Based on the information provided, it appears you are inquiring about the effectiveness of sapropterin in managing symptoms over time. Sapropterin is a medication used to reduce symptoms in individuals with phenylketonuria (PKU), a genetic disorder that affects how the body processes an amino acid called phenylalanine [1].

According to the available information, ongoing sapropterin treatment has shown positive results in keeping symptoms at bay for some patients with PKU [2]. However, it is essential to note that the effectiveness of sapropterin can vary from person to person, and it may not entirely prevent symptoms in all cases [1].

Several factors can influence the drug's effectiveness, including the severity of the patient's PKU, the individual's age, and the timing of treatment initiation [1]. Regular monitoring of blood phenylalanine levels and adherence to a low-phenylalanine diet are crucial components of an effective PKU treatment plan, even when sapropterin is used [1].

In summary, ongoing sapropterin treatment has helped many individuals with PKU manage their symptoms. However, the drug's effectiveness can differ between patients, and it may not eliminate symptoms entirely. Regular monitoring and a low-phenylalanine diet are essential components of a comprehensive PKU treatment plan [1][2].

Sources:

1. [Genetics Home Reference. Phenylketonuria.](https://medlineplus.gov/genetics/condition/phenylketonuria/)
2. [DrugPatentWatch.com. Sapropterin Dihydrochloride (KUVAN).](https://www.drugpatentwatch.com/drugs/sapropterin-dihydrochloride)