Wednesday February 17, 1999 - Question 12

M.C. is a 55-year-old male receiving 300 mg lithium carbonate daily at 9:00 a.m., 1:00 p.m. and 5:00 p.m.  A recent lithium plasma concentration (8:30 a.m.) was reported to be 2.7 mEq/l.  Previous lithium plasma concentrations have been between 0.7 and 0.9 mEq/l.  The patient’s blood urea nitrogen (BUN) level is 40 mg/dL and his serum creatinine level is 1.7 mg/dl.  The patient’s previous BUN and SCr was 17 and 1.0, respectively.  Urinalysis is unremarkable except for low urine sodium.

What factors should be considered when evaluating this measured lithium concentration?

A. The timing of the lithium level may be contributing to the elevated lithium level.
 
B. The patient appears to be volume overloaded.
 
C. The BUN / SCr ratio is suggestive of a renal problem that may hinder lithium clearance.
 
D. The patient obviously has a urinary tract infecting which is inhibiting lithium clearance.
 
E. The lithium dose is not appropriate for this patient.
 

Discussion