Is it permissible to leave a book in the pharmacy with the intention that it serves as a substitute for the price of medicines taken on credit, if the value of the book is equivalent to the price of the medicines?

If you sold medicines without receiving payment in cash, then if this was with the pharmacist's approval, you are not liable. However, if it was without his permission, you are responsible for their price. If the buyers do not pay and the pharmacist does not absolve you, you become indebted to him. Your liability is not discharged by leaving a book in exchange for the price of the medicines unless he agrees, even if the value of the book is greater. A creditor is not compelled to accept something different from the type of his debt, or something better or worse than it, but it is permissible if he accepts it willingly.