Swiss drugmaker Roche is sticking to its 2021 forecast for revenue growth, as first-quarter sales of Covid-19 tests offset a slumping main drug business that has been hurt as the pandemic limits doctor visits for other diseases.

First-quarter sales were 14.9 billion Swiss francs ($16.3 billion), down 1% from 15.1 billion francs in the year-earlier period, Roche said.

The Basel-based company, which does not report quarterly profit, said the strong Swiss franc dragged down revenue.

Diagnostics sales, driven by demand for an array of Covid-19 tests for everything from infections to antibodies in people who have recovered, rose 55% to 4.3 billion francs.

That contrasts with falling fortunes in the drug business, where revenue slipped 9% to 10.6 billion francs.

Chief executive Severin Schwan was optimistic in mid-2020 that health care systems were successfully navigating the pandemic and that revenue from drugs would normalise.

But with Covid-19 infections raging, Schwan has had to modify his hopes for a drug sales recovery, even if diagnostics pick up the slack.

"The pandemic continued to have a negative impact overall on the division's sales, especially for medicines where regular visits to hospitals or health practices are needed," Roche said.

The company still expects current-year sales growth in the low to mid-single-digit range at constant exchange rates, with similar core earnings per share growth.

Among the drugs hardest hit by the pandemic was top-selling Ocrevus, whose growth slowed to 16%, down from 24% last year, to 1.2 billion francs.

Its drugs business was lifted by Actemra, an arthritis drug repurposed for Covid-19 pneumonia whose revenue rose 22% to 779 million francs, as well as an anti-Covid-19 antibody cocktail it has partnered on with Regeneron that reaped 166 million francs.