Chapter 3
Pharmacokinetics: Drug Absorption
Drug Administration and Therapy Phases: Overview
Drugs are chemicals used for diagnosing, treating, or preventing diseases. The four phases of drug product preparation are pharmaceutic, pharmacokinetic, ...
Drug Absorption: Overview
The process of drug absorption involves the passage of a drug from its administration site into the plasma. It is influenced by factors like ...
Drug Delivery: Overview
The choice of a drug's delivery route depends on its physicochemical features, such as lipid or water solubility and ionization, as well as ...
Drug Delivery: Enteral Route
Enteral administration of drugs can occur via oral, sublingual, and buccal routes. Oral administration involves swallowing a pill; in sublingual delivery, ...
Drug Delivery: Parenteral Route
The parenteral route delivers drugs directly into the systemic circulation. It facilitates rapid onset of action and is the preferred route for poorly ...
Drug Delivery: Miscellaneous Routes
Drug delivery methods, such as oral inhalation, nasal sprays, transdermal patches, eye drops, intravitreal, and intrathecal injections, mostly offer ...
Cellular Membranes and Drug Transport
Drugs encounter multiple barriers to reach their target site within the body, including the multiple-cell layered skin, single-layered intestinal ...
Mechanisms of Drug Absorption: Paracellular, Transcellular, and Vesicular Transport
After administration, drugs must cross cell membranes to reach their target site in the body. For example, oral drugs must navigate intestinal epithelial ...
Passive Diffusion: Overview and Kinetics
Passive diffusion allows small lipophilic drugs to cross the cell membranes along a concentration gradient. During this process, the drug absorption rate ...
Pore Transport and Ion-Pair Transport
Most drugs cross the membrane barriers through passive transport mechanisms, moving along the concentration gradient.
Many low molecular weight drugs move ...
Carrier-Mediated Transport
Carrier-mediated transport facilitates the movement of lipid-insoluble drugs via membrane-spanning transporters.
As drug concentration increases during ...
Facilitated Diffusion
The plasma membrane consists of several transporters or carrier proteins interspersed between the lipid bilayer that facilitate solute transport.
...
Active Transport
Active transport is the process of moving lipid-insoluble molecules against their concentration gradient using energy and specialized transporters.
There ...
Vesicular Trasport: Endocytosis, Transcytosis and Exocytosis
Endocytosis is a process where the cell membrane folds inward as vesicles to engulf large-sized drugs.
This process includes pinocytosis and
...
Factors Influencing Drug Absorption: Anatomical Parameters
Drug absorption entails transporting drugs from the administration site to the bloodstream.
GI motility moves drugs through the digestive tract, entering ...
Factors Influencing Drug Absorption: Disease States and Pharmacology
Various disease conditions can influence the body's blood flow and the functioning of the gastrointestinal system, influencing the drug absorption ...
Factors Influencing Drug Absorption: Physicochemical Parameters
The physicochemical properties of drugs are essential parameters for designing stable and bioavailable drug products.
A drug's solubility depends on ...
Factors Influencing Drug Absorption: Pharmaceutical Parameters
For drug products like tablets and capsules, dissolution and absorption are greatly influenced by the manufacturing methods and inactive components or ...
Factors Influencing Drug Absorption: Drug Dissolution
The drug absorption process from solid oral dosage forms, like tablets or capsules, into the systemic circulation involves sequential events.
Firstly, ...
Factors Influencing Drug Absorption: Presystemic Elimination
Most oral drugs are absorbed from the intestines into the hepatic portal vein, passing through the liver before entering the systemic circulation. This ...
Theories of Dissolution: Diffusion Layer Model
Dissolution, the process of drug particles dissolving in a solvent, is explained by the diffusion layer model.
According to this model, initially, a thin ...
Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model
Various dissolution theories elucidate factors impacting the dissolution rate.
Danckwert's model postulates that the dissolution medium shows ...
Factors Affecting Dissolution: Particle Size and Effective Surface Area
Recall the Noyes-Whitney equation, which suggests a direct correlation between dissolution rate and a drug's surface area.
A solid drug's surface ...
Factors Affecting Dissolution: Polymorphism, Amorphism and Pseudopolymorphism
Drug dissolution is influenced by polymorphism, which refers to the existence of a drug substance in multiple crystalline forms like polymorphs, solvates, ...
Factors Affecting Dissolution: Drug pKa, Lipophilicity and GI pH
Drug absorption in the gastrointestinal tract depends mainly on the absorption site's pH, the drug's dissociation constant, and lipophilicity.
The ...
Factors Affecting Dissolution: Drug Permeability, Stability and Stereochemistry
Most orally administered drugs travel through the GI tract and diffuse passively through intestinal membranes to enter the systemic circulation.
The ...
Methods for Studying Drug Absorption: In vitro
Various in vitro methods utilize different biological barriers to study drug absorption.
In the diffusion cell technique, a donor compartment with the ...
Methods for Studying Drug Absorption: In situ
In situ drug absorption methods mimic in vivo conditions by perfusing a drug solution through an anesthetized rat's intestinal segment.
It includes ...
Non-Oral Extravascular Drug Absorption Routes
Non-oral extravascular routes mainly diffuse drugs passively to reach the systemic circulation. Factors influencing extravascular drug absorption include ...
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