Triptorelin

Substituting D-tryptophan at position 6 makes triptorelin resistant to the enzymatic cleavage that clears native GnRH in minutes, giving roughly a hundredfold increase in potency. Continuous exposure from a depot first produces a testosterone surge lasting 1 to 2 weeks - the flare - and then desensitises and downregulates pituitary GnRH receptors, dropping testosterone to castrate levels by around day 21. The off-label restart use exploits the opposite end of the same curve: a single small subcutaneous dose acts as one enormous GnRH pulse, releasing the entire stored pituitary LH pool at once and jolting suppressed testes back into action, without staying around long enough to cause downregulation.

Targets: GnRH receptor (GnRHR), Pituitary gonadotrophs, LH, FSH, Testosterone

• · 3.75 mg monthly, 11.25 mg every 3 months or 22.5 mg every 6 months. Antiandrogen cover is usually given for the first weeks to blunt the flare in metastatic prostate cancer.
• · A single 100 mcg subcutaneous shot. This use comes from a handful of small studies plus a large amount of bodybuilding practice, and the failure mode is significant: get the dose or timing wrong and you can desensitise the pituitary and deepen the suppression you were trying to fix. It is a one-shot tool, not something to repeat.

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• very commonHot flushes— The signature effect of androgen or oestrogen deprivation.
• very commonTestosterone flare in the first 1 to 2 weeks— Can cause clinical worsening in metastatic prostate cancer - spinal cord compression and urinary obstruction are the feared events.
• very commonLibido loss and erectile dysfunction— Expected with depot dosing; not a feature of single restart dosing.
• commonInjection-site pain
• commonFatigue and mood change
• commonBone mineral density loss— With long-term depot therapy; needs DEXA monitoring and often bisphosphonates.
• uncommonProlonged suppression after a mistimed restart dose— The specific risk of the off-label use - the drug can suppress rather than stimulate.
• rarePituitary apoplexy— Reported after a first dose in people with an undiagnosed pituitary adenoma.

• Pregnancy and breastfeeding.
• Known hypersensitivity to GnRH analogues.
• Metastatic prostate cancer with impending spinal cord compression or ureteric obstruction, unless the flare is covered with an antiandrogen.
• Undiagnosed abnormal vaginal bleeding.

• conflictgonadorelin — Occupies and desensitises the same receptor, abolishing any gonadorelin response.
• cautionhcg — Sometimes sequenced in restart protocols - hCG first to wake the testes, then triptorelin - but combining them simultaneously makes it impossible to attribute the response.
• synergyAntiandrogens such as bicalutamide — Standard flare protection at the start of depot androgen deprivation.
• redundantdegarelix — Both achieve androgen deprivation; the antagonist does it without a flare.

• · Testosterone at baseline, at 4 weeks and periodically thereafter - castrate is under 50 ng/dL, or under 20 by stricter criteria.
• · PSA in prostate cancer.
• · Bone mineral density by DEXA with long-term depot use.
• · For the off-label restart: LH, FSH and testosterone before the dose and at 2, 4 and 8 weeks after.

Prescription drug in the US, EU and most jurisdictions for prostate cancer, endometriosis, uterine fibroids and central precocious puberty. Research-chemical vials sold online are unapproved.

• Trelstar (triptorelin pamoate) prescribing information (label)
• Decapeptyl summary of product characteristics (label)
• Nieschlag & Vorona 2015, mechanisms and adverse effects of anabolic steroid abuse including axis recovery, European Journal of Endocrinology (review)

Triptorelin is the clearest demonstration in pharmacology that duration of exposure, not the drug, determines the direction of the effect. Bind the GnRH receptor briefly and you get gonadotropin release; bind it continuously and you get shutdown. The shutdown is a two-stage process and both stages matter clinically. In the first days to weeks, receptor occupancy is sustained and the gonadotroph empties its stored LH pool, producing the flare - testosterone rises 50 percent or more above baseline and metastatic prostate cancer can genuinely worsen, which is why antiandrogen cover is standard in men at risk of cord compression or urinary obstruction. Then homologous desensitisation sets in: the receptor uncouples from Gq/11, receptor number falls through downregulation of transcription and internalisation, and gonadotropin secretion collapses. Castrate testosterone arrives around day 21. The off-label restart use runs the same pharmacology in reverse by exploiting only the first minutes of the curve. A single small subcutaneous dose acts as one enormous GnRH pulse, dumping the entire stored pituitary LH pool at once into a system that has been quiet, and because triptorelin is cleared within hours from a non-depot formulation there is no sustained occupancy and therefore no downregulation. The risk in that manoeuvre is entirely about dose and repetition. Get either wrong and you have administered a small depot, and the drug that was meant to restart the axis suppresses it instead. The margin is narrower than the confidence with which this protocol circulates.

The off-label restart is where this compound hurts people, and the arithmetic is the problem. A 2 mg research vial reconstituted in 2 mL gives 1 mg per mL, so 100 mcg is 10 units on a U-100 syringe. A decimal error takes you to 1000 mcg, which is not a restart dose - it is heading toward a suppression dose in a man whose axis is already flat. The second error is repetition: someone dosed once, felt nothing after a fortnight, and dosed again, converting a pulse into continuous exposure and deepening the hypogonadism they were trying to fix. It is a one-shot tool. The third is doing it at all in a man with primary testicular failure, where no pituitary signal will help. In depot use, the flare is the classic harm - a man with spinal metastases who gets a first depot without antiandrogen cover can develop cord compression during the testosterone surge. Pituitary apoplexy after a first dose in someone with an undiagnosed adenoma is rare but catastrophic and is described with every drug in this class.

