Sapropterin: prescribing information – dosing, contraindications, interactions, side effects

Kuvan is indicated for the treatment of hyperphenylalaninaemia (HPA) in adults and paediatric patients of all ages with phenylketonuria (PKU) who have been shown to be responsive to such treatment (see section 4.2).

Kuvan is also indicated for the treatment of hyperphenylalaninaemia (HPA) in adults and paediatric patients of all ages with tetrahydrobiopterin (BH4) deficiency who have been shown to be responsive to such treatment (see section 4.2).

Treatment with Kuvan must be initiated and supervised by a physician experienced in the treatment of PKU and BH4 deficiency.

Active management of dietary phenylalanine and overall protein intake while taking this medicinal product is required to ensure adequate control of blood phenylalanine levels and nutritional balance.

As HPA due to either PKU or BH4 deficiency is a chronic condition, once responsiveness is demonstrated, Kuvan is intended for long-term use (see section 5.1).

Posology

PKU
The starting dose of Kuvan in adult and paediatric patients with PKU is 10 mg/kg body weight once daily.
The dose is adjusted, usually between 5 and 20 mg/kg/day, to achieve and maintain adequate blood phenylalanine levels as defined by the physician.

BH4 deficiency
The starting dose of Kuvan in adult and paediatric patients with BH4 deficiency is 2 to 5 mg/kg body weight total daily dose. Doses may be adjusted up to a total of 20 mg/kg per day.

Kuvan is provided as 100 mg tablets. The calculated daily dose based on body weight should be rounded to the nearest multiple of 100. For instance, a calculated dose of 401 to 450 mg should be rounded down to 400 mg corresponding to 4 tablets. A calculated dose of 451 mg to 499 mg should be rounded up to 500 mg corresponding to 5 tablets.

Dose adjustment
Treatment with sapropterin may decrease blood phenylalanine levels below the desired therapeutic level.
Adjustment of the Kuvan dose or modification of dietary phenylalanine intake may be required to achieve and maintain blood phenylalanine levels within the desired therapeutic range.

Blood phenylalanine and tyrosine levels should be tested, particularly in the paediatric population, one to two weeks after each dose adjustment and monitored frequently thereafter, under the direction of the treating physician.

If inadequate control of blood phenylalanine levels is observed during treatment with Kuvan, the patient’s adherence to the prescribed treatment, and diet, should be reviewed before considering an adjustment of the dose of sapropterin.

Discontinuation of treatment should be done only under the supervision of a physician. More frequent monitoring may be required, as blood phenylalanine levels may increase. Dietary modification may be necessary to maintain blood phenylalanine levels within the desired therapeutic range.

Determination of response
It is of primary importance to initiate treatment as early as possible to avoid the appearance of non-reversible clinical manifestations of neurological disorders in paediatric patients and cognitive deficits and psychiatric disorders in adults due to sustained elevations of blood phenylalanine.

Response to this medicinal product is determined by a decrease in blood phenylalanine. Blood phenylalanine levels should be checked before administering Kuvan and after 1 week of use at the recommended starting dose. If an unsatisfactory reduction in blood phenylalanine levels is observed, then the dose can be increased weekly to a maximum of 20 mg/kg/day, with continued weekly monitoring of blood phenylalanine levels over a one month period. The dietary phenylalanine intake should be maintained at a constant level during this period.

A satisfactory response is defined as a ≥30 percent reduction in blood phenylalanine levels or attainment of the therapeutic blood phenylalanine goals defined for an individual patient by the treating physician. Patients who fail to achieve this level of response within the described one month test period should be considered non-responsive, these patients should not be treated with Kuvan and administration of Kuvan should be discontinued.

Once responsiveness to the medicinal product has been established, the dose may be adjusted within the range of 5 to 20 mg/kg/day according to response to therapy.

It is recommended that blood phenylalanine and tyrosine levels be tested one or two weeks after each dose adjustment and monitored frequently thereafter under the direction of the treating physician.
Patients treated with Kuvan must continue a restricted phenylalanine diet and undergo regular clinical assessment (such as monitoring of blood phenylalanine and tyrosine levels, nutrient intake, and psycho- motor development).

