Opioids. Both are opioids so side effects would be very similar. The fentanyl patch is on the skin, the Dilaudid is IV so it is uncomfortable, requires venopuncture, or for chronic use a devise like a pouch under the skin on the chest which adds more side effects and complications.
They are . Used for different purposes. The patch is a good chronic pain tool because it can maintain steady levels of medication over long periods of time. Iv medication works well for acute pain.
Similar. They are very similar (as are all opioids). Obviously a transdermal product (fentanyl patch) is much easier to use than having to inject something iv. In my experience the incidence of nausea, vomiting and constipation are better with the fentayl patch. Dilaudid is available as both an immediate release oral product and an extended release product (exalgo).