The uptake of oxolinic acid by the rotifer Brachionus plicatilis, Artemia franciscana nauplii and metanauplii was studied as a function of its concentration in the enrichment medium and the duration of the enrichment period. An emulsion containing 5, 10, 20 or 30% (w/w) oxolinic acid was administered and the enrichment period lasted 4, 8, 12 or 36 h. Highest incorporation of oxolinic acid was achieved using a 20% emulsion and a 12 h enrichment for rotifers (205.05 ± 17.1 μg g−1 dry weight), a 24 h enrichment for nauplii (2528.8 ± 254.6 μg g−1 dry weight), and an 8 h enrichment for metanauplii (1236.58 ± 22.9 μg g−1 dry weight). Higher concentrations of oxolinic acid in the enrichment emulsion or longer enrichment times resulted in decreased survival. Two hours post enrichment the contents of the drug appeared significantly decreased. The concentration data of oxolinic acid were best fit to a two phase exponential elimination model, the first phase elimination half-life (t1/2α) being 1.86, 1.08 and 1.74 and the terminal phase elimination half-life (t1/2β) 26.83, 29.67 and 17.48 in rotifers, nauplii and metanauplii correspondingly. Enrichment with an emulsion containing 20% oxolinic acid is recommended employing a duration of 12, 24, or 8 h enrichment for rotifers, nauplii and metanauplii respectively, while enriched carriers should be used shortly after enrichment.