Shares of healthcare company Amgen (AMGN 0.75%) have been falling since it released its latest quarterly results on April 27. Although the company generated positive year-over-year revenue growth, earnings declined during the period.

It wasn't a great start to the year, but is it enough to worry investors and to potentially justify selling shares of this high-yielding dividend stock? Here's what was behind the numbers.

Company meeting to discuss performance.

Image source: Getty Images.

Other expenses negated what would have otherwise been a strong quarter

Amgen's revenue for the first three months of 2022 totaled $6.2 billion and rose 5.7% year over year. Even after the cost of goods sold and overhead, its operating income of $2.5 billion was looking impressive, up 17.4% from a year ago. The one line item that wrecked it all was other income and expenses, which saddled the company with $530 million in costs (versus the $13 million boost that other income gave the bottom line in the prior-year period). As a result, net earnings of under $1.5 billion were lower than the $1.6 billion profit Amgen reported a year ago.

As for what makes up this seemingly miscellaneous line, the company says that the expenses were "due to net losses recognized on our strategic equity investments." Since this has nothing to do with Amgen's operations themselves, these costs get pushed to the other income and expenses line -- but they weigh down earnings all the same.

Source: Company filings. Chart by author.

Overall, it was generally a strong quarter for Amgen as there were improvements in gross profit, cost savings in operating expenses, and even taxes were lower this past quarter.

The bigger issue for investors may lie in its growth than its overall net income number.

There wasn't much growth among the company's top drugs

Amgen's product sales in Q1 totaled $5.7 billion and increased by a modest 2% year over year. And what's concerning about this picture is that sales for the company's top 10 drugs declined. The positive, however, was that the company's other drugs collectively generated revenue growth of just over 15%.

Source: Company filings. Chart by author.

Enbrel, Amgen's top-selling rheumatoid arthritis drug, was down 7% as the company blamed a lower net selling price and lower inventory levels for the disappointing performance. Another top-10 drug, Otezla, which treats psoriatic arthritis, faced similar challenges as its sales declined by 5%. These aren't earth-shattering declines by any means, and given the supply chain issues the world is facing these days, it may be premature to assume that Amgen's top drugs are in trouble.

The positive is that new drugs are starting to contribute and grow, including its recently approved cancer drug Lumakras, which brought in $62 million in revenue last quarter (it didn't generate any revenue a year ago). This is a potential blockbuster that may bring in more than $1 billion in annual sales by 2026.

Should you buy Amgen's stock?

The results weren't great for Amgen in Q1, but they also weren't terrible, either. Nothing in these earnings numbers suggests that the company is on the wrong track or that its growth prospects don't look promising anymore. This is still a solid investment that could make for an underrated buy given the dip in price. Its earnings multiple of 23 is reasonable; the average healthcare stock within the Health Care Select Sector SPDR Fund trades at 22. Plus, its 3.4% yield is also more than double the S&P 500 average of 1.4%.

Investors shouldn't worry about these results, and any prolonged drop in price only makes Amgen that much better of a buy in the long term.