“Drug–Coformer–Drug” Multicomponent Crystals to Simultaneously Improve the Solubility of Two Insoluble Combined Drugs by Introduction of a Soluble Coformer

One “drug–drug” (GTB–RH) and two “drug–coformer–drug” (GTB–SA–RH and GTB–SA–RH·EtOH) multicomponent crystals involving two insoluble drugs, gefitinib (GTB) and rhein (RH), and succinic acid (SA) as a soluble coformer, were successfully obtained. GTB–SA–RH and GTB–SA–RH·EtOH exhibit higher solubility and faster dissolution rates of both GTB and RH as compared to GTB–RH. This study presents an opportunity for simultaneously and effectively improving the solubility of two insoluble drugs by the introduction of a soluble coformer to construct “drug–coformer–drug” multicomponent crystals to develop improved combined medicines.