Bottom Line Up Front

Why Lithium Is Its Own Category

Lithium has no metabolism and no protein binding. It is filtered at the glomerulus and then largely reabsorbed in the proximal tubule alongside sodium and water (by passive diffusion, paralleling sodium handling rather than sharing an active sodium transporter) — roughly 95% is excreted unchanged by the kidney. That single fact drives almost everything that follows. When the body senses volume depletion or salt loss, it reabsorbs more sodium and more lithium, so the serum level climbs without any change in dose. Dehydration, a low-sodium diet, vomiting or diarrhoea, a new thiazide, an NSAID, or an ACE-inhibitor can each do it.

Its small molecular weight, negligible protein binding, water solubility, and low volume of distribution also make it the textbook dialyzable drug — the basis for haemodialysis in severe toxicity (covered in the next chapter). And because the kidney is both the route of clearance and the target organ of harm, lithium sits alone: every other psychotropic is one or the other, never both.

The Nephrotoxicity Question — What the Evidence Actually Says

Lithium causes two distinct renal problems. The first, common and early, is nephrogenic diabetes insipidus (Li-NDI): lithium enters the principal cells of the collecting duct through the ENaC channel and impairs the kidney's response to ADH, producing polyuria and polydipsia. It is usually reversible early and is the first sign worth tracking. The second, slow and feared, is chronic tubulointerstitial nephropathy (Li-NP) — a gradual decline in GFR over years to decades.

Here the honest framing matters, because the old reputation outruns the data. Long-term lithium can lower GFR, and risk rises with treatment duration, age, higher serum levels, and prior episodes of toxicity. But recent large cohorts have reframed the magnitude: a large Swedish registry (Bosi 2023) found similar low absolute 10-year CKD risk for lithium and valproate (8.4% vs 8.2%) with no significant overall difference — while elevated levels above 1.0 mmol/L were the real driver of acute kidney injury; a 2024 Mayo Clinic Proceedings review reached the same conclusion on CKD-progression risk. The average annual eGFR decline in lithium-treated patients diverges from controls only after roughly ten years of exposure, and most patients who reach CKD stage 3 have been treated for twenty years or more. Lithium remains underused in the US largely because of a nephrotoxicity fear that the current evidence only partly supports.

The clinical takeaway is not complacency — it is proportion. Monitor deliberately, dose conservatively, and treat a slow eGFR drift in a 70-year-old who has done well on lithium for decades very differently from rapid decline with proteinuria in a younger patient.

Target Levels

Two principles override the table. First, target the lowest level that holds the patient well — modest levels are the single most controllable lever on long-term renal risk; even an isolated level above 1.0 mEq/L has been linked to a measurable short-term eGFR drop. Second, in older patients the serum level that was once therapeutic can, years later, deliver excessive brain exposure (rising brain-to-serum ratio), surfacing as new cognitive or mood complaints — another reason to drift the target down with age.

Dosing & the Once-Daily Strategy

Titrate in 100–200 mg increments against the 12-hour level and response. The key renal-protective choice is once-daily dosing. Lithium's plasma half-life is ~18–36 hours (longer in the elderly and in renal impairment), and its brain-tissue half-life is longer still — so a single daily dose maintains prophylactic brain levels while allowing the kidney a daily trough. The comparative data favour it: divided dosing has been associated with more structural and functional renal change, the proposed mechanism being that tubular recovery occurs during the low-concentration window that once-daily dosing creates. Single-dose schedules also cause less polyuria. Because lithium clearance falls overnight, the total daily dose can sometimes be reduced modestly when consolidating to a single bedtime dose.

In established CKD, reduced clearance means a lower dose reaches the same level, and time to steady state lengthens — check the level after 10–12 days (versus ~5 days with normal function) after any change, and recheck more often as function declines. There is no fixed mg cap; the level and the trajectory drive the dose. Below CrCl ~50 mL/min the toxicity risk at any given dose rises sharply; at that point, smaller doses, longer level intervals, and a lower target are all appropriate.

Monitoring Schedule

Draw the level as a 12-hour trough — 12 hours after the last dose, i.e., the morning before the next dose. Consistency of timing is what makes serial values comparable.

