From the Guidelines
When converting from IV morphine to oral hydrocodone, a conversion factor of 1:1 can be used to estimate the equivalent dose in morphine milligram equivalents (MMEs), but the actual conversion should be more conservative, typically starting with a ratio of 1:3 to 1:4, considering the differences in bioavailability and potency. According to the CDC clinical practice guideline for prescribing opioids for pain - United States, 2022 1, the conversion factor for hydrocodone is 1.0, similar to morphine, which is also 1.0. However, due to individual variability in genetics and pharmacokinetics, and incomplete cross-tolerance, it is recommended to start with a lower dose when converting from one opioid to another.
For example, if a patient is receiving 10 mg of IV morphine, an appropriate conversion would be approximately 30-40 mg of oral hydrocodone per day, divided into appropriate doses (typically every 4-6 hours), considering the reduced bioavailability of oral medications compared to intravenous administration. It's crucial to monitor for side effects such as sedation, respiratory depression, and constipation, and adjust the dose accordingly. Individual patient factors, including age, renal function, hepatic function, and prior opioid exposure, may necessitate further dose adjustments.
Key considerations when making this conversion include:
- Starting at the lower end of the dosing range and titrating up as needed for pain control
- Monitoring for side effects and adjusting the dose accordingly
- Ensuring appropriate tapering when discontinuing opioids to prevent withdrawal symptoms
- Considering individual patient factors that may affect opioid pharmacokinetics and pharmacodynamics.
From the Research
IV Morphine to PO Hydrocodone Conversion
- The conversion of IV morphine to PO hydrocodone is a complex process that requires careful consideration of the pharmacokinetics and pharmacodynamics of each medication 2, 3.
- Morphine is the most studied opioid analgesic and is often used as the standard against which other opioids are compared 2.
- Hydrocodone is a commonly prescribed opioid for moderate to severe pain, and its metabolism and drug-drug interactions are important considerations in patient treatment 3, 4.
- The equianalgesic dose of hydrocodone to morphine is not well established, but studies suggest that hydrocodone is approximately 0.5-1.5 times as potent as morphine 4.
- When converting from IV morphine to PO hydrocodone, the following approximate dose ratios can be used:
- 1-2 mg IV morphine = 5-10 mg PO hydrocodone
- 2-4 mg IV morphine = 10-20 mg PO hydrocodone
- 4-6 mg IV morphine = 20-30 mg PO hydrocodone
- However, these dose ratios are approximate and may vary depending on individual patient factors, such as renal function, liver function, and prior opioid exposure 3.
- It is also important to consider the potential for drug-drug interactions when converting from IV morphine to PO hydrocodone, as both medications can interact with other drugs that inhibit or induce cytochrome P450 enzymes 3.
- Gas chromatography-mass spectrometry can be used to simultaneously identify and quantitate codeine, morphine, hydrocodone, and hydromorphone in urine, which can be useful in monitoring patient compliance and detecting potential drug interactions 5.