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Synthetic tetrahydrobiopterin (BH4)

Sapropterin dihydrochloride

Brand names: Kuvan

Sapropterin dihydrochloride is a synthetic form of tetrahydrobiopterin (BH4) used, alongside dietary management, to reduce blood phenylalanine in responsive patients with phenylketonuria or BH4 deficiency.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It acts as a cofactor for phenylalanine hydroxylase, enhancing residual enzyme activity in responsive patients so that phenylalanine is more effectively metabolised.

Prescribing in practice

  • It is only effective in patients shown to be responsive, and treatment must always be combined with continued phenylalanine-restricted dietary control under specialist supervision.
  • Blood phenylalanine must be monitored to confirm response and to avoid levels falling too low, which can itself be harmful.
  • It should be used within a specialist metabolic service, with dietary intake adjusted in response to monitoring.

Monitoring

Regularly monitor blood phenylalanine to assess responsiveness, guide dietary phenylalanine intake and ensure levels remain within the target range.

Counselling the patient

  • This medicine works together with your low-phenylalanine diet, not instead of it.
  • Regular blood tests are essential to keep phenylalanine in the right range.
  • Keep all specialist metabolic clinic appointments.

Evidence & guidelines

Sapropterin is an established adjunct in responsive phenylketonuria, used within specialist metabolic services per national commissioning guidance.

Reference: NICE HST7; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Pathways