Chemical incompatibilities – examples and prevention MCQs With Answer

Introduction

Chemical incompatibilities are reactions between drugs or excipients that change potency, produce precipitates, generate toxic products or alter therapeutic effect. For B. Pharm students, understanding mechanisms—hydrolysis, oxidation, chelation, adsorption and pH‑dependent degradation—is essential for safe IV admixtures, TPN, oral dosing and parenteral compounding. Common examples include ceftriaxone‑calcium precipitates in neonates, tetracycline chelation with calcium/iron, phenytoin precipitation with dextrose, and nitroprusside light degradation. Prevention strategies cover proper dilution, pH control, using non‑PVC containers, amber protection, inline filters, flushing/Y‑site practices and consulting compatibility references. Mastering these concepts reduces medication errors and preserves drug stability. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What best defines a chemical incompatibility between two drugs?

• A physical mixture that remains chemically unchanged
• A change in drug molecular structure producing loss of potency or toxic products
• An intended pharmacologic interaction to enhance effect
• A change in patient response due to route of administration

Correct Answer: A change in drug molecular structure producing loss of potency or toxic products

Q2. Which of the following is a primary mechanism of chemical incompatibility?

• Enzymatic metabolism in the liver
• Hydrolysis, oxidation, or chelation in solution
• Receptor antagonism at tissue sites
• Renal excretion changes due to diuretics

Correct Answer: Hydrolysis, oxidation, or chelation in solution

Q3. Which incompatibility type occurs when two solutions form an insoluble solid on mixing?

• Chemical degradation
• Physical precipitation
• Therapeutic antagonism
• Enzymatic inactivation

Correct Answer: Physical precipitation

Q4. Ceftriaxone is known to precipitate when mixed with which type of IV solution in neonates?

• Dextrose 5% (D5W)
• Calcium‑containing solutions (e.g., Ringer’s lactate)
• Sodium chloride 0.9% (normal saline)
• Albumin 5% solution

Correct Answer: Calcium‑containing solutions (e.g., Ringer’s lactate)

Q5. Best prevention practice when administering ceftriaxone and calcium‑containing fluids to the same patient?

• Mix them in the same bag to minimize lines
• Avoid co‑administration; use separate lines and flush between drugs
• Always dilute ceftriaxone in Ringer’s lactate
• Heat the admixture to improve solubility

Correct Answer: Avoid co‑administration; use separate lines and flush between drugs

Q6. Which oral drug class commonly forms insoluble chelates with calcium, iron or magnesium, reducing absorption?

• Beta‑lactam antibiotics
• Tetracyclines and fluoroquinolones
• Macrolide antibiotics
• Selective serotonin reuptake inhibitors (SSRIs)

Correct Answer: Tetracyclines and fluoroquinolones

Q7. How can chelation‑related oral incompatibilities be prevented?

• Give the antibiotic with a high‑calcium meal to increase absorption
• Separate dosing times from antacids, dairy or iron supplements by at least 2 hours
• Always co‑administer with a proton pump inhibitor
• Use intravenous route for all antibiotics

Correct Answer: Separate dosing times from antacids, dairy or iron supplements by at least 2 hours

Q8. Total parenteral nutrition (TPN) admixtures are at risk of calcium‑phosphate precipitation. Which strategy reduces this risk?

• Add calcium last at high concentration without mixing
• Maintain recommended Ca:PO4 molar ratios, dilute solutions and add phosphate before calcium
• Store TPN at high temperature to increase solubility
• Use calcium chloride rather than calcium gluconate routinely

Correct Answer: Maintain recommended Ca:PO4 molar ratios, dilute solutions and add phosphate before calcium

Q9. Phenytoin IV can precipitate if mixed with which common IV fluid?

• Normal saline (0.9% NaCl)
• Dextrose 5% (D5W)
• Lactated Ringer’s solution
• Albumin 25%

Correct Answer: Dextrose 5% (D5W)

Q10. What is the recommended step before co‑administering two drugs through a Y‑site?

• Assume compatibility if both are sterile
• Consult a compatibility reference (e.g., Trissel’s) and flush line before/after
• Mix equal volumes in a syringe to test visually
• Administer both rapidly without checking

Correct Answer: Consult a compatibility reference (e.g., Trissel’s) and flush line before/after

Q11. Which drug is notably light‑sensitive and requires amber protection during infusion?

• Metronidazole
• Sodium nitroprusside
• Gentamicin
• Amoxicillin

Correct Answer: Sodium nitroprusside

Q12. Adsorption or sorption of drug to PVC infusion sets leads to which problem?

• Enhanced drug potency due to concentration
• Loss of delivered dose due to drug binding to tubing
• Immediate chemical degradation inside the bag
• Conversion to a toxic metabolite

Correct Answer: Loss of delivered dose due to drug binding to tubing

Q13. Which of these drugs is known to sorb to PVC and lose potency?

• Paracetamol (acetaminophen)
• Nitroglycerin
• Penicillin G in water
• Sodium chloride

Correct Answer: Nitroglycerin

Q14. Which common preventive measure reduces oxidative degradation of susceptible drugs?

• Expose the solution to air and light for activation
• Add antioxidants, reduce oxygen exposure and store cool/dark
• Increase pH to strongly alkaline conditions for all drugs
• Store at high temperature to speed equilibrium

Correct Answer: Add antioxidants, reduce oxygen exposure and store cool/dark

Q15. Which mechanism explains aspirin breakdown in aqueous solutions during storage?

