@kathy5645,

They are two different classes of stimulants altogether.

Here are the ingredients for Prunelax:

Dried senna and plum extract and acts as a stimulant to move stool through the bowel.

Dextrin, Dextrose Monohydrate, Sodium Carboxymethylcellulose, Soy, Lecithin and Sodium Citrate Dihydrate). Other Ingredients: Maltodextrin, Croscarmellose Sodium, Sodium Lauryl Sulphate, Silicon Dioxide, Microcrystalline Cellulose, Pregelatinized Starch, Sodium Starch Glycolate, Magnesium Stearate, Opadry Ns Clear (Coating).

Miralax contains polyethylene glycol, an osmotic drug that attracts water, distends the bowel wall and triggers the movement reflex.

It may be worth looking at again.