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The conversion ratio from intravenous (IV) hydromorphone to oral (PO) opioids in patients with cancer.

197 Background: Inpatients with cancer frequently undergo conversions from IV to PO hydromorphone (HM) or opioid rotation (OR) from IV HM to another PO opioid prior to discharge. Currently used conversion ratios (CR) between IV and PO HM range from 2-5 and opioid rotation ratios (ORR) between IV HM and oral morphine equivalent daily dose (MEDD) range from 10-20. This large variation in ratios may lead to uncontrolled pain or overdosing. Our aim was to determine the accurate CR from IV to PO HM and ORR from IV HM to PO morphine and oxycodone (measured as MEDD).


METHODS
We reviewed records of 4745 consecutive inpatient palliative care consults in our institute during 2010-14 for patients who underwent conversion from IV to PO HM or OR from IV HM to PO morphine or oxycodone. Patient characteristics, symptoms and opioid doses were determined in patients successfully discharged on oral opioids without readmission within 1 week. Linear regression analysis was used to estimate the CR or ORR between the 24 hour IV HM mg dose prior to conversion to PO and the oral opioid mg dose used in the 24 hours prior to discharge.


RESULTS
Among 394 eligible patients on IV HM, 147 underwent conversion to PO HM and 247 underwent OR to oral morphine (163) or oxycodone (84). Mean age was 54 years, 39% were male, and 95% had advanced cancer. Median time between conversion to PO and discharge was 2 days. In 147 patients the median CR (IQR) from IV to PO HM was 2.5 (2.1-2.7) and correlation of IV to PO dose of HM was .95 (P < .0001). The median CR was 2.5 in patients receiving < 30mg of IV HM/day and 2.1 in patients receiving ≥ 30mg of HM/day (P = .004). In 247 patients the median ORR (IQR) from IV HM to MEDD was 11.5 (10-13) and correlation of IV HM to MEDD was .93 (P < .0001). The median ORR was 11.5 in patients receiving < 30mg of IV HM/day and 9.9 in patients receiving ≥ 30mg of HM/day (P = .0004). ORR from IV HM to MEDDs obtained from morphine (11) and oxycodone (12.1) were significantly different (P = .0023). The CR and ORR were not significantly impacted by other variables.


CONCLUSIONS
The median CR from IV to PO HM is 2.5 and ORR from IV HM to MEDD is 11.5. This implies that 1 mg IV HM is equivalent to 2.5 mg PO HM and 11.5 mg MEDD. HM may cause hyperalgesia at doses ≥ 30 mg/day and thereby requires a lower ORR to other opioids.