Chemical & Physical Incompatibility in Prescription

Table of Contents

INCOMPATIBILITY IN PRESCRPION

Incompatibility occur as a result of mixing two or more antagonistic substances. An undesirable product is formed which affect the safety, efficacy and appearance of pharmaceutical preparation.

For Example, the interaction of that comes under incompatibilities includes

Drug with additives
drug with other drug
Additives with additives
Dosage error

Incompatibilities may occur

During compounding and dispending
During manufacturing
Packaging or
Administration of drugs

Types of Incompatibilities

(A) Physical Incompatibilities

(B) Chemical Incompatibilities

(A) Physical Incompatibilities

When two or more substances are combined together, a physical change (like Immiscibility , insolubility, precipitation, liquefaction) takes place and an unacceptable product is formed.

Interaction between two or more substances which may lead to change in color, odor, taste, viscosity etc.

Physical Incompatibilities are visible and easily corrected by applying pharmaceutical skill.

Physical incompatibility con be corrected by

Change the order of mixing
Emulsification
Addition of suspending agent
Change in form of ingredients
By addition, substitution or omission of therapeutically inactive substances

Example:-

1. Immiscibility

Rx.

Castor oil – 15ml
Water upto – 60ml

Incompatibility: Water and oil are immiscible so it is corrected by

Emulsifying agent is used to make water & Oil miscible .

2. Insolubility :-

Rx.

Ephednine sulphate – 0.25g
Menthol- 0.02ml
Liquid paraffin upto -30ml

Ephedrine sulphate is not soluble in liquid paraffin so Ephedrine is substituted with Anhydrous Ephedrine (soluble in liquid paraffin)

3. Precipitation :-

Tincture benzoin compound- 5.0ml
Glycerine- 15.0ml
Rose water upto -100ml

Tincture benzoin contain resins & upon changing solvent result into precipitation. To eliminate this type incompatibility, addition of tincture benzoin with rapid stirring to yield a fine colloidal dispersion.

4. Liquefaction

Rx.

Menthol – 5g
Camphor – 5g
Ammonium chloride -30g
Light magnesium carbonate – 60g

Menthol + Camphor + Ammonium chloride, get liquefied on mixing so Add light magnesium carbonate to get free flowing powder.

(B) Chemical Incompatibility

Chemical incompatibility result due to chemical interaction b/w ingredients to form toxic or inactive product.

So while dispensing such prescription, either prevent formation of harmful product or correct them & inform the prescriber.

Types of Chemical incompatibilities

Tolerated	Adjusted
Minimised by changing the order of mixing or mixing solution in dilute form No alteration made in formula	Incompatibility is prevented by addition or substitution on one of the reacting ingredient with another equal therapeutic value.

Chemical Incompatibility may be Intentional or Unintentional.

Intentional	Unintentional
When prescriber prescribe knowingly prescribed incompatible drugs	When prescribed without knowing the incompatibility

(C) Therapeutic Incompatibility

Therapeutic Incompatibility may result of prescribing drugs for specific degree of pharmacological action but nature or intensity of the action different from the intended by the prescriber.

THERAPEUTIC INCOMPATIBILITY (based on MECHANISM) is divided into two groups.

1. Pharmacokinetic: It involves the effect of a drug on another from the point of view that includes absorption, distribution, metabolism and excretion.

2. Pharmacodynamics: These are related to the pharmacological activity of the inter-acing drugs. Example-Synergism, antagonism, altered cellular transport, effect on the receptor site.

Therapeutic Incompatibility occurs due to

Error in dosage
Wrong drug or dosage form
Contra-indicated drugs
Synergistic or antagonistic drugs
Drug interaction

i) Error in Dosage

Atropine Suphate- 0.006 g
Phenobarbitione- 0.015 g
Aspirin- 0.300 g

Quantity of Atropine Suphate is more than maximum dose. So Pharmacist should referred back to prescriber for correction.

ii) Wrong Dose or Dosage form

Certain drugs have quite similar name so there is a danger of dispensing the wrong drug by pharmacist.

Prednisone & Prednisone
Digoxin & Digitoxin

iii) 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.

Example

Corticosteroids are contra-indicated in the patients having peptic ulcers

Sulphadiazine 250 mg
Sulphamerazine 250 mg
Ammonium chloride 500 mg

Ammonium Chloride- Urinary Acidifier- cause deposition of Sulphonamide crystal in Kidney si prescription referred back to Physician.

iv) 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

Example

Acetyl Salicylic acid- 0.6 g
Probenecid- 0.5 g

Both are used to treat goat but combination lead to neutralization of action-Antagonism.
A combination of aspirin and paracetamol increases the analgesic activity- Synergistic

v) Drug Interaction

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.

Example: Tetracycline capsule – 250mg capsules ; Direction: Take one capsule every 6 hours with milk. Causes:-Tetracycline is inactivated by calcium present in milk.

Join Our WhatsApp Group to receive the latest updates like Pharma Job notifications, study materials, admission alerts, Pharma News, etc

WhatsApp

Join Our Telegram Group to receive the latest updates like Pharma Job notifications, study materials, admission alerts, Pharma News, etc

Telegram

Join Our Telegram Group to Download Free Books & Notes, Previous papers for D.Pharm, B.Pharm, M.Pharm, Drug Inspector & GPAT……….

Telegram