Efficacy and safety are important in marketing a drug. But they're not everything. Sometimes convenience trumps them both.

At least that's what Spectrum Pharmaceuticals (Nasdaq: SPPI) hopes. The drugmaker's non-Hodgkin's lymphoma treatment, Zevalin, which it acquired from Cell Therapeutics (Nasdaq: CTIC), which in turn bought it from Biogen Idec (Nasdaq: BIIB), has never been a big seller -- just $7 million last quarter -- in part because the procedure for administering the drug is inconvenient.

Before administering the therapeutic dose, doctors had to administer a diagnostic dose and perform a bioscan. But Spectrum was able to convince the Food and Drug Administration that the bioscan was unnecessary, and the new label will reflect the easier administration procedure.

Will it be enough to convince doctors to use Zevalin in any meaningful amount? I just don't know. The data comparing Zevalin in combination with Roche and Biogen's Rituxan to Rituxan alone clearly favors the combination therapy. But if the data was really that good, doctors would certainly take the extra time and energy to do the bioscan.

Non-Hodgkin's lymphoma is, after all, a life-threatening disease. This isn't like diabetes, where doctors can justify using Merck's (NYSE: MRK) Januvia or Takeda's Actos over injectable drugs like Novo Nordisk's (NYSE: NVO) Victoza or Amylin Pharmaceuticals' (Nasdaq: AMLN) Byetta even though the latter is arguably better because the former don't require needle pricks.

It seems possible that there's something else that's really holding the sales back. Maybe the sales force needs a bigger push; maybe doctors don't want to deal with the radioactive nature of Zevalin.

The new label looks like an incremental positive for Spectrum, but I wouldn't count on seeing Zevalin become an instant blockbuster. Then again, Spectrum doesn't need a blockbuster to see meaningful growth; revenue through the first nine months of the year was only $140 million, so sales in the hundreds of millions would have a substantial impact on revenue and earnings.

Keep track of the relaunch of Zevalin by adding Spectrum to My Watchlist, the Fool's free watchlist service. Don't have My Watchlist account? Sign up for free.