Service Agreement – A

Formulation development of RHB-105 in oral solid dosage form and manufacture
of clinical supplies

Amendment 3





Exhibit 4.19



THE SYMBOL “[****]” DENOTES PLACES WHERE
PORTIONS OF THIS DOCUMENT HAVE BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT. SUCH MATERIAL HAS BEEN FILED SEPARATELY
WITH THE SECURITIES AND EXCHANGE COMMISSION.



Amendment 3 to The service
Agreement Ais made and entered in April 19th, 2012 (the “Amendment”).



|1. |  | DESCRIPTION OF THE EXTRA WORK
|-- |  | -----------------------------

| |  | 
| |  | 

The
Client requested that the GMP Omeprazole magnesium API and GMP Amoxicillin API and GMP Rifabutin API would be analyzed by Corealis
at their reception at the Corealis]facility for full testing and not only ID testing.



|a. |  | GMP Omeprazole magnesium API analytical release testing
|-- |  | -------------------------------------------------------



|ITEM                                          | Cost (USD$) |         
|--------------------------------------------- | ----------- | --------
|                                              |             |         
|ID testing                                    |             |         
|IR-Method qualification, set-up and analysis* | 0$          |         
|[****]                                        | 200$        |         
|                                              |             |         
|Assay                                         |             |         
|Method qualification                          | 2,000$      |         
|Set-up                                        | 605$        |         
|Analysis                                      | 575$        |         
|                                              |             |         
|Related substances                            |             |         
|Method qualification                          | 2,500$      |         
|Set-up**                                      | 0$          |         
|Analysis                                      | 795$        |         
|                                              |             |         
|Residual solvents                             |             |         
|Method A: [****]                              |             |         
|[****]                                        | 14,000$     |         
|Analysis                                      | 1,200$      |         
|                                              |             |         
|Water - Karl Fisher Titration (USP <921>)     |             |         
|Analysis                                      | 165$        |         
|                                              |             |         
|Appearance                                    |             |         
|Analysis                                      | 85$         |         
|                                              |             |         
|[****]                                        |             |         
|                                              |             | Analysis

















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Service Agreement – A

Formulation development of RHB-105 in oral solid dosage form and manufacture
of clinical supplies

Amendment 3







|[****]                                                       | Analysis    | 170$ | 
|------------------------------------------------------------ | ----------- | ---- | 
|                                                             |             |     
|[****]                                                       |             |     
|Analysis                                                     | 550$        |     
|                                                             |             |     
|Report****                                                   | 688$        |     
|                                                             | _______    
|                                                             |             |     
|Sub total for section 1. a.                                  | 23,608$     |     
|                                                             |             |     
|b. GMP Amoxicillin trihydrate API analytical release testing
|                                                             |             |     
|ITEM                                                         | Cost (USD$) |     
|                                                             |             |     
|ID testing                                                   |             |     
|IR-Method qualification,
set-up and analysis*                | 0$          |     
|                                                             |             |     
|Assay                                                        |             |     
|Method qualification                                         | 2,000$      |     
|Set-up                                                       | 605$        |     
|Analysis                                                     | 575$        |     
|                                                             |             |     
|Related substances                                           |             |     
|Method qualification                                         | 2,500$      |     
|Set-up**                                                     | 0$          |     
|Analysis                                                     | 795$        |     
|                                                             |             |     
|pH                                                           |             |     
|Analysis                                                     | 85$         |     
|                                                             |             |     
|Residual solvents                                            |             |     
|[****]                                                       |             |     
|[****]                                                       |             |     
|[****]                                                       |             |     
|[****]                                                       | 30,000$     |     
|[****]                                                       | 1,800$      |     
|                                                             |             |     
|Water - Karl Fisher Titration (USP <921>)                    |             |     
|Analysis                                                     | 165$        |     
|                                                             |             |     
|Appearance                                                   |             |     
|Analysis                                                     | 85$         |     
|                                                             |             |     
|Crystallinity                                                |             |     
|Analysis                                                     | 550$        |     
|                                                             |             |     
|Report****                                                   | 1,175$      |     
|                                                             | _______     |     
|                                                             |             |     
|Sub total for section 1. b.                                  | 40,335$     |     
|                                                             |             |      | 













