We tend to think of HRTs as being divided according along such lines as bioidentical vs synthetic or based on route of delivery, and certainly these characteristics have a great deal to do with how a given HRT may "fit" any given woman. But there's another factor that can be important in how we experience an HRT, and that's the uptake dynamic. What do we mean by that? It's the timing and speed with which the hormone enters, resides in, and departs our systems.
For example, an oral HRT that dissolves well, such as Estrace, will hit the stomach and very rapidly be completely absorbed into the circulation and just as rapidly greatly diminished in concentration by the "first pass effect" in the liver. An HRT of that same estradiol compounded in an oil base will be more slowly absorbed and less rapidly eliminated from circulation. By the same token, a new patch on a new location will be taken up much more rapidly by the body than an older patch on a more fully saturated location that's been in use for some days. A gel or cream HRT that is rubbed into a small area will be taken up more slowly than one spread widely, and all things being equal, a gel is more likely to be taken up more rapidly than a cream.
Going beyond the initial uptake of a dose, the curve of concentration of hormone delivered by any HRT to the body will be different over time. For example, a dose taken once daily will peak shortly after administration and then gradually fall during the day to a low point before the next dose is due. A dose take weekly, on the other hand, will describe that same curve but it will be spread over days instead of hours. For HRTs given on even longer intervals, such as rings that last three months or implants that last up to six months, a corresponding lengthening in time of those portions of the dose curve will obviously be experienced.
What difference does this all make? Different women have different levels of tolerance for hormonal fluctuations. For some women, their bodies seem to be overwhelmed by too much coming in too quickly, and the sharp rise of a quick-uptake HRT causes symptoms that don't exist once the hormone is more stably in their system. One case where women seem to run into this is where taking their HRT causes headaches that last only during the uptake period or the downward turn when a dose is wearing off. Here the culprit may not be the hormone itself, but rather the rise and fall of that particular HRT. Sometimes when these women can switch to a form with a slower period, these symptoms will abate.
Another related effect is the contrast between women who seem to do well with once-a-day dosing and those who seem to need a continuous trickle. Now, premenopausally we all experienced a daily rise and fall in our hormone levels in addition to our monthly cycle. We could call up more ovarian output when we needed it, and we could convert between active and inactive forms of estrogen as our physical demands dictated. Once in surgical meno, though, our supply is suddenly more limited. This in itself provides for a period of shock and adjustment. It's been our observation that women early in postop recovery seem to be less able to manage their hormone needs over time and tend to do better with a more constantly available trickle of intake. It's as though their bodies haven't quite had the time yet to master relying on the tricks of shuffling those hormones around between the different forms, as though their bodies put hormones away in the storage form and then misplace them, or forget how to get them back. We're anthropomorphizing here, we know, but nonetheless there seems to be a greater fragility in early postop hormone management. Once some time goes by and women get stabilized on an acceptable level of hormonal support, dose intervals become less critical for many women. In fact, the constant trickle of "just enough" doesn't provide for that caching and management that we're prepared to use in menopause, and they may increasingly have a sense that their early HRT choice is leaving them edgy and unfulfilled. At that point, in revisiting their HRT choices, many find that they are now able to move to a daily dose and their bodies can cope more gracefully with a more intermittant supply. This then, is where the dose dynamic that pertains to how long HRTs stay active in our system comes into play.
The downward side of the dose dynamic curve, the waning dose, can be anything from a minor annoyance to disabling. For some women on especially long-lived HRTs, the lag between when one dose is running out and when they can get another inserted can be most unpleasant unless they have things calculated very finely. For other women, the nighttime dip in hormones provides a few breakthrough hot flashes that tells them that their morning-scheduled daily hormone dose is just enough but no more than the minumum they need, and that nighttime flash serves as a gauge of just where they are in meeting their needs.
Dose dynamics are not necessarily something we need to fuss over when choosing an HRT, but they can become a neglected but critical element when we are troubleshooting our HRTs. Many times, when we are looking for what about an HRT is letting us down, if we consider what the delivery dynamic is providing our systems, we can gain important clues that may help us make choices that better suit our bodies. It's not something we can predict in advance, but it can be one more useful tool when we get to the tweaking, tuning and troubleshooting parts of the process.