Oral administration of Bremelanotide (PT-141) results in minimal plasma absorption in beagle dogs
Background
Bremelanotide (Vyleesi®), a cyclic heptapeptide, is currently approved for the subcutaneous treatment of premenopausal hypoactive sexual desire disorder (HSDD). Subcutaneous injection, while effective, can be a barrier to patient adherence and convenience. Developing alternative, less invasive routes of administration, such as an oral formulation, is a key goal to improve patient experience and potentially broaden the therapeutic application of this peptide. However, the oral bioavailability of peptides is notoriously low due to enzymatic degradation in the gastrointestinal tract and poor absorption across the intestinal wall. To evaluate the feasibility of an oral route for bremelanotide, a highly sensitive analytical method is required to detect the very low plasma concentrations that are expected.
Study Design
Researchers developed and validated an ultra-sensitive UHPLC-MS/MS assay to quantify bremelanotide in plasma. The assay was validated according to US Food and Drug Administration (FDA) and European Medicines Agency (EMA) guidelines, using 100 μL of beagle dog plasma. Bremelanotide was isolated from the plasma via protein precipitation. This newly established assay was then applied to determine the plasma pharmacokinetics of bremelanotide after it was administered orally to beagle dogs. The primary endpoint was to measure the resulting plasma concentrations of the peptide to assess its oral absorption.
Results
The new UHPLC-MS/MS assay demonstrated exceptional sensitivity and reliability. The lower limit of quantification (LLOQ) was established at 10 pg/mL (9.8 pM). The calibrated concentration range of 10-10,000 pg/mL was linear, with correlation coefficients greater than 0.99. Within this range, interday and intraday accuracy was 88.9-100.0%, with precision better than 8%. At the LLOQ, accuracy was 93.6-100.8% with precision better than 11%. A dilution QC test confirmed the assay could accurately quantify samples diluted 10-fold, extending its effective range up to 100,000 pg/mL. When this highly sensitive assay was applied to plasma samples from beagle dogs after oral administration of bremelanotide, the results were definitive:
The quantification of bremelanotide plasma concentrations...indicated minimal oral absorption.
This finding suggests that a simple oral formulation of bremelanotide is not a viable route of administration due to extremely poor bioavailability.
Key Findings
- A new UHPLC-MS/MS assay for bremelanotide has a lower limit of quantification (LLOQ) of 10 pg/mL.
- The assay showed high interday and intraday accuracy (88.9-100.0%) and precision (<8%).
- Accuracy at the LLOQ was 93.6-100.8% with precision <11%.
- Application of the assay to plasma from beagle dogs indicated minimal oral absorption of bremelanotide.
Why It Matters
This research provides critical data for the development of alternative bremelanotide formulations, indicating that standard oral administration is likely ineffective. For users or developers, this strongly suggests that overcoming the oral absorption barrier would require advanced drug delivery technologies, such as permeation enhancers or protective coatings, rather than simple encapsulation. The study effectively closes the door on a simple pill form of PT-141. The practical takeaway is that subcutaneous injection remains the only validated and effective route of administration for achieving therapeutic plasma levels of bremelanotide. This work also provides a valuable, ultra-sensitive analytical tool (UHPLC-MS/MS assay) that can be used in future pharmacokinetic studies for bremelanotide, regardless of the administration route, enabling precise measurement even at very low picomolar concentrations.
TitrateLab articles covering PT-141
Written by TitrateLab, separately from the study summarized above.
bremelanotide
pt-141
pharmacokinetics
oral administration
bioavailability
animal study
