Opioid Concentrations in Oral Fluid and Plasma in Cancer Patients With Pain

• Tarja Heiskanen, MD, PhD
,
• Kaarina Langel, MSc
,
• Teemu Gunnar, MSc, BSc
,
• Pirjo Lillsunde, PhD
,
• Eija A. Kalso, MD, DMedSci

Received 7 May 2014; received in revised form 30 August 2014; accepted 12 September 2014. published online 22 September 2014.
Accepted Manuscript

Abstract 

Context

Measuring opioid concentrations in pain treatment is warranted in situations where optimal opioid analgesia is difficult to reach.

Objectives

To assess the usefulness of oral fluid (OFL) as an alternative to plasma in opioid concentration monitoring in cancer patients on chronic opioid therapy.

Methods

We collected OFL and plasma samples from 64 cancer patients on controlled-release (CR) oral morphine, CR oral oxycodone or transdermal (TD) fentanyl for pain. Samples were obtained on up to five separate days.

Results

A total of of 213 OFL and plasma samples were evaluable. All patients had detectable amounts of the CR or TD opioid in both plasma and OFL samples. The plasma concentrations of oxycodone and fentanyl (determination coefficient R² = 0.628 and 0.700, respectively), but not morphine (R² = 0.292), were moderately well correlated to the daily opioid doses. In contrast to morphine and fentanyl (mean OFL/plasma ratio 2.0 and 3.0, respectively), the OFL oxycodone concentrations were significantly higher than the respective plasma concentrations (mean OFL/plasma ratio 14.9). An active transporter could explain the much higher OFL versus plasma concentrations of oxycodone compared with morphine and fentanyl.

Conclusion

OFL analysis is well suited for detecting the studied opioids. For morphine and fentanyl, an approximation of the plasma opioid concentrations is obtainable, whereas for oxycodone, the OFL/plasma concentration relationship is too variable for reliable approximation results.

Key Words: Opioid, oral fluid, plasma, concentration