Biopharmaceutics 1 Flashcards
what is biopharmaceutics
the study of the physical and chemical properties of drugs and their proper dosage as related to the onset, duration, and intensity of drug action
what is drug absorption
The process of movement of unchanged drug from its site of administration to the systemic circulation.
Following absorption, the effectiveness of a drug can only be assessed by
it’s concentration at the site of action
but this is difficult to measure so the concentration can be measured more accurately in plasma
Correlation between the plasma concentration of a drug and therapeutic response.
What are some route’s of administration
IV / IM / SC injection, buccal tablets, aerosols, suspension, tablets, modified release
Time of onset - seconds
which formulation does this?
IV injections
Time of onset - minutes
IM and SC injections, buccal tablets, aerosols, gases
Time of onset minutes to hours
which formulations
Short-term depot injections, solutions, suspensions, powders, granules, capsules, tablets, modified-release tablets
Time of onset - several hours - which formulations
enteric coated formulations
time of onset - days
depot injections and implants
Giving a drug by mouth is the … route of administration but it is also the … and requires the … pathway to the tissues.
most common
most variable
most complicated
Factors Affecting GI Absorption of a Drug From its Dosage Form - Physicochemical properties
Drug solubility & dissolution rate
Particle size and effective surface area
Polymorphism Stable / metastable
Pseudopolymorphism (hydrates / solvates) L-phenylalanine anhydrous / monohydrate
Salt form of the drug Hydrochloride / sodium / sulfate / phosphate
Lipophilicity of the drug
pKa of the drug and pH
Drug stability
Factors Affecting GI Absorption of a Drug From its Dosage Form- Dosage Form Characteristics & Pharmaceutical Ingredients
Disintegration time (tablets/capsules)
Dissolution time
Manufacturing variables e.g wet / dry granulation / direct compression
Pharmaceutical ingredients (excipients)
Nature & type of dosage form
Product age & storage conditions
Patient-Related Factors
Age
Gastric emptying time
Intestinal transit time
Gastrointestinal pH
Disease states
Blood flow through the GIT
7. Gastrointestinal contents:
Other drugs
Food
Fluids
Other normal GI contents
8. Presystemic metabolism by:
Gut wall enzymes
Bacterial enzymes
Hepatic enzymes
Advantages of oral delivery
Convenient
Can be self-administered
Pain free
Easy to take
Safe
Absorption takes place along the whole length of the GI tract
Cheap compared to most other parenteral routes
Disadvantages of oral delivery
X Some drugs have an unpleasant taste
X Irritation to gastric mucosa - nausea and vomiting
X Destruction of drugs by gastric acid
X Absorption is sometimes inefficient, only part of the drug may be absorbed
X Effect too slow for emergencies
X Unable to use in unconscious patient or who have had GI surgery
X Effect of first-pass metabolism
First pass effect:
On first pass through the liver, drug is metabolised and therefore conc entering systemic circulation reduces
SO we need a much larger dose to achieve the therapeutic effect
Mechanisms of Drug Absorption
what are the 2 mechanisms
Transcellular (Across the cells)
Paracellular (between the cells)
The transcellular pathway is further divided into:
Lipid diffusion
Carrier-mediated transport and facilitated diffusion
Endocytosis
mechanisms of drug permeation
DRAW THE DIAGRAM
on a whiteboard - draw
Passive Diffusion also known as
ionic diffusion
Fick’s first law of diffusion
The drug molecules diffuse from a region of higher concentration to one of lower concentration until equilibrium is attained & the rate of diffusion is directly proportional to the concentration gradient across the membrane.
drugs that undergo passive diffusion usually have a molecular weight between
– mol Wt of drugs ~100 – 400 Daltons. Diffusion rate proportional to conc gradient across membrane
