Canesten Thrush Pessary Canesten Thrush Pessary is a single application treatment for vaginal thrush. It contains the active ingredient clotrimazole, an antifungal agent that fights the cause of infections such as thrush, & is inserted into the vagina for treatment directly at the site of the infection. Canesten Thrush Pessary should only be used if you have been previously diagnosed by your doctor as having vaginal thrush.