Valproic Acid-related anticonvulsant hypersensitivity syndrome and subsequent olanzapine-related neutropenia and thrombocytopenia: a case report

Pharmacogenetics of antiepileptic drug-induced hypersensitivity

Antiepileptic drugs can induce potentially life-threatening hypersensitivity reactions such as Stevens–Johnson syndrome at a frequency of one in 10,000 to one in 1000 treated patients. There is a considerable cross-reactivity among different antiepileptic drugs but the mechanisms are not known. In this review we have summarized current evidence on antiepileptic drug-induced hypersensitivity reactions and performed meta-analyses of published case–control studies that investigated associations between HLA alleles and several antiepileptic drugs in diverse populations. As the heterogeneity between studies was high, we conducted subsequent subgroup analyses and showed that HLA-B*15:02 was associated with carbamazepine, lamotrigine and phenytoin-induced Stevens–Johnson syndrome in Asian populations indicating that pretreatment testing may prevent cross-reactivity. Additionally, we explored the potential of new, high-throughput technologies that may help to understand the mechanisms and predict the risk of adverse drug reactions in the future.

Interactions between valproic acid and quetiapine/olanzapine in the treatment of bipolar disorder and the role of therapeutic drug monitoring

OBJECTIVES

The anticonvulsant valproic acid and the atypical antipsychotics olanzapine and quetiapine provide synergistic mood-stabilising, antidepressant and antipsychotic activities in the treatment of bipolar and schizoaffective disorders. Existing literature shows that pharmacokinetic and pharmacodynamics drug-drug interactions (DDIs) possibly occur with the use of such a combination. Clinical reports of a possible interaction between the drugs leading to an increased risk of adverse drug reactions have also emerged. The main objective of this paper is to review the incidence of DDIs between the anticonvulsant and the antipsychotics, to postulate the possible mechanisms of the interaction and to establish whether certain target populations are at an increased susceptibility to such interactions. The usefulness of therapeutic drug monitoring (TDM) of the antipsychotics to monitor for an interaction was also assessed. A systematic database search was carried out using the search engine provided by PubMed using the following key words: olanzapine, quetiapine, valproic acid, pharmacokinetic drug-drug interaction, bipolar disorder, therapeutic drug monitoring.

KEY FINDINGS

Evidence of a possible clinically relevant DDI between valproic acid and both antipsychotics has been uncovered. A possible mechanism for the interactions has been postulated, and the importance of TDM has been discussed.

SUMMARY

Further research is required to determine whether DDIs occur with the concurrent use of valproic acid and olanzapine or quetiapine, and to investigate the potential of TDM as a clinical tool in improving pharmacotherapy and preventing toxicity.