An open-label, non-randomized, 2-arm, 2-period fixed sequence phase 1 study to evaluate the potential inhibition of nitisinone on cytochrome P450 2C9, 2D6, and 2E1 and the organic anion transporters OAT1 and OAT3 in healthy volunteers

This is an open-label, non-randomized, 2-arm, 2-period fixed-sequence drug-drug interaction study in a total of 36 (18 in each arm) male and female healthy volunteers.

The study consists of: Screening, Period 1 (substrates only), Period 2 (substrates + nitisinone) and Follow-up. In the screening period, subjects will be assessed for eligibility. Eligible subjects will be assigned to one of two treatment arms. In Arm A, the potential inhibition of nitisinone on CYP2C9, CYP2D6, and CYP2E1 will be investigated. In Arm B, the possible combined effect of nitisinone on the renal transporters OAT1 and OAT3 will be investigated.

In Period 1, the subjects will receive a single dose of a CYP cocktail of 3 substrates (Arm A) or an OAT1/OAT3 substrate (Arm B). Substrate plasma concentrations will be measured for determination of substrate PK; for up to 48 hours in Arm A and for 8 hours in Arm B.

During Period 2, the treatment and assessments will vary slightly between the 2 treatment arms. Nitisinone will be administered for 14 days, without co-administration of any substrate, in order to reach steady state and the recommended target plasma concentration, before the interaction with the substrates is studied.

In Arm A, Period 2, subjects will receive nitisinone for 16 consecutive days (14 days on nitisinone only and two days on nitisinone + substrate). Nitisinone steady state PK will be determined based on plasma and urine samples collected during one dosage interval at steady state, on the day before co-administration of the substrates. Nitisinone will then be administered together with the CYP substrates, and plasma samples for determination of their PK will be collected as in Period 1. There will be a final nitisinone dose on the day after substrate administration in order to maintain therapeutic levels throughout the 48-hour sampling period.

In Arm B, Period 2, subjects will receive nitisinone for 15 consecutive days (14 days on nitisinone only and one day on nitisinone + substrate). No nitisinone steady state PK characterization will be conducted in this arm. On the last treatment day, the subjects will receive nitisinone together with the OAT1/OAT3 substrate. This will be followed by 8 hours of blood sampling for determination of substrate PK.

Inclusion Criteria:

1. Healthy male and female volunteers, 18 - 55 years of age inclusive, who are judged by the investigator to be healthy on the basis of a pre-study physical examination, which includes clinical chemistry, hematology and urinalysis, vital signs (pulse and blood pressure), and ECG.

2. Female subject must be either:

   a. Of none childbearing potential: i. post-menopausal (defined as at least 1 year without any menstruation without an alternative medical cause) , prior to Screening, or ii. documented surgically sterile or status post hysterectomy (at least 1 month prior to Screening).

   b. Or, if of childbearing potential, i. must have a negative urine/serum pregnancy test at Screening, and ii. must be using highly effective methods of birth control [Acceptable forms of birth control include: 1) Placement of an intrauterine device (IUD) or intrauterine system (IUS). The devices must not release any hormones. (Note: The IUD must have a failure rate < 1 %) 2) the subject's male partner has undergone effective surgical sterilization before the female subject entered the clinical trial and he is the sole sexual partner of the female subject during the clinical trial. 3) Observe abstinence (acceptable only if it is the subject's usual lifestyle). ] (failure rate < 1% per year when used consistently and correctly) at least 3 months prior to Screening until 4 weeks after study termination in combination with an approved barrier method [Approved barrier methods of contraception include: condom (without spermicidal foam/gel/film/cream/suppository or fat- or oil-containing lubricants), or occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository.]. Women should be informed of the potential risks associated with becoming pregnant while enrolled.

3. Male subjects must agree to use a condom when having sexual intercourse with female partners of childbearing potential during treatment and up to 4 weeks after the last dose of study treatment.

4. Body weight 64 to 100 kg.

5. Body mass index (BMI) 18 - 30 kg/m2

6. Signed informed consent.

Exclusion Criteria:

1. Any medical condition which in the opinion of the investigator makes the subject unsuitable for inclusion.
2. Recent history or presence of clinically significant gastrointestinal, hepatic, renal, cardiovascular, hematological, metabolic, urological, pulmonary, neurological or psychiatric disorder.
3. History of hypoglycemia.
4. Current keratopathy, or other clinically relevant abnormalities, found by ophthalmologic slit-lamp examination.
5. Poor or ultra-rapid metabolism of CYP2D6 substrates confirmed by genotyping (exclusion criteria for Arm A only).
6. History of allergy, hypersensitivity or known contraindication to any of the drugs, or their excipients, used in this study.
7. History of sulfonamide allergy.
8. Continuous use of any non-topical medication within 1 month, over-the-counter preparations, herbal remedies , and all other medication within 14 days or less than 5 times the half-life of that medication, whichever is the longer, prior to first intake of an IMP.
9. Daily smoking > 10 cigarettes.
10. Daily consumption of more than 5 cups of coffee.
11. History of drug and/or alcohol abuse.
12. Positive drug screen or alcohol test.
13. Positive screens for HBsAg, anti-HCV, anti-HBc Ab, HepC, HIV 1 2 antibodies.
14. Pregnancy or breast feeding.
15. Female subjects using hormonal contraceptives.
16. Enrollment in another concurrent clinical study, or intake of an experimental drug, within 3 months prior to inclusion in this study.
17. Donation of more than 400 mL of blood within 90 days prior to drug administration or donation of more than 1.5 liters of blood in the 10 months prior to first intake of an IMP.
18. Foreseeable inability to cooperate with given instructions or study procedures.
19. Inability to give written informed consent or to comply fully with the protocol.
20. Vulnerable subjects, e.g., subjects kept in detention.
21. Soldiers, investigator, employees of the Sponsor or CRO.
22. Subject is not able to read, write and speak German.