chapter  61
Clinical Testing of Microneedles for Transdermal Drug Delivery
ByRaja K. Sivamani, Gabriel C. Wu, Boris Stoeber, Dorian Liepmann, Hongbo Zhai, Howard I. Maibach
Pages 8

Much research has been done in developing drug delivery methods different from traditional oral ingestion and hypodermic needle injections. Oral and subdermal delivery routes are successful methods of drug delivery but have drawbacks that can affect efficacy and patient comfort. Orally ingested drugs pass through the acidic environment of the stomach and then are absorbed in the intestines. The acid in the stomach can degrade or denature many drugs and serves as one barrier in oral ingestion. When the drug passes through the stomach, it must be small enough to be absorbed through the intestinal wall. Larger drugs, like insulin, are not absorbed through the intestinal wall and are ineffective when taken orally. Once the drug passes through the intestinal wall, it then passes through the hepatic circulation and the drug can be significantly cleared by the liver before passing onto the rest of the body. Only then, can the drug take effect. As a result, the bioavailability of orally ingested drugs can be low. Also, because the drug must pass through the liver, drugs that have significant liver toxicity would not be suitable as an oral drug agent.