The pharmacokinetics of intravenous lithium chloride in patients and normal volunteers

Objectives: To study the pharmacokinetics of lithium chloride administered intravenously to patients who had undergone cardiac surgery within the prev ious 12 h and to normal volunteers, since lithium is used in a new indicato r dilution method for measuring cardiac output. Methods: A prospective study was carried out in a London teaching hospital. Lithium chloride was administered intravenously and blood samples taken at intervals for up to one hour. Plasma lithium levels were measured by induc tively coupled plasma optical emission spectrometry and standard pharmacoki netic parameters were calculated Results: Two groups of patients were investigated; the first (n = 10) recei ved five doses of 0.6 mmol LiCl at 2 min intervals, the second (n = 10) a s ingle dose of 0.6 mmol LiCl. A further group of six normal volunteers also received a single dose of 0.6 mmol LiCl. Biexponential curves were fitted t o the data. For the three groups the half-lives of the first exponentials ( T(1/2)alpha) were 3.3, 4.2 and 3.9 min, respectively; the half-lives of the second exponentials (T(1/2)beta) were 100, 83 and 102 min, respectively; t he volume of distribution at steady state in all three groups was 0.21 kg(- 1). Conclusion: Since lithium chloride is used diagnostically for measurement o f cardiac output, knowledge of the rate constants for disappearance of lith ium from the vascular compartment allows recommendations for the safe maxim um frequency of lithium dilution cardiac output determinations to be made.