EXHIBIT A JOINT FILING AGREEMENT
EXHIBIT A
In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the
undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G
(including amendments thereto) with respect to the Common Stock of Somaxon Pharmaceuticals, Inc.
and further agree that this agreement be included as an exhibit to such filing. Each party to the
agreement expressly authorizes each other party to file on its behalf any and all amendments to
such statement. Each party to this agreement agrees that this joint filing agreement may be signed
in counterparts.
In evidence whereof, the undersigned have caused this Agreement to be executed on their behalf
this 11th day of February, 2009.
| MPM BIOVENTURES III, L.P. | MPM BIOVENTURES III-QP, L.P. | |||||||||
By:
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MPM BioVentures III GP, L.P., | By: | MPM BioVentures III GP, L.P., | |||||||
| its General Partner | its General Partner | |||||||||
By:
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MPM BioVentures III LLC, | By: | MPM BioVentures III LLC, | |||||||
| its General Partner | its General Partner | |||||||||
By:
|
/s/ Xxxx Xxxxx
|
By: | /s/ Xxxx Xxxxx
|
|||||||
| Title: Series A Member | Title: Series A Member | |||||||||
| MPM BIOVENTURES III PARALLEL FUND, L.P. | MPM BIOVENTURES III GMBH & CO. BETEILIGUNGS KG | |||||||||
By:
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MPM BioVentures III GP, L.P., | By: | MPM BioVentures III GP, L.P., | |||||||
| its General Partner | in its capacity as the Managing Limited Partner | |||||||||
By:
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MPM BioVentures III LLC, | By: | MPM BioVentures III LLC, | |||||||
| its General Partner | its General Partner | |||||||||
By:
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/s/ Xxxx Xxxxx | By: | /s/ Xxxx Xxxxx | |||||||
| Name: Xxxx Xxxxx | Name: Xxxx Xxxxx | |||||||||
| Title: Series A Member | Title: Series A Member | |||||||||
| MPM ASSET MANAGEMENT INVESTORS 2005 BVIII LLC |
MPM BIOVENTURES III GP, L.P. | |||||||||
By:
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/s/ Xxxx Xxxxx | By: | MPM BioVentures III LLC, | |||||||
| its General Partner | ||||||||||
| Title: Manager | ||||||||||
| By: | /s/ Xxxx Xxxxx | |||||||||
| MPM BIOVENTURES III LLC | Name: | Xxxx Xxxxx | ||||||||
| Title: | Series A Member | |||||||||
By:
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/s/ Xxxx Xxxxx | |||||||||
Name:
|
Xxxx Xxxxx | By: | /s/ Xxxxxxx Xxxxxxx | |||||||
| Title: | Series A Member | Name: Xxxxxxx Xxxxxxx | ||||||||
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By:
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/s/ Xxxx Xxxxx
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By: | /s/ Xxxxxxxx Xxxxxxxxx
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|||||||
| Name: Xxxx Xxxxx | Name: Xxxxxxxx Xxxxxxxxx | |||||||||
By:
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/s/ Xxxxxxx Xxxxxxxxx | By: | /s/ Xxxx Xxxxxxx | |||||||
| Name: Xxxxxxx Xxxxxxxxx | Name: Xxxx Xxxxxxx | |||||||||
By:
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/s/ Xxxxxxxx Xxxxx III | By: | /s/ Xxxxxx Xxxxxx | |||||||
| Name: Xxxxxxxx Xxxxx III | Name: Xxxxxx Xxxxxx |
Page 24 of 24
