LithiumPoisoningwhenishemodialysisindicated.pptVIP

Lithium Poisoning: when is hemodialysis indicated? Kent R. Olson, MD Medical Director - SF Division California Poison Control System Case A 32 year old woman ingested 20 lithium carbonate 300 mg tablets in a suicide attempt She is drowsy and her speech is slurred Her serum Li = 6 mEq/L Hemodialysis needed? Lithium Alkali metal (like Na, K) Widely used for bipolar disorder Therapeutic range 0.6-1.2 mEq/L Toxicity = mainly CNS Tremor, slurred speech, muscle twitching Confusion, delirium, seizures, coma Recovery may take weeks Toxicity may occur as a result of acute overdose or chronic use Pharmacokinetics Completely absorbed orally Volume of distribution approx 0.8 L/kg Slow entry into CNS Initial serum levels do NOT reflect brain levels Eliminated entirely by the kidneys Half-life 14-20 hours Prolonged in patients with renal insufficiency Promoting saline excretion hastens Li removal Li Case, continued Na = 140 K = 4.0 Cl = 110 HCO3 = 26 BUN = 8 Cr = 1.0 Glucose = 98 EtOH = 0.16 gm% U Tox (+) benzo’s Enhanced drug elimination: Who needs it? Will it work? What’s the best technique? Who needs it? Critically ill despite supportive care eg, phenobarbital OD w/ intractable shock Known lethal dose or blood level eg, salicylate; methanol / ethylene glycol Usual route of elimination impaired eg, lithium OD in oliguric patient Risk of prolonged coma eg, phenobarbital OD w/ level of 250 Will it work? Volume of distribution: is the drug accessible? how big a volume to clear? Clearance (CL): does the method efficiently cleanse the blood? Volume of distribution (Vd) A calculated number - not real= amt. of drug / plasma conc.= mg/kg / mg/L = L/kg Total body water = 0.7 L/kg or ~ 50 L ECF = 0.25 L/kg or about 15 L in adult Blood or plasma = 0.07 L/kg or ~ 5 L Vd for some common drugs Large Vd: camphor antidepressants digoxin opioids phencyclidine phenothiazines Small Vd: alcohols lithium phenobarbital phenytoin salicylate valproic acid “But they reported t