The preparation and use of a protected organic aldehyde is described wherein bioavailability of the orally administered therapeutic aldehyde is improved. The protected aldehyde is prepared by reacting the aldehyde with a protecting group, for example, condensing the aldehyde chemically with a thiazolidine-4-carboxylic acid. The improved bioavailability of such orally administered drugs increases the feasibility of delivering sufficient amounts of vanillin or other therapeutic organic aldehydes in vivo to prevent sickling in sickle cell anemia. Combination therapy is also described wherein a protected organic aldehyde is administered to a subject in treatment of sickle cell anemia in conjunction with one or more other drugs, such as pain killers, used in treatment of the symptoms of sickle cell anemia or sickle cell disease.