Avoiding neurotoxicity with lithium-carbamazepine combinations

A therapeutic synergism has been well documented with carbamazepine (CBZ) and lithium in some patients who do not respond adequately to either drug alone. Because both of these drugs can induce neurotoxicity, concern has been expressed about their safety when combined. The serum levels for effective and safe dosage have been determined when these drugs are used alone. Unfortunately, this information does not give us automatic insight into the range of safe serum levels for each drug when these drugs are combined. We do not know whether the contribution of each drug to the neurotoxicity is the same. We have plotted the paired serum levels on a two-dimensional graph and quantitatively determined the region where we begin to encounter neurotoxicity. When we examine the available data on this graph, we see no evidence for synergistic neurotoxicity.