ECONOMIC EVALUATION OF HLA-B*1502 GENE SCREENING FOR THE PREVENTION OF CARBAMAZEPINE-INDUCED TOXIC EFFECTS IN TAIWAN

Purpose: Carbamazepine, a commonly prescribed anticonvulsant, is associated with two rare toxic effects, Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis (SJS/TEN) leading to significant morbidity and mortality.  This drug is used to treat several conditions and while alternative drugs associated with lower risks of SJS/TEN are available, they have varying effectiveness and costs.  Recently, use of a human leukocyte antigen, HLA-B*1502, linked to the occurrence of SJS/TEN has been proposed to identify individuals at the highest risk prior to prescribing decisions.  Because 7.7% of the Taiwanese population carry HLA-B*1502 and over 50,000 new people use Carbamazepine each year, this study aims to determine under which conditions, if any, is screening prior to prescribing is preferable to using an alternative, possibly less effective, drug from the perspective of the Taiwanese government.

Method: We built a decision model to compare the SJS/TEN deaths averted and costs from Carbamazepine use alone; screening prior to prescribing; and use of an alterative drug alone.  Model inputs on costs and health effects were drawn from the published literature.  We included a hypothetical “penalty” cost to represent additional costs of treating uncontrolled conditions when a less effective alternative drug was used.

Result: Assuming 50,000 Taiwanese may take Carbamazepine each year, we estimated this would result in 19 deaths for a total cost of US$130,389.  Screening prior to prescribing would reduce the number of deaths to 2.5 but increase the cost to over $5 million.  However screening would be dominated by the use of any equally effective alternative drug unless the price per screen is reduced from $106 to less than $10.  Use of an alternative drug relative to Carbamazepine without screening would cost an additional $34,000 per death averted for an alternative drug with 10 times the Carbamazepine’s price.  If the alternative drug is inferior to Carbamazepine however, incurring penalties of up to 15 times the price of Carbamazepine.

Conclusion: Using the current compensation amount as a benchmark for willingness to pay to avert a death, use of similarly effective and priced alternative drugs relative to using Carbamazepine is a reasonable investment for the Taiwanese government.  Our results suggest that alternative drugs of equivalent quality should be recommended and used as first line therapies unless the price of screening is dramatically reduced.