Special population
Elderly
Safety and efficacy of Kuvan in patients above 65 years of age have not been established. Caution must be exercised when prescribing to elderly patients.

Renal or hepatic impairment
Safety and efficacy of Kuvan in patients with renal or hepatic insufficiency have not been established.
Caution must be exercised when prescribing to such patients.

Paediatric population
The posology is the same in adults, children, and adolescents.

Method of administration

Kuvan tablets should be administered with a meal to increase the absorption.

For patients with PKU, Kuvan should be administered as a single daily dose, and at the same time each day preferably in the morning.

For patients with BH4 deficiency, divide the total daily dose into 2 or 3 administrations, distributed over the day.

Patients should be advised not to swallow the desiccant capsule found in the bottle.

The prescribed number of tablets should be placed in a glass or cup of water and stirred until dissolved. It may take a few minutes for the tablets to dissolve. To make the tablets dissolve faster they can be crushed.
Small particles may be visible in the solution and will not affect the effectiveness of the medicinal product.
The solution should be drunk within 15 to 20 minutes.

Patients above 20 kg body weight
The prescribed number of tablets should be placed in a glass or cup with 120 to 240 ml of water and stirred until dissolved.

Children up to 20 kg body weight
The measuring devices required for dosing in children up to 20 kg body weight (i.e. cup with graduations at 20, 40, 60, 80 ml; 10 ml and 20 ml oral syringes with graduation at 1 ml divisions) are not included in the Kuvan pack. These devices are supplied to the specialised paediatric centers for inborn errors of metabolism to be provided to the caregivers of the patients.

Depending on the dose (in mg/kg/day) the appropriate number of tablets should be dissolved in a volume of water as depicted in Tables 1-4, whereby the volume of the solution to be administered is calculated according to the prescribed total daily dose. The prescribed number of tablets for a 2, 5, 10 and 20 mg/kg/day dose should be placed in a cup (that shows the appropriate graduation markings at 20, 40, 60 and 80 ml) with the amount of water as depicted in Tables 1-4 and stirred until dissolved.

If only a portion of this solution needs to be administered, an oral syringe should be used to withdraw the volume of solution to be administered. The solution may then be transferred to another cup for administration of the medicinal product. For small infants an oral syringe can be used. A 10 ml oral syringe should be used for administration of volumes of ≤10 ml and a 20 ml oral syringe for administration of volumes of >10 ml.

Table 1: 2 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of tablets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 20 minutes for tablet solution.

Table 2: 5 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of tablets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 20 minutes for tablet solution.

Table 3: 10 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of tablets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 20 minutes for tablet solution.

Table 4: 20 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of tablets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 20 minutes for tablet solution.

For cleaning, the plunger should be removed from the barrel of the oral syringe. Both parts of the oral syringe and the cup should be washed with warm water and air dry. When the oral syringe is dry, the plunger should be put back into the barrel. The oral syringe and the cup should be stored for next use.

Treatment with Kuvan must be initiated and supervised by a physician experienced in the treatment of PKU and BH4 deficiency.

Active management of dietary phenylalanine and overall protein intake while taking this medicinal product is required to ensure adequate control of blood phenylalanine levels and nutritional balance.

As HPA due to either PKU or BH4 deficiency is a chronic condition, once responsiveness is demonstrated, Kuvan is intended for long-term use (see section 5.1).

Posology

PKU
The starting dose of Kuvan in adult and paediatric patients with PKU is 10 mg/kg body weight once daily.
The dose is adjusted, usually between 5 and 20 mg/kg/day, to achieve and maintain adequate blood phenylalanine levels as defined by the physician.

BH4 deficiency
The starting dose of Kuvan in adult and paediatric patients with BH4 deficiency is 2 to 5 mg/kg body weight total daily dose. Doses may be adjusted up to a total of 20 mg/kg per day.

