PHCY211 Exam Questions With Correct
Answers 100% Verified
Importance of drug stability - ANSWER The capacity of a pharmaceutical to remain
within specifications established to ensure its identity, strength, quality and purity.
There is physical, microbial and chemical stability.
Maintain activity, potency and purity. Safety of patients. Look in production, storage,
transporting and storage in hospitals/pharmacies. Typically only 1-2% degradation, can
be up to 10% if the drug has a wide therapeutic window.
Shelf-life - ANSWER Expiration dating period. Time during which a drug product is
expected to remain within the approved specification for use provided it is correctly
stored
First Order - ANSWER -d[D]/dt = Kobs . [D] independant of concentration only
dependant on time (units, time-1 e.g. s-1)
to make linear ln[D] = ln[D0] - Kobs . t
[D] = [D]0 . e^-Kobs . t
Half life = 0.693/Kobs
Shelf life = 0.105/Kobs
Apparent ZERO order - ANSWER Units conc.time-1, dependant on initial concentration
and time
-d[D]/dt = Kobs
Half life = 0.5 [D]0/Kobs
Shelf life = 0.1 [D]0/Kobs
Temperature Effects: Arrhenius equation - ANSWER Increase in degradation rate of
drugs in solution
k = A.e^-Ea/RT
lnK=lnA-Ea/RT
Shelf life equation
Rule of thumb
What do you mean by disintegration of solid dosage forms? - ANSWER Process in which
,a solid dosage form is broken down into smaller particles thereby increasing surface
area
What is the importance of disintegration? - ANSWER Ensuring and maximising the
bioavailability of the drug, so the whole drug is able to dissolve, reliable clinical
performance, quicker absorption of the drug and faster onset of the desired effect
Give examples of solid dosage forms for which disintegration is very important step for
drug release. - ANSWER Immediate release tablets: designed to full disintegrate and
dissolve upon exposure to physiological fluids within a short period of time (2.5-10
mins). Important for the rapid onset of action, or to enhance bioavailability of a poorly
soluble drug
Orally dispersible/disintegrating tablets: Designed to disintegrate in the mouth in less
than a minute before swallowing. ODT have faster onset of effects than tablets or
capsules and have the convince of a tablet that can be taken without water.
Mention three mechanisms of disintegration. - ANSWER Facilitate water uptake and
transport liquid into pores of the tablet (SDS)
Produce gas in contact with moisture (tartaric acid + sodium bicarbonate)
Swell open with contact with water (starch)
Define dissolution. Mention two steps of dissolution. - ANSWER Process by which a
chemical or drug passes from a solid into solution
Two steps: 1 Liberation: Detachment of molecules from the solid surface to form
solvated molecules at the solid-liquid interface. 2. Diffusion: Transport from this
interface to the bulk solution. This is a prerequisite to absorption.
Give pharmaceutical examples where dissolution is important. - ANSWER Release from
normal capsules
Release from conventional tablets
Release from matrix tablets or pellets, lipid matrix (non-hydrating) and swellable
(hydrating) matrix
Release from coated tablet or coated granules/pellets, where the coat remains intact;
liquid and dissolving drug may precipitate the film coat
Continued release from ointments or creams in which drug is present in excess of its
solubility
Continued release of drug from an oral mixture which is suspended
Describe Noyes-Whitney equation and Nernst-Brunner equation for determining
dissolution of drugs from a tablet. - ANSWER Noyes-Whitney: Basic transport-rate
controlled model for solid dissolution. When SA constant the dissolution rate if a drug is
, proportional to the difference between its solubility and bulk solution conc. k is a
constant (mass transfer coefficient). dW/dt = k(Cs-Cb).
Nernst-Brunner: Diffusion layer model, suggests diffusion occurs across a thin stagnant
layer at saturated solution called the diffusion layer (or hydrodynamic boundary layer)
into the bulk solution. dW/dt = DA/h (Cs-Cb)
Mention the assumptions that have been made in derivation of Nernst-Brunner equation.
- ANSWER Drug dissolves uniformly from all surfaces of the particles
Particles are spherical
h is constant
Both h and Cs are assumed to be independent of particle size
In reality drug particles are neither spherical nor uniform in size
Describe the factors that influence dissolution of drugs from oral solid dosage forms -
ANSWER Surface area, saturated concentration, diffusion coefficient, thickness of
diffusion layer, bulk concentration drug, volume of solvent
Give examples of influence of particle size and crystallinity on dissolution of drugs -
ANSWER Smaller SA more dissolution, crystalline less dissolution
Mention the physiological changes expected upon the intake of a fatty meal - ANSWER
Fatty meals from the presence of lipophilic components and native surfactants. Food
intake will trigger many of the secretions in the small intestine. The composition of fed
state intestinal fluid can greatly vary from fasted state. The volume of GI fluid is higher in
red condition, changes in upper GI pH (increase in pH), longer upper GI residence time.
Show with example how the fed and fasted conditions influence the dissolution of drugs
- ANSWER Phenytoin (higher dissolution in fed state)
Danazol (lower dissolution in fed state)
Give one example how the fed and fasted conditions influence the absorption of drugs -
ANSWER Danazol - more absorbed preprandial.
Poorly soluble compounds are especially prone to higher systemic exposure when given
in the fed state with the main effect being faster and more extensive dissolution under
fed conditions.
Dissolution of weak bases is additionally influenced by variations in upper GI pH, making
these drugs especially prone to food effects
Lipophilic drugs, co-administration with an meal has been shown to increase
bioavailability compared to fasted state
Define bioavailability, bioequivalence, pharmaceutical equivalents, therapeutic
Answers 100% Verified
Importance of drug stability - ANSWER The capacity of a pharmaceutical to remain
within specifications established to ensure its identity, strength, quality and purity.
