Clearly, we have exceeded expectations for the first year after launch. Looking more closely at the second quarter, demand for DIFICID continue to grow. Ex-factory gross sales grew from $16.4 million to $18 million, an increase of over 9%. Ex-wholesaler sales grew by 11%. Net sales grew by 6% as discounts expanded the gross to net from 12.6% to 15.2% as a result of new contracts with group purchasing organizations, expanded coverage from providers and the impact of the Medicare Part D coverage gap, commonly referred to as the donut hole. Given the success we are seeing across all payors channels where Optimer contract, especially Medicare Part D, where we not only contract with the actual payors but also incur liabilities related to the Medicare Part D doughnut hole, and institutional care settings where Optimer also make contract, such as long-term care. We expect that our projected gross to net will moderately -- will be moderately higher than the 15% range previously guided.
Given that demand in this setting is continuing to mature, we're hesitant at this point to give a specific number. Ex-factory growth was affected by a quarter end decrease in inventory levels at the wholesalers, which led to a softer than expected June. This trend was the opposite of what happened in quarter 1 when ex-factory net sales grew by 21%, while ex-wholesalers sale grew by 19%.
In the first 4 weeks of July, we experienced a growth of 13% in the average exposure of demand when compared to the June weekly average demand regaining momentum.
I believe, we continue to make significant progress in executing an impactful launch. As one would expect, we have learned a lot about C. diff and how hospitals treat it.Our flexibility and nimbleness to rapidly adapt to the market, as well as DIFICID's profile and the need for a new and innovative medicine to combat C. diff will allow us to continue to help patients execute an impactful launch and build value for our shareholders. Read the rest of this transcript for free on seekingalpha.com