What is the ruling on purchasing medicines on credit, without the exchange taking place in the same sitting?

Medicines are not subject to usury (riba) such that immediate possession (taqabud) is required when dealing with them. Rather, it is permissible to sell usurious items on credit if they are sold for cash. Immediate possession is required before separation, by consensus, in currency exchange (sarf). However, it is not required, by consensus, in the sale of foodstuffs and other commodities for cash. Selling for an unknown term is not permissible.