Tolerance during long-term administration of intrathecal morphine

We studied the time course of development of tolerance in four terminally ill cancer patients who were treated for intractable pain by intrathecal morphine administered by an implanted catheter and pump. The duration of treatment varied from 1.8 to 10.5 months. Our study shows that with disease progression, there was a constant patient-specific time rate of increase in the morphine dose requirements. Hence, for any given patient, the slope of the dose v time curve is effectively a constant over long periods. We also found that patients tolerate very high doses of intrathecal morphine without serious side effects.