Bernard J. Birkett
Senior Vice President, Chief Financial and Operations Officer at West Pharmaceutical Services
Thank you, Eric, and good morning. Let's review the numbers in more detail. We'll first look at Q1 2024 revenues and profits where, as expected, we saw a low single-digit decrease in organic sales, a decline in operating profit and diluted EPS compared to the first quarter 2023, given the current market dynamics. I will take you through the drivers impacting sales and margin in the quarter as well as some balance sheet takeaways. And finally, we will provide an update to our 2024 guidance. First up, Q1. Our financial results are summarized on Slide eight, and the reconciliation of non-U.S. GAAP measures are described in Slides 15 to 18. We recorded net sales of $695.4 million, representing an organic sales decline of 3%.
Looking at Slide nine. Proprietary Products organic net sales decreased 4% in the quarter. High-value products, which made up 72% of Proprietary Products sales in the quarter, declined by low single digits primarily due to decreased sales from our FluroTec products and Westar components. Looking at the performance of the market units, the biologics market unit delivered low single-digit growth, led primarily by sales of NovaPure. The pharma market unit saw a high single-digit decline, primarily due to a reduction in sales of Envision and standard components, while the generics market unit declined double digits, primarily due to decreased sales from our Westar and FluroTec components.
Our Contract Manufacturing segment experienced low single-digit net sales growth in the first quarter, primarily driven by an increase in sales of components associated with diagnostic devices. Our adjusted operating profit margin, 17.7%, was a 530 basis point decrease from the same period last year. Finally, adjusted diluted EPS declined 21.2% for Q1. Excluding stock-based compensation tax benefit, EPS decreased by approximately 23%. Now let's review the drivers in both our revenue and profit performance. On Slide 10, we show the contribution to organic sales decline in the quarter. Sales price increases contributed $24.1 million, a 3.4 percentage points of growth in the quarter, as did a foreign currency tailwind of approximately $3.4 million.
More than offsetting price was a negative volume and mix impact of $45.5 million primarily due to lower sales volume caused by customer inventory management decisions in the period. Looking at margin performance. Slide 11 shows our consolidated gross profit margin of 33.1% of Q1 2024, down from 37.9% in Q1 2023. Proprietary Products first quarter gross profit margin of 37% was 550 basis points lower than the margin achieved in the first quarter of 2023.
The key drivers for the decline in Proprietary Products gross profit margin were lower sales volume and an unfavorable mix of products sold, partially offset by increased sales prices. Contract Manufacturing first quarter gross profit margin of 17% was 60 basis points below the margin achieved in the first quarter of 2023, primarily due to inflationary labor costs and an unfavorable mix of products sold, partially offset by increased sales prices.
Now let's look at our balance sheet and review how we've done in terms of generating cash for the business. On Slide 12, we have listed some key cash flow metrics. Operating cash flow was $118.2 million for the three months ended March 2024, a decrease of $19.9 million compared to the same period last year, a 14.4% decrease primarily due to a decline in operating results. Our first quarter 2024 year-to-date capital spending was $90.6 million, $8.5 million higher than the same period last year. We continue to leverage our capex to increase both our high-value products and our Contract Manufacturing capacity.
Working capital of approximately $1.04 billion at March 31, 2024, decreased by $220.1 million from December 31, 2023 primarily due to a reduction in our cash balance. Our cash balance at March 31, 2024 was $601.8 million, which was $252.1 million lower than our December 2023 balance. The decrease in cash is primarily due to $267 million of share repurchases and our capital expenditures offset by cash from operations. Turning to guidance. Slide seven provides a high-level summary. We are reaffirming our full year 2024 net sales guidance in the range of $3 billion to $3.025 billion. There is an estimated full year 2024 headwind of approximately $8 million based on current foreign exchange rates. We expect organic sales growth to be approximately 2% to 3%, unchanged from prior guidance.
We are raising our full year 2024 adjusted diluted EPS guidance to be in a range of $7.63 to $7.88, compared to a prior range of $7.50 to $7.75. Also, our capex guidance of $350 million for the year, unchanged from prior guidance. There are some key elements I want to bring your attention to as you review our guidance. Full year 2024 adjusted diluted EPS guidance range includes an estimated FX headwind of approximately $0.04 based on current foreign currency exchange rate, which is an increase from the prior guidance of $0.02. The updated guidance also includes EPS of $0.15 associated with first quarter 2024 tax benefits from stock-based compensation. Our guidance excludes future tax benefits from stock-based compensation.
I would now like to turn the call back over to Eric.