Incompatibility is defined as a change resulting and an undesirable product is formed, which may affect the safety, efficacy, appearance and stability of the pharmaceutical product. It is of three types. It includes physical, chemical and therapeutic incompatibilities. The below described article gives the detailed information about the types, causes and how to overcome these types of incompatibilities. The occurrence of chemical incompatibilities can be overcome by two methods which include method A&B.
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Incompatibilities occur during
• Compounding
• Formulation
• Manufacturing
• Packaging
• Dispensing
• Storage
• Administration
of drugs
The incompatibilities may be detected by changes in the
physical, chemical, and therapeutic qualities of the medicine.
TYPES OF INCOMPATIBILITIES:-
The incompatibilities occur when
the components of a medicine interact in such a way that properties of that
medicine are adversely affected.
1. Physical
incompatibilities
2. Chemical
incompatibilities
3. Therapeutic
incompatibilities
PHYSICAL INCOMPATIBILITIES:-
When two or more than two substances are combined
together, a physical change takes place and an unacceptable product is formed.
Interaction between two or more substances which may
lead to change in colour, odour, taste, viscosity and morphology. It is also
called as pharmaceutical incompatibility.
Manifestations of physical incompatibility:-
The following list outlines the various ways
incompatibility between or among drug agents may be manifested.
A.
Insolubility:- insolubility of prescribed agents
in vehicle
B.
Immiscibility:- Immiscibility of two or more
liquids
C.
Precipitation:- It occurs due to solvent is
insoluble when it is added to solution
D.
Liquefaction:- Liquefaction of solids mixed in a
dry state (called eutexia)
INSOLUBILITY
It means the
inability of material to dissolve in a particular solvent system. The majority
of incompatibilities is due to insolubility of the inorganic as well as organic
compounds in particular solvents.
The following factors affect the solubility of prescribed
agent in vehicle and may render it less soluble.
- Change in PH
- Milling
- Surfactant
- Chemical reaction
- Complex formation
- Co-solvent
- Any change in previous factors may lead to precipitation of drugs and change in their properties.
- Substances like chalk, acetyl salicylic acid, succinylsulphothiazzole, zinc oxide, and calamine are the commonexamples of in diffusible solids.
- Some tinctures containing resins or chlorophyll may provide precipitation when added to the aqueous system.
E.g.:-Mixture of prepared chalk
Rx
Chalk powder
–2g
Tincture
catechu – 2ml
Cinnamon water
– 2ml
Causes: - Chalk
powder is not soluble in water.It gets precipitated when added to aqueous
medium. These precipitates are found in diffusible in nature which results in
physical incompatibility.
Remedy: - Use of
suspending agents is necessary to suspend the precipitated chalk particles.
Generally 2% W/V of compound tragacanth
powder is recommended as suspending agent. The corrected prescription is
Mixture of prepared chalk
Rx
Chalk powder
–2g
Tragacanth –
0.4g
Tincture
catechu – 2ml
Cinnamon water
up to 30ml
IMMISCIBILITY
When two
such ingredients are combined resulting in a non- homogenous product, such
ingredients are called immiscible to each other and the phenomenon is called
immiscibility. This manifestation appears clearly in emulsions, creams, lotions,
some types of ointments. Separation in two phases is noticed in this
pharmaceutical dosage form. Storage must be in room temperature to prevent
separation.
The following factors lead to immiscibility
- Incomplete mixing
- Addition of surfactant with
- Unsuitable concentration
- False time of addition
- Unsuitable for the type of emulsion
- Presence of micro – organisms
- Some bacteria grow on constituents of mixture.
E.g.:- Gelatin Arabic gum:
Others produce enzymes which oxidize the surfactant.
Temperature:
Oils and water are immiscible with each other which shows physical incompatibility
E.g.:- Castor oil emulsion
Rx
Castor oil – 15ml
Water – 60ml
Causes: -In this
prescription castor oil is immiscible with water due to high interfacial
tensions, which is a sign of incompatibility.
