The purpose of this study is to assess the effects of strong cytochrome P450 (CYP) 3A4 inhibitors (Itraconazole and Clarithromycin), on pharmacokinetics (PK) (study of the way a drug enters and leaves the blood and tissues over time) of single dose of JNJ-54861911 in healthy male participants.

This is a single-center, open-label (participants and researchers are aware about the treatment, participants are receiving), fixed-sequence study in healthy male participants consisting of 2 sequential parts. For all participants enrolled in either part, the study consists of 3 phases: Screening Phase (within 21 to 2 days prior to the first dose administration on Day 1), Open-label Treatment Phase (Day 1 up to Day 12), and Follow-up Phase (7 to 14 days after last dose administration). The maximum duration of study will be 7 weeks per participant. Study will be conducted in 2 parts to understand the relative role of CYP3A4 and amide hydrolysis pathways in JNJ-54861911 metabolism and any potential drug-drug interaction liability with inhibitors of these pathways. Itraconazole will be administered in Part 1 as mixed CYP3A4 and potential amide hydrolysis inhibitor. Clarithromycin will be administered in Part 2 as a pure CYP3A4 inhibitor. However, Part 2 of the study will only be conducted if a relevant interaction is observed with itraconazole based on an interim review of Part 1 data. Participants enrolled in Part 1 will receive single dose of JNJ-54861911, 25 milligram (mg) tablet orally on Day 1 and Day 9 along with itraconazole 200 mg (2*100 mg capsule) orally once daily from Day 5 to Day 12. Participants enrolled in Part 2 will receive single dose of JNJ-54861911, 25 mg tablet orally on Day 1 and Day 9 along with clarithromycin 500 mg immediate release tablet orally twice daily from Day 5 to Day 12. Blood samples will be collected pre-dose (Day 1) up to Day 13 to understand the PK characteristics of JNJ-54861911 and diaminothiazine (DIAT, a metabolite formed after amide hydrolysis of JNJ-54861911). In addition, a blood sample will be collected on Day -1 from all enrolled participants to study genotyping of CYP3A4 gene and other genetic factors that may influence the PK, safety, and/or tolerability of JNJ-54861911 and CYP3A4 inhibitors. Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Signed an informed consent document indicating they understand the purpose of and procedures required for the study, and are willing to participate in the study
• Body mass index between 18 and 30 kilogram per square meter
• Must be healthy on the basis of physical examination, medical history, vital signs, and 12-lead electrocardiogram (ECG) performed at Screening or admission (up to Day 1 predose)
• Man, who is sexually active with a woman of child-bearing potential and has not had a vasectomy, must agree to use an adequate contraception method as deemed appropriate by the investigator, and must also agree to not donate sperm during the study and for 90 days after receiving the study drug
• Participant must be healthy on the basis of clinical laboratory tests performed at Screening and/or admission and as per investigator's judgment

Exclusion Criteria:

• History of or current liver or renal impairment, significant cardiac, vascular, pulmonary, gastrointestinal, endocrine, neurologic, hematologic, rheumatologic, psychiatric, dermatological or metabolic disturbances
• Known allergies, hypersensitivity, or intolerance to JNJ-54861911 or its excipients, itraconazole (Part 1 only) or clarithromycin (Part 2 only)
• History of human immunodeficiency virus (HIV) antibody positive, or tests positive for HIV at Screening
• History of drug or alcohol abuse within 6 months before Screening or positive test result(s) for alcohol and/or drugs of abuse (including barbiturates, opiates, cocaine, cannabinoids, amphetamines, benzodiazepines and cotinine) at Screening or admission
• Smoking of cigarettes (or equivalent) and/or used nicotine based products within 3 months prior to study drug administration