Which of the following is NOT a rectal administration form?

Tinctures are primarily liquid preparations that contain active ingredients dissolved in alcohol or another solvent and are typically used for oral administration or topical application rather than for rectal use. This makes tinctures distinct from the other options listed, which are commonly used rectal administration forms.

Solutions can be formulated for rectal use as they are liquids that can be delivered in a variety of ways, including enemas. Suppositories are specifically designed for rectal administration, providing a way for medications to be absorbed through the rectal mucosa. Ointments may be formulated for rectal application as well, particularly in the treatment of local conditions.

In summary, the key difference is that tinctures are not used rectally, whereas the other forms – solutions, suppositories, and ointments – are all suitable for rectal administration.