Hydrophobic ion pairs of teriparatide were prepared and solubilised in pure ethanol as described under Section Error! Reference source not found.. The peptide content was measured by HPLC immediately after preparation as well as after predefined time points stored as prepared at room temperature. Figure .1a shows the peptide stability in aqueous-ethanolic solutions after a 10 min exposure. Peptide stability was evaluated as the percentage of area under the curve (AUC) compared to a 100% aqueous solution. It can be observed that ethanol concentrations exceeding 40% resulted in a decrease in the AUC of teriparatide. At the same time the appearance of a second peak was observed. This was exaggerated with the increase of the ethanol concentration. Therefore, it was concluded that teriparatide is unstable in aqueousethanolic solutions exceeding 40% and it is likely that longer exposure to <40% ethanol could result in similar observations. Similar observations were made when teriparatide was incubated in methanolic solutions, with the onset of reduction in %AUC observed for solutions exceeding 60% methanol. In contrast, no change in AUC, retention time or peak shape was observed for teriparatide stored in aqueous solution of acetonitrile.