Case Study Two
GR is a 24-month-old boy whois brought to the emergencyroom by his mother. Hehad been playing outsidewhen he suddenlybegan blinking rapidly,dropped to the ground,and began shaking all over.During this episode, he also vomited.
Immediately after the episode, GRbecame extremely lethargic. His mother denies that he hasexperienced any recent head trauma, fever, or other illness.
The physician decides to admit GR for observation. BeforeGR is transferred to a hospital room, the nurse witnesses anotherseizure. She reports rapid eye movement and lip smacking,along with tonic-clonic movements of GR's arms and legs.
On physical examination, GR is lethargic but in no acutedistress. He cries during the exam but is easily consoled byhis mother. The remainder of his exam is within normal limits.
Laboratory tests performed on admission are within normallimits. Preliminary results on blood cultures are negative. TheEEG results are still pending.
The physician diagnoses GR with new-onset tonic-clonicseizures. He starts GR on carbamazepine.
Per hospital policy, the pharmacy prints out a report of allpatients receiving medications that require monitoring of levels.When the pharmacist notices that GR has been startedon carbamazepine, she goes to the floor to review his chart.She notices that GR has not been given a loading dose ofcarbamazepine and that he is receiving carbamazepineevery 8 hours. The physician has already ordered that hiscarbamazepine level be tested before the third dose. As shewrites her note in the chart, she considers when GR's carbamazepinewill reach steady state.
Will GR's carbamazepine levels be at steady state beforethe third dose?
Dr. Schlesselman is a clinical pharmacist based in Niantic, Conn.
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During initiation of therapy, the half-life of carbamazepine is 21 to 28 days. As therapy continues,carbamazepine will induce its own metabolism through hepatic enzymes. This induction will lead to a reduction in its half-life to approximately 15 hours.After 2 doses of carbamazepine dosed every 8 hours (without a loading dose), GR's levels will not be at steady state.