Desonate is a steroid. It prevents the release of substances in the body that cause inflammation. Desonate topical (for the skin) is used to treat the inflammation and itching caused by a number of skin conditions such as allergic reactions, eczema, and psoriasis.
Generic Flexeril is a muscle relaxant. It works by blocking nerve impulses (or pain sensations) that are sent to your brain.
Generic Flexeril is used together with rest and physical therapy to treat skeletal muscle conditions such as pain or injury.