• Sarah J Nolan, Catrin Tudur Smith, Jennifer Pulman, and Anthony G Marson.
• Department of Biostatistics, University of Liverpool, Liverpool, UK. sarah.nolan@liv.ac.uk.
• Cochrane Db Syst Rev. 2013 Jan 31 (1): CD002217CD002217.

BackgroundThis is an updated version of the original Cochrane review published in The Cochrane Library 2001, Issue 4.Worldwide, particularly in the developing world, phenytoin and phenobarbitone are commonly used antiepileptic drugs, primarily because they are inexpensive. The aim of this review is to summarise data from existing trials comparing phenytoin and phenobarbitone.ObjectivesTo review the best evidence comparing phenobarbitone and phenytoin when used as monotherapy in participants with partial onset seizures or generalised tonic-clonic seizures with or without other generalised seizure types.Search MethodsWe searched the Cochrane Epilepsy Group trials register (31 May 2012), the Cochrane Central Register of Controlled Trials (CENTRAL Issue 5 of 12, The Cochrane Library 2012) and MEDLINE (1946 to May week 4, 2012). We hand-searched relevant journals, contacted pharmaceutical companies, original trial investigators and experts in the field.  Selection CriteriaRandomised controlled trials in children or adults with partial onset seizures or generalised onset tonic-clonic seizures with a comparison of phenobarbitone monotherapy with phenytoin monotherapy.Data Collection And AnalysisThis was an individual participant data (IPD) review. Outcomes were time to (a) treatment withdrawal (b) 12-month remission (c) six-month remission and (d) first seizure post randomisation. Cox proportional hazards regression models were used to obtain study-specific estimates of hazard ratios (HRs) with 95% confidence intervals (CIs) with the generic inverse variance method used to obtain the overall pooled estimate of HRs and 95% CIs.Main ResultsData have been obtained for four of eight studies meeting the inclusion criteria, amounting to 599 individuals, or approximately 63% of the potential data.The main overall results (pooled HR, 95% CI) were (a) time to treatment withdrawal 1.62 (1.23 to 2.14); (b) time to 12-month remission 0.90 (0.69 to 1.18) (c) time to six-month remission 0.92 (0.73 to 1.16) and (d) time to first seizure 0.85 (0.68 to 1.05). These results indicate a statistically significant clinical advantage for phenytoin in terms of treatment withdrawal. However, this result may have been confounded by several factors including substantial statistical heterogeneity between studies and lack of blinding in two studies.Authors' ConclusionsThe results of this review show that phenobarbitone was significantly more likely to be withdrawn than phenytoin. Given that no significant differences for seizure outcomes were found, the higher withdrawal rate with phenobarbitone may be due to adverse effects. Several factors may have confounded the results of this review.  

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