Effect of acute inflammatory brain injury on accumulation of morphine and morphine 3- and 6-glucuronide in the human brain *

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Abstract

Objective:

In animals, central nervous system inflammation increases drug accumulation in the brain partly due to a loss of central nervous system drug efflux transporter function at the blood-brain barrier. To determine whether a similar loss of active drug efflux occurs in humans after acute inflammatory brain injury.

Design:

Observational human pharmacokinetic study.

Setting:

Medical-surgical-neurosurgical intensive care unit at a university-affiliated, Canadian tertiary care center.

Patients:

Patients with acute inflammatory brain injury, including subarachnoid hemorrhage (n = 10), intracerebral and/or intraventricular hemorrhage (n = 4), or closed head trauma (n = 2) who received morphine intravenously after being fitted with cerebrospinal fluid ventriculostomy and peripheral arterial catheters.

Interventions:

We correlated the cerebrospinal fluid distribution of morphine, morphine-3-glucuronide, and morphine-6-glucuronide with the cerebrospinal fluid and plasma concentration of the proinflammatory cytokine interleukin-6 and the passive marker of blood-brain barrier permeability, albumin.

Measurements and Main Results:

Acute brain injury produced a robust inflammatory response in the central nervous system as reflected by the elevated concentration of interleukin-6 in cerebrospinal fluid. Penetration of morphine metabolites into the central nervous system increased in proportion to the neuroinflammatory response as demonstrated by the positive correlation between cerebrospinal fluid interleukin-6 exposure and the area under the curve cerebrospinal fluid/plasma ratio for morphine-3-glucuronide (r= .49,p< .001) and morphine-6-glucuronide (r= .51,p< .001). In contrast, distribution of morphine into the brain was not linked with cerebrospinal fluid interleukin-6 exposure (r= .073,p= .54). Albumin concentrations in plasma and cerebrospinal fluid were consistently in the normal range, indicating that the physical integrity of the blood-brain barrier was likely undisturbed.

Conclusions:

Our results suggest that central nervous system inflammation following acute brain injury may selectively inhibit the activity of specific drug efflux transporters within the blood-brain barrier. This finding may have significant implications for patients with neuroinflammatory conditions when administered centrally acting drugs normally excluded from the brain by such transporters.

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