On Monday we began the story of Slewpy’s Star, excerpted from the book Equine ER, with background on the experimental drug SLO. When we last left Dr. Michelle Leblanc, she had tried the drug for the first time as a last resort to treat a mare with excessive scar tissue.

Detoxified streptolysin O, or SLO, is described by its maker, Beech Tree Labs, as “a single molecule, which is a nontoxic form of a bacterial toxin.” By getting rid of the molecule’s toxicity, the biological activity it possesses that produces a decrease in scar tissue is enhanced, says Beech Tree’s founder, immunologist and virologist Dr. John McMichael. He stumbled across the usage of SLO in treating scar tissue about seven or eight years ago when testing the drug for another purpose Ð to help with Tourette’s-like movement disorders rooted in childhood strep infections.

Patients reported not only a reduction in things like twitches and jerks, but the fact that their scars had become less visible or disappeared. One woman had badly scarred hands from boiling water being accidentally spilled on her in her mother’s kitchen 20 years earlier. After 30 days on SLO, the scars had disappeared. A 70-year-old male patient with acne scars also saw them go away.

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