The U.S. drugmaker said two large trials of the oral antiviral being developed with Ridgeback Biotherapeutics would begin in September. Merck said it can manufacture "many millions of doses" of the drug before year end.
Gilead Sciences Inc's intravenous antiviral remdesivir is currently being widely used as a treatment for hospitalized COVID-19 patients.
Merck also expects its two experimental coronavirus vaccines to start human trials later this year, lagging some rivals who have begun late-stage studies.
The vaccine it picked up through its acquisition of Themis Bioscience should start clinical studies in the current quarter, while another being developed with nonprofit research organization IAVI should begin trials by year end.
Effective treatments and vaccines are seen as essential to halting a pandemic that has killed over 674,000 people worldwide and battered global economies.
Merck said it hopes its experimental coronavirus vaccines can be effective with a single dose
"In dealing with an aggressive, globally dispersed disease like COVID-19, we believe that it is wise to lower the barrier to vaccination as much as possible, for example, by launching a vaccine that is effective with just a single administration," Merck research head Roger Perlmutter said on a conference call.
Merck said it now expects a 2020 revenue decline of $1.95 billion due to the precipitous drop in medical visits early in the pandemic, from its prior estimate of $2.1 billion. The company said it expects a return to normal levels in the fourth quarter.
"Business conditions have clearly improved and ... we believe the healthcare system is better positioned to provide patient access as we move through the balance of the year," said Chief Financial Officer Robert Davis.
The company noted that it still had strong second-quarter sales from blockbuster cancer drug Keytruda. Keytruda sale rose nearly 29% to $3.39 billion, ahead of Wall Street expectations.
Total sales fell 7.6% to $10.87 billion due to a $1.6 billion pandemic-related hit in the quarter. That still exceeded analysts' estimates of $10.39 billion.
Merck raised its full-year adjusted profit forecast to $5.63 to $5.78 per share from a prior range of $5.17 and $5.37.
(Reporting by Manas Mishra in Bengaluru and Michael Erman in Maplewood, New Jersey.; Editing by Bernard Orr, Jonathan Oatis and Bill Berkrot)
By Manas Mishra and Michael Erman