1. cream/oint - I could go on & on & talk about viscosity, thixotropy, etc...more than you want to know. On the easy side - a cream is a smoother product which will cover, but less occlusively than an ointment, which is "greasier". Therapeutically, depending on the state, it is within the pharmacists realm of responsibilty to interchange them. So, you need to learn the chemistry behind them. (Its not hard to learn, just more than you want here). If you want good penetration, particularly through a thick epidermal site - an ointment will be a good choice. If you want coverage and need to wear clothing over the site - a cream might work better. There are few cases in which only one will be preferable over another.
2. Extended release products can be made in a variety of ways. Some - like Ambien CR are designed to have two layers of medication, one which releases fast & one slower - for a reason. The fast layer helps with sleep induction, the slower helps with maintaining sleep.
Other products can be put into a "matrix" which controls release out of the matrix. Others are granules within a capsule formulation. After the outer capsule dissolves in the stomach, the granules are designed to either dissolve there as well or move down into the intestine & dissolve & become absorbed there. Most drugs are actually absorbed in the small intestine, not the stomach, but by controlling the dissolution & the coating we can control where each part of that occurs.
Some drugs have slow release & we don't even know why. Dilantin is a good example of that. It wasn't until Dilantin went off patent & generic products were made that it was discovered the kinetics of phenytoin were actually delayed in the Dilantin product. There is an extended release phenytoin product, but it is not interchangable with Dilantin because the manufacturer really doesn't know why their product continues to have the kinetics different than the extended release generic. Both are equally acceptable as long as you stay within the product you have chosen & don't switch products.
3. Insulin is an extremely unstable protein to acid - thus it can't be taken orally - the stomach acid would inactivate it. It is absorbed across the mucosa - thus the inhaled insulin, altho that product has its own issues. If you're referring to "topical" as in absorbed thru the skin - that is difficult for any product since the epidermal layer is uniquely designed to keep things "out" which don't belong & things "in" which do. We can design products - topical catapres, ntg, fentanyl patches which can be absorbed through the skin. But, again, the skin is a bit on the acidic side, so the drug must be stable (insuline is not stable in acidic environments) & the patch must be designed so it is occlusive enough to actually penetrate the epidermis. This method of drug delivery is great for chronic continuous medications - like catapres or fentanyl. Its not so great for a drug which must be given in response or anticipation of a varying physiologic event - like blood sugar.
Hope that answers your questions....
