ABSTRACT
The term drug delivery covers a very broad range of techniques used to get therapeutic agents into the human body. The limitations of the most obvious and trusted drug delivery techniques, those of the ingested tablet and of the intravenous (IV)/subcutaneous/intramuscular (IM) injec tions, have been recognized for some time now. The former delivers drug into the blood only through the hepatic system, and hence the amount in the bloodstream may be much lower than the amount formulated into the tablet (i.e., it has low bioavailability); furthermore, liver dam age is an unfortunate side effect of many soluble tableted drugs. The injection mode of delivery can be used to deliver any size of drug molecule and is versatile in this regard, but it suffers from the obvious disadvantage of being invasive and painful, and the less obvious disadvantage of shortness of duration (for drugs with short half-lives). To overcome some of these limita tions, other modes of delivery of drugs into the body were investigated, beginning in the early 1970s. Transdermal (through the intact skin), transmucosal (through the intact mucosa of the mouth, intestine, rectum, vagina, or nose), transocular (through the eye), transalveolar (inhala tion, through lung tissue), implantable (subcutaneous and deeper implants, delivery into sur rounding tissue), and injectable (IM or subcutaneous) modes of delivery have all been explored extensively over the last 25 years, with varying degrees of commercial and therapeutic success. Of the above modes, the transdermal, transmucosal (specifically intestinal), transocular, in jectables and the subcutaneous implant have found varying degrees of commercial acceptance. Of the rest, the inhalation route appears promising for a limited class of agents and at least three companies have products in advanced clinical trials. In the next 5 years, this route of adminis tration is very likely to become acceptable to patients and hence commercially successful.
