Two case reports describe a marked fall in
theophylline levels when
carbamazepine was given. Another single case report and a pharmacokinetic study describe a fall in
serum carbamazepine levels when
theophylline was given.
The general importance of these reports is uncertain. Concurrent use need not be avoided, but it would be prudent to check that the
serum concentrations of each drug (and their effects) do not become subtherapeutic.