Drug stability - edited

Abstract

Drug stability

Full text

Drug Stability
(General review)
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Introduced by:
Dr. Ahmed NA
University of Basrah / College of pharmacy
Pharmaceutics

Outlines:
Introduction
Factors aecting drug stability
Types of stability
Packaging and stability
The instability possibilities in dierent
formulations
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Introduction
Drug stability means the ability of the
pharmaceutical dosage form to maintain the
physical, chemical, therapeutic and microbial
properties during the time of storage and usage by
the patient.
It is measured by the rate of changes that take place
in the pharmaceutical dosage forms.
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Expiry date: means that drug can not be used after
this date because the concentration of drug is
decreased and become lower than therapeutic
concentration.
In addition, some products of drug degradation are
toxic and harmful to patients.
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After the opening of the drug
container, the expiry date will
be shorter as a result of the
decreased concentration of drug
during usage and the effects of
external factors.
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Examples:
Eye drops: can be used for one month after
opening the droppers.
Syrups and suspension of antibiotics: can be used
for one week by storage in room temperature and
for two weeks by storage in 4C°.
Ampoules: must be used immediately but the
vials (multi-dose) are stable for (24 h or more) due
to presence of preservatives.
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Factors affecting drug stability:
1. Temperature: If high, accelerate oxidation,
reduction and hydrolysis reaction.
2. pH: need adjustment: if not a water-miscible
solvent may be involved into the product. It will
increase stability by:
A) ↓ ionization.
B)↓ the extreme pH required to achieve solubility.
C) ↑ solubility
D) ↓ the water activity.
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3. Moisture:
a. Water catalyzes the chemical reactions.
b. Water promotes microbial growth.
4. Light (yellow, white, sunlight) : affects drug stability through its
energy or thermal effect which lead to oxidation.
5. Pharmaceutical dosage forms: solid dosage forms are more stable
than liquid dosage forms for presence of water.
6. Concentration: rate of drug degradation is constant for the solutions
of the same drug with different concentration.
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7. Drug incompatibility: reactions between
components of pharmaceutical dosage forms it
self or between these components and cover of
the container or after mixing of different liquid
formulations.
8. Oxygen: exposure of drug formulations to
oxygen affects their stability
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Three stabilities of drug must be considered::
1. Physical stability
2. Chemical stability
3. Microbiologicall stability
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Types of stability

Physical instabilities possibilities are:
1) Crystal formation in pharmaceutical preparations.
2) Loss of volatile substances from pharmaceutical
dosage forms.
3) Loss of water (evaporation or over-dry storage).
4) Absorption of water:
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The physical stability

Many drugs are susceptible to some
forms of chemical decomposition when
formulated in either liquid or even solid
dosage forms.
Such degradation not only leads to a loss
of potency of the drug but may, in some
cases, cause changes in the physical
appearance of the dosage forms, for
example, discoloration following the
photochemical decomposition of the drug.
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The chemical stability

The chemical instabilities
includes:
1) Hydrolysis
2) Oxidation
3) Isomerization
4) Photochemical degradation
5) Polymerization
6) Protein drug degrdation
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Hydrolysis
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Ex. Aspirin
Ex. Cinchocaine
Ex. Penicillins

Compounds susceptible to
oxidation
Steroids and sterols (with alkene moieties).
Polyunsaturated fatty acids.
Simvastatin (conjugated double bonds).
Polyene antibiotics, such as
amphotericin B with (heptaene moiety).
Azole group (ether group)
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Examples on Isomerization
At low pH,
max. at
3.2, and
catalysts
like PO4
and
Citrate
ions
Toxic
In active

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Enzyme
catalyzed
Less
active

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Highly
antigenic
Polymerization

Protein drug instabilities
Chemical degradation
Protein denaturation
Aggregation
Fibrillation: an aggregate consisting of
protein strands.
Adsorption: a monomolecular layer of
protein molecules accumulated at a surface
through unspecified attractive forces.
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For all drugs, The chemical stability
can be maintained using suitable
storage conditions.
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Do not store the hydrolysable drugs in the
bathroom or in the refrigerator. (Ideal humidity is
40–60%).

