Generic substitution of lamotrigine among medicaid patients with diverse indications: a cohort-crossover study.
BACKGROUND
Controversy exists about the safety of substituting generic antiepileptic drugs (AEDs). Lamotrigine, the prototypical newer AED, is often used for psychiatric and neurological conditions other than epilepsy. The safety of generic substitution of lamotrigine in diverse populations of AED users is unclear.


OBJECTIVE
The objective of this study was to evaluate potential associations between generic substitution of lamotrigine and adverse consequences in a population of diverse users of this drug.


METHODS
This study was a retrospective cohort-crossover design using state Medicaid claims data from July 2006 through June 2009.


METHODS
Subjects were included in the cohort if they converted from brand to generic lamotrigine and had 2 years of lamotrigine use prior to conversion. The frequency of emergency department (ED) visits, hospitalizations and condition-specific ED visits or hospitalizations were recorded in the 60 days immediately following the conversion to generic lamotrigine, then compared with the incidence of the same events during a randomly selected time period indexed to one of the patient's past refills of branded lamotrigine. Multivariate conditional logistic regression was used to quantify the association between generic conversion and health services utilization while controlling for changes in lamotrigine dose and concurrent drug use.


RESULTS
Of the 616 unique subjects included in this analysis, epilepsy was the most common diagnosis (41%), followed by bipolar disorder (32%), pain (30%) and migraine (18%). Conversion to generic lamotrigine was not associated with a statistically significant increase in the odds of an ED visit (adjusted odds ratio [AOR] = 1.35; 95% confidence interval [CI] 0.92, 1.97), hospitalization (AOR = 1.21; 95% CI 0.60, 2.50) or condition-specific encounter (AOR 1.75; 95 CI 0.87, 3.51).


CONCLUSIONS
A statistically significant increase in ED visits, hospitalizations or condition-specific encounters was not observed following the switch from brand to generic lamotrigine, although a type II error cannot be ruled out.
Oregon State University College of Pharmacy, Oregon Health & Science University, Portland, OR 97239, USA. hartungd@ohsu.edu
Daniel M
DM
Hartung
Luke
L
Middleton
Leanne
L
Svoboda
Jessina C
JC
McGregor
D000927:Anticonvulsants / Q000009:adverse effects / Q000627:therapeutic use*; D015331:Cohort Studies; D018592:Cross-Over Studies; D057915:Drug Substitution; D004363:Drug Utilization / Q000191:economics; D016568:Drugs, Generic / Q000009:adverse effects / Q000627:therapeutic use*; D004827:Epilepsy / Q000188:drug therapy*; D006760:Hospitalization / Q000191:economics; D006801:Humans; D000077213:Lamotrigine; D008484:Medicaid / Q000191:economics; D012189:Retrospective Studies; D014227:Triazines / Q000009:adverse effects / Q000627:therapeutic use*; D014481:United States
D000927:Anticonvulsants; D016568:Drugs, Generic; D014227:Triazines; D000077213:Lamotrigine