Amorphous And Crystalline Drugs: Which Will Give More Stable Dosage Form And Why

Both amorphous and crystalline drugs play distinct and important roles in pharmaceutical formulation, particularly in terms of stability, bioavailability, solubility, and dissolution. Crystalline drugs possess a well-ordered, stable molecular structure that results in slower dissolution and lower solubility, whereas amorphous drugs, lacking a defined lattice arrangement, exhibit higher solubility and faster dissolution rates but are thermodynamically less stable. Amorphous forms are often utilised to enhance the bioavailability of poorly water-soluble drugs; however, because they tend to revert to the more stable crystalline state over time, stabilisation of the amorphous form is essential for maintaining product performance and shelf life.

1. What is the Difference between Amorphous and Crystalline Drugs?

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2. What is Amorphous Solubility?

Amorphous solubility refers to the maximum concentration of a drug that can dissolve in a solvent when the drug is in its amorphous (non-crystalline) form.

Because the amorphous form has higher internal energy and lacks a crystal lattice, it usually has greater apparent solubility compared to the crystalline form.
However, this solubility may be metastable, meaning the amorphous drug may eventually crystallise in solution, reducing solubility over time.

3. Which gives a more stable dosage form: Amorphous or Crystalline, and why?

• Crystalline drugs give a more stable dosage form.
• This is because their molecules are in a low-energy, ordered arrangement, making them thermodynamically stable and less prone to changes such as recrystallisation, degradation, or moisture absorption.

In contrast, amorphous drugs are in a high-energy, disordered state and tend to revert to the crystalline form over time, especially under stress conditions (temperature, humidity).

4. What are the Main Difference Between Crystalline and Amorphous?

• The main difference lies in the arrangement of particles:
  • Crystalline: orderly, repeating pattern.
  • Amorphous: random, disordered arrangement.

5. What is Amorphous in Pharmacy?

In pharmacy, the term amorphous refers to a non-crystalline form of a solid drug or excipient where the molecules lack a definite arrangement or lattice.

Importance in pharmacy:

• Amorphous forms are used to enhance the solubility and bioavailability of poorly water-soluble drugs.
• However, they require careful formulation and stabilisation (e.g., using polymers) due to their tendency to crystallise.

6. What is Better for Tablet Formulation: Amorphous or Crystalline Solids?

• It depends on the formulation goal:
  • If stability is the priority → Crystalline form is better.
  • If solubility and bioavailability are the priority (for poorly soluble drugs) → Amorphous form may be better.

In tablet formulation, amorphous solids may provide faster dissolution and higher absorption, but need stabilisers (like PVP or HPMC) to prevent crystallisation.

7. Differences Between Crystalline and Amorphous Materials

8. What are the Examples of Amorphous and Crystalline Solids?

Amorphous Solids:

1. Glass
2. Plastic
3. Rubber
4. Gels
5. Waxes
6. Pitch (tar)
7. Cotton candy
8. Butter
9. Amorphous silica
10. Polystyrene
11. Amorphous sucrose

Crystalline Solids:

1. Sodium chloride (NaCl)
2. Sucrose (crystalline sugar)
3. Ice
4. Quartz (SiO₂)
5. Diamond
6. Graphite
7. Copper sulfate (CuSO₄·5H₂O)
8. Sodium nitrate
9. Urea
10. Iodine
11. Zinc sulfate

9. Which is More Stable: Crystalline or Amorphous?

• Crystalline is more stable due to its low internal energy and ordered structure.
• Amorphous is less stable, more prone to recrystallisation and chemical degradation.

10. Which is More Soluble: Crystalline or Amorphous?

• Amorphous is more soluble because of its higher free energy and lack of crystal lattice, which makes molecules easier to dissolve.
• Crystalline solids dissolve more slowly due to strong lattice forces.

11. Similarities Between Crystalline and Amorphous Solids

12. Is Crystalline Stronger than Amorphous?

Yes.
Crystalline solids are generally stronger and harder due to the strong, regular bonding between their particles in a lattice structure.
Amorphous solids, with irregular arrangement, are softer and weaker mechanically.

Crystalline Vs Amorphous: Summary Table

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Further Reading:

• Why does the amorphous form of drug have better …