Thanks to John Rex for notifying me about the two
developments I will discuss here.
The first is an upcoming (March 1) FDA Workshop entitled,
“Current State and Further Development of Animal Models of Serious Infections
Caused by Acinetobacter baumannii and
Pseudomonas aeruginosa.” The FDA recognizes that clinical trials for
pathogen-specific antibiotics will be difficult when the number of infections
targeted by the product is expected to be small. They also recognize the value
of animal models in predicting both antibiotic dosing and efficacy in humans.
As summarized by the FDA, the purpose of this workshop is to discuss “the
additional scientific work needed to evaluate current animal models of
infection and evaluate potential animal models that may predict response in
humans could advance the development of antibacterial drugs targeting a single
species.” No briefing materials are posted for the workshop, so I can’t provide
specifics as to FDA thinking here.
During the last
FDA workshop on pathogen-specific antibiotics, we discussed the potential
to use the animal efficacy rule that the FDA has established for special
pathogens like antrax and plague where clinical trials for efficacy are not
feasible at all. This is Rex
et. al.’s (requires subscription – sorry) Tier D pathway for antibiotic
approval. I thought that the consensus at the workshop was that such an
approach was not necessary since some clinical data relevant to efficacy could
be obtained even if the data were limited.
On the other hand, as I noted, Paul Ambrose kept pointing
out that if inferential trials for these products were not possible, animal
models and PK/PD could provide a strong rationale for approval. It looks like
the FDA may be trying to put investors’ money in Paul’s mouth (or something
like that). It looks to me, trying to
read between these lines, like the FDA wants to try and put a more standard
definition around the kind of animal models, perhaps even specifying strains of
bacteria to be studied and methods to be used, such that uniform datasets can
be evaluated when looking at different products. I would anticipate that some
clinical data will also be required for approval.
It seems clear that this will be an important workshop for
those interested in pathogen-specific antibiotics and especially for those with
expertise in animal models and PK/PD. Will we see further guidance on this from
FDA this year?
A separate development that might be of interest to
antibiotic developers comes from Europe and EMA. I mentioned
in my previous discussion of pathogen-specific antibiotics that Europe had more
tools available with which to approve products where robust clinical trial data
are not readily available. One of these is conditional market approval (CMA). The FDA has a similar pathway for approval –
but it relies specifically on the availability of biomarkers – something we do
not have for antibiotics (with the exception of TB). The EMA just completed an analysis
of products approved under their conditional approval pathway since 2006. According
to EMA, “medicines that were granted a CMA target seriously debilitating or
life-threatening conditions such as HIV infection, breast cancer, severe
epilepsy in infants or multi-drug resistant tuberculosis. 14 were orphan
medicines.” But a CMA is valid only for
one year at which time the conditional approval must be renewed or new data
must be presented to allow for full approval.
In 90% of cases, sponsors complied with the requirements of EMA in
seeking full market approval and in 70% of cases, sponsors were able to comply
with pre-discussed timelines for achieving full approval. Obtaining the data
required for full approval took an average of four years. But this means that for those four years,
important new medicines were available for the patients that needed them during
which time companies were able to successfully gather data to further support
marketing approval (See Figure below). Although the FDA is still faster than
EMA for full approvals in general, one must envy the Europeans for their more
broadly applicable conditional approval pathway.
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