This document discusses different types of incompatibilities that can occur in prescriptions, including physical, chemical, and therapeutic incompatibilities. Physical incompatibilities involve changes in a medication's appearance, taste, or odor due to issues like immiscibility, insolubility, or precipitation. Chemical incompatibilities occur due to chemical reactions between ingredients and can be detected by precipitation, effervescence, decomposition, or color changes. Therapeutic incompatibilities arise when medications do not produce their intended pharmacological effect, often due to dosing errors, prescribing contraindicated drugs, or drug interactions. The document provides examples of each type of incompatibility and methods for correcting physical and chemical issues.

1. INCOMPATIBILITIES IN
PRESCRIPTION
Prepared By:
Lecturer: Mr. S. S. Mistree
M-pharm (P’ceutics)
Sub: Pharmaceutics-II
Ishwar Deshmukh Institute of Pharmacy, Digras
Yavatmal-445302
2020-21

2. INDEX
Introduction
Definition Of Incompatibility
Types Of Incompatibilities:
Physical Incompatibility
Chemical Incompatibility
Therapeutic Incompatibility
Reference

3. Introduction
• In olden days pharmacist himself compounded and
dispensed the prescription, thus chances of occurring
incompatibilities.
• Drug with another drug or a drug with its excipients are
interact with each other are comes under incompatibility.
• Incompatibility happened during compounding, dispensing
and also at any step of manufacturing, formulation,
packaging, etc.
• Nowadays, the compounding of prescription are totally
eliminated, due to availability of ready-made medicines,

4. manufactured by many pharmaceutical companies.
• Therefore, the chances of occurring incompatibility became
less.
• But also, when branded medicines are mix together or store
in unsuitable place by patient, May small chances of
occurring incompatibilities.
• Hence, it is very necessary that the pharmacist has thorough
knowledge about incompatibilities of prescription.

5. DEFINITION OF INCOMPATIBILITY:
• It is a outcome of mixing two or more opposite type of
substance and got unaccepted or undesirable preparation,
which may change the appearance, safety and efficacy of
pharmaceutical Preparation.

6. TYPES OF INCOMPATIBILITIES
There are three kinds of incompatibilities, which are generally
occurred in prescription:
(A)Physical Incompatibility
(B)Chemical Incompatibility
(C)Therapeutic Incompatibility

7. (A) PHYSICAL INCOMPATIBILITY:
 Definition: A mixing of more than one substance together ,
a physical changes occur with formulation and undesirable
preparation is formed.
• In Physical incompatibility, physical changes are occurred
such as, change in appearance, taste, odor etc.
• These changes, we can easily seen as well as correct out.
 Reason of occurring physical incompatibility:
1. Immiscibility
2. Insolubility
3. Precipitate formation
4. Liquefaction of solid materials

8.  Correction method of physical incompatibility:
• By altering the order of mixing of ingredient
• By emulsification
• By addition or substitution of therapeutically inactive
substance.
• By adding suspending agent
 Example of physical incompatibility and their method of
correction:
(a) Immiscibility:
• Oil and water immiscible with each other, can be miscible
by adding emulsifying agent.

9. (b) Insolubility:
• It is define as the inability of material to dissolve in solvent
system.
• The main reason of occurring physical incompatibility is
insolubility of organic as well as inorganic substance in
solvent.
 Eg: Chalk, Acetyl salicylic acid, Zinc oxide and Calamine
(In diffusible Solid) are not easily soluble in solvent.
• By adding suspending agent, its help to maintain uniform
distribution of insoluble substance for long time after
shaking and we may get stable preparation.

10. (C) Precipitation:
• Precipitation means separation of solid from a liquid.
 Eg: 1) resin are insoluble in water :
• When tincture containing resin added to water , resin
precipitate out.
• This can be corrected by slowly adding undiluted tincture
with stirring or by adding suitable thickening agent.
2) If preparation containing organic solvent mixed with
preparation containing water then precipitation will
occur.
• Eg: when tincture mixed with syrup ,we will get ppt.

