Long-term observation of the relation between pain intensity and serum carbamazepine concentration in elderly patients with trigeminal neuralgia.

The relation between changes in pain intensity and serum carbamazepine (CBZ) concentration was studied in five elderly patients with trigeminal neuralgia. Measurement of pain intensity and serum CBZ concentration, and blood studies, were performed approximately every 2 or 3 months after initiation of CBZ therapy. Fluctuations in pain intensity were observed in four patients. In these patients, even when the serum CBZ concentration was maintained within a relatively high range, there were periods in which pain intensity increased. On the other hand, there were periods in which pain was relatively well controlled even though the CBZ concentration was relatively low. There were considerable interindividual differences in response to CBZ. The fluctuations in pain showed that the CBZ response curve varies from period to period even within an individual. It was concluded that it is essential to observe spontaneous variations in pain intensity and monitor serum CBZ during long-term administration.