A practical trigger to act: a creatinine rise > 30% from baseline, or an eGFR fall > 25%, warrants a medication review, a hunt for reversible contributors, and a possible dose reduction — not automatic discontinuation.

The Interactions That Spike the Level

Every one of these works through the same mechanism: less sodium/water delivered or more reabsorbed means more lithium reabsorbed. Memorise the offenders — they cause more real-world toxicity than overdose does.

Sick-day rule: during any intercurrent illness with vomiting, diarrhoea, fever, or reduced intake — and especially if eGFR is already < 60 — counsel patients to hold lithium and seek review, because that is exactly when levels climb fastest.

The Hard Call: Continue or Stop?

This is the question in the chapter title, and it has no clean numeric answer. Three facts frame it. First, stopping lithium carries its own grave risks — relapse, hospitalisation, and a documented loss of its anti-suicidal effect; patients who stop because of CKD have more mood episodes and more medication trials afterward. Second, discontinuation does not reliably reverse the damage: below an eGFR of roughly 40 mL/min (estimates range 25–40), decline may continue regardless — a debated "point of no return," though some recent data suggest stopping can still slow the slope. Third, formal decision analysis found that even after 20 years of treatment with established CKD, stopping is favoured only if the probability of progressing to ESRD exceeds about 41% — a bar most individual patients do not meet.

So the move is rarely "stop." It is optimise and co-manage:

• Confirm the picture — trend eGFR, quantify proteinuria, exclude other causes
• Remove other nephrotoxins (NSAIDs) and manage BP, diabetes, volume
• Consolidate to once-daily; target the lowest effective level
• Treat Li-NDI — amiloride blocks ENaC and reduces polyuria
• Refer to nephrology for: eGFR decline > 4 mL/min/1.73m²/yr, proteinuria or haematuria, or eGFR < 30
• Make the stop/continue decision jointly — psychiatry, nephrology, and the patient

Discontinuation moves from "rarely" toward "consider" as eGFR falls below ~30 and especially toward 20 mL/min, when accumulation risk and the slope of decline both worsen — but even then it is a shared, individualised judgement, and if lithium is stopped, a credible mood-stabilising alternative must be in place first.

The Action Ladder

Clinical Pearls

Red Flags — Stop and Escalate

Patient Counseling Script

EMR / Documentation Template

References

1. Lerma EV, et al. Lithium and Kidney Disease. Mayo Clin Proc. 2024;99(12) — absolute CKD-progression risk low and similar to valproate; lithium underutilisation.
2. Gitlin M. Lithium and long-term renal effects: a complex clinical concern. Bipolar Disord. 2023;25(5):359–363 — continued decline below ~eGFR 32; risk of stopping.
3. Werneke U, Ott M, Renberg ES, et al. A decision analysis of long-term lithium treatment and the risk of renal failure. Acta Psychiatr Scand. 2012;126(3):186–197 — the ~41% ESRD-threshold for favouring discontinuation.
4. Schoot TS, Molmans THJ, Grootens KP, Kerckhoffs APM. Systematic review and practical guideline for the prevention and management of the renal side effects of lithium therapy. Eur Neuropsychopharmacol. 2020;31:16–32 — once-daily dosing, lowest effective level, Li-NDI/Li-NP monitoring.
5. Shulman KI, Almeida OP, Herrmann N, et al. Delphi survey of maintenance lithium treatment in older age bipolar disorder (OABD): target serum levels by age band. Bipolar Disord. 2019;21(2):117–123.
6. Bosi A, Clase CM, Ceriani L, et al. Absolute and Relative Risks of Kidney Outcomes Associated With Lithium vs Valproate Use in Sweden. JAMA Netw Open. 2023;6(7):e2322056 — similar low absolute CKD risk; elevated levels (>1.0 mmol/L) associated with AKI.
7. Lithium carbonate prescribing information (FDA label, DailyMed) — narrow therapeutic index, renal excretion, monitoring.

Last reviewed June 2026. Part of the Psychiatry Education Forum Academy; for clinician education — it supports, and does not replace, individual clinical judgment and current local protocols.