Why Some Medicine Taken Orally and Some Injected?

Each drug needs to get from where you take it (the site of administration) to its ultimate intended destination (the site of action). The site of action might be as localized as a patch of skin or a particular organ, or as dispersed as chemical receptors found throughout your body. For example, morphine, a strong painkiller, acts on receptors found in the brain, spinal cord, limbic system, and even in your digestive tract. Many medications need to get into the general circulation of fluids in your body — the bloodstream, in particular — in order to flow to their sites of action. Ideally, 100% of a drug gets to its destination. In practice, most medications need to pass through multiple barriers in your body (biologic membranes) and undergo a complex series of biochemical reactions along the way, some of which “use up” a portion of the active ingredient. When a medication is given intravenously, it enters the circulation directly and is considered 100% available to your body. When taken by mouth, it has to go through part of your digestive system first. Only some of the drug makes it to the site of action; the rest is effectively processed as waste. This concept is called bioavailability: the portion of the drug that actually makes it into your circulation. #medicine #intravenousMedicine #polypeptide #hormons #aminoAcids #proteins #peptides