Why do drugs that are protein like that of an insulin always be injected rather than taken by mouth?

Answer 1

Simply, first the mouth introduces an enzyme to help break down proteins.
The stomach mixes it with gastric juice and initiates the digestion of proteins, and carries on a limited amount of absorption. Pepsin is secreted to break down proteins into individual amino acids.
Next the pancreas secretes pancreatic juice which contains 3 types of enzymes that also digest proteins.
Next, the most vital liver functions are probably those related to protein metabolism. Once absorbed, the amino acids travel to the liver, which releases them into general circulation.
Next the small intestine, aiding digestion by the most complete absorption of the nutrients from the stomach.
The next is the large intestine, any parts not digested and absorbed continue through and pass out of the body.

So to introduce something into the blood stream without the function of the digestive system, one way is to inject it into the blood stream directly.

Answer 2

medicine that you take per orem are broken down by saliva and gastric acid, those that are absorbed immediately are broken down by the liver, a phenomenon known as first pass hepatic metabolism... depending on the drug, only about 15-30 percent ends up being absorbed per orem... in contrast, those that are injected do not pass thru the first pass hepatic metabolism cycle, and are not obviously degraded by saliva and gastric acid, hence as much as 90-100% of the drug reaches its intended site of action...

Answer 3

The stomach acid and bile break down the protein before it is absorbed.

Answer 4

Because it get's to the area quicker then tablets