Forteo (teriparatide) followed by HRT: My Experience

I just got back P1NP and CTX results. I was on Forteo for 6 months and a half dose of Tymlos for 17 months. I have been on 14mcg Menostar for 6 months. I quit taking Tymlos and started progesterone cream a month ago, because of abdominal pain. I have a history of endometriosis and thought that the progesterone might help with pain if it was from that. An ultrasound of my pelvis showed a fluid filled Fallopian tube and an abdominal ultrasound showed hydroureteronephrosis. A second ultrasound of the kidneys no longer showed that. The abdominal pain is now gone. I am sensitive to medications and prefer not to take Reclast or Prolia.

The best ratio I have had was on 10/1/25 when I had been on both 40 mcg Tymlos and 6 months of Menostar. P1NP was 147 and CTX was 654. There has been a big change without the Tymlos and with the added progesterone cream. P1NP is now 38 and CTX is 371. I am pleased that CTX is lower, but very concerned that P1NP is so low. Should I be concerned enough to increase estrogen, decrease progesterone or start taking Tymlos again? I still have Tymlos in my refrigerator. My endocrinologist doesn't want to see me until May, and my gynecologist can't get me in until April.

What is the ratio of P1NP to CTX supposed to be when trying to hold in gains?

@lynn59 that's very nice of you to say. I think I've just spent more time than i should admit reading and falling down the osteoporosis rabbit holes - retirement has provided a lot of time for "deep diving". You've clearly done your own due diligence as well, which is the best way to navigate all the conflicting opinions out there.

It sounds like you’re nearing a final decision for your path forward. In your shoes, I’d be thinking twice (even thrice!) about HRT as well. Your endocrinologist and team physicians are definitely the best ones to guide you through the next steps. While the Reclast protocol is often individualized, all the right lifestyle habits will certainly help. Please update us on how your endo manages your maintenance phase - I'd love to hear how it is done.

@drsuefowler, here are my thoughts: your current bone marker levels are primarily determined by your estrogen (an antiresorptive), since you’ve stopped Tymlos for a month now. If you adjust estrogen dose, your CTX (resorption) will move accordingly. There isn't a way to 'fine-tune' the CTX P1NP ratio because of the coupling effect.

Adding or restarting Tymlos at this point is an unknown, as most of the anabolic effects of a PTH analog diminish after 18–24 months for the majority. If you do decide to reintroduce Tymlos, I’d love to see how your bone markers change, so please keep me in the loop.

I don’t believe there is a consensus on a magic 'ratio' for holding gains. However, it does appear most experts agree that the key is ensuring resorption (CTX) doesn’t start to accelerate once an anabolic treatment ends. Given that you've transitioned to HRT, have your doctor(s) mentioned any specific target levels they want to see for your markers?

Thanks so much @mayblin for your response. Unfortunately, my doctors don't seem to know as much as I do about this. I see my PCP next week and will get her opinion. Maybe I could get an appointment with the PA who suggested estrogen in the first place, but wouldn't prescribe it. The estrogen is prescribed by a functional physician, so I could ask her. My endocrinologists will just tell me to take Evenity, Prolia or Reclast, but I will ask the one who has mychart. From what you wrote, it is good that my CTX went down not up.

I am considering taking more calcium, since my blood level went down to 91 from 94. Also, I am considering taking Strontium again. My first bone marker results on 12/23 were P1NP 78 and CTX 519. At that time, I had been on 20 mcg, 2 clicks, for a month and 300 mg of Strontium citrate for a year. That was a better ratio than what I have now, 38 and 371.

I also wonder if the progesterone cream is lowering the influence of estrogen. If I stopped using the cream, would that lower the CTX? It does help me sleep.

@drsuefowler, no doubt estrogen is the primary driver for you right now. While there have been studies on progesterone’s effect on osteoblasts years ago, the effects are samll and probably not strong enough to override estrogen’s role. Since it helps you sleep, which is vital for bone health - my opinion is it’s probably best to keep it - double check with your team physicians.

Here are two references on using BTMs as a guide if you want to see the 'maintenance' benchmarks researchers are using:
https://pmc.ncbi.nlm.nih.gov/articles/PMC12064614/
https://academic.oup.com/jbmrplus/article/6/6/e10633/7479596
A move from 9.4 to 9.1 in blood calcium level could be just normal physiological variation. However, getting sufficient calcium through natural food source rather than supplements is always a good idea, especially given the ongoing debates around cvd risk with high-dose supplementation. And im sure you are aware the fact that strontium distorts DXA results. If you're trying to get a clear picture of how well the HRT is maintaining your Tymlos gains, adding strontium might make your future data harder to interpret

Thanks @mayblin. I always appreciate your input. Interesting studies, but the CTX values used in the one study were very low compared to my 371. I try to get as much calcium from food as I can, but usually still need to supplement a little. You are right, the calcium level change is probably not significant. I quit Strontium 2 years ago because of the DEXA problem, but maybe it helps to stop fractures? I have an appointment with my endocrinology PA on Monday and will discuss all this. I am scared that I may have lost all my gains from the anabolics. I am almost done with a course of physical therapy for my knee, hips and balance. You would think that all that resistance exercise would help my P1NP score. Apparently not.

@broken13
Why is that? Why would you not use hormone replacement again since you feel that stopping the HRT seemed to lead to a rapid decline in your bone health and was possibly tied to your fractures?

@drsuefowler, i hope my previous reply didn't inadvertently add any anxiety! 1mo is not going to cause a noticeable change in bmd after Tymlos, even while you and your doctors are still determining how you respond to this HRT dose for maintenance.

You are right that the ctx and p1np targets in that study are quite low - and it’s important to note that the study cohort was made up of fracture patients, rather than people specifically transitioning from an anabolic like Tymlos. While this JBMR Plus article explicitly sets those BTM targets, trials such as ACTIVExtend (Alendronate after Tymlos) used strong bisphosphonates to ensure bone turnover is kept low enough to 'lock in' those gains.

Using bone markers for decision making isn't yet standard clinical practice but transitioning to a strong antiresorptive is the go-to strategy for maintenance after anabolic treatment. The availability of various estrogen dosages gives us the advantage of being able to 'titrate' to the desired effects.

I had similar observations as you did - both of my ctx and p1np are very low and they don't change much whether I was active or not. In a way, im having the opposite concern: im not sure if staying in my current low bone turnover state is ideal for very long periods.

To add one more point: if you have extra Tymlos pens and want to use them with Menostar, why not? Those pens are expensive! I actually used my 3 leftover Forteo pens myself with HRT for short periods. Ideally, Id have preferred to wait and use them after at least 1yr break, but the pens were near expiration date. Even though the 3 pens didn't give a huge anabolic signal, my L-spine gained an additional 5%. My endo pointed out that while the estrogen was reducing my turnover, Forteo had likely reached its limits after 22 months anyway. There are several ways to explain that gain or btm, but it clearly helped lock in the progress regardless.

@kathleen1314 Because if stopping it made that rapid of decline, that is concerning to me with my severe case. I have experienced too many times when the pharmacy was not able to get in a specific medication. Just last week they changed my Teriparatide to another brand and provider because the one I had been already taking for 16 months was not available, which I found very stressful. Plus my sister and aunt have both had breast cancer. As much as possible, I want something stable that I can count on.