When teaching a client about oral suspension phenytoin, which instruction is essential?

The correct choice emphasizes the importance of shaking the suspension vigorously before pouring the medication. Oral suspensions require agitation to ensure that the active ingredient is evenly distributed throughout the liquid. If not shaken well, the patient may receive an inaccurate dose, leading to subtherapeutic effects or toxicity due to inconsistent dosing.

This point is particularly crucial with phenytoin, as it is a medication that needs to maintain therapeutic drug levels to effectively prevent seizures. Proper mixing also helps avoid variations in concentration that can arise from settling of the solid particles in the suspension.

While other instructions may have relevance (e.g., taking medications with food can aid in tolerability for some drugs, or storing medications properly prevents degradation), the most essential instruction related to the pharmacological effectiveness and safety of the oral suspension in this case is shaking the bottle vigorously before use.