A pharmaceutical preparation containing sapropterin hydrochloride can be used to administer sapropterin hydrochloride, an effective therapeutic agent for the treatment of tetrahydrobiopterin-responsive hyperphenylalaninemia, to patients of a wide range of ages, ranging from infants to adults, in a single preparation. One specific example is a pharmaceutical preparation for the treatment of BH4-responsive hyperphenylalaninemia provided in the form of granule, fine granule, or dry syrup, comprising sapropterin hydrochloride as an active ingredient a flavoring agent a coloring agent which is stable to acid and oxidation and ascorbic acid or L-cysteine hydrochloride as a stabilizer, wherein the preparation has a moisture content (weight loss on drying) of 0.9% or less. Also provided is the pharmaceutical preparation in which the amount of sapropterin hydrochloride is from 2.5 to 20 wt%.
