**1.3 Orphan diseases and drugs**

There is no defined definition for orphan diseases (ODs). In the US it is defined as if the disease prevalence affects less than 1 in <200,000, in Japan <50,000 and in Australia <2000. WHO defines the prevalence of less than 6.5–10 in 10,000 [10]. The drug which is used in the treatment of orphan disease is referred to as an orphan drug. For example; haem arginate, is being used to treat porphyria (acute intermittent, variegate and hereditary), ibuprofen to treat patent ductus arteriosus in neonates [11] and N-acetylcysteine for paracetamol poisoning. In orphan diseases (ODs) and their management, the count for orphan diseases exists approximately 6000 but the efforts that are putting off by pharmaceutical and R&D sectors for developing new drugs in their management are negligible cause the huge amount involved in *de novo* drug development [12]. Only 5% of pharmaceutical industries are taking interest in developing new drugs in orphan disease management [12]. At present, approximately 325 drugs are available in the market, which are being used to treat only 5% of orphan diseases. Drug


#### **Table 1.**

*Examples of off-label drug use (OLDU).*

**Figure 2.** *Resource database for orphan diseases (ODs) and drugs.*

repurposing provides one of the best faster and economical ways to find new treatment options in ODs (**Figure 2**). To facilitate drug development and treatment options in orphan disease management FDA Orphan Drug Act (ODA) 1983, has provided many of the benefits or incentives to pharmaceutical and research companies including (i) tax credits (ii) clinical research aids, (iii) fast-track marketing authorization procedures (FDA approval), and (iv) marketing exclusivity [13].
