So What’s the Difference

In my last post, I discussed pregnancy categories and how they are defined. The difficulty with using these pregnancy categories is that they are not all black and white with clear, defined features. When looking at category D and category X drugs, both have shown evidence of fetal damage in animals and humans; however, category D medications can be used when the benefits out weigh the risks while category X medications should never be used. There are no clear cut rules that define what would constitute a benefit that out weighs a risk of the medication and, for me, this makes it difficult to understand the difference between the two categories. How was it decided that one medication should be a category D over category X? Are there alternative therapies that are safer or was a drug placed in category D because there are currently no other available options for treatment? Is it a life-saving treatment?

The use of letters to denote a category also makes me view the categories hierarchically, where A represents the safest medications and the safety profile drops with each drop in letter, but this is not entirely correct. For example, category C medications represent a group of medications where there is not enough evidence to suggest harm or safety. At this point, we do not know if the medication will show damage to the fetus or not. So we really do not know if it is safer to use than a category D or X drug but we also do not know if it is more harmful than a category A or B drugs, yet it is placed in the middle just to confuse me. Category B drugs can have positive evidence for safety in animals and not enough evidence in humans or there were adverse effects seen in animals studies but human data has not shown adverse effects. Why did we see harm in animal studies but it appears that there is no harm in humans? Can evidence of safety in animals correlate to evidence of safety in humans if you can have evidence of harm in animals but evidence of safety in humans?

Category A medications are those that have not been shown to cause harm in the first trimester nor have they shown harm in later trimesters. I feel as though this category should be really straight forward but it is not for me. These are medications that have not shown harm but this does not mean that there is 0 potential for harm.

It is important to note that a lack of evidence does not suggest safety or harm and should not be viewed in a positive or a negative way. A lack of evidence should be treated for what it is, a lack of evidence.


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