Desmethylflunitrazepam (also known as norflunitrazepam, Ro05-4435 and fonazepam) is a benzodiazepine that is a metabolite of flunitrazepam and has been sold online as a designer drug. It has an IC50 value of 1.499 nM for the GABAA receptor. Desmethylflunitrazepam (also known as norflunitrazepam, Ro05-4435 and fonazepam) is a benzodiazepine that is a metabolite of flunitrazepam and has been sold online as a designer drug. It has an IC50 value of 1.499 nM for the GABAA receptor.