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By mouth |
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Biological half-life | 4 hours (healthy adults) 6–7 hours (PKU patients) |
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Formula | C9H15N5O3 |
Molar mass | 241.25 g/mol |
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Tetrahydrobiopterin (BH4, THB), also known as sapropterin, is a naturally occurring essential cofactor of the three aromatic amino acid hydroxylase enzymes, used in the degradation of amino acid phenylalanine and in the biosynthesis of the neurotransmitters serotonin (5-hydroxytryptamine, 5-HT), melatonin, dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), and is a cofactor for the production of nitric oxide (NO) by the nitric oxide synthases. Chemically, its structure is that of a reduced pteridine derivative.
Tetrahydrobiopterin is available as a tablet for oral administration in the form of tetrahydrobiopterin dihydrochloride (BH4*2HCL). BH4*2HCL is FDA approved under the trade name Kuvan. The typical cost of treating a patient with Kuvan is $100,000 per year.BioMarin holds the patent for Kuvan until at least 2024, but Par Pharmaceutical has a right to produce a generic version by 2020.
BH4*2HCL is indicated in tetrahydrobiopterin deficiency caused by GTPCH deficiency or PTPS deficiency. Also, BH4*2HCL is FDA approved for use in phenylketonuria, along with dietary measures. Most people with phenylketonuria, however, have little or no benefit of BH4*2HCL.
The most common adverse effects, observed in more than 10% of patients, include headache and a running or obstructed nose. Diarrhea and vomiting are also relatively common, seen in at least 1% of patients.
No interaction studies have been conducted. Because of its mechanism, tetrahydrobiopterin might interact with dihydrofolate reductase inhibitors like methotrexate and trimethoprim, and NO-enhancing drugs like nitroglycerin, molsidomine, minoxidil, and PDE5 inhibitors. Combination of tetrahydrobiopterin with levodopa can lead to increased excitability.