Problem:

A novel dosing form of Lidocaine required the quantitation of the parent compound and one key metabolite in plasma, urine and tissue at trace levels (50 pg/g). Prior attempts were unsuccessful at meeting sensitivity, precision and accuracy requirements.

Proposal:

We proposed using a two-stage extraction procedure and dual analyses of the single extracts combined with valve switching to eliminate significant ion suppression in meeting sensitivity requirements.

Outcome:

The resulting methods were successfully validated using this approach. A second complicating factor for this project involved incurred sample repeat (ISR) analysis for rat tissues weighing ≤ 100 mg. In consultation with the FDA, the use of ISR from larger species (dog) were proposed and accepted for rat tissue analyses.

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