Exhibit 10.4

LA JOLLA PHARMACEUTICAL COMPANY

January 19, 2012

George Tidmarsh, M.D., Ph.D.

Re: Offer of Employment

Dear George:

La Jolla Pharmaceutical Company (the “Company”) is pleased to offer you the
full-time position of Chief Executive Officer and President. In conjunction with
your employment, you will also serve as a member of the Board of Directors of
the Company (the “Board”). Your anticipated starting date will be January 19,
2012, effective upon the Closing (as defined in the Asset Purchase Agreement by
and between the Company and Solana Therapeutics, Inc., dated January 19, 2012).
This offer and your employment relationship will be subject to the terms and
conditions of this letter.

If you decide to join us, your initial annual base salary will be $240,000, less
applicable withholdings and deductions, paid in accordance with the Company’s
normal payroll practices. Your annual base salary will be increased to $420,000
on the one-year anniversary of the date your employment commences (the
“Employment Start Date”). Thereafter, you will be considered for annual
increases in base salary in accordance with Company policy and subject to review
and approval by the Compensation Committee of the Board.

In addition, on the date that is four weeks following the Conversion Price
Adjustment Date (as defined in the Consent and Amendment Agreement by and among
the Company and the Holders (as defined therein) and dated as of January 19,
2012) you will be granted an option to purchase a number of shares of common
stock of the Company equal to 7.5% of the Company’s fully diluted shares (on an
as-converted to common stock basis) outstanding on such date (the “First
Option”) subject to the terms and conditions set forth in the La Jolla
Pharmaceutical Company 2010 Equity Plan (the “Equity Plan”) and any applicable
award agreements and other restrictions and limitations generally applicable to
common stock of the Company or equity awards held by Company executives or
otherwise imposed by law. Subject to applicable terms and conditions, the First
Option shall vest with respect to 25% of the underlying shares on the one-year
anniversary of the Employment Start Date and shall vest with respect to the
remaining 75% of the underlying shares, monthly, in equal monthly installments,
over the three years following the one-year anniversary of the Employment Start
Date. The First Option will be exercisable at a price equal to the fair market
value of a share of common stock of the Company on the date of the grant of the
First Option.

On the two-year anniversary of the Employment Start Date, you will be granted an
additional option to purchase a number of shares of common stock of the Company
equal to 7.5% of the Company’s fully diluted shares (on an as-converted to
common stock basis) outstanding on such date less the number of shares
underlying the First Option on the First Option grant date (as adjusted for
stock splits, stock dividends, combinations, recapitalizations,
reclassifications or the like) (the “Second Option”), subject to the terms and
conditions set forth in the Equity Plan and any applicable award agreement and
other restrictions and limitations generally applicable to common stock of the
Company or equity awards held by Company executives or otherwise imposed by law.
Subject to applicable terms and conditions, the Second Option shall vest with
respect to 50% of the underlying

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shares, immediately on the date of the grant and shall vest with respect to the
remaining 50% of the underlying shares, monthly, in equal monthly installments,
over the two years thereafter. The Second Option will be exercisable at a price
equal to the fair market value of a share of common stock of the Company on the
date of the grant of the Second Option.

For clarity, during the time you are a member of the Board and also serving as
the Company’s Chief Executive Officer and President, you will not be entitled to
additional cash or equity compensation for Board-related services.

During your employment, you will be eligible to participate in any and all
employee benefit plans made available by the Company from time to time to its
executives generally, subject to plan terms and generally applicable Company
policies. In addition to holidays observed by the Company, you will be eligible
to earn and use vacation in accordance with the policies of the Company, as in
effect from time to time. Your initial vacation accrual will be at the rate of
four weeks per year. The Company reserves the right to change or eliminate its
benefits on a prospective basis at any time.

You will be expected to devote your full business time and your best
professional efforts, judgment, knowledge and skill exclusively to the
performance of your duties and responsibilities for the Company and its
affiliates, and to abide by all Company policies and codes of conduct, as in
effect from time to time, provided, however, that you may engage in business
activities with Anavex Therapeutics and Citizen’s Oncology Foundation, so long
as you do not spend more than twenty (20) hours per month on activities relating
to such entities and so long as your activities for such entities do not breach
any terms of your employment or any policies of the Company. As Chief Executive
Officer and President, you will be expected to perform the duties of your
position and such other duties as may be assigned to you from time to time.

If you accept our offer, your employment with Company will be “at-will.” This
means your employment is not for any specific period of time and can be
terminated by you at any time for any reason. Likewise, the Company may
terminate the employment relationship at any time, with or without cause or
advance notice. In addition, the Company reserves the right to modify your
position, duties or reporting relationship to meet business needs, and to use
its managerial discretion in deciding on appropriate discipline when it deems
circumstances so warrant. Any change to the at-will employment relationship must
be by a specific, written agreement signed by you and Company’s Chairman of the
Board.

This offer is contingent upon the following:

 

  •  

You signing and abiding by Company’s Proprietary Information, Nondisclosure, and
Assignment Agreement (see enclosed);

 

  •  

You signing the Company’s Mutual Agreement to Arbitrate (see enclosed);

 

  •  

Your compliance with federal I-9 requirements (although you have three days to
complete this process, please provide suitable documentation on your first day
of work verifying your identity and legal authorization to work in the United
States).

This letter, including the enclosed Proprietary Information, Nondisclosure, and
Assignment Agreement and Mutual Agreement to Arbitrate, constitutes the entire
agreement between you and Company relating to this subject matter, and
supersedes all prior or contemporaneous agreements, understandings, negotiations
and representations, whether oral or written, express or implied, on this
subject. This letter may not be modified or amended, and no breach is to be
regarded as waived, unless agreed to in a specific, written agreement signed by
you and Company’s Board. This letter shall be governed and construed in
accordance with the laws of the State of California, without regard to the
conflict of laws principles thereof.

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To indicate your acceptance of Company’s offer on the terms and conditions set
forth in this letter, please sign and date this letter in the space provided
below and return it to our offices at 4370 La Jolla Village Drive, Suite 400,
San Diego, CA 92122 or by email to gail.sloan@ljpc.com. If you do accept as
provided, this letter will take effect as a binding agreement between you and
the Company on the date it is received, provided that you sign, date and return
the Company’s Proprietary Information, Nondisclosure, and Assignment Agreement
and Mutual Agreement to Arbitrate and satisfy the other conditions set forth
above in a timely manner.

We hope your employment with Company will prove mutually rewarding, and we look
forward to having you join us. If you have any questions, please feel free to
call me at (858) 646-6644.

Sincerely,

 

/s/ Saiid Zarrabian Saiid Zarrabian Director

* * *

Accepted and agreed:

 

Dated January 19, 2012       /s/ George Tidmarsh       George Tidmarsh