For patients above 20 kg body weight, the calculated daily dose based on body weight should be rounded to the nearest multiple of 100 mg.

Dose adjustment
Treatment with sapropterin may decrease blood phenylalanine levels below the desired therapeutic level.
Adjustment of the Kuvan dose or modification of dietary phenylalanine intake may be required to achieve and maintain blood phenylalanine levels within the desired therapeutic range.

Blood phenylalanine and tyrosine levels should be tested, particularly in the paediatric population, one to two weeks after each dose adjustment and monitored frequently thereafter, under the direction of the treating physician.

If inadequate control of blood phenylalanine levels is observed during treatment with Kuvan, the patient’s adherence to the prescribed treatment, and diet, should be reviewed before considering an adjustment of the dose of sapropterin.

Discontinuation of treatment should be done only under the supervision of a physician. More frequent monitoring may be required, as blood phenylalanine levels may increase. Dietary modification may be necessary to maintain blood phenylalanine levels within the desired therapeutic range.

Determination of response
It is of primary importance to initiate treatment as early as possible to avoid the appearance of non-reversible clinical manifestations of neurological disorders in paediatric patients and cognitive deficits and psychiatric disorders in adults due to sustained elevations of blood phenylalanine.

Response to this medicinal product is determined by a decrease in blood phenylalanine. Blood phenylalanine levels should be checked before administering Kuvan and after 1 week of use at the recommended starting dose. If an unsatisfactory reduction in blood phenylalanine levels is observed, then the dose can be increased weekly to a maximum of 20 mg/kg/day, with continued weekly monitoring of blood phenylalanine levels over a one month period. The dietary phenylalanine intake should be maintained at a constant level during this period.

A satisfactory response is defined as a ≥30 percent reduction in blood phenylalanine levels or attainment of the therapeutic blood phenylalanine goals defined for an individual patient by the treating physician. Patients who fail to achieve this level of response within the described one month test period should be considered non-responsive, these patients should not be treated with Kuvan and administration of Kuvan should be discontinued.

Once responsiveness to the medicinal product has been established, the dose may be adjusted within the range of 5 to 20 mg/kg/day according to response to therapy.

It is recommended that blood phenylalanine and tyrosine levels be tested one or two weeks after each dose adjustment and monitored frequently thereafter under the direction of the treating physician.
Patients treated with Kuvan must continue a restricted phenylalanine diet and undergo regular clinical assessment (such as monitoring of blood phenylalanine and tyrosine levels, nutrient intake, and psycho-motor development).

Special population
Elderly
Safety and efficacy of Kuvan in patients above 65 years of age have not been established. Caution must be exercised when prescribing to elderly patients.

Renal or hepatic impairment
Safety and efficacy of Kuvan in patients with renal or hepatic insufficiency have not been established.
Caution must be exercised when prescribing to such patients.

Paediatric population
The posology is the same in adults, children and adolescents.

Method of administration

Kuvan should be administered with a meal, to increase the absorption.

For patients with PKU, Kuvan should be administered as a single daily dose, and at the same time each day preferably in the morning.

For patients with BH4 deficiency, divide the total daily dose into 2 or 3 administrations, distributed over the day.

The solution should be consumed within 30 minutes of initial dissolution. Unused solution should be discarded after administration.

Patients above 20 kg body weight
The contents of the sachet(s) should be placed in 120 to 240 ml of water and stirred until dissolved.

Children up to 20 kg body weight (use only 100 mg powder sachet(s))
The measuring devices required for dosing in children up to 20 kg body weight (i.e. cup with graduations at 20, 40, 60, 80 ml; 10 ml and 20 ml oral syringes with graduation at 1 ml divisions) are not included in the Kuvan pack. These devices are supplied to the specialised paediatric centers for inborn errors of metabolism to be provided to the caregivers of the patients.

The appropriate number of 100 mg sachet(s) should be dissolved in a volume of water depicted in Tables 1-4 based on the prescribed total daily dose.