Remedy:-To
overcome this type of incompatibility emulsification is necessary with the help
of an emulsifying agent. The corrected
prescription is
Castor oil emulsion
Rx
Castor oil – 15ml
Acacia – 2% W/V
Water– upto 60ml
LIQUIFACTION
When certain low melting point solids are mixed together, a
liquid or soft mass know as eutectic mixture is produced. This occurs due to the
lowering of the melting point of the mixture to below room temperature and
liberation of hydrates.
If such conditions take place, compounding such powders becomes difficult since the ultimate mixture turns to liquid. The medicaments showing this type of behavior are camphor, menthol, phenol, thymol, chloral hydrate, aspirin, sodium salicylates, etc.
E.g.:-Insufflations
Rx
Menthol – 5g
Camphor – 5g
Water – 60ml
Causes: - This
mixture is a physical incompatibility because both the ingredients in the
prescription are liquefiable of mixed together.
Remedy:-These
substances can be dispensed by any one of the following method. Triturate
together to form liquid and mixed with an absorbent (light kaolin, magnesium
carbonate) to produce the following powder. The individual medicaments is
powdered separately and mixed with an adsorbent and then combined together
tightly and filled in a suitable container.
Hence the corrected prescription is
Rx
Menthol – 5g
Camphor – 5g
Light kaolin– 0.2g
PRECIPITATION
Solubilized substances may
precipitate from it solution if a non-solvent for the substances is added to
the solution.
E.g.:- Resins are insoluble in
water
Alcoholic solution of resins +
water =precipitated resins.
Aqueous dispersions of hydrophilic colloids (polysaccharide
mucilage + high concentration of alcohol or salts) = precipitated colloids.
a) High concentration of electrolytes
causes cracking of soap emulsion by salting out the emulsifying agents.
Vehicles (one or more organic liquids) use to dissolve medicaments of low solubility; water soluble adjuvant practically inorganic salts may be precipitated in such vehicles. When tinctures containing resinous matter are added in water, resin agglomerates forms in diffusible precipitates. This can be prevented by slowly adding the undiluted tincture with vigorous shake. Suspension or by adding some suitable thickening agent.
E.g.:- Lotion of compound tincture of
benzoin
Rx
Tincture benzoin compound – 5g
Glycerin – 10ml
Rose water upto
100ml
Causes: - Tincture benzoin compound contain
resins. This change in solvent system results in an unavoidable precipitate.
Remedy: - Addition
of tincture with rapid stirring yields a fine colloidal dispersion. So there is
no need of any suspending agents.
CHEMICAL INCOMPATIBILITIES
Reaction between two or more substances which lead to change
in chemical properties of pharmaceutical dosage form. As a result of this a
toxic or inactive or product may be formed.
Occurrence:-
Chemical incompatibilities occur, due to the chemical
properties of drugs and additive like,
- pH change
- Oxidation-reduction reactions
- Acid-base hydrolysis
- Double decomposition
- Complex formation
These reactions may be noticed by
- Precipitation
- Effervescence
- Decomposition
- Colour change
- Explosion
TYPES OF CHEMICAL INCOMPATIBILITIES
Based on chemical interactions
Tolerated incompatibility: - In this type incompatibility,
the chemical interactions can be changing the order of mixing the solutions
in dilute forms, without or by changing the order of mixing.
Adjusted incompatibilities:
- In adjusted incompatibility change in
the formulation is needed with a compound having equal therapeutic value.
E.g.: substitution of caffeine citrate with caffeine in sodium
salicylate and caffeine citrate mixture.
Based on nature of chemical reaction
Immediate incompatibilities: - If the chemical reaction takes place,
immediately after combining the prescription ingredients, they are called
immediate incompatibilities. Hence, they should be dispensed only after
correction.
Delayed incompatibility: - When the chemical reaction
proceeds at a very slow rate and no appreciable visible change occurs which may
develop on keeping the product for along time are called delayed incompatibility.
Based on the prescriber
Intentional:- When the prescriber knowingly prescribes the
incompatible drugs.
