2. Biktarvy

Gilead's HIV combo sold $1.94 billion in its first four full quarters on the market. (Gilead Sciences)

2. Biktarvy
Company: Gilead Sciences
Disease: HIV
Approved: Feb. 7, 2018
First four full quarters sales: $1.94 billion

Gilead Sciences’ HIV combo Biktarvy took off so quickly, it became the top new-to-brand HIV regimen in the U.S. during its second full quarter on the market—overtaking the Big Biotech’s own Genvoya. Biktarvy also took Genvoya's place as the most successful HIV launch in history as measured by the first four full quarters of sales, with a score of $1.94 billion versus $1.48 billion.

For a disease as big as HIV, Biktarvy comes in a small package. Combining new integrase strand transfer inhibitor (INSTI) bictegravir with Descovy (FTC/TAF), a single pill of Biktarvy weighs only 275 mg. In contrast, GlaxoSmithKline’s rival therapy Triumeq is 950 mg per tablet. Taking a smaller pill could lighten some psychological burden on patients, but that advantage itself doesn’t explain Biktarvy’s success so far.

Bictegravir has shown a high barrier to resistance and few drug interactions, but so has a key rival, GSK’s INSTI drug Tivicay (dolutegravir). In a head-to-head trial, Biktarvy matched up to Triumeq, a combo med that contains Tivicay.

Perhaps more importantly, though, was another stat from that trial: The Gilead drug demonstrated a lower rate of treatment-related side effects than did the GSK cocktail.

Biktarvy also doesn't face a prescribing hurdle that Triumeq does. To qualify for the GSK cocktail, patients must be screened for a genetic variation linked to hypersensitivity to one of the drugs in the combo, Ziagen (abacavir)

RELATED: The top 10 drugs by sales increase in 20202. Biktarvy

But Biktarvy’s true rivals aren’t traditional three- or four-drug combos. At the end of 2017, the FDA approved GSK’s Juluca, the first two-drug HIV regimen, for virally suppressed patients. Then in April 2019, GSK’s ViiV Healthcare unit won clearance to sell another Tivicay-based two-drug therapy, Dovato, in newly diagnosed patients.

GSK argues its doublet therapies, by cutting the number of drug ingredients a patient's exposed to, can reduce potential drug-drug interactions and side effects over the long term, all while maintaining high viral-suppressing effect.

However, changing the treatment paradigm takes time. Although there’s no evidence showing patients on Dovato or Juluca are at higher risk of developing drug resistance compared to standard triplets, some industry watchers and doctors have yet to fully embrace the two-drug idea. They worry that signs of resistance might show up down the road, especially if patients doesn't take their meds as directed.

The debate will likely linger for a few years until long-term clinical data are available and doctors gain more real-world experience with two-drug regimens. Till then, Biktarvy could well continue to overshadow the two drugs. For 2019, Juluca and Dovato together delivered sales of £422 million ($526 million), while Biktarvy generated $4.74 billion.

According to Gilead CEO Daniel O’Day on a conference call in February, currently about one in every two U.S. patients who are new to therapy or switching are initiating on Biktarvy.

Meanwhile, amid its fast U.S. growth, Biktarvy quickly embarked on a global rollout, winning EU green light in June 2018, Japanese nod in March 2019 and Chinese go-ahead last August.

2. Biktarvy