If only a portion of this solution needs to be administered, an oral syringe should be used to withdraw the volume of solution to be administered. The solution may then be transferred to another cup for administration of the medicinal product. For small infants, an oral syringe can be used. A 10 ml oral syringe should be used for administration of volumes of ≤10 ml and a 20 ml oral syringe for administration of volumes of >10 ml.

Table 1: 2 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of sachets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 30 minutes for powder solution.

Table 2: 5 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of sachets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 30 minutes for powder solution.

Table 3: 10 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of sachets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 30 minutes for powder solution.

Table 4: 20 mg/kg per day dosing table for children weighing up to 20 kg

Weight (kg)
Total dose
(mg/day)
Number of sachets to be dissolved
(100 mg strength only)
Volume of dissolution
(ml)
Volume of solution to be administered
(ml)*
*Reflects volume for total daily dose.
Discard unused solution within 30 minutes for powder solution.

For cleaning, the plunger should be removed from the barrel of the oral syringe. Both parts of the oral syringe and the cup should be washed with warm water and air dry. When the oral syringe is dry, the plunger should be put back into the barrel. The oral syringe and the cup should be stored for next use.

Hypersensitivity to the active substance or to any of the excipients listed in section 6.1.

Summary of the safety profile

Approximately 35% of the 579 patients aged 4 years and over who received treatment with sapropterin dihydrochloride (5 to 20 mg/kg/day) in the clinical trials for Kuvan experienced adverse reactions. The most commonly reported adverse reactions are headache and rhinorrhoea.

In a further clinical trial, approximately 30% of the 27 children aged below 4 years who received treatment with sapropterin dihydrochloride (10 or 20 mg/kg/day) experienced adverse reactions. The most commonly reported adverse reactions are “amino acid level decreased” (hypophenylalaninaemia), vomiting and rhinitis.

Tabulated list of adverse reactions

In the pivotal clinical trials and in the post-marketing experience for Kuvan, the following adverse reactions have been identified.

The following definitions apply to the frequency terminology used hereafter:

very common (≥1/10), common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), rare (≥1/10,000 to <1/1,000), very rare (<1/10,000), not known (cannot be estimated from available data)

Within each frequency grouping, adverse reactions are presented in order of decreasing seriousness.

Immune system disorders
Not known:
Hypersensitivity reactions (including serious allergic reactions) and rash

Metabolism and nutrition disorders
Common:
Hypophenylalaninaemia

Nervous system disorders
Very common:
Headache

Respiratory, thoracic and mediastinal disorders
Very common:
Rhinorrhoea
Common:
Pharyngolaryngeal pain, nasal congestion, cough

Gastrointestinal disorders
Common:
Diarrhoea, vomiting, abdominal pain, dyspepsia, nausea
Not known:
Gastritis, oesophagitis

Paediatric population
Frequency, type and severity of adverse reactions in children were essentially similar to those in adults.

Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the national reporting system listed in Appendix V.

Summary of the safety profile

Approximately 35% of the 579 patients aged 4 years and over who received treatment with sapropterin dihydrochloride (5 to 20 mg/kg/day) in the clinical trials for Kuvan experienced adverse reactions. The most commonly reported adverse reactions are headache and rhinorrhoea.

In a further clinical trial, approximately 30% of the 27 children aged below 4 years who received treatment with sapropterin dihydrochloride (10 or 20 mg/kg/day) experienced adverse reactions. The most commonly reported adverse reactions are “amino acid level decreased” (hypophenylalaninaemia), vomiting and rhinitis.

Tabulated list of adverse reactions

In the pivotal clinical trials and in the post-marketing experience for Kuvan, the following adverse reactions have been identified.

The following definitions apply to the frequency terminology used hereafter:
very common (≥1/10), common (≥1/100 to <1/10), uncommon (≥1/1,000 to <1/100), rare (≥1/10,000 to <1/1,000), very rare (<1/10,000), not known (cannot be estimated from available data).

Within each frequency grouping, adverse reactions are presented in order of decreasing seriousness.

