I can't believe that the myth about using toothpaste as a spot treatment for pimples is still being promoted.
I just read this recommendation in an article on Ezine Articles:
Do NOT do this! Toothpaste has irritants in it that can aggravate an already inflamed pimple and make it much worse. Stick with gently cleansing the area and applying a little acne treatment containing benzoyl peroxide or salicylic acid. I prefer something with an antibiotic in it as well, like Duac. - Sharyn
Editor, Makeup for Acne