The one way that gels stand out from, say, creams or lotions, is that they dry on the skin rather than having the hrt, medium and all, absorbed into it. Product labels warn of enhanced risk for transferring gel-delivered hormones to others and for diminishing the delivered dose by washing too soon after application (where "too soon" is a much longer period than with other media).
The gels
It's also puzzling to women trying to calculate doses from one form to another of hrt just how the relatively large amounts of estrogen in the typically-recommended gel hrt doses should be compared to the amounts delivered by other hrt forms.
One of the members of our discussion list just came up with this excellent article that may shed some light on all of this: "Comparison of the transdermal delivery of estradiol from two gel formulations." According to this test, which compares two widely-sold gel hrts, the delivered dose of the hormone was only 13-20% of the amount applied.
All hrt deliveries involve some losses: that's one reason why we can't just convert from one hrt to another of a different route and go on using the same dose numbers. But in the case of gels, we need to recognize that there will be a big difference because only such a small amount of the hormone actually gets into our bodies this way. And with such low proportional delivery when used according to directions, it doesn't take much imagination to suspect that this could be further reduced by incorrect application.
Yep, that's a lot of loss. Where does it go? Well, onto our spouses and kids, if we're not careful. Onto our clothing and towels and bed linens, I'm sure. Ultimately, down the drains of our showers and washing machines, into our sewers and septic systems, thus contributing to the contamination of water supplies that today test in community after community as having elevated estrogen contents and perhaps contributing to the cancer and other hormone risks of an entire population. It's not our place to raise ethical issues here, but this might be a point that women would want to consider when they make their own choices.
Other transdermals
As we said above, each hrt, even within the family of transdermals, has its own delivery profile. That includes things like how the uptake "feels" to us and how efficiently it moves the hormones it contains into our systems. We've seen way too many women just slam themselves with excessive doses when they thought that because they needed Xmg of dose in one transdermal hrt, they needed to multiply normal doses of another hrt to get that same number.
That's not how it works.
We can get a better sense of dose equivalency from the "usual starting dose" figure that's part of the basic prescribing information with any hrt. That's the dose that incorporates enough to make up for losses in delivery and still provides enough to make up "usual" coverage in a woman's system.
Yes, this is confusing. One of our discussion list members assembled this very handy chart comparing dose to delivered amounts in transdermal products available in the US and the UK. It doesn't cover every hrt, but it does give us a great overview of how much variation there is in all of this.
So how do I use this information?
Basically, it reinforces the premise that we really can't do an absolute conversion from any one hrt to any other hrt. But it does help us feel more comfortable letting go of dose numbers as even a rough conversion factor and switching our attention to more useful figures.
More useful in moving from one hrt to another is how we felt on what dose of our original hrt. If we felt sort of okay on, say, the usual starting dose of our old hrt, then we might want to start the new hrt at whatever is pegged as the usual starting dose for that one. Similarly if we were one up or one down from the usual starter of our old hrt (or we would have preferred to have been), we might look to that many iterations off of usual starting for the new one. It's a really rough system and no, the manufacturers aren't going to provide us with anything better because their profit lies in holding us captive to their brand, not in facilitating our moving to someone else's.
We can also use our understanding of this to help explain why we may feel really different when we switch brands. We typically see this when we're having problems with one brand and our doctor switches us to another and whammo, we're feeling as though our hrt has just evaporated. Many doctors don't keep up with the trend that some hrts now come out in ultra low doses meant for women in natural menopause who just want a tiny hormone boost for its value in combatting osteoporosis. Those doses aren't typically enough for most women in surgical meno, so even swapping to the "usual" of the ultra-low hrts is a huge dose cut. Again, when we look at the figures for what is being delivered, we can get a sense, albeit rough, that we've actually had a big cut in what our bodies have to work with. So in this case, we're not crazy: we actually aren't taking anywhere near the same thing and we need to take this fact back to our doctors to use in troubleshooting our correct dose.
Obviously, dose amount and delivery amount aren't the only factors in working with the behavior of different transdermal hrts, but they are an important factor to understand when we are troubleshooting.