Metformin and other drugs

Greetings! Our lab would like to use metformin as a control in a series of life-span experiments. We assumed that this would be fairly straightforward, as it has been published to extend lifespan on several occasions. I’ve tried a range of concentrations from 5mM-100mM, adding freshly prepared 1.2 M metformin to cooled, still molten NGM + FuDR. I initially plate L4 worms and prepare fresh plates every 2 days. I have tried both live and heat killed OP50. I’ve tried this a number of times (at 20 deg), with metformin from at least two different manufactures. I have also tried other drugs reported to extend life-span (ie rapamycin, resevertol, etc). No dice.
I have quite a bit of experience with lifespan assays, but I can’t get this to work! Is there something I’m missing? Any advice on what to try or what I might be doing incorrectly??
Your expertise is more than appreciated!! Best wishes and thank you

Hi, I use metformin hydrochloride from Sigma, adding a 1.5 M stock to warm (not too hot, but I think it’s pretty thermally stable so shouldn’t matter much) NGM to a final concentration of 50 mM, and seed the plates with OP50. I personally haven’t done lifespan experiments on it, but I’m from the same lab as Wouter De Haes (Metformin promotes lifespan through mitohormesis via the peroxiredoxin PRDX-2, 2014) and he used the same for his lifespans. He moved them from plate to plate every day during their reproductive period, and every three days thereafter, not using FUdR. Not sure if this is much help, but hope you solve your problem soon!