Morphine-3-glucuronide

Morphine-3-glucuronide (M3G) is a major metabolite of morphine which is formed in the body following administration of morphine. It is excreted in the urine and is detectable for several days after morphine is taken. M3G has no significant analgesic effect.

Pharmacology

M3G is formed in the body by the action of the enzyme UDP-glucuronosyltransferase on morphine. This process, known as glucuronidation, is a major pathway for the elimination of many drugs and toxins from the body. M3G is excreted in the urine, along with a smaller amount of another morphine metabolite, morphine-6-glucuronide (M6G).

M3G has no significant analgesic effect, and does not bind to the mu opioid receptor or the delta opioid receptor. However, it has been suggested that M3G may have some effects on the nervous system which are not mediated by opioid receptors. These effects may include neuroexcitation, and may contribute to the side effects of morphine.

Clinical significance

The formation of M3G from morphine is an important factor in the pharmacokinetics of morphine. The rate at which this process occurs can vary between individuals, and this can affect the duration and intensity of the effects of morphine. In particular, individuals who are rapid metabolizers of morphine may experience less analgesia and more side effects than slow metabolizers.

The presence of M3G in the urine can be used as a marker for recent use of morphine or other opioids. However, it is not a reliable indicator of the amount of morphine taken, as the rate of formation of M3G can vary between individuals.

See also

• Morphine
• Morphine-6-glucuronide
• Glucuronidation
• UDP-glucuronosyltransferase

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