After 16 years as a public company, Alnylam Pharmaceuticals, Inc. (NASDAQ:ALNY) finally got the go-ahead to launch its first product earlier this month. Onpattro is the first in a new class of drugs that alter gene expression, but Pfizer, Inc. (NYSE:PFE) just reported some impressive results with a possible competitor that works a lot differently.

Just how worried should Alnylam investors be about the country's largest pharmaceutical company? Here are six things you need to understand to decide for yourself.

Colorful pills on a pile of cash money.

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1. It's a me-first drug

Onpattro's the first treatment the Food and Drug Administration's ever approved to treat a disease caused by transthyretin amyloidosis, but Pfizer's candidate isn't a "me-too" drug. In fact, the big pharma's been marketing it in the EU as Vyndaqel since 2011.

Pfizer doesn't market the drug in the U.S. yet, because the FDA sent Pfizer's first tafamidis application back with a request for solid evidence that tafamidis actually provides a survival benefit. The oral therapy had been nearly forgotten while investigators gathered the evidence the FDA was looking for.

2. It works a lot differently

Everyone needs a protein called transthyretin (TTR) to carry vitamin A and a thyroid hormone around through their bloodstream. For people with TTR amyloidosis (ATTR), the protein unravels easily and the sticky fragments that build up can cause all sorts of damage.

Tafamidis tries to keep TTR from unraveling in the bloodstream after it's already been produced, generally in the liver. Onpattro steps in a bit earlier and slows down TTR production altogether.

Two laboratory workers examining a slide.

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3. It saves lives

Investigators recently published results of a very long study that's sure to get the FDA's attention. Over a 30-month period, patients in the groups receiving tafamidis were 30% less likely to die from any cause than those given a placebo.

Since TTR amyloidosis is a rare disease, enrolling 441 patients in a long-term outcome trial took Pfizer an awfully long time. It could be years before Alnylam can counter with outcome data for Onpattro, and there's always the chance that it won't impress.

4. It's aimed at a different audience

Tafamidis produced survival benefit data in a group of people with heart problems, or cardiomyopathy caused by inherited ATTR, or hATTR and an uninherited form that tends to occur in older adults. According to Vantage, Pfizer plans to file an application for the cardiomyopathy indication first, then consider challenging Alnylam for neuropathy patients down the road.

Onpattro is aimed specifically at hATTR patients with nerve damage, or neuropathy partly because the FDA didn't allow Alnylam to include any data related to cardiomyopathy on its prescribing label. In 2016, Alnylam scrapped an experimental drug similar to Onpattro that was aimed at the hATTR cardiomyopathy population due to safety concerns.

Lab worker holding test tubes in front of her face.

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5. Its European launch flopped

Pfizer began marketing tafamidis as Vyndaqel in the EU around seven years ago, but sales figures are too low to deserve a separate line item on the company's enormous financial statements. Instead, it gets lumped in with "All other Rare Disease" drugs, which racked up a combined $81 million during the second quarter.

Now that the company's overseas sales teams can point to a meaningful survival benefit, sales might pick up. So far, though, Pfizer's formidable sales force hasn't been able to lift Vyndaqel off the ground.  

6. It probably won't torpedo Onpattro's launch

Pfizer hasn't completed an application for ATTR cardiomyopathy yet, and we still don't know if it will attempt adding tafamidis to ATTR neuropathy patients' list of treatment options. That means Alnylam's first-mover advantage in this niche will probably be upset by a similar treatment coming through Ionis Pharmaceuticals' late-stage pipeline before tafamidis enters the fray.

Over 130 different TTR mutations drive patients to seek treatment and it seems like tafamidis works better for some than others. Onpattro, though, is approved to treat hATTR polyneuropathy regardless of what mutation patients have.  

Going up against Pfizer is a daunting prospect for any drugmaker, and the last thing a company launching its first drug wants to deal with. Alnylam investors are going to want to keep their eyes on Pfizer's ATTR drug, but it isn't worth losing any sleep over right now.

Cory Renauer has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Alnylam Pharmaceuticals and Ionis Pharmaceuticals. The Motley Fool has a disclosure policy.