Diterpene lactones have been identified as active compounds in several medicinal plants, including Andrographis paniculata (Burm. f.) Nees, which is a medicinal plant that has been used for centuries across the world. Andrographolide is the major diterpene from A. paniculata and the main bioactive constituent of this species. The effectiveness of diterpenes can be affected by factors that limit their oral bioavailability, such as their poor water solubility, slow dissolution rates, low gastrointestinal absorption, high chemical and metabolic instability, and rapid excretion. In this context, the purpose of the present review is to compile and compare literature data on the bioavailability of diterpene lactones from A. paniculata after oral administration in medicinal plant extracts or in their free forms and to highlight strategies that have been used to improve their oral bioavailability. Considering that medicinal plant extracts are commonly used as dried powder that is reconstituted in water before oral administration, novel pharmaceutical formulation strategies that are used to overcome difficulties with diterpene solubility are also compiled in this review. The use of self-microemulsifying drug delivery systems is a good strategy to enhance the dissolution and consequently the bioavailability of andrographolide after oral administration of A. paniculata extract formulations. On the other hand, herbosome technology, pH-sensitive nanoparticles, nanosuspensions, nanoemulsions, nanocrystal suspensions, nanocrystal-based solid dispersions, and solid dispersion systems are useful to formulate andrographolide in its free form and increase its oral bioavailability. The use of a suitable andrographolide delivery system is essential to achieve its therapeutic potential.
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