Oral drugs have been the mainstay of treatment for pain during past centuries, and the use of drugs to treat pain has expanded exponentially in recent years, with increases in expenditures of 188% between 1996 and 2005 (Martin et al. 2008).
Retail sales for opioids, the most common class of drug prescribed in the USA, increased by 176% from 1997 to 2006. However, their use remains controversial both with respect to efficacy and adverse physical effects (Stein et al., 2010).
A meta analysis evaluating the effectiveness of opioids for the treatment of chronic pain demonstrated that opioids result in a small improvement in pain severity and functional improvement compared with placebo (Furlan et al., 2006).
Notably, the placebo response rate for opioid trials is around 10%, and when active placebos that mimic the side effects of opioids are used, the response rate increases to an average across studies of 21% (Turk, 2002). This suggests that setting of realistic expectations with patients is crucial.
Side-effects associated with opioids are nausea, constipation, somnolence. In addition, a few patients with long-term opioid treatment can develop opioid-induced hyperalgesia: when patients taking opioids become hypersensitive to nociceptive stimuli (Chu et al., 2008). Thus, opioids are recommended as the second-line or third-line treatment (Attal et al., 2010; Turk et al. 2011).
2. Non-steroidal anti-inflammatory drugs
The efficacy of non-steroidal anti-inflammatory drugs (NSAIDs) has been reported for patients with osteoarthritis, rheumatoid arthritis and back pain (Roelofs et al., 2008). The most prominent members of NSAIDs are aspirin, ibuprofen, and naproxen.
NSAIDs gastropathy is regarded as one of the most common adverse effects (Griffin et al., 2001). Careful scrutiny for the development of adverse reactions should be undertaken, particularly with long-term use of NSAIDs.
Selective cyclo-oxygenase (COX)-2 inhibitors have fewer gastrointestinal (GI) side effects than traditional NSAIDs, but they are associated with increased cardiovascular risk (Roelofs et al., 2008).
Although paracetamol (acetaminophen) is used to treat inflammatory pain, it is not generally classified as NSAIDs because it exhibits only weak anti-inflammatory activity. Paracetamol is a slightly weaker analgesic than NSAIDs, but is a reasonable alternative because of reduced gastrointestinal complications and low cost (Kroenke et al., 2009). The widespread use of paracetamol, combined with the small margin of safety between therapeutic and toxic dose, often result in un-intentional overdose (Guggenheimer et al. 2011). On the basis of growing rates of un-intentional overdose and hepatic failure associated with paracetamol, the FDA revised the drug’s warning label in April, 2010 (Turk et al. 2011).