• Chelation with divalent metals
• Hydrolysis of the ester bond to salicylic acid
• Photolytic deamination
• Enzymatic cleavage by glass surfaces

Correct Answer: Hydrolysis of the ester bond to salicylic acid

Q16. A parenteral drug requires protection from adsorption to container surfaces. Which container material is preferred?

• PVC bags for all drugs
• Polyolefin or glass containers when PVC sorption is a concern
• Use rubberized containers only
• Metal cans for aqueous solutions

Correct Answer: Polyolefin or glass containers when PVC sorption is a concern

Q17. Using an inline filter during infusion primarily helps to prevent what?

• Increase drug potency
• Removal of particulates, precipitates and microbial debris
• Complete sterilization of a contaminated bag
• Neutralization of drug incompatibilities

Correct Answer: Removal of particulates, precipitates and microbial debris

Q18. Which of the following is a safe prevention strategy when an IV drug is incompatible with dextrose?

• Always mix in dextrose for stability
• Use normal saline or separate infusion lines instead
• Freeze the admixture to stabilize it
• Add calcium to counter precipitation

Correct Answer: Use normal saline or separate infusion lines instead

Q19. Which statement about pH and drug stability is correct?

• All drugs are most stable at pH 7.0
• Each drug has a pH‑stability profile; adjusting pH can prevent hydrolysis or precipitation
• Raising pH always increases drug stability
• pH has no effect on parenteral drug compatibility

Correct Answer: Each drug has a pH‑stability profile; adjusting pH can prevent hydrolysis or precipitation

Q20. Which oral co‑administered product is most likely to reduce absorption of ciprofloxacin?

• Vitamin C tablet
• Calcium‑containing antacid
• Acetaminophen tablet
• Caffeinated beverage

Correct Answer: Calcium‑containing antacid

Q21. What is the safest practice when intravenous compatibility information is not available for two drugs?

• Mix them in the same syringe in small volume
• Administer sequentially using separate lines or flush the line thoroughly between drugs
• Assume they are compatible if both are common antibiotics
• Increase infusion rate to reduce contact time

Correct Answer: Administer sequentially using separate lines or flush the line thoroughly between drugs

Q22. Which chemical incompatibility can reduce the antimicrobial activity of tetracyclines when given orally?

• Complexation with divalent/trivalent cations like Ca2+ or Fe3+
• Oxidative decarboxylation in the stomach
• Vaporization in the intestine
• Enzymatic activation by bile salts

Correct Answer: Complexation with divalent/trivalent cations like Ca2+ or Fe3+

Q23. Which practice prevents light‑induced degradation during infusion of a light‑sensitive drug?

• Use clear plastic tubing and bright room lights
• Wrap the infusion bag and tubing in amber covers or use amber syringes
• Heat the bag to compensate for light exposure
• Expose the bag to UV light intermittently

Correct Answer: Wrap the infusion bag and tubing in amber covers or use amber syringes

Q24. Which of the following is a known incompatibility concern for amphotericin B deoxycholate?

• Stable in all parenteral fluids without concern
• Incompatible with many solutions; requires appropriate diluent and attention to precipitation
• It forms chelates with sodium chloride improving activity
• It is only inactivated by oral antacids

Correct Answer: Incompatible with many solutions; requires appropriate diluent and attention to precipitation

Q25. Which reference is widely used by pharmacists to check injectable drug compatibility?

• Gray’s Anatomy
• Trissel’s Handbook on Injectable Drugs
• Goodman & Gilman’s Manual of Surgery
• Pharmacology by Katzung (unabridged)

Correct Answer: Trissel’s Handbook on Injectable Drugs

Q26. Which action is appropriate if two drugs are known to be Y‑site incompatible but both must be given?

• Mix them in the same syringe in alternating layers
• Use separate IV lines or stagger administration times and flush between
• Administer both rapidly at the same Y‑site
• Increase concentration to reduce infusion time

Correct Answer: Use separate IV lines or stagger administration times and flush between

Q27. Multi‑dose vials with benzyl alcohol preservative are contraindicated in which population due to toxicity risk?

• Healthy adults
• Neonates (risk of “gasping syndrome”)
• Elderly patients without comorbidities
• Patients with well‑controlled diabetes

Correct Answer: Neonates (risk of “gasping syndrome”)

Q28. Which preventive measure reduces loss of protein drugs by adsorption to infusion sets?

• Use untreated PVC tubing exclusively
• Use tubing with low adsorption properties or pre‑flush with albumin/saline to saturate binding sites
• Administer proteins with metal ions to stabilize
• Store protein in polypropylene syringes at room temperature for days

Correct Answer: Use tubing with low adsorption properties or pre‑flush with albumin/saline to saturate binding sites

Q29. Which laboratory observation suggests a chemical incompatibility after mixing two injectable drugs?

• Solution remains clear and colorless
• Appearance of turbidity, particulate formation or color change
• No change in pH after mixing
• Decrease in temperature of the admixture

Correct Answer: Appearance of turbidity, particulate formation or color change

Q30. For safe compounding and prevention of incompatibilities, which practice is essential in the pharmacy?

• Ignore compatibility data for commonly used combinations
• Follow validated compatibility resources, standard operating procedures, and verify stability before admixing
• Always mix multiple drugs in one bag to save time
• Rely on visual inspection only without consulting references

Correct Answer: Follow validated compatibility resources, standard operating procedures, and verify stability before admixing

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