Background: Nowadays, it is still important to develop effective anti-opisthorchiasis agents. In this work, we tested a complex of praziquantel (PZQ) with a plant origin compound—disodium glycyrrhizinate—in the ratio 1:10 PZQ:Na2GA, containing 11-fold less of the active ingredient. Our aim was to study various ways to treat trematode Opisthorchis felineus with this complex in vitro. Additionally, an in vitro comparison of the anthelmintic action was made among racemic-PZQ, (R)-PZQ, and (S)-PZQ on juvenile and adult maritae of O. felineus. Methods: Worms extracted from the hamsters were subjected to various regimens of administration of the complex: once a day for 3 days or three times within 1 day. Moreover, mature maritae and juvenile worms of O. felineus were subjected to the comparison the anthelmintic effectiveness of racemic-PZQ, (R)-PZQ, and (S)-PZQ. Results: The O. felineus maritae that received PZQ:Na2GA (1:10) thrice within 1 day were most strongly affected by the drug. Their motility substantially decreased already on the second day after the last dose, and the percentage of live worms by the end of the experimental period was the lowest. These results indicate a cumulative anthelmintic effect of this substance under the regimen “three times within 1 day.” For the first time, we report that among the three substances (racemic-PZQ and two enantiomers), (R)-PZQ has the highest anthelmintic activity, toward both juvenile and sexually mature maritae of O. felineus. Conclusion: These findings suggest that the development of a supramolecular complex of (R)-PZQ with disodium glycyrrhizinate and administration of this complex three times within 1 day are promising approaches.