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|Date: April 19th, 2012 |             | 












Service Agreement – A

Formulation development of RHB-105 in oral solid dosage form and manufacture
of clinical supplies

Amendment 3





c. GMP Rifabutin API analytical release testing





|ITEM                                          | Cost (USD$) |  | 
|--------------------------------------------- | ----------- |  | 
|                                              |             | 
|ID testing                                    |             | 
|IR-Method qualification,
set-up and analysis* | 0$          | 
|[****]                                        | 575$        | 
|                                              |             | 
|Assay                                         |             | 
|Method qualification                          | 2,000$      | 
|Set-up                                        | 605$        | 
|Analysis                                      | 575$        | 
|                                              |             | 
|Related substances                            |             | 
|Method qualification                          | 2,500$      | 
|Set-up**                                      | 0$         
|Analysis                                      | 795$        | 
|                                              |             | 
|Water - Karl Fisher Titration (USP <921>)     | 165$        | 
|Analysis                                      |             | 
|                                              |             | 
|Limit of N-Iso Butylpiperidone (TLC)          |             | 
|Qualification,
set-up and analysis            | 1,650$      | 
|                                              |             | 
|Residual solvents                             |             | 
|[****].                                       |             | 
|[****].                                       |             | 
|[****]                                        | 24,000$     | 
|Analysis                                      | 1,800$      | 
|Qualification
[****]***                       | 2,000$      | 
|                                              |             | 
|Appearance                                    |             | 
|Analysis                                      | 85$         | 
|                                              |             | 
|Report****                                    | 1,103$      | 
|                                              | _______     | 
|                                              |             | 
|Sub total for section 1. c.                   | 37,853$     | 
|                                              | _______     | 
|                                              |             | 
|Total cost of the amendment                   | 101,795$    | 
|* Already included in Service Agreement A.    |             | 
|                                              |             |  | 















|Corealis               | Page 3 of 5 | 
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|Date: April 19th, 2012 |             | 


















Service Agreement – A

Formulation development of RHB-105 in oral solid dosage form and manufacture
of clinical supplies

Amendment 3





** Included in the set-up cost of the Assay.

***Analysis to be outsourced to a Corealis qualified vendor.
[****] in Toronto using the validated analytical methods of [****].

**** Cost for the documentation and the CofA- 3% of the total cost of the analysis.



| | 2. | COST AND PAYMENTS
| | -- | -----------------

| | 2.1 | The cost of the Services for the Extra Work detailed in section
1 is:
| | --- | ---------------------------------------------------------------------

| | 2.1.1 | $101,795 if the following installments are:
| | ----- | -------------------------------------------

| | · | 50% at the signature of this Agreement; and
| | - | -------------------------------------------

| | · | the balance at the completion of the release testing.
| | - | -----------------------------------------------------

OR

| | 2.1.2 | $89,783 if $89,783 is paid within 7 days from the signature of this
Agreement.
| | ----- | ------------------------------------------------------------------------------



| | 2.2 | The Client shall pay to Corealis the following installments in
United-States currency ($USD):
| | --- | ---------------------------------------------------------------------------------------------



| | 3. | TIMELINES FOR AMENDMENT 3
| | -- | -------------------------

[****]













IN WITNESS THEREOF, the Parties have executed this Amendment
as of the Date written above, by their authorised representatives, who by signing confirm their authority and intention to bind
the Parties they represent.





|Corealis               | Page 4 of 5 | 
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|Date: April 19th, 2012 |             | 










Service Agreement – A

Formulation development of RHB-105 in oral solid dosage form and manufacture
of clinical supplies

Amendment 3







|Corealis Pharma Inc.        |  | 7810962                            | 
|--------------------------- |  | ---------------------------------- | 
|Canada Inc.                 |  |                                   
|                            |  |                                   
|Per: /s/___________________ |  | Per: /s/ Alain Guimond PhD        
|                            |  |                                    | 
|Name: Yves Roy, Ph.D.       |  | Name: Alain Guimond PhD           
|                            |  |                                   
|Title: President            |  | Title: Senior director of Research























|Corealis               | Page 5 of 5 | 
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|Date: April 19th, 2012 |             |