Advances in Analgesic Drug Design and Delivery: A Current Survey

Increasingly, pain is being recognized as a major medical problem. Pain is defined by the International Association for the Study of Pain (IASP) as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”1. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life1. Pain is widely underestimated and undertreated. In Western countries, 10% of population have acute or chronic pain, and up to 30% of those with disabilities suffer from chronic pain2. The most common types of chronic noncancer pain are arthritis, low back pain, other musculoskeletal pain or stiffness, and fibromyalgia. Chronic pain, defined by the IASP as “pain that persists beyond the normal time of healing... ”3, is a significant problem associated with many long-term diseases, including musculoskeletal disorders, various neurological conditions such as diabetic, HIV-related, or postherpetic neuropathies, and cancer. Most patients find oral medications effective. However, some patients with chronic pain have inadequate pain relief, intolerable side effects, progressive lack of efficacy (tolerance) or allergy associated with oral medications4.