21 Orphan Drugs

1

Bert Spilker

21.1 Introduction

In the United States, ‘rare disease’ is defined as a
disease with a prevalence of less than 200 000
patients. Some countries have defined a rare dis-
ease based on a prevalence of 0.1–0.5% of the
population. A rare disease is sometimes referred
to as an orphan disease. An ‘orphan drug’ is defined
as a drug to treat a rare disease. The term ‘orphan
drug’ originated from the belief that there were
drugs that no pharmaceutical sponsor wanted to
develop and market, and thus they were like home-
less orphans.
There are an estimated 4000–8000 rare diseases,
but no one has actually counted them. Many of
these diseases involve genetic problems and often
are related to birth defects that are poorly charac-
terized or involve permanent defects of nerve,
muscle or bone which cannot be corrected with
drugs.

Almost all marketed drugs are used to treat some

rare diseases. A few examples among the largest

selling drugs in the world include propranolol,

which is used to treat idiopathic hypertrophic

subaortic stenosis (in addition to the more well-

known cardiovascular diseases), cimetidine, which

is used to treat Zollinger–Ellison Syndrome (in

addition to duodenal ulcers), and all antibiotics

used to treat rare bacterial infections, in addition

to common ones.

21.2 Principles

One of the most important principles about orphan

drugs is that they are a very heterogeneous group of

drugs. In fact, they are as heterogeneous as any

other group of drugs and, in most cases, should

not be considered as a separate group. Orphan

drugs are heterogeneous for the reasons given in

Table 21.1.

Pharmaceutical companies have always devel-

oped orphan drugs. This did not change suddenly

when the Orphan Drug Act was passed in 1983 in

the United States, but the Act stimulated the devel-

opment of more such drugs.

If one compares orphan drug status with a

patent, either a compound or use patent for a

Principles and Practice of Pharmaceutical Medicine, 2nd Edition Edited by L. D. Edwards, A. J. Fletcher, A. W. Fox and P. D. Stonier
#2007 John Wiley & Sons, Ltd ISBN: 978-0-470-09313-9

(^1) This chapter contains material originally published in Spilker
B. 1996. ‘Orphan drug challenges for pharmaceutical
companies’.Drug News Perspect. 9 : 399; and Spilker B.

1996. ‘Orphan Drug Act of 1983’.Drug News Perspect. 9 :


1997. Copyright Prous Science Publishers. Reprinted with
      permission.