When medication turns dangerous: lithium toxicity and other emergencies

Transcript

RyanA man in his seventies has taken the same dose of lithium for years. Stable. Never misses, never doubles up. Then he catches a stomach bug. Four days of vomiting and diarrhea.

SoheeAnd now his hands are shaking, he's unsteady on his feet, and he's confused.

RyanSame pill, same dose, for years. So what changed?

SoheeWelcome to EPPP Prep, the podcast. I'm Sohee.

RyanI'm Ryan. Today's episode is about the side effects that turn into emergencies. Lithium toxicity, neuroleptic malignant syndrome, serotonin syndrome, tardive dyskinesia, the food reaction with monoamine oxidase inhibitors, or MAOIs, clozapine's blood risk, and the antidepressant warning for young people.

SoheeAnd the exam loves to put these side by side, so we'll focus on what tells them apart. Our sources are the prescribing information approved by the U.S. Food and Drug Administration, the FDA, for each drug, and the National Institute of Mental Health, NIMH.

RyanLet's solve our opening case. The FDA label for lithium says something exam-critical in four words: lithium is not metabolized.

SoheeSo the liver isn't the route out. The label says lithium is eliminated primarily through the kidney.

RyanAnd here's the second key. The label says toxic concentrations, at or above 1.5 milliequivalents per liter, are close to the therapeutic range of 0.8 to 1.2. A narrow margin. Some unusually sensitive patients even show toxic signs within the therapeutic range. Those are the label's lab values for prescribers to interpret, not targets for anyone to act on.

SoheePut those together. If the kidneys clear less lithium, the level rises, even though the dose hasn't changed. The study notes in our question bank put it plainly: lithium toxicity most often comes from the kidneys clearing less lithium, not from taking too much.

RyanSo what lowers clearance? The label lists risk factors: impaired kidney function, volume depletion or dehydration, a recent illness with fever, changes in electrolytes, especially sodium and potassium, and certain drug interactions.

SoheeIt also says decreased tolerance to lithium has been reported with protracted sweating or diarrhea. That's our man with the stomach bug.

RyanAnd the drug interactions are classic exam material. Diuretics, like hydrochlorothiazide: the label says diuretic-induced sodium loss may reduce lithium clearance. Nonsteroidal anti-inflammatories, NSAIDs, like ibuprofen and naproxen: they decrease blood flow to the kidneys, so clearance drops.

SoheeAnd blood pressure drugs that act on the renin-angiotensin system, like lisinopril, can increase lithium levels too.

RyanSalt matters as well. Lithium can cause low sodium by decreasing sodium reabsorption in the kidneys, and the label says it's essential for people on lithium to keep a normal diet, including salt, and adequate fluids, at least during the early stabilization period.

SoheeWhat does toxicity look like? The label describes a range. Mild: fine tremor, lightheadedness, lack of coordination, weakness. Moderate: drowsiness, muscle twitching, ataxia, which is unsteady gait, blurred vision, ringing in the ears, slurred speech.

RyanAnd severe: clonus, confusion, seizure, coma and death. Plus nausea, vomiting and diarrhea. There's no specific antidote.

SoheeOne more twist. Lithium may take up to 24 hours to distribute into brain tissue, so acute symptoms may be delayed.

RyanPause and think. A woman stable on lithium starts a thiazide diuretic for blood pressure. Two weeks later: nausea, worse tremor, slurred speech. She hasn't taken extra pills. Toxicity from overdose, from liver failure, or from reduced kidney clearance?

SoheeReduced kidney clearance. The diuretic causes sodium loss, which reduces lithium clearance. The liver answer is tempting if you assume all drugs are broken down in the liver, but lithium isn't metabolized. And no extra pills rules out an overdose.

RyanNow, our question bank uses lithium cases with a deliberate set of distractors. Neuroleptic malignant syndrome and tardive dyskinesia. So let's understand why those are wrong in a lithium case.

SoheeBoth are linked to antipsychotic drugs. The risperidone label says antipsychotic drugs can cause a potentially fatal symptom complex called neuroleptic malignant syndrome, or NMS.

RyanIts features: very high fever, muscle rigidity, altered mental status, and autonomic instability, meaning irregular pulse or blood pressure, rapid heart rate, sweating and heart rhythm problems. Lab signs can include elevated creatine phosphokinase and muscle breakdown, and it can lead to acute kidney failure.

SoheeManagement starts with immediately stopping antipsychotic drugs, plus intensive symptomatic treatment and medical monitoring.

RyanTardive dyskinesia is different in time course. It's a syndrome of potentially irreversible, involuntary movements. The risk and the chance it becomes irreversible are believed to rise with longer treatment and a higher total cumulative dose.

SoheeThough it can develop, much less commonly, after brief, low-dose treatment. It may remit partly or fully if the antipsychotic is withdrawn. And here's a subtle point. The antipsychotic itself may suppress the signs and mask the underlying process.

