Which situation is an example of a medication error?

Receiving an extra dose of medication due to a lack of documentation of a prior dose exemplifies a medication error because it directly impacts the client's safety and treatment effectiveness. In this scenario, the nurse's failure to document the first dose created a situation where the client inadvertently received more medication than intended. This additional dose could lead to potential complications such as toxicity or adverse effects depending on the medication in question.

In contrast, the other situations, while they illustrate medication management challenges, do not necessarily qualify as errors in the same way. For instance, giving the wrong medication constitutes a clear medication error, but it directly involves a misadministration rather than documentation. Refusing medication is a client's right and not an error by the provider. Taking medication an hour late may affect timing, but unless it specifically endangers the patient's health or alters the treatment's efficacy significantly, it is generally not categorized as an error.