The physical form of a drug describes its structural arrangement at the molecular level, which directly affects its solubility, stability, and bioavailability.
A) Crystalline state:
Definition:
A crystalline drug has a well-defined and ordered molecular structure. Molecules are arranged in a regular, repeating pattern known as a lattice structure.
Characteristics:
High melting point due to strong intermolecular forces.
Higher stability compared to amorphous forms.
Typically, less soluble in water, leading to slower dissolution rates and possibly reduced bioavailability.
Importance:
Suitable for long-term stability.
Used when slower drug release is desired.
B) Amorphous state:
Definition:
An amorphous drug lacks a defined molecular arrangement, resulting in a random or disordered structure.
Characteristics:
Lower melting point and reduced stability.
Higher solubility and faster dissolution rates due to higher free energy.
Importance:
Ideal for enhancing bioavailability of poorly soluble drugs.
Requires stabilization techniques (e.g., polymers or solid dispersions) to prevent recrystallization during storage.
Comparison Table:
Property | Crystalline Form | Amorphous Form |
Structure | Ordered molecular lattice | Disordered structure |
Melting Point | Defined | No defined melting point |
Diffraction | Sharp patterns (X-ray visible) | Broad, less defined patterns |
Stability | More stable | Less stable, prone to recrystallization |
Solubility | Lower solubility | Higher solubility and faster dissolution |
Bioavailability | Lower due to low solubility | Higher due to increased solubility |
Advantages | Predictable, easier to handle | Improved drug delivery, higher solubility |
Disadvantages | Lower solubility, polymorphism variability | Less stable, sensitive to environment |