(a) Non-GAAP financial measures should be considered in addition to, but not as a substitute for, the information provided in accordance with GAAP. Reconciliations for non-GAAP financial items to the most directly comparable GAAP financial items are provided under Reconciliation of Non-GAAP Financial Measures at the end of this release.
First Quarter 2021 Results
Net sales for the first quarter of 2021 were $1.10 billion, an increase of 3% compared to the first quarter of 2020. Non-GAAP organic net sales, which adjusts for changes in foreign exchange and the impact from mergers, acquisitions and divestiture activity, increased 4% year-over-year, reflecting a healthy companion animal end-market, strong sales execution and strength in prescription management. These positive trends were partially offset by a difficult comparison from the prior year as a result of inventory stocking by some of the Company’s customers in many of its international markets during the onset of COVID-