Lecture 3.1 Flashcards
(19 cards)
What are the critical steps in drug absorption?
- Disintegration
- Dissolution
- Inactivation/Removal
- Absorption
These steps outline the processes a drug undergoes before it can be absorbed into the systemic circulation.
What clinical factors affect drug absorption?
- Formulation
- Physicochemical properties of drug
- Environment
- Physiology (pH, enzymes, time at absorption site, variable perfusion and membrane properties)
- Extrinsic factors (food, other drugs)
- Disease (e.g., Crohn’s, Coeliac)
These factors can significantly influence how well a drug is absorbed after administration.
What formulation factors influence drug absorption?
- Nature of formulation (dosage form)
- Solution vs. suspension
- Nature of solvent/vehicle (aqueous vs. oily)
- IM route of administration
- Solid dose form (e.g., tablet, capsule)
- Modified release forms
- Sublingual or transdermal routes
Altering the formulation can change the absorption pattern and concentration-time profile.
What physicochemical factors are important for drug absorption?
- Solubility
- Polarity
- Lipophilicity
- Molecular size
- Ionisation
These factors determine how well a drug can dissolve and permeate biological membranes.
Fill in the blank: The process governed by concentration gradient for drug absorption is known as _______.
Passive Diffusion
What is the role of passive absorption in drug absorption?
- Governed by concentration gradient
- Amount absorbed increases as dose increases
- Rate of absorption higher with larger doses
Passive absorption is a crucial mechanism for most orally administered drugs.
What are the absorption processes involved in drug absorption?
- Passive Diffusion
- Active Absorption
- Paracellular transport
These processes describe how drugs cross biological membranes to enter systemic circulation.
True or False: Most drugs are absorbed in the small intestine.
True
What factors influence gastric emptying?
- Food intake
- Drug interactions
- Disease states
Gastric emptying affects the time drugs take to reach the intestine and therefore influences absorption.
What is the significance of the biopharmaceutical classification system?
It categorizes drugs based on solubility and permeability, which impacts absorption.
What factors can alter GI transit time?
- Food
- Drugs (e.g., anticholinergics, opioids)
- Disease states
Altered GI transit times can affect drug absorption and effectiveness.
How does food impact drug absorption?
- Slow gastric emptying
- Alters extent of absorption
- Affects acid-labile drugs
The presence of food can either enhance or hinder the absorption of certain medications.
What is the first pass metabolism?
The metabolism of a drug in the liver after it enters the portal circulation, which can reduce the bioavailability of orally administered drugs.
What are the absorption parameters of interest?
- Absorption rate constant (ka)
- Absorption half-life (t1/2,abs)
- Maximum concentration (Cmax)
- Time of Cmax (tmax)
- Absorption lag time (tlag)
- Bioavailability (F)
These parameters help in understanding the kinetics of drug absorption.
Fill in the blank: A drug must be _______ enough to dissolve in GI fluids and _______ enough to cross membranes.
Hydrophilic; Lipophilic
What are the barriers to drugs reaching systemic circulation?
- Degradation in the lumen
- Metabolism by CYP3A4 in enterocytes
- Export by P-glycoprotein
- Metabolism in portal blood
- Metabolism or excretion in the liver
These barriers can significantly reduce the amount of active drug that reaches circulation.
What is enterohepatic recirculation?
The process where drugs or their metabolites are reabsorbed from the intestine back into the liver after being excreted in bile.
What are the physiological factors that influence drug absorption?
- pH levels
- Enzyme activity
- Time at absorption site
- Perfusion rates
- Membrane properties
These factors can vary significantly and affect how drugs are absorbed in the gastrointestinal tract.
What role does gastric pH play in drug absorption?
It affects dissolution and absorption, with varying pH levels in different parts of the GI tract.
