What is the main characteristic of complex compounded sterile preparations?

The main characteristic of complex compounded sterile preparations is that they typically involve greater than two ingredients. This means that such preparations often require a combination of multiple active pharmaceutical ingredients, as well as various excipients, to achieve a specific therapeutic outcome. These complex preparations are usually made to meet the unique needs of patients, particularly when standard commercial products do not suffice.

In contrast, the other choices do not define complex compounded sterile preparations accurately. For instance, these preparations can indeed involve multiple staff members during the compounding process to ensure safety and efficiency. Additionally, they may contain more than just one ingredient, which is consistent with their definition; hence, this highlights the importance of having more than two ingredients. Lastly, while natural products may be used in some formulations, complex compounded sterile preparations include synthetic ingredients as well based on the therapeutic requirements, thus eliminating the notion that these preparations are solely made using natural products.