There is physical, microbial and chemical stability.
Maintain activity, potency and purity. Safety of patients. Look in production, storage,
transporting and storage in hospitals/pharmacies. Typically only 1-2% degradation, can
be up to 10% if the drug has a wide therapeutic window.
Shelf-life - ANSWER Expiration dating period. Time during which a drug product is
expected to remain within the approved specification for use provided it is correctly
stored
First Order - ANSWER -d[D]/dt = Kobs . [D] independant of concentration only
dependant on time (units, time-1 e.g. s-1)
to make linear ln[D] = ln[D0] - Kobs . t
[D] = [D]0 . e^-Kobs . t
Half life = 0.693/Kobs
Shelf life = 0.105/Kobs
Apparent ZERO order - ANSWER Units conc.time-1, dependant on initial concentration
and time
-d[D]/dt = Kobs
Half life = 0.5 [D]0/Kobs
Shelf life = 0.1 [D]0/Kobs
Temperature Effects: Arrhenius equation - ANSWER Increase in degradation rate of
drugs in solution
k = A.e^-Ea/RT
lnK=lnA-Ea/RT
Shelf life equation
Rule of thumb
What do you mean by disintegration of solid dosage forms? - ANSWER Process in which
,a solid dosage form is broken down into smaller particles thereby increasing surface
area
What is the importance of disintegration? - ANSWER Ensuring and maximising the
bioavailability of the drug, so the whole drug is able to dissolve, reliable clinical
performance, quicker absorption of the drug and faster onset of the desired effect
Give examples of solid dosage forms for which disintegration is very important step for
drug release. - ANSWER Immediate release tablets: designed to full disintegrate and
dissolve upon exposure to physiological fluids within a short period of time (2.5-10
mins). Important for the rapid onset of action, or to enhance bioavailability of a poorly
soluble drug
Orally dispersible/disintegrating tablets: Designed to disintegrate in the mouth in less
than a minute before swallowing. ODT have faster onset of effects than tablets or
capsules and have the convince of a tablet that can be taken without water.
Mention three mechanisms of disintegration. - ANSWER Facilitate water uptake and
transport liquid into pores of the tablet (SDS)
Produce gas in contact with moisture (tartaric acid + sodium bicarbonate)
Swell open with contact with water (starch)
Define dissolution. Mention two steps of dissolution. - ANSWER Process by which a
chemical or drug passes from a solid into solution
Two steps: 1 Liberation: Detachment of molecules from the solid surface to form
solvated molecules at the solid-liquid interface. 2. Diffusion: Transport from this
interface to the bulk solution. This is a prerequisite to absorption.
Give pharmaceutical examples where dissolution is important. - ANSWER Release from
normal capsules
Release from conventional tablets
Release from matrix tablets or pellets, lipid matrix (non-hydrating) and swellable
(hydrating) matrix
Release from coated tablet or coated granules/pellets, where the coat remains intact;
liquid and dissolving drug may precipitate the film coat
Continued release from ointments or creams in which drug is present in excess of its
solubility
Continued release of drug from an oral mixture which is suspended
Describe Noyes-Whitney equation and Nernst-Brunner equation for determining
dissolution of drugs from a tablet. - ANSWER Noyes-Whitney: Basic transport-rate
controlled model for solid dissolution. When SA constant the dissolution rate if a drug is
, proportional to the difference between its solubility and bulk solution conc. k is a
constant (mass transfer coefficient). dW/dt = k(Cs-Cb).
Nernst-Brunner: Diffusion layer model, suggests diffusion occurs across a thin stagnant
layer at saturated solution called the diffusion layer (or hydrodynamic boundary layer)
into the bulk solution. dW/dt = DA/h (Cs-Cb)
Mention the assumptions that have been made in derivation of Nernst-Brunner equation.
- ANSWER Drug dissolves uniformly from all surfaces of the particles
Particles are spherical
h is constant
Both h and Cs are assumed to be independent of particle size
In reality drug particles are neither spherical nor uniform in size
Describe the factors that influence dissolution of drugs from oral solid dosage forms -
ANSWER Surface area, saturated concentration, diffusion coefficient, thickness of
diffusion layer, bulk concentration drug, volume of solvent
Give examples of influence of particle size and crystallinity on dissolution of drugs -
ANSWER Smaller SA more dissolution, crystalline less dissolution
Mention the physiological changes expected upon the intake of a fatty meal - ANSWER
Fatty meals from the presence of lipophilic components and native surfactants. Food
intake will trigger many of the secretions in the small intestine. The composition of fed
state intestinal fluid can greatly vary from fasted state. The volume of GI fluid is higher in
red condition, changes in upper GI pH (increase in pH), longer upper GI residence time.
Show with example how the fed and fasted conditions influence the dissolution of drugs
- ANSWER Phenytoin (higher dissolution in fed state)
Danazol (lower dissolution in fed state)
Give one example how the fed and fasted conditions influence the absorption of drugs -
ANSWER Danazol - more absorbed preprandial.
Poorly soluble compounds are especially prone to higher systemic exposure when given
in the fed state with the main effect being faster and more extensive dissolution under
fed conditions.
Dissolution of weak bases is additionally influenced by variations in upper GI pH, making
these drugs especially prone to food effects
Lipophilic drugs, co-administration with an meal has been shown to increase
bioavailability compared to fasted state
Define bioavailability, bioequivalence, pharmaceutical equivalents, therapeutic
