The goal of this clinical trial is to investigate the effects of the blood pressure-lowering drug losartan on the blood levels and urinary excretion of the antibiotic cephalexin during simultaneous and staggered ingestion in healthy volunteers. The main questions it aims to answer are:

1. Does losartan affect cephalexin levels and excretion when ingested at the same time?
2. Does a three-hour interval between ingestion of losartan and cephalexin eliminate a possible effect?

Researchers will compare the effects of losartan ingested at the same time, losartan ingested three hours prior, and no losartan ingested on oral cephalexin in each participant to see whether an interaction exists and could be avoided.

Participants will visit the research laboratory on three days during which they will ingest single doses of losartan at the same time with, three hours prior to, and not at all prior to ingesting single doses of cephalexin.

Inclusion Criteria:

• written informed consent
• 18-40 years of age
• good health
• systolic blood pressure of at least 115 mmHg
• all screening laboratory results (P-Krea, Pt-GFReEPI, P-Na, P-K, P-ALAT, P-AFOS, P-GT, B-PVK+T) acceptable; minor deviations from reference ranges are acceptable at the discretion of a physician-scientist with the exceptions of Pt-GFReEPI which must be at or above the reference limit and P-K which must be at or below the higher reference limit (Reference limits: Tyks Laboratories, Turku University Hospital)
• regarding female subjects, a negative pregnancy test (S-HCG-O) before the study, and the use of a highly effective contraceptive method (e.g. copper intrauterine device, bilateral tubal occlusion, vasectomised partner, or abstinence from heterosexual intercourse), according to CTFG Recommendations related to contraception and pregnancy testing in clinical trials, are required

Exclusion Criteria:

• inability to provide written informed consent in Finnish
• remarkable illness
• confirmed or reasonably suspected allergy to cephalexin, amoxicillin, benzylpenicillin, phenoxymethylpenicillin, piperacillin, cefaclor, or cefamandole
• confirmed or reasonably suspected severe delayed allergic reaction to any beta-lactam antibiotic
• underweight (BMI less than 18.5 kg/m2)
• obesity (BMI greater than 30 kg/m2)
• smoking
• regular medication, including hormonal contraception in the form of pills, intrauterine device, subdermal implant etc.
• current or planned pregnancy, and breastfeeding
• less than three months elapsed since a prior clinical trial
• less than three months elapsed since donating blood

The individual data supporting the findings of this study cannot be made available to other researchers to protect the privacy of the study subjects in accordance with European legislation and ethical requirements.