Maganin isotonic shine mafita wanda yawan abubuwan solutes (kamar gishiri ko sukari) daidai yake da wanda ake samu a cikin sel masu rai ko plasma na jini. Wannan yana nufin cewa maganin yana da matsa lamba osmotic iri ɗaya kamar ruwan da ke cikin sel kuma, a sakamakon haka, babu motsin ruwa a cikin tantanin halitta. A wasu kalmomi, ƙaddamar da abubuwan solutes yana daidaitawa a bangarorin biyu na membrane na tantanin halitta, kuma babu wani muhimmin motsi na ruwa tsakanin ruwaye na ciki da na waje. Ana amfani da mafita na isotonic a cikin saitunan likita don sake cika ruwa da electrolytes a cikin jiki.