A nurse is reviewing a patient's laboratory findings prior to medication administration. The most recent serum lithium level is 2.2 mEq/L and was drawn yesterday. The patient takes 300 mg of lithium carbonate four times a day. Which of the following is the nurse's most appropriate action?
A. Administer the drug as prescribed
B. Recognize that the dose is subtherapeutic
C. Administer half of the dose
D. Hold the next dose and notify prescriber