Not all sales declines are unexpected.

Ever since Genentech's (NYSE:DNA) Lucentis entered the U.S. market last year, declines have certainly been expected with drug developer QLT's (NASDAQ:QLTI) lead compound, macular degeneration treatment Visudyne. Today QLT pre-announced its latest sales numbers for the drug.

Sales of Visudyne by partner Novartis (NYSE:NVS) dropped precipitously in the U.S. vs. the second quarter of last year, down 46% to $10 million, because of the competition from Lucentis. International sales didn't fare much better, falling 36% to $49 million.

It's important to remember that QLT only gets to book a portion of these sales as revenue (about 25% of sales last quarter), and QLT's margins fall as Visudyne sales decline. There's still plenty of room for international sales to drop further, but U.S. sales are finally starting to level off on a quarter-over-quarter basis, with Q1 sales of $8 million.

The real story with the Visudyne sales announcement is not that Novartis' sales of the drug fell precipitously again, but rather how much value to QLT the drug has. QLT and others are trying to resuscitate the drug's future through further clinical testing of the drug.

The hope is that combination use of Visudyne with Lucentis or its cheaper brother Avastin will show improved efficacy versus Lucentis monotherapy, or as salvage therapy for patients who fail to adequately be treated with Lucentis. Some of the larger clinical studies with these compounds won't be completed until 2009, though, which could mean another year of declining sales for Visudyne.

Looking for more Foolish drug stock coverage? Check out the Fool's market-beating Rule Breakers newsletter. You can check out all our recommendations, as well as get access to our message boards and exclusive content, with a 30-day free trial.

Fool contributor Brian Lawler does not own shares of any company mentioned in this article.