Event – Stribild constituents could underline Gilead’s lead in HIV

Having set Stribild on the path to becoming the best-selling anti-HIV drug in the world by 2018, Gilead is now breaking it down for parts. Two components of the four-drug pill, the HIV integrase inhibitor elvitegravir and its potentiator cobicistat, have their separate US approval decision dates on the last weekend of April.

While they will be nowhere near as lucrative as the combination, elvitegravir and cobicistat could still be important in extending Gilead’s reach. Stribild is only approved for use in treatment-naïve patients, whereas the separate drugs could enable it to address patients who have already taken – and perhaps those who are still taking – other pills.

Company  Gilead Sciences  
Product  Elvitegravir  Cobicistat 
Market cap  $73.6bn
Product NPV  $937m $406m
% of market cap  1% 1%
Event type  PDUFA
Date  April 27, 2013 April 28, 2013

Pill burden

Phase III data on elvitegravir showed that it was non-inferior to Merck and Co's Isentress, which will be the fourth-biggest selling HIV treatment in 2018, according to EvaluatePharma’s consensus forecasts. In fact, the data favoured elvitegravir over Isentress, and its once-a-day dosing means it has an important advantage over Merck’s twice-daily drug (Gilead takes small but important step with elvitegravir data, March 23, 2011).

Elvitegravir is an HIV integrase inhibitor, belonging to the same class as Isentress and GlaxoSmithKline’s dolutegravir, the latter of which has a PDUFA date of August 16. Both are expected to become blockbusters by 2018, compared with which elvitegravir’s forecast sales of $389m seem a little anaemic.

Forecast worldwide sales of HIV integrase inhibitors ($m)
Status Product Generic Name Company 2013 2018
Marketed Isentress raltegravir potassium Merck & Co 1,672 1,624
Filed Dolutegravir dolutegravir GlaxoSmithKline 46 1,492
Filed Elvitegravir elvitegravir Gilead Sciences 39 389

Cobicistat is not an antiviral. The compound inhibits cytochrome P450 3A, which breaks down many drugs, including elvitegravir, thereby enhancing their activity.

Much of the emphasis in HIV drug development is now on reducing patients’ pill burden; this is part of the reason for Stribild’s success. Perhaps Gilead will seek to combine elvitegravir and cobicistat into a single tablet. However, the individual drugs will be useful on their own. Cobicistat has been shown to potentiate protease inhibitors such as Bristol-Myers Squibb’s atazanavir, and Gilead is working with BMS on the development of a fixed-dose combination of the two drugs among other collaborations, and elvitegravir has succeeded in phase III trials alongside Johnson & Johnson’s Intelence and Roche’s Fuzeon.

Pricing will be an important consideration. Stribild costs $28,000 per patient per year and presumably insurers will balk at paying more than half of this for two of its four constituents.

If the FDA refuses approval for either project, Gilead can still forge ahead with the other. The company has a lock on the HIV market with its Stribild, Truvada and Complera occupying the first, second and third places on the 2018 bestseller list.

But US approval for elvitegravir and cobicistat will allow it to mop up a few more patients, and, for the company’s competitors, will add insult to injury.

To contact the writer of this story email Elizabeth Cairns in London at elizabethc@epvantage.com or follow @LizEPVantage on Twitter

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