Questions and Answers
What is a reason for differing drug absorption from various formulations containing the same amount of active ingredient?
What is an example of passive targeting in drug delivery?
How is Ivacaftor metabolized to improve its pharmacokinetics?
Which bond is stronger, contributing to a slower rate of metabolism for modified drugs?
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What advantage does using deuterium atoms instead of hydrogen atoms offer in drug design?
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What characteristic of tumors can be exploited for active targeting drug delivery?
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What is a potential consequence of alternative metabolic pathways in drug metabolism?
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What underlying mechanism allows the use of drugs activated at low oxygen levels in tumors?
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What pharmacokinetic benefit is associated with slower metabolic rates of certain drugs?
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What is true regarding drug delivery mechanisms in cancer treatment?
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Study Notes
Drug Absorption - Oral
- Epithelial cell layer controls drug absorption; intestinal epithelium acts as a major barrier.
- Transcellular pathway facilitates drug absorption by allowing drug molecules to partition into cell membranes.
- Drug passage occurs at the apical side (mucosa) then through the basolateral side into systemic circulation, mostly via passive transport.
- Passive transport is energy-independent, occurs through simple diffusion, and follows concentration gradients.
- Predominantly applicable to small lipophilic compounds that can penetrate the phospholipid bilayer of cell membranes.
Lipophilic and Hydrophilic
- Lipophilic substances dissolve well in lipids and non-polar solvents.
- Hydrophilic substances dissolve well in water and polar solvents.
- Principle "like dissolves like"; lipophilic molecules tend to permeate cell membranes due to compatibility with lipid bilayer.
Measuring Drug Lipophilicity
- Simulated absorption using a mixture of lipophilic solvent (octanol) and hydrophilic solvent (water).
- Distribution between the two phases indicates drug's lipophilicity; complete presence in octanol indicates high lipophilicity.
Partition Coefficient and Log P
- Higher Log P values indicate higher lipophilicity; lower Log P values indicate greater hydrophilicity.
- Optimal Log P values determine gastrointestinal absorption efficiency for oral drugs.
- Excessive Log P (e.g., > 5) can lead to bioaccumulation risks (e.g., polychlorinated biphenyls).
Drug Absorption Constraints
- Ionization significantly impacts drug absorption; weak acids and bases can change lipophilicity based on medium pH (Log D).
- Basic functional groups include amines; acidic functional groups include carboxylic acids and phenols.
Oral Pharmaceutical Formulation
- Oral pharmaceuticals, like tablets, contain active pharmaceutical ingredients (API) and excipients which influence bioavailability.
- API characteristics (physical state, particle size) affect absorption.
- Excipients (fillers and lubricants) assist in drug manufacturing and release.
Bioequivalence
- Bioequivalence studies evaluate the comparability of bioavailability between different formulations of the same drug.
- Differences in absorption can arise from variations in drug release kinetics.
- Pharmacokinetic parameters are assessed by comparing serum concentrations after administration.
Targeted Drug Delivery
- Passive Targeting: Utilizes hypoxic conditions within tumors for localized drug activation.
- Active Targeting: Involves drug conjugation to antibodies for specific tissue recognition.
- Example: Ivacaftor for cystic fibrosis, altered by replacing hydrogen atoms with deuterium to enhance pharmacokinetics by reducing metabolic rates and improving efficacy and safety.
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Description
Explore the mechanisms of drug absorption through the intestinal epithelium. This quiz covers pathways, barriers, and transport processes involved in the absorption of orally administered drugs. Test your understanding of how drugs navigate through cellular membranes into systemic circulation.
