The stock market has finally gotten some upward momentum, and Wall Street tried to carry it further into Wednesday's premarket session. As of 8:30 a.m. ET, Dow Jones Industrial Average (DJINDICES: ^DJI) futures were up 46 points to 36,174. S&P 500 (SNPINDEX: ^GSPC) futures had picked up 5 points to 4,710, and Nasdaq Composite (NASDAQINDEX: ^IXIC) futures had risen 35 points to 15,866.

Yet a couple of stocks stood out because of steep drops in premarket trading. Biogen (NASDAQ: BIIB) was particularly noteworthy, because news about its treatment for Alzheimer's disease is setting up a potential financial battle between the biotech stock and the U.S. government's Medicare program. Meanwhile, Koninklijke Philips (NYSE: PHG), also called Royal Philips, also moved lower as it gave some guidance on how its fourth-quarter financial results are likely to look.

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Biogen gets a Medicare snub

Shares of Biogen fell almost 10% in premarket trading Wednesday. The move followed a proposal from government regulators regarding potential reimbursements for its amyloid-targeting Aduhelm treatment for Alzheimer's disease.

The Centers for Medicare & Medicaid Services proposal would limit program coverage for Medicare participants for taking Aduhelm. Only those who are enrolled in qualifying clinical trials would be eligible for reimbursement for the treatment. Biogen responded with a stern statement saying it is "imperative to change this draft decision" to give patients access to treatments that have received approval from the U.S. Food and Drug Administration.

At issue is the cost of Aduhelm. Medicare coverage for the treatment, which had initially borne a cost of $56,000, was a key component of the rise in Part B Medicare premiums from $148.50 to $170.10 per month. However, Biogen agreed at the beginning of 2022 to cut the price of the treatment in half, and advocates hope this might lead Medicare to reduce the extent of the premium hike.

Of course, limiting coverage to a tiny portion of the Medicare-eligible population would potentially cut program costs even further. Yet there's sure to be plenty of controversy throughout the public comment period, with a final determination expected on April 11.

Philips deals with the ongoing pandemic

Meanwhile, shares of global health technology company Philips were down even more sharply, falling 16% in premarket trading. The company gave an update on its fourth-quarter numbers that left shareholders concerned about its prospects.

Philips said that it now expects sales for the quarter to come in at about 4.9 million euros. That's 350 million euros lower than the company's previous guidance, with Philips blaming the shortfall on global supply chain shortages and postponements in customers choosing to install equipment. The revenue number would represent a comparable sales decline of about 10%, with the recall of the Philips Respironics line of certain CPAP and mechanical ventilator medical devices also weighing on the company's top-line results.

As a result, full-year 2021 sales should be about 17.2 billion euros, corresponding to a 1% drop in comparable sales. Philips quantified the impact of the supply chain challenges and recall at about 5 percentage points.

Philips also warned that its bottom line would be affected. Pretax operating earnings of 650 million euros in the fourth quarter and 2.1 billion euros for the full year were lower than most investors had expected.

The news from Philips makes clear that the pandemic continues to hurt companies around the world, and supply chain issues aren't letting up. That could affect Philips and others well into 2022.

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Dan Caplinger has no position in any of the stocks mentioned. The Motley Fool recommends Biogen. The Motley Fool has a disclosure policy.