Biomaterial-Based Particulate Drug Carriers - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 2

1.1 Introduction

1.1.1 The Needs for Drug Carriers

The majority of approved drug formulations as well as those under
development, irrespective of dosage form and route of administration,
are formulations of free drug. The meeting between a free drug
and a living system is often an unfriendly encounter, arising from
deficiencies of treatment with free drug — diminishing efficacy and
damaging the biological system, as summarized in Figure 1.1

Figure 1.1 Deficiencies of treatment with free drugs.

Four processes, each separately and more so their combinations,
reduce treatment efficacy: dilution of the administered dose,
irrespective of administration route; lack of self-targeting, hence
indiscriminate distribution within the living system; premature (i.e.,
before reaching the molecular sites of drug action) clearance from
the whole system as well as from the target zone; vulnerability to
premature enzyme-catalyzed degradation, metabolism, and other
processes of inactivation. The end result of all or some of these
processes is severely diminished efficacy. A rather small share of
the administered dose reaches the target in active form and remains
there for a sufficient time span, to generate the desirable therapeutic
responses. The other side of the coin is damage to the biological
system mostly due to the lack of targeting. Many drugs cause adverse
eff ects, toxicity, and undesirable immune responses. Thus, even
if a satisfactory level of efficacy is obtained, the damage severely
undermines the therapy. Attempts to increase efficacy by increasing