Pharmaceutical incompatibilities – definition and classification MCQs With Answer

Introduction

Pharmaceutical incompatibilities are undesirable physical, chemical, or therapeutic interactions that occur when drugs and excipients are combined, leading to loss of stability, efficacy, or safety. Understanding the definition and classification of incompatibilities—physical (precipitation, liquefaction), chemical (hydrolysis, oxidation, complexation), and therapeutic (pharmacodynamic/pharmacokinetic)—is essential for B. Pharm students involved in dispensing, extemporaneous compounding, and IV admixtures. Key factors include pH, temperature, concentration, solvent, order of mixing, packaging interactions (sorption, leaching), and light/metal catalysis. Prevention relies on buffers, antioxidants, chelators, co-solvents, emulsifiers, and proper container-closure selection. Grasping examples like phenytoin precipitation, calcium–phosphate incompatibility, and nitroglycerin sorption helps bridge theory to practice. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which statement best distinguishes pharmaceutical incompatibility from instability?

• Incompatibility occurs upon mixing components; instability occurs over time even without mixing
• Incompatibility always involves chemical reactions; instability is only physical
• Incompatibility only affects parenterals; instability affects all dosage forms
• Incompatibility improves drug efficacy; instability reduces efficacy

Correct Answer: Incompatibility occurs upon mixing components; instability occurs over time even without mixing

Q2. Which is NOT a major class in the classification of pharmaceutical incompatibilities?

• Physical incompatibility
• Chemical incompatibility
• Therapeutic incompatibility
• Genetic incompatibility

Correct Answer: Genetic incompatibility

Q3. Precipitation due to pH change when mixing two solutions is best classified as:

• Physical incompatibility
• Chemical incompatibility
• Therapeutic incompatibility
• Pharmacogenomic incompatibility

Correct Answer: Physical incompatibility

Q4. Oxidation of adrenaline (epinephrine) in solution leading to color change and potency loss is a:

• Physical incompatibility
• Chemical incompatibility
• Therapeutic incompatibility
• Packaging incompatibility

Correct Answer: Chemical incompatibility

Q5. Antagonism between propranolol and salbutamol given together leading to reduced bronchodilation is a:

• Physical incompatibility
• Chemical incompatibility
• Therapeutic incompatibility
• Container–closure incompatibility

Correct Answer: Therapeutic incompatibility

Q6. Which combination commonly causes precipitation in parenteral nutrition admixtures?

• Calcium and phosphate at high concentrations
• Sodium and chloride at isotonic concentrations
• Potassium and magnesium at low temperature
• Sucrose and dextrose in acidic medium

Correct Answer: Calcium and phosphate at high concentrations

Q7. What is the most appropriate stabilizer to reduce metal-catalyzed oxidation in solutions?

• Disodium EDTA (chelating agent)
• Sodium chloride (tonicity adjuster)
• Sucrose (bulking agent)
• Bentonite (suspending agent)

Correct Answer: Disodium EDTA (chelating agent)

Q8. Amphotericin B deoxycholate for IV infusion should be diluted in:

• 5% dextrose (D5W) only
• 0.9% sodium chloride (normal saline) only
• Lactated Ringer’s only
• Any isotonic solution

Correct Answer: 5% dextrose (D5W) only

Q9. Phenytoin sodium precipitates when diluted in which diluent due to pH-dependent solubility?

• 5% dextrose (D5W)
• 0.9% sodium chloride (normal saline)
• Sterile water for injection
• Lactated Ringer’s

Correct Answer: 5% dextrose (D5W)

Q10. Which is a typical eutectic pair causing liquefaction in powders?

• Camphor and menthol
• Lactose and starch
• Sodium chloride and potassium chloride
• Magnesium oxide and talc

Correct Answer: Camphor and menthol

Q11. Which strategy best prevents liquefaction of eutectic mixtures during compounding?

• Mix with adsorbents like light magnesium carbonate
• Increase temperature during trituration
• Add water to reduce friction
• Use strong alkaline solutions

Correct Answer: Mix with adsorbents like light magnesium carbonate

Q12. Benzalkonium chloride (BAK) preservative is inactivated by:

• Anionic surfactants such as sodium lauryl sulfate
• Cationic surfactants like cetylpyridinium
• Nonionic surfactants like polysorbate 80
• Polyols like glycerol

Correct Answer: Anionic surfactants such as sodium lauryl sulfate

Q13. Which drug is notably adsorbed to PVC infusion sets, reducing delivered dose?

• Nitroglycerin
• Paracetamol
• Cefazolin
• Metformin

Correct Answer: Nitroglycerin

Q14. Which factor most increases the risk of calcium–phosphate precipitation in TPN?