11. 3) Volatile oils are soluble in alcohol:
• Eg: when alcoholic solution of volatile oil added into water
, oil get precipitate and turbidity appears.
(d) Liquefaction:
• It means the solid become liquid after come in contact with
temperature and humidity.
 Eutectic mixture: It is a result of mixing two low melting
point solids together, will get a liquid or soft mass.
• It is happen due to lowering the melting point of mixture to
below room temp.
• These can be stable at room temperature or normal humidity
but these compound will release their water under increasing

12. Temperature or decreasing humidity.
 Eg: camphor, menthol, phenol and aspirin
These type of example create a problem, when dispense in
powder form.
• Solutions: 1) Triturate together to form liquid and add light
Mg. carbonate to get free flowing powder.
2) Individual substance powdered separately and mix with
absorbent lightly.

13. (B) CHEMICAL INCOMPATIBILITY:
 Definition: It is a result of chemical interaction between
ingredients of preparation and may formed toxic or inactive
preparation.
• Hence, during prescribing prescription care should be taken
to prevent the formation of harmful product.
 Reason of chemical incompatibility:
1. Oxidation-reduction
2. Acid-base hydrolysis
3. Combination reaction

14.  We can notice these reaction by:
1. Precipitation
2. Effervescence
3. Decomposition
4. Color changes
• Hence it is very necessary, when prescription have
chemical incompatibility should be dispensed after
correction by doctor.
 Type of chemical incompatibility:
1. Tolerated
2. Adjusted

15.  Tolerated chemical incompatibility:
• We can minimize chemical interaction by changing order of
mixing, but no alteration made in the formulation.
 Adjusted chemical incompatibility:
• In which, chemical interaction prevented by altering one
reacting ingredient with another.
 Other type of chemical incompatibility:
• Intentional: When doctor intentionally prescribed
incompatible drugs.
• Unintentional: When doctor not know that prescribed
prescription contain incompatible drugs.

16.  Examples of chemical incompatibility:
1. Alkaloidal incompatibility
2. Soluble salicylates incompatibility
3. Soluble iodide incompatibility
4. Causing evaluation of CO2 gas

17. (C) THERAPEUTIC INCOMPATIBILITY:
Definition: It is a result of prescribing a drugs by doctor to
patient with intension to produce pharmacological action
but they do not produce it.
Reason of therapeutic incompatibility:
1. Error in dose
2. Wrong dose or dosage form
3. Contra-indicated drugs
4. Synergistic and antagonistic drugs
5. Drug interaction

18. 1. Error in dosage:
• Many therapeutic incompatibility occur due to error in
writing dose.
• Most serious type of dosage error is to dispense overdose of
medicines.
• Hence it is necessary, pharmacist should detect error, when
dispensing medicines.
2. Wrong dose or dosage form:
• In market no. of medicines are available with similar
spelling, look or pronunciation. Hence, may chances of
dispensing wrong drugs.
Eg: prednisone=prednisolone

19. • Also many medicines are available in different dosage form.
• Hence, necessary to mention specific dosage form in
prescription by doctors.
3. Contra-indicated drugs:
• There are many drugs which are contra-indicated to
particular patient, who is allergic to it.
Eg: penicillin is contra-indicated to patient who is allergic to
it.
4. Synergistic and antagonistic drug:
• Many medicines produce synergistic or antagonistic effect,
when administered in combination.
Synergism: Taking two drug together, they increases activity
of each other.

20. Antagonism: Administration of two medicines in
combination may decreases activity of one drug by the other
and not get desired action.
5. Drug interaction: It is a reaction between drug with drug
or drug with food, may decrease the activity of drug or form
undesirable action.
• It may corrected by proper adjusting of dosage, if
interaction detected.
• Eg: Tetracycline become inactive by calcium if taken with
milk.

21. REFERENCE:
R. M. Mehta, pharmaceutics-II, second adition-2003,reprint
2010,vallabh prakashan. Pg. No. 44 to 62
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