pH determination as a quality standard for the elaboration of oral liquid compounding formula

pH is a critical factor for all those medications prepared as aqueous  liquid forms, because it has an impact on the solubility of the molecule, determining the stability of medications, the biological tolerability of  the formulation, and the activity of the molecule. The objective of this study is to determine the optimum pH range for the oral liquid formulations more frequently prepared at the Pharmacy Unit, in order to standardize and incorporate said  value into the standard protocols of action as a quality control criterion.

The study was conducted in three stages. The first stage consisted in a retrospective study of the records of preparation of those oral liquid formulations prepared at least 5 times since January, 2015 to December, 2016, in our  Pharmacy Unit; the main value and standard deviation of the pH values recorded for each formulation were calculated. In a second stage, there was a  bibliographic search in order to understand the pH for the maximum stability of  the molecule, and to confirm if this characteristic was recorded as a requirement for quality control in the procedures described in the formulation guidelines. In  the third stage, it was confirmed if the pH values determined coincided with the  maximum stability pH described in literature, and acceptance ranges were  established.

In total, 31 formulations were reviewed (14 solutions / 17  suspensions). The maximum stability pH value was known for 19 (61.3%) of the molecules and/or oral liquid formulations evaluated; 15 (78.9%) of these were  within this range, and the remaining 4 (21.1%) presented a standard deviation  of ± 0.5 regarding the pH value referenced in the bibliography. The pH range for the same standard work procedure ranged between 0.32 and 1.51. An  acceptance pH range of ± 0.75 was determined as quality control.

An optimal pH range has been determined for the 31 oral liquid  formulations more widely prescribed in our hospital. This characteristic should be part of the galenic validation for these preparations, as well as of its routine  quality control, in order to ensure their quality and efficacy.