Thermosensitive systems based on poloxamer 407 are widely used in targeted drug delivery; however, the stability of the phase transition temperature remains insufficiently studied. This article presents the results of a study on the effect of adding polyethylene glycols (PEG) with different molecular weights and some classical gel-forming polymers on the gelation temperature of thermoreversible compositions based on poloxamer 407 in a long-term experiment. The study showed a positive effect of PEG addition with average molecular weights at concentrations of 1.5–2.0%, as well as gelling agents at a concentration below the critical gelation concentration. The proposed rheological test for studying the samples’ adhesion can give an indirect forecast of the composition adhesive rate. Based on the conducted studies, three experimental binary systems based on poloxamer 407 were selected, with the addition of HPMC 0.5%, sodium alginate 0.5%, and PEG 1500 1.5%. These systems are the most promising for the further development of in situ targeted drug delivery systems.

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Objective: The article presents the results of studying the parameters of in situ systems based on poloxamers. Methods: Natural, synthetic and semi-synthetic polymers were considered as additional gel-forming agents. The above-mentioned agents were cellulose derivatives, as well as rare-cross-linked acrylic polymers, alginic acid salts, and xanthan gum. The gelation temperature was visually recorded during the gradual heating. Mucoadhesion was determined by measuring the separation force of the sample from the mucosal model using pig stomach mucin. The concentration of gel formation was determined using an Ostwald capillary viscometer. Results: During the experiment, 20 samples based on poloxamer 407 18% were examined with the addition of excipients in concentrations of 0.5-2.0%. It was found that the introduction of additional gel-forming agents has a positive effect on the mucoadhesive properties of poloxamer 407. To increase the temperature of gelation of the binary mixture, it is necessary to take into account the own concentration of gelation of the introduced additional polymer, which was confirmed by capillary viscometry. Also, additional viscometric studies revealed the reasons for the absence of a thermoreversible effect in the composition of a poloxamer with xanthan gum and confirmed its use as an excipient in the thermoreversible matrix of poloxamer 407 is impractical. Composition with the best-investigated biopharmaceutical properties-the composition with HEC in a concentration of 0.5% Conclusion: The obtained results can be explained by the fact that when the concentration of additional polymer was exceeded, binary mixtures showed a decrease in the gel formation temperature up to a complete loss of the ability to temperature-dependent sol-gel transition. The choice of an additional gel-forming agent to improve the properties of the system should be based on some specific properties that affect the thermoreversible properties of the system.