Finally, there is an excellent study on down-regulation modeling. This paper has some good modeling graphs. I use 1,000-2,000 IU E3D now.
"The model we developed allows us to simulate arbitrary dosing schemes. The example we provide shows an informal way to obtain a maximum response while using the minimum amount of drug.
The simulated testosterone levels show that to reach a target testosterone concentration of 25 nmol/liter [~720 ng/dL], a dose of 1000 IU of rhCG every other 4 days would be sufficient. A higher 2500 or 5000 IU dose would produce a slightly higher response, but the highest dose will produce a lesser response according to the model. Clearly, the predicted pattern of decreased response at high doses and the pronounced rebound effect at treatment cessation is intriguing. The extrapolation to a clinical setting certainly deserves confirmation."
Gries JM, Munafo A, Porchet HC, Verotta D. Down-regulation models and modeling of testosterone production induced by recombinant human choriogonadotropin. J Pharmacol Exp Ther 1999;289(1):371-7. http://jpet.aspetjournals.org/content/289/1/371.full
Chorionic gonadotropin (CG) is a glycoprotein hormone, whose action is mediated by the luteinizing hormone/CG receptor. Testosterone concentrations from six pituitary-desensitized, healthy male volunteers were obtained after four different administrations of recombinant-human CG (rhCG). We present a modeling study to provide a possible explanation for the observations that increased exposure to rhCG induces higher and then lower testosterone concentrations and that marked rebound effects are observed at the end of repeated administration of rhCG. We used semimechanistic models (in which flexible functions represent unknown parts of the models) to identify the relationship of rhCG concentrations to the testosterone levels. Based on the results obtained with the semimechanistic models, different mechanistic down-regulation models were devised and tested. The final model uses a one-compartment model to describe the endogenous production rate of testosterone; rhCG affects the production rate with a mechanism consistent with a two-site binding site, with effect proportional to one-site bound concentration. The modeling results indicate that when rhCG concentration increases, the testosterone production rate increases to 45 times the baseline value. However, at an rhCG concentration of more than about 30 IU/liter, the production rate decreases. Simulations showed that both dose and dosing interval profoundly influence testosterone response to rhCG.