Kahar Method: A Novel Calculation Method of Tonicity Adjustment

BACKGROUND: Hypertonic and hypotonic conditions in pharmaceutical preparations decrease the drug’s absorption and bioavailability. In addition, it can cause tissue damage. There are several calculation methods to regulate hypotonic preparations. However, there are no methods that can be used to regulate hypertonic preparations without causing dose-dividing problem. OBJECTIVE: This study aimed to develop a new calculation using basic principle of freezing point depression method (cryoscopic) that can solve hypotonic and hypertonic problems, especially for hypertonic preparations through reducing the levels of additional ingredients. METHODS: The calculation of Kahar method was successfully obtained by substitution and simplification in the basic principle equation of cryoscopic method, and then evaluated by resolving the problems in 42 sterile formula preparations and compared with White–Vincent method, cryoscopic method, equivalent NaCl method, and milliequivalent method through the analysis of its similarity and reliability. RESULTS: The results of similarity analysis between Kahar method and other methods showed good similarity values with more than 0.880. Kahar method and cryoscopic method have the highest similarity of the calculation result with a similarity value of 1. The reliability analysis obtained very good result with Cronbach α = 0.990. CONCLUSIONS: These results suggest that Kahar method provides reliable equation with complete and efficient solution to hypotonic and hypertonic problems.