Gilead's converting Truvada PrEP users to Descovy faster than expected: analyst

One big task for Gilead Sciences’ HIV franchise in the coming year is to save some $2.5 billion in annual sales by switching as many PrEP patients as possible from Truvada to newly approved Descovy before generics hit.

So far, the company’s doing a good job.

In just two months since the FDA approved Descovy to prevent HIV, Gilead has converted about 10% of Truvada patients to the new drug, a Jefferies team led by analyst Michael Yee noted in a Friday report based on IQVIA scripts data.

For the week ended Nov. 22, Descovy's total U.S. prescriptions hit 19,295—up about 4,000 from the week ended Oct. 11, the first after its FDA go-ahead. During the same period, Truvada scripts per week dropped by around 3,000 from between 34,000 and 35,000.

At that rate, Gilead could switch about 50% to 60% of PrEP users off Truvada by the time Teva launches its copycat in September 2020, Yee estimates. That's well ahead of the 35% Wall Street currently expects.

Yee’s team also mapped out a scenario in which all Truvada scripts were transferred at a steady weekly rate to Descovy by Teva’s anticipated launch date, and it found that Descovy is tracking even faster than that. But of course, 100% conversion is almost impossible, and Yee attributed some of Descovy's growth to organic expansion beyond Truvada switch-overs. Some of that is coming from tandem use with ViiV Healthcare’s Tivicay (dolutgravir) for the treatment of HIV, rather than prevention.

A recent Jefferies doctor survey also suggested the Truvada-Descovy swap would go slower than the HIV treatment switchover from TDF-to-TAF-based regimens, which now stands at about 75%. The difference between Descovy and Truvada is that, besides the shared component of emtricitabine, the newer drug uses tenofovir alafenamide (TAF), which is generally considered a safer option than the tenofovir disoproxil fumarate (TDF) used in the latter.

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Gilead’s playing up that advantage in convincing doctors and patients to use the new version. The Big Biotech recently detailed data from the phase 3 Discover trial, showing significantly better bone mineral density and renal safety outcomes for Descovy patients than for those on Truvada.

The company knows what’s at stake: about $2.6 billion in Truvada annual sales is on the line. With that in mind, it has bulked up Descovy's rep ranks, moving many sales reps off a cardiopulmonary portfolio that's been hit by generics and retraining them to detail Descovy, Gilead’s chief commercial officer, Johanna Mercier, told investors on a conference call in October.

Mercier noted that over half of PrEP scripts are “very concentrated,” coming from a couple of thousand specialists who are also treating HIV patients. These docs have been Gilead’s initial target for the Descovy swap because they “have experienced converting from TDF to TAF and also understand the value of Descovy and its clinical profile specifically around the safety with bone and renal,” she said.