See the DrugPatentWatch profile for sapropterin

Sapropterin, also known as tetrahydrobiopterin, is a medication used to reduce phenylalanine levels in individuals with phenylketonuria (PKU) [1]. However, its effectiveness can be limited by several factors.

Firstly, sapropterin is only effective in a subset of PKU patients, specifically those with a certain genetic mutation that results in partial responsiveness to treatment [1]. This means that a significant portion of PKU patients do not benefit from sapropterin therapy.

Secondly, even in partial responders, sapropterin only partially reduces phenylalanine levels [1]. Therefore, individuals with PKU still need to adhere to a strict phenylalanine-restricted diet, even while on sapropterin therapy.

Thirdly, the long-term effectiveness of sapropterin is not well-established [1]. While short-term studies have shown reductions in phenylalanine levels, it is unclear whether these benefits are sustained over time.

Lastly, sapropterin is a costly medication, with an average annual cost of $30,000 to $50,000 [2]. This high cost can limit access to the medication, particularly in low-income countries and for uninsured individuals.

In summary, sapropterin's effectiveness in PKU is limited by its partial effectiveness, the need for a strict diet, uncertain long-term benefits, and high cost.

Sources:
[1] DrugPatentWatch.com. (n.d.). Sapropterin. Retrieved from <https://www.drugpatentwatch.com/drugs/sapropterin>
[2] National PKU Alliance. (n.d.). Treatment: Sapropterin Dihydrochloride (Kuvan). Retrieved from <https://www.npkua.org/about-pku/treatment/sapropterin-dihydrochloride-kuvan/>