Highlight
– This novel repeated-measures 7Li MRI study evaluates brain lithium distribution over a 10-hour day in euthymic bipolar disorder patients on stable lithium carbonate therapy.
– Brain lithium concentrations mirror serum lithium levels closely but differ across the day depending on once-daily versus twice-daily dosing regimens.
– White matter shows higher lithium accumulation than grey matter, with faster equilibration observed in grey matter versus cerebrospinal fluid and white matter.
– Findings support nuanced clinical strategies for lithium therapeutic monitoring considering temporal pharmacokinetics in the brain and may influence regimen selection to optimize efficacy and safety.
Study Background
Lithium remains a cornerstone treatment for bipolar disorder, valued for its efficacy in mood stabilization and suicide risk reduction. Despite long-standing use, substantial variability exists in clinical dosing schedules, with once-daily and twice-daily regimens commonly employed. While clinical effectiveness between these regimens appears comparable, their serum lithium concentration-time profiles deviate, leading to questions about lithium’s brain kinetics and potential implications for efficacy, side effects, and therapeutic drug monitoring.
Historically, serum lithium levels at 12 hours post-dose have informed dosing adjustments. However, whether serum fluctuations with different regimens translate into parallel changes within cerebral compartments has been unclear. This gap undermines confident interpretation of therapeutic levels and regimen optimization tailored to individual patient needs.
Study Design
This cross-sectional, repeated-measures imaging study was conducted at four psychiatric outpatient centers in Dresden, Germany. Forty-one euthymic adults (18–50 years) with bipolar disorder type I or II, all White European, undergoing clinically stable lithium carbonate treatment were enrolled. Participants were split into once-daily (n=20) and twice-daily (n=21) lithium dosing groups.
During the assessment week, dosing was standardized: the full once-daily dose or evening dose for twice-daily patients was administered at 20:00, with the morning dose (only in the twice-daily group) given after the 08:00 sampling on the assessment day. The core protocol involved three sequential whole-brain 7Li MRI scans and matched serum lithium sampling at 08:00, 14:00, and 18:00 over a 10-hour observation period.
The primary outcome was regional and whole-brain lithium levels by dosing regimen over time assessed via region-of-interest (ROI) analysis using established lithium MRI imaging pipelines. Secondary analyses explored tissue-specific lithium distributions and relationships between serum concentrations and brain lithium using repeated-measures ANOVA, linear mixed-effect models, and population pharmacokinetic modeling.
The study was supported by sustained patient and public involvement to enhance relevance and acceptability among those with lived bipolar disorder experience.
Key Findings
At the 12-hour post-dose baseline timepoint (08:00), brain lithium MRI signal intensities and corresponding serum lithium concentrations were statistically equivalent between once- and twice-daily dosing groups, corroborating the clinical convention of sampling lithium levels at this interval regardless of regimen.
Across the day, however, distinct pharmacokinetic patterns emerged. The once-daily group exhibited a steady decline in serum lithium concentrations from morning through evening. Conversely, in the twice-daily group, serum lithium levels showed a biphasic pattern: an increase following the morning dose coupled with a gradual decrease later in the day.
These changes in serum levels were mirrored closely in brain lithium MRI intensities, establishing a strong temporal concordance between peripheral and central lithium dynamics. Notably, brain lithium accumulation was significantly higher in white matter than grey matter across both dosing regimens. Pharmacokinetic modeling elucidated more rapid equilibration of lithium in grey matter compared to cerebrospinal fluid and white matter, suggesting differential uptake and clearance mechanisms within brain compartments.
No significant adverse events or lithium toxicity signals were reported, supporting the safety of both dosing schedules in the studied population.
Expert Commentary
This landmark study leverages advanced 7Li MRI technology to noninvasively quantify brain lithium distribution and kinetics, a tool previously limited to indirect serum monitoring or invasive approaches. The demonstration of regimen-dependent temporal lithium profiles in the brain challenges the one-size-fits-all approach of using 12-hour serum levels as a universal therapeutic benchmark.
Clinically, these data suggest that serum lithium measurement timing and dosing regimen context should be carefully considered during therapeutic drug monitoring to avoid misinterpretation of lithium exposure in the brain. The observed regional differences in lithium brain accumulation also hint at potential links to therapeutic mechanisms and side effect profiles, given the role of white and grey matter in mood regulation and cognition.
Limitations include the cross-sectional design and a relatively homogeneous participant demographic, affecting generalizability to other ethnicities and age groups. Future longitudinal studies integrating clinical outcomes and neuropsychological correlates are warranted to connect these pharmacokinetic insights to efficacy and tolerability more directly.
Conclusion
This study provides robust evidence that brain lithium concentrations closely track circulating serum levels but that these profiles vary substantially with once- versus twice-daily dosing regimens throughout the day. Importantly, at the standard 12-hour post-dose measurement, brain lithium levels converge across regimens, supporting continued use of this timepoint for clinical monitoring while advocating for nuanced application based on dosing schedules.
The differentiation in brain lithium kinetics by tissue type and temporal exposure offers new avenues to tailor lithium therapy better, potentially enhancing clinical outcomes and minimizing toxicity. Integrating these insights could refine therapeutic drug monitoring protocols and inform personalized lithium dosing strategies in bipolar disorder management.
Funding
This research was funded by the Baszucki Brain Research Foundation and the Deutsche Forschungsgemeinschaft (German Research Foundation).
References
Ritter P, Edelmann K, Thelwall PE, et al. Brain lithium temporospatial kinetics in bipolar disorder: a repeated-measures 7Li MRI study of dosing regimens in Germany. Lancet Psychiatry. 2026;13(8):647-656. PMID: 42365853.
Geddes JR, Burgess S, Hawton K, Jamison K, Goodwin GM. Long-term lithium therapy for bipolar disorder: systematic review and meta-analysis of randomized controlled trials. Am J Psychiatry. 2004 Feb;161(2):217-22.
Young LT, Cooke RG, Dursun SM. Lithium in bipolar disorder: pharmacological, clinical and neurobiological perspectives. Pharmacopsychiatry. 2004 Sep;37(Suppl 1):S1-9.