From the Guidelines
The half-life of morphine is 2-4 hours.
Key Points
- The plasma elimination half-life of morphine is 2-4 hours 1
- Steady state is achieved within 4-5 half-lives (that is, within 24 hours) after the start of treatment and following dose adjustment 1
- The duration of analgesia for immediate release morphine is 4 hours, while controlled release morphine has a duration of analgesia of 12 hours 1
- The time to peak plasma concentration for immediate release morphine is 0.25-1.0 hours, while controlled release morphine has a time to peak plasma concentration of 2-4 hours 1
From the FDA Drug Label
The effective terminal half-life of morphine sulfate after IV administration is reported to be approximately 2 hours. In some studies involving longer periods of plasma sampling, a longer terminal half-life of morphine sulfate of about 15 hours was reported
- The half-life of morphine is reported to be approximately 2 hours after IV administration, but may be as long as 15 hours in some cases.
- However, the provided information is for IV administration, and the question does not specify the route of administration.
- Since the label does not provide information on the half-life of morphine for the specific formulation (PO), no conclusion can be drawn for the oral formulation 2
From the Research
Half-Life of Morphine
The half-life of morphine has been studied in various research papers.
- According to 3, the half-life of morphine is between 2 to 3 hours and is not influenced by the age of the patient.
- In contrast, 4 reports a half-life of 15.1 +/- 6.5 hours for morphine, with the terminal half-lives of its metabolites, M3G and M6G, being 11.2 +/- 2.7 hours and 12.9 +/- 4.5 hours, respectively.
- Another study 5 found that the terminal elimination half-life of morphine was similar in normal subjects and patients with chronic renal failure, with a mean value of around 2-3 hours.
- However, 4 suggests that the half-life of morphine may be longer, with a terminal half-life of around 15 hours, and that the drug may undergo enterohepatic cycling, which could affect its pharmacokinetics.
Factors Affecting Half-Life
Several factors can affect the half-life of morphine, including:
- Route of administration: The half-life of morphine may vary depending on the route of administration, with oral administration resulting in a longer half-life compared to intravenous administration 4.
- Renal function: Patients with chronic renal failure may have altered morphine pharmacokinetics, although the terminal elimination half-life may not be significantly affected 5.
- Metabolism: Morphine is metabolized to several metabolites, including M3G and M6G, which may have different half-lives and pharmacological activities 4.