Immune system disorders
Not known:
Hypersensitivity reactions (including serious allergic reactions) and rash

Metabolism and nutrition disorders
Common:
Hypophenylalaninaemia

Nervous system disorders
Very common:
Headache

Respiratory, thoracic and mediastinal disorders
Very common:
Rhinorrhoea
Common:
Pharyngolaryngeal pain, nasal congestion, cough

Gastrointestinal disorders
Common:
Diarrhoea, vomiting, abdominal pain, dyspepsia, nausea
Not known:
Gastritis, oesophagitis

Paediatric population
Frequency, type and severity of adverse reactions in children were essentially similar to those in adults.

Reporting of suspected adverse reactions
Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the national reporting system listed in Appendix V.

Dietary intake

Patients treated with Kuvan must continue a restricted phenylalanine diet and undergo regular clinical assessment (such as monitoring of blood phenylalanine and tyrosine levels, nutrient intake, and psycho- motor development).

Low blood phenylalanine and tyrosine levels

Sustained or recurrent dysfunction in the phenylalanine-tyrosine-dihydroxy-L-phenylalanine (DOPA) metabolic pathway can result in deficient body protein and neurotransmitter synthesis. Prolonged exposure to low blood phenylalanine and tyrosine levels during infancy has been associated with impaired neurodevelopmental outcome. Active management of dietary phenylalanine and overall protein intake while taking Kuvan is required to ensure adequate control of blood phenylalanine and tyrosine levels and nutritional balance.

Health disturbances

Consultation with a physician is recommended during illness as blood phenylalanine levels may increase.

Convulsions disorders

Caution should be exercised when prescribing Kuvan to patients receiving treatment with levodopa. Cases of convulsion, exacerbation of convulsion, increased excitability and irritability have been observed during co- administration of levodopa and sapropterin in BH4-deficient patients (see section 4.5).

Discontinuation of treatment

Rebound, as defined by an increase in blood phenylalanine levels above pre-treatment levels, may occur upon cessation of treatment.

Sodium content

This medicinal product contains less than 1 mmol sodium (23 mg) per tablet, that is to say essentially ‘sodium-free’.

Dietary intake

Patients treated with Kuvan must continue a restricted phenylalanine diet and undergo regular clinical assessment (such as monitoring of blood phenylalanine and tyrosine levels, nutrient intake, and psycho- motor development).

Low blood phenylalanine and tyrosine levels

Sustained or recurrent dysfunction in the phenylalanine-tyrosine-dihydroxy-L-phenylalanine (DOPA) metabolic pathway can result in deficient body protein and neurotransmitter synthesis. Prolonged exposure to low blood phenylalanine and tyrosine levels during infancy has been associated with impaired neurodevelopmental outcome. Active management of dietary phenylalanine and overall protein intake while taking Kuvan is required to ensure adequate control of blood phenylalanine and tyrosine levels and nutritional balance.

Health disturbances

Consultation with a physician is recommended during illness as blood phenylalanine levels may increase.

Convulsions disorders

Caution should be exercised when prescribing Kuvan to patients receiving treatment with levodopa. Cases of convulsion, exacerbation of convulsion, increased excitability and irritability have been observed during co- administration of levodopa and sapropterin in BH4-deficient patients (see section 4.5).

Discontinuation of treatment

Rebound, as defined by an increase in blood phenylalanine levels above pre-treatment levels, may occur upon cessation of treatment.

Potassium content

Kuvan 100 mg powder for oral solution
This medicinal product contains 0.3 mmol (12.6 mg) potassium per sachet. To be taken into consideration by patients with reduced kidney function or patients on a controlled potassium diet.

Kuvan 500 mg powder for oral solution
This medicinal product contains 1.6 mmol (62.7 mg) potassium per sachet. To be taken into consideration by patients with reduced kidney function or patients on a controlled potassium diet.

Although concomitant administration of inhibitors of dihydrofolate reductase (e.g. methotrexate, trimethoprim) has not been studied, such medicinal products may interfere with BH4 metabolism. Caution is recommended when using such medicinal products while taking Kuvan.

