It is the aim of the study to investigate the functioning of a drug delivery system (drug-rich particles forming hot-melt extruded amorphous solid dispersions) with respect to mechanisms of bioavailability of poorly soluble drug substances.

Poor drug solubility, and therefore low bioavailability, remains a problem in drug development that causes many drug candidates to drop out during drug development. Bioavailability is linked to drug solubility and intestinal permeability. A promising method to increase drug solubility, and therefore bioavailability, is the formulation of the drug as hot-melt extruded amorphous solid dispersion drug delivery systems, which have been shown to potentially increase in vivo and clinical bioavailability.The mechanisms that lead to increased bioavailability are not understood completely.

In this study, investigators investigate the role of amorphous solid dispersions and thereof generated drug-rich particles on bioavailability and their in vivo behaviour. Investigators do so by administering the delivery system at different stages in the process of drug availability.

Primary objectives are the pharmacokinetic analysis of a model formulation using efavirenz as model drug tracer in human.

• Comparison of pharmacokinetic parameters such as relative bioavailability and further parameters derived from pharmacokinetic analysis and corresponding interpatient variabilities.
• Mechanistic analysis of pharmacokinetic data, such as determination of in vivo dissolution from the solid formulation (study product 1) to drug rich particles (study product 2) using numerical deconvolution or analysis of the effect of drug rich particles on the absorption rate of Efavirenz in comparison to the solution of Efavirenz (study product 3).

Secondary objectives are the comparison of obtained pharmacokinetic profiles to existing data of a conventional formulation with respect to:

• Comparison of pharmacokinetic parameters such as relative bioavailability and further parameters derived from pharmacokinetic analysis and corresponding interpatient variabilities.
• Extrapolation investigation from in vitro to in vivo data.

Safety objectives are the recording of any side effects or tolerability issues of the investigational drug delivery system.

Inclusion Criteria:

• Full mental and legal capacity, ability and willingness to understand and comply to study interventions and restrictions and to communicate with study personnel.
• Informed Consent, documented by signature (Informed Consent Form).
• Physically and mentally healthy male participants, age of 18 to 50 years.
• Body mass index (BMI) of 18.0 to 29.9 kg/m2, systolic blood pressure (SBP) 100-145 mmHg, diastolic blood pressure (DBP) 50- 90 mmHg and heart rate (HR) 45-90 bpm, measured on the leading arm, after 5 minutes in supine position, Hemoglobin ≥ 11 g/dl at screening.
• Normal physical examination, vital signs, laboratory workup (clinical chemistry and hematology), and electrocardiogram (ECG) (in opinion of the principal investigator).
• Normal renal and liver function based on blood tests (in opinion of the investigator).
• Medical history that is in line with the eligibility criteria. (in opinion of the investigator).
• No other conditions or circumstances that might compromise compliance with the study protocol or the quality of retrieved data (in opinion of the investigator).

Exclusion Criteria:

• Any acute or chronic illness or other clinically relevant findings at screening.
• Any physical or mental disorder or circumstance at present or in medical history that could interfere with the participant's safety during the clinical trial or with the study objectives.
• Any regular drug treatment within the last two weeks or planned for the time of the study (exceptions possible in opinion of the investigator).
• At presence of irregular drug treatment before the study, planned for the time of the study or irregular/regular substitution of endogenous substances, minerals, or trace elements, the investigator decides on exclusion on an individual basis valuing the safety of the participant and the quality of retrieved data (e.g. interactions with Efavirenz). For minor to moderate painful conditions, such as headaches or abdominal discomfort, paracetamol up to 1 g every 6 hours is acceptable.
• Any intake of a substance known to induce or inhibit drug metabolizing enzymes or transport system enzymes relevant for Efavirenz (CYP 2B6 and CYP 3A4) within a period of less than 10 times the respective elimination half-life.
• Vaccination (active or passive) ≤ one month before screening.
• Presence or history of allergies (except for mild forms of hay fever).
• History of hypersensitivity reactions to medication.
• History or presence of eating disorders.
• Presence of contraindications to treatment with Efavirenz, namely less than 40 kg body weight, co-medication with voriconazole, paritaprevir, ritonavir, dasabuvir, simeprevir, and hypericum perforatum.any co-medication (also plant products), or any liver disease.
• Presence of warnings concerning the treatment with Efavirenz, namely severe skin irritations in the medical history, psychiatric symptoms in the medical history, convulsions in the medical history, hepatitis B or C, presence of osteonecrosis in the medical history, or dyslipidemia at present or in medical history.
• History or presence of smoking, alcohol drinking (>20 g alcohol per day), or drug abuse.
• Blood donation or significant blood loss within 4 weeks prior to screening
• Known or suspected non-compliance
• Participation in another study with investigational drug within the 30 days preceding and during the present study
• Previous enrolment into the current study