Since then patches, implants, gels and nasal spray preparations have been used. Oral preparations have the advantage of being cheap, convenient, with a range of different types. They can be combined with a cyclical or continuous progestogen should there be a need to protect the endometrium. A relatively large bolus of oestrogen is introduced to the systemic circulation, with levels peaking after 4-8 hours. With problems of reduced bioavailability and variable absorption, the plasma levels of oestradiol may be insufficient to achieve osteo-protection, or relief of climacteric symptoms.
Oral preparations are subject to the hepatic first-pass metabolism effect.
As a result of this, the production of coagulation factors and renin substrate is increased. For this reason, this route of administration should be avoided in any woman with an increased thrombotic potential. However, the production of lipid apoproteins is similarly increased, which will conversely have a cardioprotective role. Non-oral preparations avoid many of the pitfalls of oral oestrogen delivery. There is no hepatic first-pass effect, and the physiological ratio of oestradiol to oestrone are maintained.