• Higher pH of the admixture
• Lower temperature of storage
• Use of calcium gluconate instead of calcium chloride
• Lower concentrations of calcium and phosphate

Correct Answer: Higher pH of the admixture

Q15. Tetracycline taken with milk results in reduced absorption due to:

• Complexation with calcium (therapeutic incompatibility)
• Hydrolysis in alkaline pH (chemical incompatibility)
• Oxidation by dissolved oxygen (chemical incompatibility)
• Precipitation by ethanol (physical incompatibility)

Correct Answer: Complexation with calcium (therapeutic incompatibility)

Q16. Which approach is best to prevent oxidation-sensitive drug degradation?

• Use antioxidants and purge headspace with nitrogen
• Increase solution pH and exposure to air
• Use clear glass containers under bright light
• Add electrolytes to raise ionic strength

Correct Answer: Use antioxidants and purge headspace with nitrogen

Q17. Matching emulsifier HLB to the oil phase primarily prevents which incompatibility?

• Emulsion cracking (physical incompatibility)
• Hydrolysis of esters (chemical incompatibility)
• Therapeutic antagonism (therapeutic incompatibility)
• Container leaching (packaging incompatibility)

Correct Answer: Emulsion cracking (physical incompatibility)

Q18. Which example best represents a chemical incompatibility in IV admixtures?

• Inactivation of aminoglycosides when mixed with beta-lactam antibiotics
• Precipitation of phenytoin due to pH shift
• Adsorption of insulin to PVC tubing
• Reduced absorption of ciprofloxacin with iron

Correct Answer: Inactivation of aminoglycosides when mixed with beta-lactam antibiotics

Q19. For weakly acidic drugs in solution, lowering the pH typically:

• Decreases solubility, increasing risk of precipitation
• Increases solubility, reducing precipitation
• Has no effect on solubility
• Converts them into stable salts

Correct Answer: Decreases solubility, increasing risk of precipitation

Q20. Which is an appropriate oil-soluble antioxidant for oleaginous preparations?

• Butylated hydroxytoluene (BHT)
• Sodium metabisulfite
• Ascorbic acid
• Disodium EDTA

Correct Answer: Butylated hydroxytoluene (BHT)

Q21. Which packaging interaction involves migration of plasticizer DEHP into a drug product?

• Leaching
• Sorption
• Permeation
• Corrosion

Correct Answer: Leaching

Q22. To minimize light-induced degradation (photolysis), the best practice is to:

• Use amber containers and protect from light
• Increase headspace oxygen for stability
• Add strong acids regardless of drug type
• Switch to PVC to absorb radiation

Correct Answer: Use amber containers and protect from light

Q23. A practical compounding rule to limit precipitation when reconstituting powders is to:

• Add drug slowly into the diluent with gentle mixing
• Add diluent rapidly into the drug powder
• Shake vigorously to dissolve faster
• Raise temperature to near boiling

Correct Answer: Add drug slowly into the diluent with gentle mixing

Q24. Which observation most strongly suggests a physical incompatibility in an IV admixture?

• Turbidity or visible particulate formation after mixing
• Gradual potency loss over months without mixing
• Pharmacodynamic antagonism in vivo
• Color stability and clarity maintained

Correct Answer: Turbidity or visible particulate formation after mixing

Q25. A suitable co-solvent strategy to enhance solubility of a poorly water-soluble drug is to use:

• Propylene glycol, ethanol, or PEG 400
• Sodium chloride and calcium chloride
• Talc and bentonite
• Lactose and microcrystalline cellulose

Correct Answer: Propylene glycol, ethanol, or PEG 400

Q26. Which pair is a classic example of pH-dependent precipitation due to acid–base interaction?

• Alkaloidal salts with sodium bicarbonate
• Glucose with sodium chloride
• Sucrose with citric acid
• Magnesium sulfate with water

Correct Answer: Alkaloidal salts with sodium bicarbonate

Q27. Which practice reduces insulin loss due to sorption during infusion?

• Use low-binding tubing (e.g., polyethylene) and prime the line
• Use PVC tubing and avoid priming
• Increase line length to increase contact area
• Expose the set to bright light

Correct Answer: Use low-binding tubing (e.g., polyethylene) and prime the line

Q28. Ceftriaxone should not be co-administered with calcium-containing solutions in neonates primarily due to:

• Risk of calcium–ceftriaxone precipitation
• Risk of severe alkalosis
• Oxidation of ceftriaxone in light
• Adsorption to glass containers

Correct Answer: Risk of calcium–ceftriaxone precipitation

Q29. Which factor commonly accelerates hydrolysis of ester-containing drugs?

• High pH and elevated temperature
• Low pH and protection from moisture
• Use of nonaqueous solvents only
• Storage at refrigerated conditions

Correct Answer: High pH and elevated temperature

Q30. Which is NOT an appropriate strategy to prevent pharmaceutical incompatibilities?

• Verify Y-site and admixture compatibility before mixing
• Use buffers, antioxidants, and chelators as needed
• Optimize order of mixing and concentrations
• Intentionally increase temperature to speed reactions

Correct Answer: Intentionally increase temperature to speed reactions

Download