RyanSo the exam logic: NMS is a potentially fatal emergency with very high fever and rigidity. Tardive dyskinesia is mostly a risk of longer use. And both need exposure to a dopamine-blocking drug, like an antipsychotic. If the stem rules that out, rule them out.

SoheeNext, serotonin syndrome. NIMH says combining antidepressants with other drugs or supplements that act on serotonin, such as triptans for migraine or the supplement St. John's wort, can cause a rare but life-threatening illness called serotonin syndrome.

RyanNIMH lists agitation, muscle twitches, hallucinations, high temperature and unusual blood pressure changes. And for most people, the risk of such extreme reactions is low.

SoheeInterestingly, the lithium label warns that lithium itself can precipitate serotonin syndrome, with higher risk alongside other serotonergic drugs like selective serotonin reuptake inhibitors, serotonin-norepinephrine reuptake inhibitors, triptans, tricyclics, tramadol, buspirone and St. John's wort, and with MAOIs.

RyanIts list of signs groups them nicely. Mental status changes like agitation and delirium. Autonomic instability like a racing heart, sweating and high temperature. Neuromuscular signs like tremor, rigidity, myoclonus, which is jerking, and overactive reflexes. Plus nausea, vomiting and diarrhea.

SoheeSo how do you tell it from NMS on a test? Start with the drug history. Serotonin syndrome follows serotonergic drugs, often combined. NMS follows a dopamine-blocking drug, like an antipsychotic. Both lists include high temperature, mental status changes and rigidity, so the medication history is the clue.

RyanPause and think. A client on an SSRI tells you she started St. John's wort from the health food store. Now she's agitated, twitchy and feverish. What should come to mind?

SoheeSerotonin syndrome. Both act on the serotonin system, and NIMH names St. John's wort specifically. NMS would be the tempting distractor, but there's no antipsychotic here. Clinically, this is a get-medical-help-now situation.

RyanNow the MAOIs. The Parnate label, for tranylcypromine, carries a boxed warning for hypertensive crisis with significant tyramine use.

SoheeHere's the mechanism. The drug inhibits monoamine oxidase in the intestine, the enzyme that normally breaks down tyramine from food. So large amounts of tyramine can reach the bloodstream and cause a sudden rise in blood pressure, or a hypertensive crisis.

RyanThe label's foods to avoid include aged cheeses, air-dried, aged and fermented meats, tap beer, sauerkraut, concentrated yeast extracts, and most soy products, including soy sauce. And patients avoid them during treatment and for two weeks after stopping.

SoheeBecause MAO inhibition can last up to 10 days after the drug is stopped. And notice why MAOIs aren't first-line. The label says Parnate isn't for the initial treatment of depression, because of serious adverse reactions, drug interactions, and the need for dietary restrictions.

RyanClozapine next. Its label's boxed warning starts with severe neutropenia, which it ties to an increased risk of serious and fatal infections. Before starting, prescribers get a baseline absolute neutrophil count, a blood test. NIMH says the potentially dangerous side effect occurs in one to two percent of people.

SoheeThat's why people on clozapine need regular blood tests. The boxed warning also covers orthostatic hypotension, seizures, and inflammation of the heart muscle. And clozapine is reserved for severely ill patients with schizophrenia who haven't responded adequately to standard antipsychotics, and for reducing recurrent suicidal behavior in schizophrenia.

RyanLast, the antidepressant boxed warning. Antidepressants increased the risk of suicidal thoughts and behaviors in pediatric and young adult patients in short-term studies.

SoheeNIMH puts it as children, teenagers and young adults under 25, especially in the first few weeks or after a dose change. And it says people of all ages on antidepressants should be watched closely early in treatment.

RyanFor a psychologist, that's a concrete monitoring job. Check in about suicidal thinking more closely when a young client starts or changes an antidepressant.

SoheeRecap. Lithium isn't metabolized. It's cleared by the kidneys, with a narrow gap between therapeutic and toxic. Dehydration, vomiting or diarrhea, low salt, diuretics, NSAIDs and kidney decline can push levels up on an unchanged dose.

RyanNMS and tardive dyskinesia need exposure to a dopamine-blocking drug, like an antipsychotic. NMS is a potentially fatal emergency: very high fever, rigidity, altered mental status, autonomic instability. Tardive dyskinesia risk grows with longer use and higher cumulative dose, and it may be irreversible.

SoheeSerotonin syndrome follows serotonergic drugs, often in combination, including St. John's wort. MAOIs plus tyramine can cause hypertensive crisis. Clozapine means blood monitoring for neutropenia. And antidepressants carry a warning for suicidality in young people.

RyanThis is dense, high-stakes material, and if a few of these blurred together, that's normal. Come back to the comparison of NMS and serotonin syndrome tomorrow with fresh eyes. Spaced review is how this sticks.

SoheeAnd then try the lithium question in the practice bank. You know exactly what to look for now. Thanks for listening to EPPP Prep.

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