Confusion from carbamazepine

Tolerability" should not be confused with the term "tolerance", which describes the diminution in effects of a drug on prolonged exposure. Tolerance may be due to increased clearance because of autoinduction of the enzymes that metabolise the drug, such as occurs with some antiepileptic drugs, for example, carbamazepine. Tolerance may also result from altered pharmacodynamics, which is common with drugs acting on the CNS. 

Other studies have similarly found 40 to 60% falls in plasma haloperidol levels in patients taking carbamazepine, " with the occasional patient having undetectable levels. Decreases in plasma haloperidol levels of unspecified amounts have also been described. A study in 9 patients t ing haloperidol 6 mg twice daily who were then given carbamazepine, with the daily dose increased at fortnightly intervals from 100 to 300 and to 600 mg, found a dose-dependent reduction in haloperidol levels. Mean plasma haloperidol levels were reduced by 25%, 61%, and 82%, respectively. A few patients have had clinical worsening or increased adverse effects. " Three patients had two to fivefold increases in plasma haloperidol levels and clinical improvement when carbamazepine 1.2 to 1.4 g daily was stopped, but extrapyramidal adverse effects developed within 1 to 30 days. Three cases of neurotoxicity (drowsiness, slurred speech, confusion) have also been described in patients taking haloperidol and carbamazepine. ... 

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