BH4 is a cofactor for nitric oxide synthetase. Caution is recommended during concomitant use of Kuvan with all medicinal products that cause vasodilation, including those administered topically, by affecting nitric oxide (NO) metabolism or action including classical NO donors (e.g. glyceryl trinitrate (GTN), isosorbide dinitrate (ISDN), sodium nitroprusside (SNP), molsidomin), phosphodiesterase type 5 (PDE-5) inhibitors and minoxidil.

Caution should be exercised when prescribing Kuvan to patients receiving treatment with levodopa. Cases of convulsion, exacerbation of convulsion, increased excitability and irritability have been observed during co- administration of levodopa and sapropterin in BH4-deficient patients.

Pregnancy

There is a limited amount of data from the use of sapropterin in pregnant women, including data from the Kuvan registries KAMPER and PKUDOS. The data are too limited to conclude on malformative or foeto- neonatal toxicity. Animal studies do not indicate direct or indirect harmful effects with respect to reproductive toxicity (see section 5.3).

Uncontrolled maternal phenylalanine levels are associated with a high incidence of intellectual impairment, microcephaly, cardiac anomalies, growth restriction and facial dysmorphism in the offspring. Maternal blood phenylalanine levels must therefore be strictly controlled before and during pregnancy. Physician-supervised restriction of dietary phenylalanine intake prior to and throughout pregnancy is the first choice of treatment in this patient group.

The use of Kuvan should be considered only if strict dietary management does not adequately reduce blood phenylalanine levels. Caution must be exercised when prescribing sapropterin to pregnant women.

Breast-feeding

It is not known whether sapropterin or its metabolites are excreted in human breast milk. Kuvan should not be used during breast-feeding.

Fertility

In preclinical studies, no effects of sapropterin on male and female fertility were observed.

Pregnancy

There is a limited amount of data from the use of sapropterin in pregnant women, including data from the Kuvan registries KAMPER and PKUDOS. The data are too limited to conclude on malformative or foeto- neonatal toxicity. Animal studies do not indicate direct or indirect harmful effects with respect to reproductive toxicity (see section 5.3).

Uncontrolled maternal phenylalanine levels are associated with a high incidence of intellectual impairment, microcephaly, cardiac anomalies, growth restriction and facial dysmorphism in the offspring. Maternal blood phenylalanine levels must therefore be strictly controlled before and during pregnancy. . Physician-supervised restriction of dietary phenylalanine intake prior to and throughout pregnancy is the first choice of treatment in this patient group.

The use of Kuvan should be considered only if strict dietary management does not adequately reduce blood phenylalanine levels. Caution must be exercised when prescribing sapropterin to pregnant women.

Breast-feeding

It is not known whether sapropterin or its metabolites are excreted in human breast milk. Kuvan should not be used during breast-feeding.

Fertility

In preclinical studies, no effects of sapropterin on male and female fertility were observed.

Kuvan has no or negligible influence on the ability to drive and use machines.

Headache and dizziness have been reported after the administration of sapropterin dihydrochloride above the recommended maximum dose of 20 mg/kg/day. Treatment of overdose should be directed to symptoms. A shortening of the QT interval (-8.32 msec) was observed in a study with a single supra-therapeutic dose of 100 mg/kg (5 times the maximum recommended dose); this should be taken into consideration in managing patients who have a pre-existing shortened QT interval (e.g. patients with familial short QT syndrome).

5.
PHARMACOLOGICAL PROPERTIES

Pharmacotherapeutic group: Other alimentary tract and metabolism products, Various alimentary tract and metabolism products, ATC code: A16AX07

Mechanism of action

Hyperphenylalaninaemia (HPA) is diagnosed as an abnormal elevation in blood phenylalanine levels and is usually caused by autosomal recessive mutations in the genes encoding for phenylalanine hydroxylase enzyme (in the case of phenylketonuria, PKU) or for the enzymes involved in 6R-tetrahydrobiopterin (6R-BH4) biosynthesis or regeneration (in the case of BH4 deficiency). BH4 deficiency is a group of disorders arising from mutations or deletions in the genes encoding for one of the five enzymes involved in the biosynthesis or recycling of BH4. In both cases, phenylalanine cannot be effectively transformed into the amino acid tyrosine, leading to increased phenylalanine levels in the blood.

