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Safety of chronic intrathecal morphine infusion in a sheep model
Tamara Lee Gradert1, Wallace B Baze, William C Satterfield
1Department of Veterinary Sciences, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
Background:
The safety of chronically administered intrathecal morphine has been questioned. Therefore, the authors examined the behavioral and neurologic effects and neurotoxicity of continuous intrathecal morphine administration in sheep.
Methods:
Groups of three sheep were implanted with intrathecal infusion systems for the continuous administration of morphine (3, 6, 9, 12, or 18 mg/day) or saline at a fixed infusion rate of 1.92 ml/day beginning approximately 7 days after implantation. Sheep were examined daily for any changes in behavior or neurologic function. After 28-30 days, the animals were humanely killed. Cerebrospinal fluid samples were collected and analyzed for protein, erythrocytes and leukocytes, and morphine content. The spinal cord and meninges with the catheter in situ was removed en bloc and fixed in formalin for histologic analysis.
Results:
Unilateral hind-leg gait deficits were observed in two of three animals in each of the 12- and 18-mg/day dose groups. Gross and microscopic evaluation of spinal cord tissue from these animals revealed intradural-extramedullary inflammatory masses that compressed the spinal cord at the catheter-tip and mid-catheter areas. This inflammation was ipsilateral to extremities that exhibited gait deficits and had acute and chronic cellular components.
Conclusions:
The toxicity of intrathecal morphine seems to be dependent on the amount of morphine infused, although the effects of dose versus concentration cannot be clearly distinguished in this study. Intrathecal morphine doses of 12- 18 mg/day produced inflammatory masses extending from the catheter tip down the length of the catheter within the subarachnoid space. Doses of 6-9 mg/day produced mild-to-moderate inflammation 5 cm cranial to the catheter tip. A dose of 3 mg/day produced no neurotoxicity and spinal histopathologic changes that were equivalent to those observed in the saline-treated animals.
Insights
Continuous intrathecal morphine at high doses (12-18 mg/day) caused neurotoxicity in sheep, leading to inflammatory masses and gait deficits. Lower doses (3 mg/day) showed no adverse effects, suggesting dose-dependent toxicity.
Area of Science:
- Neuroscience
- Pharmacology
- Veterinary Medicine
Background:
- Chronic intrathecal morphine safety is debated.
- Continuous intrathecal morphine administration requires safety evaluation.
Purpose of the Study:
- To investigate the behavioral, neurologic, and neurotoxic effects of continuous intrathecal morphine in sheep.
Main Methods:
- Sheep received continuous intrathecal morphine (3-18 mg/day) or saline via infusion systems.
- Animals were monitored daily for neurologic and behavioral changes.
- Spinal cords and cerebrospinal fluid were analyzed histologically and biochemically.
Main Results:
- Doses of 12-18 mg/day morphine induced unilateral hind-leg gait deficits.
- Histopathology revealed inflammatory masses compressing the spinal cord at the catheter site.
- Inflammation correlated with gait deficits and dose.
Conclusions:
- Intrathecal morphine toxicity is dose-dependent, with 12-18 mg/day causing significant neurotoxicity.
- Lower doses (3 mg/day) did not produce neurotoxicity or histopathologic changes.
- Inflammatory masses formed in the subarachnoid space at higher doses.
