For DSIP specifically, the substitution is far more consequential, and the reason follows directly from the half-life: Subcutaneous absorption competes with a 24 minute clearance
Clin Gastroenterol Hepatol (2010) 8(2):10510
Foods high in sulfur amino acids such as broccoli, cauliflower, Brussels sprouts, cabbage, garlic, kale, eggs, fish, meat, mushrooms, and onions support the body's production of glutathione.* Glutathione is fragile and breaks down easily in the digestive tract, leading to poor absorption and low blood levels when taking most supplements
developed mixed Pluronic (F-127)-Cremophor polymeric micelles for poorly soluble antibiotic norfloxacin
Normal reduced glutathione powder might break down before it gets into the system