Sapropterin is a synthetic version of the naturally occurring 6R-BH4, which is a cofactor of the hydroxylases for phenylalanine, tyrosine and tryptophan.

The rationale for administration of Kuvan in patients with BH4-responsive PKU is to enhance the activity of the defective phenylalanine hydroxylase and thereby increase or restore the oxidative metabolism of phenylalanine sufficient to reduce or maintain blood phenylalanine levels, prevent or decrease further phenylalanine accumulation, and increase tolerance to phenylalanine intake in the diet. The rationale for administration of Kuvan in patients with BH4 Deficiency is to replace the deficient levels of BH4, thereby restoring the activity of phenylalanine hydroxylase.

Clinical efficacy

The Phase III clinical development program for Kuvan included 2, randomised placebo-controlled studies in patients with PKU. The results of these studies demonstrate the efficacy of Kuvan to reduce blood phenylalanine levels and to increase dietary phenylalanine tolerance.

In 88 subjects with poorly controlled PKU who had elevated blood phenylalanine levels at screening, sapropterin dihydrochloride 10 mg/kg/day significantly reduced blood phenylalanine levels as compared to placebo. The baseline blood phenylalanine levels for the Kuvan-treated group and the placebo group were similar, with mean ± SD baseline blood phenylalanine levels of 843 ± 300 μmol/l and 888 ± 323 μmol/l, respectively. The mean ± SD decrease from baseline in blood phenylalanine levels at the end of the 6 week study period was 236 ± 257 μmol/l for the sapropterin treated group (n=41) as compared to an increase of 2.9 ± 240 μmol/l for the placebo group (n=47) (p<0.001). For patients with baseline blood phenylalanine levels ≥600 µmol/l, 41.9% (13/31) of those treated with sapropterin and 13.2% (5/38) of those treated with placebo had blood phenylalanine levels < 600 µmol/l at the end of the 6-week study period (p=0.012).

Absorption

Sapropterin is absorbed after oral administration of the dissolved tablet, and the maximum blood concentration (Cmax) is achieved 3 to 4 hours after dosing in the fasted state. The rate and extent of absorption of sapropterin is influenced by food. The absorption of sapropterin is higher after a high-fat, high-calorie meal as compared to fasting, resulting, in average, in 40-85% higher maximum blood concentrations achieved 4 to 5 hours after administration.

Absolute bioavailability or bioavailability for humans after oral administration is not known.

Distribution

In non-clinical studies, sapropterin was primarily distributed to the kidneys, adrenal glands, and liver as assessed by levels of total and reduced biopterin concentrations. In rats, following intravenous radiolabeled sapropterin administration, radioactivity was found to distribute in foetuses. Excretion of total biopterin in milk was demonstrated in rats by intravenous route. No increase in total biopterin concentrations in either foetuses or milk was observed in rats after oral administration of 10 mg/kg sapropterin dihydrochloride.

Biotransformation

Sapropterin dihydrochloride is primarily metabolised in the liver to dihydrobiopterin and biopterin. Since sapropterin dihydrochloride is a synthetic version of the naturally occurring 6R-BH4, it can be reasonably anticipated to undergo the same metabolism, including 6R-BH4 regeneration.

Elimination

Following intravenous administration in rats, sapropterin dihydrochloride is mainly excreted in the urine.
Following oral administration it is mainly eliminated through faeces while a small proportion is excreted in urine.

Population pharmacokinetics

Population pharmacokinetic analysis of sapropterin including patients from birth to 49 years of age showed that body weight is the only covariate substantially affecting clearance or volume of distribution.

Drug interactions

In vitro studies