Assess the Blood-Oxygen-Level-Dependent (BOLD) Signal Changes in the Brain by Paracetamol as Measured by Functional Magnetic Resonance Imaging (fMRI) in Subjects With Osteoarthritis (OA)

• BOLD response in the patello-femoral joint of knee osteoarthritis: [BOLD (p-f)] [ Time Frame: Approximately 2-5 hours after taking the fourth assigned dose ] [ Designated as safety issue: No ]
  BOLD response to mechanical stimulation (painful pressure stimuli) was evaluated in the patello-femoral joint of the knee osteoarthritis using functional magnetic response imaging (fMRI).
• Subjective numerical rating scale (NRS) response for treatment effect on OA knee before stimulation: [NRS (TRT)] [ Time Frame: Approximately 2-5 hours after taking the fourth assigned dose ] [ Designated as safety issue: No ]
  Subjective NRS response for each participant was calculated as difference of pre-treatment NRS pain assessment before stimulus and post-treatment NRS pain assessment before stimulus. NRS responses was based on an 11 scale rating (0-10), with 0 corresponding to "No Pain" and 10 corresponding to "Extreme Pain or Pain as bad as you can imagine".
• Subjective NRS response for treatment effect on tibio-femoral stimulation prior the fMRI scan: [NRS (t-f Pre-scan)] [ Time Frame: Approximately 2-5 hours after taking the fourth assigned dose ] [ Designated as safety issue: No ]
  Subjective NRS response was calculated for each participant as difference of pre-treatment pain assessment after stimulus and post-treatment pre-scan pain assessment after stimulus on tibio-femoral joint. NRS responses was based on an 11 scale rating (0-10), with 0 corresponding to "No Pain" and 10 corresponding to "Extreme Pain or Pain as bad as you can imagine".
• Subjective NRS response for treatment effect on patello-femoral stimulation prior the fMRI scan: [NRS (p-f Pre-scan)] [ Time Frame: Approximately 2-5 hours after taking the fourth assigned dose ] [ Designated as safety issue: No ]
  Subjective NRS response was calculated for each participant as difference of pre-treatment pain assessment after stimulus and post-treatment pre-scan pain assessment after stimulus on patello-femoral. NRS responses was based on an 11 scale rating (0-10), with 0 corresponding to "No Pain" and 10 corresponding to "Extreme Pain or Pain as bad as you can imagine".
• Subjective NRS response for treatment effect on tibio-femoral stimulation after the fMRI scan: [NRS (t-f Post-scan)] [ Time Frame: Approximately 2-5 hours after taking the fourth assigned dose ] [ Designated as safety issue: No ]
  Subjective NRS response for treatment effect on tibio-femoral stimulus after the fMRI scan was calculated for each participant as difference of pre-treatment pain assessment after stimulus and post-treatment post-scan pain assessment after stimulus on tibio-femoral. NRS responses was based on an 11 scale rating (0-10), with 0 corresponding to "No Pain" and 10 corresponding to "Extreme Pain or Pain as bad as you can imagine".
• Subjective NRS response for treatment effect on patello-femoral stimulation after the fMRI scan: [NRS (p-f Post-scan)] [ Time Frame: Approximately 2-5 hours after taking the fourth assigned dose ] [ Designated as safety issue: No ]
  Subjective NRS response for each participant for treatment effect on tibio-femoral stimulus after the fMRI scan was calculated as difference of pre-treatment pain assessment after stimulus and post-treatment post-scan pain assessment after stimulus on patello-femoral. NRS responses was based on an 11 scale rating (0-10), with 0 corresponding to "No Pain" and 10 corresponding to "Extreme Pain or Pain as bad as you can imagine".

Blood-Oxygen-Level-Dependent (BOLD) responses to painful mechanical stimulation of the OA knee following treatment with four consecutive doses (at 8 hour intervals) on giving sustained released paracetamol treatment or placebo will be compared. The fMRI and pain assessments will occur approximately 2-5 hours after taking the final dose.

The objective of this study is to investigate if functional magnetic response imaging (fMRI) can detect the effects of a known pain medicine at over-the-counter doses in people with osteoarthritis (OA) of the knee. The fMRI is a harmless and painless technique that is used in the current study to collect images of brain activity to see if is changed when feeling pain. In this study, BOLD response to mechanical stimulation via pressure stimuli applied to the tibio-femoral joint and patello-femoral in participants with knee OA following four treatment doses of any of three treatment will be compared.

• Drug: Paracetamol
  665 mg sustained release paracetamol caplets
• Drug: Placebo
  Placebo caplets

• Experimental: Paracetamol caplets
  Two 665 mg sustained release paracetamol caplets administered orally with water.
  Intervention: Drug: Paracetamol
• Placebo Comparator: Placebo caplets
  Two placebo caplets administered orally with water.
  Intervention: Drug: Placebo

Inclusion Criteria:

• Diagnosis of osteoarthritis of at least one knee for 3 months
• Male or female at least 45 years of age
• Score a minimum of 4 out of 10 on the numerical pain rating and a maximum of 8 at screening

Exclusion Criteria:

• If female, is pregnant, lactating, or breast feeding
• Has secondary cause of knee arthritis
• Lower extremity surgery in the last 6 months
• Prior injury in the last twelve months to the index knee
• Used any analgesics (NSAIDs, COX2 inhibitor, etc) within 5 half lives of study start
• Recently used oral or injected glucocorticoids