion is the primary mechanism of drug absorption, driven by concentration gradients.
pH-Partition Theory states that drug absorption depends on drug's dissociation constant, lipid solubility, and absorption site pH.
Basic drugs optimally absorb at higher pH levels, while acidic drugs prefer lower pH levels.
Aspirin, an acidic drug, is best absorbed in stomach due to its low pH and unionized state.
Passive diffusion is depicted by a linear relationship between concentration and absorption rate, unlike active transport.
Enalapril, a prodrug, is converted to active form through enzymatic hydrolysis.
Drug metabolism transforms lipid-soluble compounds into water-soluble forms, aiding excretion.
Phase I metabolism includes mild reactions, while Phase II involves conjugation reactions.
Lipinski Rule of 5 is a guideline for drug-like molecules, focusing on molecular mass, lipophilicity, and hydrogen bonding.
Bioisosterism is the substitution of one atom or group with another having similar electronic and steric configurations.
Pyridine ring, tetrazole ring, amide, and fluorine are optimal isosteres for phenyl rings, carboxylic acids, esters, and methyl groups, respectively.
Ester-containing drugs have high in vivo lability and low metabolic stability due to the presence of esterases.
Amide bonds can be used to increase the metabolic stability of ester-containing drugs.
Fluorine is an ideal biostere for methyl groups due to its increased stability against cytochrome P450 oxidases.
Replacing the para-methyl group in celecoxib with fluorine enhances metabolic stability by preventing metabolic hydroxylation.

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