Commercially available products
aected by heat
Dactacort® cream
Chloramphenicol eye drop
Neurobine® ampoules
D3 drops, One alpha drop
Minrin® nasal spray
Most of injectable protein products
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Contamination from M.O. is
a big problem for all
formulations containing
moisture and some solid dosage
containing natural polymers.
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The microbiological stability

The source The microbial contaminants
Water Low demand gram-negative groups: Pseudomonas,
Xanthamonas, Flavobacterium, Achromobacter
Air Mould spores: Penicillium, Mucor, Aspergillus
Bacterial spores: Bacillus spp. Yeasts
Row materials Micrococci
Earths Anaerobic spore formers: Clostridium spp
Pigments Salmonella
starch Coliforms
Gums Actinomyces
Animal products Salmonella, Coliforms
Personnel Coliforms, Staphylococci, Sterptococci, Coryembacteria
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Sources of microbial contaminants

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Packaging of the drug product is very important
when its stability is being considered.
The immediate container and closure are
particularly important in affecting product
stability.
Glass, plastic, rubber (natural and synthetic) and
metal are the four types of containers commonly
utilized for packing drug products.
Packaging And Stability

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Glass

Glass is resistant to chemical and physical change and is the
most commonly used material, but it has the limitations of :
1. Its alkaline surface may raise the pH. 2. Ionic radicals present
in the drug may precipitate insoluble crystals from the glass
3. More photo-degradation (transparent glass).
Reduced by use of borosilicate glass, buffers, Amber coloured
glass which transmits light only at wavelengths above 470 nm.

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Plastics

Plastics include a wide range of polymers of varying density and molecular
weight, each possessing different physicochemical properties.
The problems are:
1. Leakage of product
2. Transfer of environmental moisture, oxygen, and other elements into the
pharmaceutical product.
3. Leaching of container ingredients into the drug.
4. Adsorption or absorption of the active drug or excipients by the plastic.

For all these problems, the chemical pretreatment may be used.

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Metals
Various alloys and aluminium tubes may be utilized as
containers for aerosols, emulsions, ointments, creams and
pastes.
They may cause corrosion and precipitation in the drug
product.
Coating the tubes with polymers or epoxy may reduce these
tendencies.

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Rubber
Rubber also has the problems of extraction of drug
ingredients and leaching of container ingredients.
The chemical pretreatment may reduces drug-container
interactions.
The pretreatment of rubber vial stoppers and closures with
water and steam removes surface blooms and also reduces
potential leaching.

The instability possibilities in different
formulations
1. Oral solutions
Loss of flavour, Change in taste, odor and color,
precipitation.
Steps to prevent instability
Use of proper excipients and suitable packing
materials
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2. Parenteral solutions
Physical instability occurs due to:
1. Interaction of the contents with the
container.
2. Changes in Chemical composition.
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Instability problems
1. Discoloration.
2. Presence of “whiskers”.
long lines of crystals formed on the outside of the vial which are
called whiskers. This may happen due too small hole (<0.5 μm) going
undetected or the crack developed during storage.
3. ppt. and clouds, may be due to:
a. Chemical changes
b. polymorphism.
c. Product-packaging incompatibility
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Effects
Change in appearance and bioavailability.
Steps to prevent instability
1. Use of antioxidants or chelating agents to prevent
discoloration.
2. Change in stopper or material of the container will eliminate
the problem.
3. Checking of the manufacturing process Increasing solubility by
the use of co-solvents.
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3. Suspensions
This instability occurs due to:
Particle diameter, concentration of S.A., viscosity,
temperature, pH and presence of microbes.
Instability problems
Settling, caking and crystal growth
Effects
Loss of drug content uniformity in different doses
from the bottle and loss of elegance.
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4. Emulsions
This instability occurs due to:
Droplet diameter, viscosity, density diff.,
temperature, pH and presence of microbes.
Instability problems
1. Creaming
2. Cracking
Effects
Loss of drug content uniformity in different doses
from the bottle and loss of elegance.
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5. Semisolids (Ointments and suppositories)
Instability problems
1. Changes in: particle size, polymorphic state,
consistency or drug release rate
2. Caking or coalescence.
Effects
Loss of drug content uniformity, loss of elegance
and change in drug release rate.
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6. Tablets
Instability problems
Change in
a. Disintegration time b. Dissolution profile
c. Hardness d. Appearance
Effects
Change in drug release
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7. Capsules
Instability problems
Change in
a. Appearance b. Dissolution c. Strength
Effects
Change in drug release
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OUR AIM