Entries at Drugs.com have a section on "Side Effects... For Healthcare Professionals" which present percentages for incidence rates of side effects. However, I've found that the rates reported there are wildly at odds with those reported on manufacturer and FDA-approved drug sheets, or any other reference I can find. (Note that Drugs.com collaborates directly with the FDA, and in fact the FDA directs readers to Drugs.com for information on drugs.)
Here's a slice of one example. Researching Reclast, among the numerous side effects listed on Drugs.com, the following are included:
Very common (10% or more): Nausea (29.1% to 46%), vomiting (14% to 32%), constipation (26.7% to 31%), diarrhea (17.4% to 24%), abdominal pain (14% to 16.3%), dyspepsia (10%)...
Very common (10% or more): Bone pain (55%), myalgia (23%), arthralgia (21%), back pain (15%), and limb pain (14%)...
I'll compare to the prescribing information document, produced by the manufacturer Novartis and approved by the FDA, and available on both of their websites (e.g., at FDA). The following is an excerpt from Table 1.
Comparing a few of the side-effect rates noted (Drugs.com vs. Prescribing Information document):
- Nausea: 29.1-46% vs. 4.5-8.5%.
- Vomiting: 14-32% vs. 3.4-4.6%
- Diarrhea: 17.4-24% vs. 5.2-6.0%
- Bone pain: 55% vs. 3.2-5.8%
- Myalgia: 21% vs. 4.9-11.7%
The Prescribing Information document has a few other tables reporting on other studies (for osteopenia, for men, and for Paget's disease), but the incidence rates are all quite similar to those in Table 1.
On Drugs.com, individual numbers are not given specific citations, although there is a general list of references at the bottom of the page. In the case of Reclast, there are five: (1) the Product Information document from Novartis, (2) UK summary, (3) Australian APPGuide online, (4) Australian product information, and (5) Kidney Int report (specific to tubular necrosis). Having looked at all of them, the UK and Australian reports give only qualitative descriptors for incidence rates (no percentage numbers), and the APPGuide Online doesn't appear to exist anymore.
In short: I can't find any source for the incidence rates shown on Drugs.com, and the numbers shown there are dramatically different from those in the prescribing information document from Novartis and the FDA. In some cases the rates are off by up to 50 percentage points.
Furthermore, this is true for all of the larger list of side effects shown for Reclast. And if I look at any other drug I see the same situation (e.g., currently investigating osteoporosis drugs: Fosamax, Boniva, Forteo, and Prolia).
So: Why are the side-effect incidence rates shown on Drugs.com so different from the FDA-approved prescribing information report? Where are Drugs.com getting these numbers? Which one should be considered more reliable?