Sapropterin, a drug used to reduce elevated phenylalanine (Phe) levels in the blood of individuals with phenylketonuria (PKU), has been shown to modify biomarker levels, although it may not be characterized as rapid [1]. PKU is a genetic disorder that affects the body's ability to break down Phe, an amino acid found in proteins [1].

Clinical studies have demonstrated that sapropterin can lead to a significant decrease in Phe levels in both adult and pediatric PKU patients [1][2]. However, the term "rapid" is subjective and may vary depending on the context. While sapropterin can effectively lower Phe levels over time, it does not provide an immediate reduction [1].

According to DrugPatentWatch.com, sapropterin's patent expired in 2019, which may lead to the introduction of generic versions of the drug [3]. This could increase accessibility and affordability for PKU patients, contributing to better management of their condition and Phe levels.

In summary, sapropterin can modify biomarker levels in PKU patients by decreasing Phe levels, but it should not be considered a rapid modification [1][2]. The drug's patent expiration in 2019 may have implications for PKU patients regarding accessibility and affordability [3].

Sources:
[1] "Sapropterin dihydrochloride." National Center for Biotechnology Information, U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/compound/Sapropterin-dihydrochloride.
[2] Burton, B. K., et al. "Sapropterin dihydrochloride for the management of phenylketonuria: a systematic review." Orphanet Journal of Rare Diseases, BioMed Central, 11 Jan. 2017, oarjournal.biomedcentral.com/articles/10.1186/s13023-016-0525-z.
[3] "Sapropterin Dihydrochloride." DrugPatentWatch, drugpatentwatch.com/drugs/sapropterin-dihydrochloride.