To increase the residency of furosemide in the stomach after oral administration, a gastroretentive dosage form (GRDF) of furosemide has been developed. In the current study, the new formulation (30mg furosemide coated tablet) will be tested in healthy male subjects. Absorption will be characterised by an effective and safe imaging technique - Magnetic Marker Monitoring (MMM), based on Fe3O4 added to the drug product to generate magnetic signal that can be used for up to 12 h after furosemide administration to localize the medication in the gastrointestinal tract. Fe3O4 is frequently used as colouring pigment in medicinal products. It does not exhibit own pharmacodynamic activity and is considered as an inactive ingredient.