• GnRH receptor (GnRHR) on pituitary gonadotrophs — Roughly a hundredfold the potency of native GnRH; a specific Kd was not resolved here.

  Initial Gq/11 activation and gonadotropin release, then receptor uncoupling and downregulation under continuous exposure, ending in castrate sex steroid levels.

• LH and FSH

  Surge then profound suppression with a depot. With a single low subcutaneous dose, a discrete LH pulse and nothing more.

• Extrapituitary GnRH receptors on prostate and breast tumour cells

  A direct antiproliferative effect independent of androgen deprivation has been described in tumour cell lines. Its contribution to clinical benefit in humans is not established.

• Trelstar 3.75 mg registration study 3 · n=137 · 36 weeks

  Achievement and maintenance of castrate testosterone in advanced prostate cancer: 91.2 percent castrate by day 29 and 96.2 percent maintained from day 57 to 253.

• Trelstar 11.25 mg registration study 3 · n=171 · 36 weeks

  97.7 percent castrate by day 29 and 94.4 percent maintained from day 57 to 253.

• Trelstar 22.5 mg registration study 3 · n=120 · 48 weeks

  97.5 percent castrate by day 29 and 93.3 percent maintained from day 57 to 337 on six-monthly dosing.

With a depot, LH and testosterone surge within 24 hours and stay elevated for one to two weeks, then fall, reaching castrate levels around day 21 to 29 - the registration data put over 90 percent of men castrate by day 29. Hot flushes typically start as testosterone falls, so they arrive in weeks two to four rather than immediately. Bone and metabolic effects accumulate over months to years. For the off-label single subcutaneous dose, LH rises within hours, testosterone follows over one to three days, and whether the axis stays awake is a question answered at weeks two to eight, not on day three. After stopping long-term depot therapy, axis recovery takes 3 to 12 months and is sometimes incomplete in older men or after years of treatment.

In oncology the standard partner is an antiandrogen such as bicalutamide, started before or with the first depot and continued for a few weeks to blunt the flare. That is not optional in metastatic disease with cord compression risk. In restart protocols, triptorelin is sometimes sequenced after hCG - hCG first to wake the testis, then a single triptorelin dose to restore the pituitary signal, then a SERM to hold it - but running them at the same time makes the result uninterpretable, and interpretability is the only defence you have when the failure mode is prolonged suppression. Gonadorelin is pointless alongside triptorelin, since the receptor is either flooded or desensitised. Degarelix achieves the same castration without a flare and is an alternative rather than a partner. In long-term depot use, the meaningful co-therapies are bone protection with calcium, vitamin D and sometimes a bisphosphonate or denosumab, plus attention to QT-prolonging drugs since androgen deprivation lengthens the QT interval on its own.

Against leuprolide, triptorelin is the same idea with a different position-6 substitution and comparable castration rates; the practical differences are formulation options and injection-site experience rather than pharmacology. Against degarelix, the difference is real and clinically important: degarelix is an antagonist and produces castration in three days with no flare, whereas triptorelin takes about three weeks and passes through a testosterone surge first, which is why antagonists are preferred when disease burden makes a flare dangerous. Against gonadorelin, triptorelin is the same molecule with one substitution that changes everything, and the two drugs sit at opposite ends of the same dose-duration curve. For the restart application specifically, triptorelin has a plausible mechanism, a handful of small studies and a very large amount of forum practice, and it should not be spoken of in the same register as its oncology indications, where the evidence is large and randomised.

$150–$700/month. Depot triptorelin in the US has typically run several hundred to over a thousand dollars per administration depending on formulation and payer, which works out to roughly 150 to 700 dollars a month amortised across a 1, 3 or 6 month product. Research-chemical 2 mg vials used for restart dosing are cheap - tens of dollars - and a single restart uses a fraction of one vial. Figures are indicative and were not verified in this session.

• ?The three-letter sequence given here is reconstructed from the D-Trp6 substitution described in the Core record rather than re-verified against a primary structural source in this session.
• ?The single-dose 100 mcg subcutaneous restart protocol has no adequate published trial. It rests on a small number of studies in men with anabolic-steroid-induced hypogonadism plus extensive off-label practice, and the dose was not validated against alternatives.
• ?Protein binding is listed as zero because the label states there is no significant plasma protein binding at clinically relevant concentrations; that is the label's wording rather than a measured percentage.
• ?The year of each registration study is not recorded in the label section retrieved, so those fields are null.
• ?Blood-brain barrier penetration is marked as no on the basis of peptide physicochemistry and the pituitary being outside the barrier, not on direct measurement.
• ?Cost figures are indicative and were not verified in this session.

• TRELSTAR (triptorelin pamoate for injectable suspension) - FDA prescribing information DailyMed / FDA

  Source of the pharmacokinetics and of all three registration study outcomes. The renal and hepatic impairment clearance figures in section 12.3 are the practically important part and are rarely quoted anywhere else.

• Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA, Journal of Clinical Endocrinology and Metabolism, 2018 · PMID 29562364

  The framework for managing hypogonadism properly, which is what the off-label restart crowd is attempting to shortcut.