Knipp's 2nd Set Flashcards
(44 cards)
Sites of Drug Metabolism
- First Pass Metabolism: GI, liver
- Systemic Metabolism: blood stream
Classes of Metabolism
Phase 1: metabolism of main compound
Ex. decarboxylases, oxygenase, deamidation
Phase 2: metabolism through addition, conjugation
Ex. glucuronidation, sulfation
Phase 3: transport - multidrug resistance
Objectives of Drug Metabolism
- eliminate the pharmacological activity of drug
- make a compound continuously more soluble until it cannot escape excretion
How to get Drug Metabolism
- change molecules shape to block its receptor binding
- change molecules lipophilic character to a more hydrophilic character & increase solubility
- increase molecules size
- make molecule more recognizable to efflux pumps
Metabolic Enzymes
- defense mechanism to highly lipophilic, aromatics that naturally occur in environment
Phase 1 Metabolism Focus
Cytochrome P450 –> CYP3A4
CYP3A5 actually metabolize many compounds thought to be done by CYP3A4
Process of Oral Absorption
- Drug molecule at surface dissolves to form saturated solution
- Dissolve drug pass throughout the dissolve fluid and diffuse from high to low concentration
- Drug molecules diffuse through bulk solution to mucosa
- Absorbed
Particle Size
- surface area increases as solids are broken into smaller pieces
- Increased SA leads to Increased Dissolution Rate
Dissolution
Rate of Dissolution
- dM/dt
- change in amount of mass of solution over time
Dependents of Dissolution
D: diffusion coefficient
S: surface area of tablet
h: thickness of layer
Cd: concentration of drug in donor
Ca: concentration of drug in bulk solution
Noyes Whitney Equation
dM/dt = DS/h (Cd-Ca)
- dissolution rate is proportional to D
- increase rate of diffusion –> increase dissolution
- dissolution rate is proportional to particle surface area
- dissolution rate is proportional to difference in concentration gradient
- high to low
- dissolution rate is inverse proportional to h
- increased h = less steep concentration gradient
- decrease h by increasing stirring rate
Permeability
- diffusion across a cell membrane barrier
Factors Limiting Oral Drug Absorption
Solubility
Dissolution
Permeability
Limited Solubility
Dissolution is fast
Permeability is Fast
Drug doesn’t get in solution
Observations:
- gut is saturated by high dose
- absorption does not increase with increased dose
Limited Dissolution
Tdiss is greater than residence time
Permeability is fast
Cant get out of dosage form
Observations:
- dissolution can be enhanced by particle size reduction
- absorption increases with increasing dose
Limited Permeability
Dissolution is fast
Permeability is low
Observations:
- amount of drug absorbed increases with increased dose
Rate Limiting Factors of Permeability
Physiochemical properties of drug
Physiochemical properties of membrane
Rate Limiting Factors of Dissolution
Physiochemical properties of drug
Physiochemical properties of formulation
Definition of Generic Drug
drug product that is comparable to brand in dosage form, strength, route of administration, quality and performance, and intended use
Therapeutic Equivalence
Pharmaceutical Equivalence
Bioequivalence
Pharmaceutical Equvalence
The same:
- API
- dosage form
- route of administration
- identical strength/concentration
Differ:
- shape, excipients, color
Bioequivalence
pharmaceutical equivalents whose rate and extent of absorption are not statistically different when administered to humans at same dose
a drug product is considered bioequivalent if 90% confidence interval of ratios of the test mean values for AUC and Cmax are within 80%-125%
Generic vs Brand Therapeutic Equivalence
- can contain the same AUC but not the same therapeutic effect
Study on Switch to Generic
2885 patients examined
- 70.5% no problems
- 10.8% including reappearance of problem
- 9.8% unspecified issue
- 8.8% other issues
30% of respondents reported an issue