A Single Patient Multiple Cross-Over Study To Determine The Efficacy Of Paracetamol In Relieving Pain Suffered By Patients With Advanced Cancer Taking Regular Opioids.

INTERVENTION: The Intervention treatment will be SR paracetamol 665 mg tabs (encapsulated) to be taken orally with water. The patient will be randomly assigned to one drug. The patient will then be administerd the drug 3 to 4 times daily in a 3 day period. The drug will then be switched. The patient will then be administered the second drug 3 to 4 times daily for a 3 day period. The 6 day period is called a cycle. The cycle will be repeated 3 times. A washout period will be registered on the first day of each 3 day period. On these day, pain scores will not be included in the final analysis. CONDITION: Advanced Stage Cancer Patients PRIMARY OUTCOME: The primary outcome is an average pain score measured by a Brief Pain Inventory (BPI). This 11‐point numerical scale encompasses an assessment of average pain, worst pain, pain right now and pain relief as well as the impact on daily functioning. The BPI has demonstrated reliability and validity across cultures and languages. A clinically significant response is a BPI average score reduction of 2 points from baseline score SECONDARY OUTCOME: The Patient Global Impression of Changes is a patient rated 7 point scale provides information about the patient perception of their change in pain, specifically their improvement since the commencement of the study. This ; will allow the investigators to compare the pain rating using the Numerical Rating Scheme (NRS) with patient perception of improvement. The results of this scale over the study period will assist to determine the clinical significance of any improvement seen. The number of breakthrough doses in a single day while patient is on trial. A breakthrough dose is defined as an unregular opiod dose required by the patient due to uncontrolled pain while on trial. INCLUSION CRITERIA: a) aged >18 years b) a clinical diagnosis of chronic cancer‐related pain with a Brief Pain Inventory (BPI) average pain score of < 3 over previous 24 hours; c) taking a regular dose of opioid analgesia (excluding codeine or tramadol) with no change in baseline opioid dose in the 48 hours prior to study d) no more than three doses of breakthrough opioid/day in the 48 hours prior to trial commencement and no increase in dose of breakthrough during this time e) a stable dose of other regular pain medications (i.e. coanalgesics) for at least 48 hours prior to trial commencement. Patients already on paracetamol are eligible, but must also stop paracetamol 3 days before the trial; f) no intervention e.g. radiotherapy, chemotherapy, surgery that might alter pain levels during the 2 weeks prior to the study period or plans to undergo such during the study period; g) an intact Gastro Intestinal tract (necessary for absorption of extended release pr