The Effect of Losartan on Cephalexin (KEFALOS)

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.

Study Overview

• Status: Recruiting
• Conditions: Healthy; Possible Interaction Between Losartan and Cephalexin
• Intervention / Treatment: Drug: losartan; Drug: cephalexin

• Study Type: Interventional
• Enrollment (Estimated): 12
• Phase: Phase 1

Contacts and Locations

• Study Contact: Name: Aleksi Tornio, M.D., Ph.D.; Phone Number: +358504765715; Email: aleksi.tornio@utu.fi

Study Locations

• Finland
  • Southwest Finland
    • Turku, Southwest Finland, Finland, FI-20520
      • Recruiting
      • Unit of Clinical Pharmacology, Turku University Hospital
      • Contact: Aleksi Tornio, M.D., Ph.D.; Phone Number: +358504765715; Email: aleksi.tornio@utu.fi
      • Principal Investigator: Aleksi Tornio, M.D., Ph.D.
      • Sub-Investigator: Mikael OW Piha, M.D.

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

6

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Sequence A; water at 7.30, cephalexin 500 mg at 10.30; then water at 7.30, losartan 100 mg and cephalexin 500 mg at 10.30; then losartan 100 mg at 7.30, cephalexin 500 mg at 10.30	Drug: losartan; 100 mg tablet orally, single dose; Other Names: Cozaar; Drug: cephalexin; 500 mg tablet orally, single dose; Other Names: Kefalex; Kefexin
Other: Sequence B; water at 7.30, losartan 100 mg and cephalexin 500 mg at 10.30; then water at 7.30, cephalexin 500 mg at 10.30; then losartan 100 mg at 7.30, cephalexin 500 mg at 10.30	Drug: losartan; 100 mg tablet orally, single dose; Other Names: Cozaar; Drug: cephalexin; 500 mg tablet orally, single dose; Other Names: Kefalex; Kefexin
Other: Sequence C; losartan 100 mg at 7.30, cephalexin 500 mg at 10.30; then water at 7.30, losartan 100 mg and cephalexin 500 mg at 10.30; then water at 7.30, cephalexin 500 mg at 10.30	Drug: losartan; 100 mg tablet orally, single dose; Other Names: Cozaar; Drug: cephalexin; 500 mg tablet orally, single dose; Other Names: Kefalex; Kefexin
Other: Sequence D; water at 7.30, cephalexin 500 mg at 10.30; then losartan 100 mg at 7.30, cephalexin 500 mg at 10.30; then water at 7.30, losartan 100 mg and cephalexin 500 mg at 10.30	Drug: losartan; 100 mg tablet orally, single dose; Other Names: Cozaar; Drug: cephalexin; 500 mg tablet orally, single dose; Other Names: Kefalex; Kefexin
Other: Sequence E; water at 7.30, losartan 100 mg and cephalexin 500 mg at 10.30; then losartan 100 mg at 7.30, cephalexin 500 mg at 10.30; then water at 7.30, cephalexin 500 mg at 10.30	Drug: losartan; 100 mg tablet orally, single dose; Other Names: Cozaar; Drug: cephalexin; 500 mg tablet orally, single dose; Other Names: Kefalex; Kefexin
Other: Sequence F; losartan 100 mg at 7.30, cephalexin 500 mg at 10.30; then water at 7.30, cephalexin 500 mg at 10.30; then water at 7.30, losartan 100 mg and cephalexin 500 mg at 10.30	Drug: losartan; 100 mg tablet orally, single dose; Other Names: Cozaar; Drug: cephalexin; 500 mg tablet orally, single dose; Other Names: Kefalex; Kefexin

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Plasma concentrations of cephalexin over time, the cumulative urinary excretion of cephalexin, and the pharmacokinetic parameters derived from these measurements following simultaneous or staggered ingestion of losartan	up to 8 hours after ingestion of cephalexin on three consecutive days separated by at least one-week intervals

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Plasma concentrations of losartan and losartan carboxylic acid over time, the cumulative urinary excretion of losartan and losartan carboxylic acid, and the pharmacokinetic parameters derived from these measurements	following simultaneous and staggered ingestion of cephalexin	up to 11 hours after ingestion of losartan or water on three consecutive days separated by at least one-week intervals

Other Outcome Measures

Outcome Measure	Time Frame
Plasma and urinary concentrations of endogenous and diet-derived metabolites, and the effects of genetic variants and other individual factors on the pharmacokinetic parameters of cephalexin and losartan	up to 11½ hours on three consecutive days separated by at least one-week intervals

Collaborators and Investigators

• Sponsor: Aleksi Tornio
• Collaborators: Turku University Hospital; Helsinki University Central Hospital; University of Turku; University of Helsinki
• Investigators: Principal Investigator: Aleksi Tornio, M.D., Ph.D., Unit of Clinical Pharmacology, Turku University Hospital

Study record dates

Study Major Dates

• Study Start (Actual): March 4, 2026
• Primary Completion (Estimated): May 8, 2026
• Study Completion (Estimated): May 8, 2026

Study Registration Dates

• First Submitted: November 27, 2025
• First Submitted That Met QC Criteria: December 17, 2025
• First Posted (Actual): December 24, 2025

Study Record Updates

• Last Update Posted (Actual): March 25, 2026
• Last Update Submitted That Met QC Criteria: March 21, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: losartan; absorption; pharmacokinetic interaction; cephalexin
• Additional Relevant MeSH Terms: Sulfur Compounds; Organic Chemicals; Heterocyclic Compounds, 1-Ring; Heterocyclic Compounds; Heterocyclic Compounds, 2-Ring; Heterocyclic Compounds, Fused-Ring; Azoles; Hydrocarbons; Hydrocarbons, Cyclic; Hydrocarbons, Aromatic; Imidazoles; Amides; Benzene Derivatives; beta-Lactams; Lactams; Cephalosporins; Thiazines; Tetrazoles; Biphenyl Compounds; Cephalexin; Losartan
• Other Study ID Numbers: T2025/25858; 2025-525059-23-00 (Ctis)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: 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.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No