Regarding lithium pharmacology and clinical use, all of the following are true EXCEPT:

Explanation

## Lithium Metabolism and Elimination **Key Point:** Lithium is NOT metabolized by the liver. It is an inorganic ion that is excreted unchanged by the kidneys, making renal function the primary determinant of lithium clearance. ### Why This Matters Unlike most psychotropic drugs, lithium undergoes **zero hepatic metabolism**. This has critical clinical implications: - **No drug–drug interactions** via CYP450 inhibition or induction - **Renal clearance is the sole elimination route** — approximately 80% is reabsorbed in the proximal tubule and 20% is excreted in urine - **Renal impairment directly increases lithium levels** and toxicity risk ### Therapeutic Window and Monitoring | Parameter | Value | Clinical Significance | |-----------|-------|----------------------| | Therapeutic range (acute mania) | 0.6–1.2 mEq/L | Narrow margin; toxicity begins ~1.5 mEq/L | | Therapeutic range (maintenance) | 0.4–0.8 mEq/L | Lower levels reduce side effects | | Toxic level | >1.5 mEq/L | Risk of neurotoxicity, arrhythmias | | Half-life | 18–24 hours | Steady state reached in 5–7 days | **High-Yield:** Lithium is **not metabolized**; it is **renally excreted unchanged**. Any condition reducing GFR (dehydration, NSAIDs, ACE inhibitors, thiazide diuretics, CKD) increases serum lithium and toxicity risk. ### Mechanism of Action 1. Inhibits **inositol monophosphatase** → ↓ intracellular inositol 2. Disrupts **phosphatidylinositol (PI) signalling** → ↓ second messenger cascade 3. Inhibits **glycogen synthase kinase-3β (GSK-3β)** → ↑ β-catenin signalling (neuroprotective) 4. Net effect: mood stabilization and antisuicidal properties **Clinical Pearl:** Because lithium is renally cleared and has no hepatic metabolism, it is one of the safest drugs to use in patients with hepatic impairment but requires careful monitoring in renal disease. ## Summary The **incorrect statement** is that lithium undergoes hepatic metabolism. Lithium is an inorganic ion eliminated entirely by the kidneys, which is why renal function monitoring and dose adjustment are essential.