A Method for Approximating Future Entry of Generic Drugs



To develop and test a method for approximating generic entry of top-selling drugs.


The procedure involved 1) identifying products’ key patents as those with a patent term restoration extension (whenever relevant) or otherwise as the first expiring patent listed in the US Food and Drug Administration’s patent register, 2) determining whether the key patent had been extended through an associated pediatric extension, 3) identifying other regulatory exclusivities associated with the drug, and 4) categorizing key patents as active ingredient (or extended) patents versus secondary patents. The accuracy and precision of the procedure’s predictions were then tested against a database containing the timing of generic entry for 170 top-selling drugs that lost market exclusivity between 2000 and 2012, on the basis of Medicaid data.


Overall, the procedure predicted a median market exclusivity period of 12.5 years (interquartile range [IQR] 7.25–14.5) compared with the median actual period of 12.5 years (IQR 8.5–14.75 years). Among the 131 drugs (77%) with active ingredient patents, the median predicted market exclusivity was 12.25 years (IQR 7.5–14.5) compared with a median actual period of 13.0 years (IQR 10.0–14.75). Among the 38 (22%) drugs protected only by secondary patents, the median predicted market exclusivity was 16.0 years (IQR 6.75–19.5), but the median actual market exclusivity was only 8.25 years (IQR 6.25–13.5).


The procedure approximated median actual exclusivity with reasonable accuracy and precision for drugs with active ingredient patents, but substantially overestimated exclusivity for drugs with only secondary patents.


Reed F. Beall Jonathan J. Darrow Aaron S. Kesselheim

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