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Follistim Pen vs. Conventional Syringe

Before the Follistim Pen and AQ cartridge were approved in the United States in 2004, the FDA required testing be done to ensure the new presentation was bioequivalent to the Follistim lyophilized powder1.

At the conclusion of this study, it was determined that the Follistim Pen delivered 18% more drug than the reconstituted lyophilized powder, delivered by conventional syringe. The authors of this study initially observed this difference by noticing that the Cmax or peak serum concentration for the pen was significantly higher than the powder. The only logical explanation for this pharmacokinetic difference was that the pen was actually delivering more drug than the conventional syringe. To prove this theory, the authors weighed the conventional syringe just before and after the recFSH injection, and showed that the actual injected amount of recFSH was 18% less than anticipated. This loss of drug was attributed to the void volume or dead space of the syringe, and losses while filling the syringe and/or removing excess air.

To avoid possible overstimulation and to make physicians aware of this drug delivering difference; the following dosing recommendations are given in the Follistim AQ package insert2:

Lyophilized recombinant FSH dosing in ampules or vials, using conventional syringe Follistim® AQ Cartridge dosing with the Follistim Pen®
75 IU 50 IU
150 IU 125 IU
225 IU 175 IU
300 IU 250 IU
375 IU 300 IU
450 IU 375 IU
*Each value represents an 18% difference rounded to the nearest 25 IU increment.

The authors of the above study point out that in clinical practice, the 18% extra drug being delivered with the Follistim Pen would not be noticed, especially since the dose would be individually titrated based on ovarian response. On the other hand, this 18% drug gain and the usage of similar or recommended doses from the Follistim AQ PI could significantly impact a patient’s ability to save money. In fact this same point was concluded by the authors of the following abstract, published in Fertility and Sterility in 2010:

Is it Possible to Distinguish a Difference in Response Between 200 IU and 225 IU of Follistim AQ Cartridges in Young Women Undergoing In VitroFertilization?.3

Despite the possible savings with the pen versus the conventional syringe process to deliver gonadotropins, patients and providers would also benefit from no mixing, no measuring, and the flexibility raising or lowering the dose by 25 IU increments, instead of the standard 75 IU.


1. Bioequivalence of subcutaneous injections of recombinant human follicle hormone (Puregon) by Pen-injector and syringe, Gerrit Voortman, Human Reproduction, vol 14 no. 7 pp. 1698-1702, 1999 http://www.healthbanks.com/PracticeCollateral/Upload/A93A2D08-AF45_Voortman%20Paper.pdf.

2. Follistim Package Insert: http://www.healthbanks.com/PracticeCollateral/Upload/AE4BEDCB-EBA8_New%20Follistim%20PI.pdf.

3. Is it Possible to Distinguish a Difference in Response Between 200 IU and 225 IU of Follistim AQ Cartridges in Young Women Undergoing In VitroFertilization? The Follistim AQ Study Group: M. Feinman, M. Jacobs,K. Doody, L. Barmat, and J. Stelling. http://www.healthbanks.com/PracticeCollateral/Upload/F5CF5CAE-5103_Comparison%20of%20Follistim%20200%20IU%20vs.%20225%20IU%20Abstract.pdf.

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