Increased lithium serum and red blood cell concentrations during ketorolac coadministration

Drug Interactions with Lithium: An Update

Lithium has been used for the management of psychiatric illnesses for over 50 years and it continues to be regarded as a first-line agent for the treatment and prevention of bipolar disorder. Lithium possesses a narrow therapeutic index and comparatively minor alterations in plasma concentrations can have significant clinical sequelae. Several drug classes have been implicated in the development of lithium toxicity over the years, including diuretics and non-steroidal anti-inflammatory compounds, but much of the anecdotal and experimental evidence supporting these interactions is dated, and many newer medications and medication classes have been introduced during the intervening years. This review is intended to provide an update on the accumulated evidence documenting potential interactions with lithium, with a focus on pharmacokinetic insights gained within the last two decades. The clinical relevance and ramifications of these interactions are discussed.

Lithium: updated human knowledge using an evidence-based approach. Part II: Clinical pharmacology and therapeutic monitoring

After a single dose, lithium, usually given as carbonate, reaches a peak plasma concentration at 1.0-2.0 hours for standard-release dosage forms, and 4-5 hours for sustained-release forms. Its bioavailability is 80-100%, its total clearance 10-40 mL/min and its elimination half-life is 18-36 hours. Use of the sustained-release formulation results in 30-50% reductions in peak plasma concentrations without major changes in the area under the plasma concentration curve. Lithium distribution to the brain, evaluated using 7Li magnetic resonance spectroscopy, showed brain concentrations to be approximately half those in serum, occasionally increasing to 75-80%. Brain concentrations were weakly correlated with serum concentrations. Lithium is almost exclusively excreted via the kidney as a free ion and lithium clearance is considered to decrease with aging. No gender- or race-related differences in kinetics have been demonstrated. Renal insufficiency is associated with a considerable reduction in renal clearance of lithium and is considered a contraindication to its use, especially if a sodium-poor diet is required. During the last months of pregnancy, lithium clearance increases by 30-50% as a result of an increase in glomerular filtration rate. Lithium also passes freely from maternal plasma into breast milk. Numerous kinetic interactions have been described for lithium, usually involving a decrease in the drug's clearance and therefore increasing its potential toxicity. Clinical pharmacology studies performed in healthy volunteers have investigated a possible effect of lithium on cognitive functions. Most of these studies reported a slight, negative effect on vigilance, alertness, learning and short-term memory after long-term administration only. Because of the narrow therapeutic range of lithium, therapeutic monitoring is the basis for optimal use and administration of this drug. Lithium dosages should be adjusted on the basis of the serum concentration drawn (optimally) 12 hours after the last dose. In patients receiving once-daily administration, the serum concentration at 24 hours should serve as the control value. The efficacy of lithium is clearly dose-dependent and reliably correlates with serum concentrations. It is now generally accepted that concentrations should be maintained between 0.6 and 0.8 mmol/L, although some authors still favour 0.8-1.2 mmol/L. With sustained-release preparations, and because of the later peak of serum lithium concentration, it is advised to keep serum concentrations within the upper range (0.8-1 mmol/L), rather than 0.6-0.8 mmol/L for standard formulations. It is controversial whether a reduced concentration is required in elderly people. The usual maintenance daily dose is 25-35 mmol (lithium carbonate 925-1300 mg) for patients aged <40 years; 20-25 mmol (740-925 mg) for those aged 40-60 years; and 15-20 mmol (550-740 mg) for patients aged >60 years. The initial recommended dose is usually 12-24 mmol (450-900 mg) per day, depending on age and bodyweight. The classical administration schedule is two or three times daily, although there is no strong evidence in favour of a three-times-daily schedule, and compliance with the midday dose is questionable. With a modern sustained-release preparation, the twice-daily schedule is well established, although one single evening dose is being recommended by a number of expert panels.

Comparison of lithium concentrations in red blood cells and plasma in samples collected for TDM, acute toxicity, or acute-on-chronic toxicity

BACKGROUND

Lithium salts (Li+) are still one of the most appropriate treatments in manic-depressive disorders. Since Li+ has a narrow therapeutic index, plasma levels must be closely monitored to verify maintenance pharmacotherapy, to prevent side effects, to evaluate compliance and to avoid increasing rates of relapse. Although it has been reported that Li+ concentrations in red blood cells (RBC) should be a better indicator of brain levels, therapeutic drug monitoring (TDM) of Li+ is not based on its routine assessment.

OBJECTIVE

The aim of this retrospective study was to compare Li+ concentrations in RBC and plasma and the calculated ratio (LiR= RBC/plasma concentrations) in the three groups of patients.

METHODS

During the past 3 years, 309 Li+ measures were collected corresponding to 165 patients classified into three subgroups (TDM, acute or acute-on-chronic intoxication). Li+ plasma (Cplasma) and RBC (CRBC) concentrations were determined by atomic absorption spectrophotometry.

RESULTS

Results showed that Li+ concentrations in plasma are significantly correlated to Li+ concentration in RBC (r=0.81, P<0.0001). Although a wide inter- and intra-variability was found, Cplasma, CRBC and LiR were statistically different in the three groups. Compared with TDM, Cplasma was more elevated in cases of acute intoxication whereas Li+ accumulated preferentially in RBC in cases of acute-on-chronic intoxication.

CONCLUSION

This study shows the interest of determining Li+ in RBC and plasma for TDM, and that LiR could be a sensitive marker of intoxication and of Li+ impregnation.

Steady-state pharmacokinetics of lithium in healthy volunteers receiving concomitant meloxicam

AIMS

This open, controlled study investigated the effect of concomitant 15 mg oral meloxicam on the pharmacokinetics of lithium in healthy male volunteers.

METHODS

On days 1-14 lithium was coadministered with meloxicam to 16 volunteers; on days 10-14 lithium was administered in individualized dosage regimes to achieve stable lithium plasma concentrations in the lower therapeutic range of 0.3-0.7 mmol l(-1). A 12 h steady-state concentration profile for lithium was obtained at day 14, after which meloxicam was withdrawn. The lithium dose remained unchanged from day 15 to day 22, at which time a second lithium concentration profile was determined.

RESULTS

Lithium and meloxicam were well tolerated throughout the study and all 16 volunteers completed the study. Lithium predose concentrations (Cpre,ss) and area under the curve (AUCss) values both increased by 21% (paired t-test P = 0.0002; 90% confidence intervals for test/reference ratios: 113-130% and 115-128%, respectively) when lithium was coadministered with meloxicam compared with values obtained for lithium alone. The geometric mean lithium Cpre,ss was 0.65 mmol l(-1) when coadministered with meloxicam and 0.54 mmol l(-1) for lithium alone. Lithium Cmax,ss values were increased by 16% by coadministration of meloxicam, from 0.97 mmol l(-1) to 1.12 mmol l(-1). The total plasma clearance of lithium was lower with concomitant meloxicam administration (82.5% of value for lithium alone).

CONCLUSIONS

Meloxicam (15 mg) moderately increased the plasma concentration of lithium in healthy volunteers, but by a magnitude thought to be of low clinical relevance. Nevertheless, lithium plasma concentrations should be closely monitored in patients receiving concomitant meloxicam and lithium therapy.