Clinical trial context

The Herald has a headline: Babies die after their mothers took Viagra while pregnant during a medical trial.  The story is pretty informative, even though its only cited source is the Daily Mail, but there are a few things that are missing.

First, the death rates in this Amsterdam study sound huge. They are. This is a study in pregnancies with extremely poor expected outcomes. Eleven deaths are potentially attributed to the treatment; there are a further 17 deaths from other causes, split about equally between the treatment and control groups.

Second, there are two other studies mentioned, in the UK and Canada.  These are actually part of a pre-planned group of trials, since no single country has enough of these high-risk pregnancies to do the study on its own.  The UK study didn’t see any excess risk, and while we don’t know the results of the Canadian study yet, if it had seen a huge excess risk it would presumably have already stopped, too.

One other major study from this group isn’t mentioned. There’s an Australia/NZ study, which saw slightly better outcomes in the group getting Viagra. It hasn’t been formally published yet, but the results were presented to a conference and were reported in the Herald earlier this year.  It looks as though something might have been different about the Amsterdam study — although it’s also possible they were extremely unlucky.

The other important piece of context, which is in a story in the Guardian, is that Viagra treatment was already being chosen by some women and their doctors in  the hope it would help, but without any convincing information on safety or effectiveness.   A trial that shows a treatment is ineffective or harmful is a bad result for people in the trial, but it should still save lives in the future.