When penicillin was first used medically, in 1940, it was a time of austerity. While Alexander Fleming first discovered penicillin in 1928, his world-changing observations had garnered hardly any notice, and it wasn't until 1938 that another team of reserachers finally began to isolate and test the active chemical ingredients in the world's first antibiotic.* By that time, World War II was raging, and medical manufacturing capacity that could be devoted to experimental treatments was in short supply.

Producing usable penicillin from Penicillium notatum mold was no easy feat, says PBS: “In spite of efforts to increase the yield from the mold cultures, it took 2,000 liters of mold culture fluid to obtain enough pure penicillin to treat a single case of sepsis in a person.”

Pencilin production couldn't happen nearly fast enough to match rising demand. To make up the shortfall, writes Rebecca Kreston for her Body Horrors blog at Discover Magazine, researchers came up with a novel way to get the penicillin they needed: extracting and isolating it from patients' urine.

Not all of the penicillin given to a patient is broken down. Some—in fact, most—of the penicillin passes through the body unchanged. According to Kreston:

[A]nywhere from 40 to 99 percent of the antibiotic is excreted in urine in its fully functional form about 4 hours after administration thanks to our efficient and hardworking kidneys. Due to this distinct feature of its pharmacokinetics, penicillin could be extracted from the crystalized urine of a treated patient and then used to treat another patient in the throes of serious bacterial infection just next door.

Eventually, penicillin production reached a pace that could match doctors' needs. But even today, some portion of the active ingredient from many drugs passes through our bodies unchanged. Instead of isolating and recycling them, though, we send them down the toilet and out into the world.

As the Harvard Health Letter wrote back in 2011, some water experts are growing increasingly concerned about the flow of drugs from pharmacy to stream. More than just an issue of pharmaceutical waste, these drugs seem to be having an effect on the behavior and health of animals living downstream. Doctors are no longer short on antibiotics, but it might be worth considering how to revive those early recycling strategies, anyway.

*This sentence was updated for accuracy.