Unidirectional:- When the prescriber prescribes the
drugs without knowing that there is incompatibility between the prescribed
drugs.
Generally reaction between strong solution proceed at
a faster rate and the precipitates are formed are thick and do not diffuse
readily. Reaction between the dilute solutions proceeds at a slow rate and the
precipitates formed are light and diffuse readily in the solution. Hence the
reacting substances should be diluted as much as possible before mixing.
Precipitate yielding interactions
The precipitates so formed may be diffusible or non-diffusible. The method A or B is followed in dispensing the prescription
yielding diffusible and non-diffusible precipitates respectively. The preparation
should contain a thickening agent if the precipitate is non-diffusible.
Method A:
This method is suitable for diffusible precipitates following steps are carried out. Divide the vehicle into two portions.
Dissolve the reactants in separate portions and mix the two portions by slowly by adding one into other with constant stirring.
Method B:
This method is suitable for in diffusible precipitates
following steps are carried out23.
Divide the vehicle into two portions.
Dissolve the one of the reacting substance in one portion.
Place second portion of vehicle in mortar and incorporate suitable amount of compound. Tragacanth powder (2g/100ml of preparation) with constant trituration until a smooth mucilage is produced.
Add and dissolve the other reacting substance to the
mucilage.
Add the solution of first reactant to the mucilage slowly with constant stirring.
A secondary label ― SHAKE THE BOTTLE BEFORE USE‖ should be fixed on the container whenever method A or method B is followed in dispensing the prescription. Examples of chemical incompatibilities and their correction.
Alkaloid incompatibility:-
1. Alkaloidal
salts with alkaloid substances
2. Alkaloidal
salts with soluble iodides
3. Alkaloidal
salts with tannins
4. Alkaloid
salts with salicylates
5. Alkaloid with soluble iodides and bromides.
Soluble salicylates incompatibility:-
1.Soluble salicylates with ferric salts
2.Soluble salicylates with alkali bicarbonates
3.Soluble salicylates and benzoates with acids.
Soluble iodides incompatibility:-
1.Oxidation of iodides with potassium chlorate
2.Oxidation of iodides with quinine sulphate.
Chemical
incompatibility causing evolution of carbon dioxide gas:-
1.Sodium bicarbonate with soluble calcium or magnesium
salts
2.Bismuthsubnitrate and sodium bicarbonate
3.Borax with sodium bicarbonate and glycerine.
Miscellaneous incompatibilities:-
1.Soluble barbiturates with ammonium bromide
2.Potassium chlorate with oxdisible substances
3. Incompatibility
of emulsifying agent
4. Color
stability of dyes
5. Incompatibilities
of liquorices liquid extract
Eg-1: strychnine hydrochloride mixture
Rx
Strychnine
hydrochloride solution -6ml
Aromatic spirit
of ammonia -4ml
Water up to - 120ml
Causes:-
The
quantity of strychnine hydrochloride is more than its solubility in water (1:30).
The
aromatic spirit of ammonia contains negligible amount alcohol.
Remedy: -
Strychnine hydrochloride gets precipitated yielding diffusible precipitate,
hence follow method A.
E.g-2.:Quinine hydrochloride mixture
Rx
Quinine
hydrochloride -0.12ml
Sodium salicylate -4g
Water -100ml
Causes: - When
quinine hydrochloride combined with the sodium salicylates it forms quinine
salicylates which is an in diffusible precipitate.
Remedy: - Hence
follow method B for precipitate yielding interactions.
THERAPEUTIC INCOMPATIBILITY
It is the modification of the therapeutic effect of one
drug by the prior concomitant administration of another. It may be as a result
of prescribing certain drugs to a patient with the intention to produce a
specific degree of pharmacological action, but have restore or intensity of the
action produced is different room that intended by the prescriber.
MECHANISM:
It is divided into two groups. They are:
Pharmacokinetic: It involves the effect of a drug on another from
the point of view that includes absorption, distribution, metabolism and
excretion.
Pharmacodynamics: These are related to the pharmacological activity of the inter-acing drugs.
