Introduction to Intrinsic Dissolution Rate
The intrinsic dissolution rate (IDR) and the dissolution rate both describes how fast the compound is released from the crystal lattice into solution. The rate of dissolution is of major importance in regard to the behavior of the compound in vivo. Quantitative/kinetic solubility information obtained from IDR and dissolution rate measurements, especially as a function of pH, may determine the extent of regulatory concern about the different solid forms.
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IDR is used for:
- Evaluation of the drug solubility in accordance to the biopharmaceutical classification system (BCS)
- Comparison of different forms/salts of the same compound (is a higher dissolution rate obtained by changing salt?)
- Setting specifications for particles sizes
- Development of dissolution methods
Instrument and measuring principle
The intrinsic dissolution rate is defined as the rate of dissolution of a pure pharmaceutical active ingredient when surface area, stirring speed, pH and ionic-strength of the dissolution medium are kept constant. I.e. the surface area of the compound is well defined in contrast to in a dissolution rate measurement. Thus, it is measured as the release of API from a tablet with a flat and well-defined surface area into an aqueous solution at a given pH value.
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| Technical info | |
| Instrument | Vankel VK8000 Dissolution Sampling Station with Woods apparatus (tablet diameter 0.5 cm) |
| Sample amount | 30-50 mg |
| Temperatures | 25-50 °C |
| Stirring rates | 50 or 100 RPM |
| Result | Reported as curve and IDR (mg/cm2/min) |
The intrinsic dissolution rate is measured by releasing the sample from a tablet surface placed in a rotating assembly.