E.g., Synergism, antagonism, altered cellular transport,
effect on the receptor site.
Therapeutic incompatibilities occurs due to following
reasons
a. Error
in dosage
b. Wrong
dose or dosage form
c. Contra-indicated
drugs
d. Synergistic
and antagonistic drugs
e. Drug
interactions
ERROR
IN DOSAGE
Many therapeutic incompatibilities result from errors in writing or interpreting the prescription order. The most serious type of the dosage error in the dispensing is overdose of a medication. E.g., Atropine sulphate capsules.
Rx
Atropine sulphate - 0.005g
Phenobarbitone - 0.015g
Aspirin - 0.300g
Causes:- In this
prescription, the quantity of the atropine sulphate in each capsule is more
than its recommended dose.
Remedy:- The
prescription is referred back to the prescriber to correct the overdose of the
atropine sulphate. The recommended dose of atropine for a single capsule is
0.25 to 2mg.
WRONFG
DOSE OR DOSAGE FORM
There are certain drugs which have quite similar names and
there is always a danger of dispensing the wrong drug.
E.g., Prednisone and Prednisolone
Digoxin and Dig toxin
Some times many drugs are available in the different dosage
forms and hence, if the dosage form is not clearly mentioned on the prescription,
it becomes necessary to seek clarification from the prescriber.
The responsibility of the pharmacist becomes to check the
prescription intensively and if he finds these types of errors he should
immediately consult the prescriber for the clarification.
PRESCRIBING
CONTRA-INDICATED DRUGS
There are certain drugs which may be contra-indicated in a
particular disease or a particular patient who is allergic to it.
• Corticosteroids
are contra-indicated in the patients having peptic ulcers.
• The
penicillin and sulphur drugs are contra-indicated in the patients who are
allergic.
• Vasoconstrictors
are contra-indicated in hypertensive patients.
• Barbiturates
and morphine should not be given to the asthmatic patients.
E.g., Sulphadiazine capsules
Causes:-Ammonium chloride is a urinary acidifier. It causes the
deposition of the
Sulphonamide crystals in the
kidney.
Remedy: - Before prescribing such substances a doctor must be
careful. If he does not, a
Pharmacist shows his caliber to point out such type of the
doctor’s error. Such must
Immediately be referred back to
the concerned doctor and get corrected.
PRESCRIBING SYNERGISTIC OR ANTAGONISTIC DRUGS
When two drugs are prescribed together, they tend to increase
the activity of each other which is known as SYNERGISM. When two drugs are
prescribed together, they tend to decrease the activity of each other which is
known as ANTAGONISM.
E.g.,
• A
combination of aspirin and paracetamol increases the analgesic activity.
• A
combination of penicillin and streptomycin increases the antibacterial
activity.
• Amphetamines
show its antagonists effect with the barbiturates.
E.g., Amphetamine sulphate syrup
Causes:-In this
prescription, there is a combination of two sympathomimetic drugs.
There by causing additive effect.
Remedy:- The
prescription is referred back to the prescriber for necessary corrections.
DRUG
INTERACTIONS
The effect of one drug is altered by the prior or
simultaneous administration of another drug. The drug interaction can usually
be corrected by the proper adjustment of dosage if the suspected interaction is
detected.
E.g., Tetracycline capsule - 250mg capsules
Direction: Take one capsule every 6 hours with milk.
Causes:-Tetracycline
is inactivated by calcium present in milk. So, it should not be taken with
milk.
Remedy: In
this prescription, the therapeutic incompatibility is unintentional. So, the
prescription is referred back to the prescriber to change the direction.
CONCLUSION:
Incompatibility is defined as a
change resulting and an undesirable product is formed, which may affect the
safety, efficacy, appearance and stability of the pharmaceutical product. It is
of three types. It includes physical, chemical and therapeutic
incompatibilities. The below described article gives the detailed information
about the types, causes and how to overcome these types of incompatibilities.
The occurrence of chemical incompatibilities can be overcome by two methods
which include method A&B.
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