I was astonished that Dr. Melvin G. McInnis’ article on using lithium to treat bipolar disorder (BD) (Current Psychiatry, June 2014, p. 38-44; [http://bit.ly/1sszAUr]) did not address all the potential hazards of the medication. He discussed side effects, but only how to manage them so that patients will adhere to treatment.
I have used lithium for patients with BD, and often it is efficacious, although hazardous in overdose. Lithium toxicity can cause cardiac arrhythmias, and must be monitored closely. In addition, the effects of hydration and exercise on the lithium level, especially during summer, often are ignored.
Two of my patients, an adolescent and an adult, were well-maintained on lithium, adhered to treatment, and had no concurrent medical problems, but developed significant toxicity for no reason that I could determine. The adult had a lithium level of 2.0 mEq/L in the emergency room; the adolescent had a lithium level of 1.8 mEq/L. Levels this high are considered potentially lethal, and because it happened without warning and without a cause that I could determine, I consider lithium to be one of the riskier mood stabilizers. I still prescribe it, but with great caution.
Dr. McInnis also did not mention the possibility of lithium-induced diabetes insipidus, a condition in which the kidneys are no longer able to concentrate urine and that is marked by excessive urination, concomitant water intake, and low urine specific gravity. It is uncommon, but I have seen it 3 times in 30 years, in a practice that specializes in psychotherapy and does not see a high percentage of patients with BD. I consider it a condition that must be kept in mind as we follow our patients in long-term treatment.
Mary Davis, MD
Lancaster, Pennsylvania
Dr. McInnis responds
Dr. Davis raises the issue of lithium toxicity and provides examples of 2 patients who developed levels of 2.0 mEq/L and 1.8 mEq/L. These levels clearly are well beyond the toxicity threshold of 1.3 mEq/L, and the patients wisely sought urgent care. These scenarios exemplify the need for regular monitoring of the lithium level—in particular, when there is any change in physical or mental health status. Development of significant toxicity generally has some lead-time with emerging short-term side effects (outlined in Table 2 of my article), which underscores the importance of discussing the nature of emerging side effects with your patient.
Dr. Davis is correct in noting that the practitioner must be aware of long-term side effects of lithium. I find it helpful to discuss these effects with the patient in the context of short-term (days or weeks), intermediate (weeks or months), and long-term (months or years) time frames (Table 2). Diabetes insipidus is listed as an intermediate side effect.
I am grateful to Dr. Davis for raising the issue of hydration and summer heat, a concern among parents and coaches when student athletes practice strenuously for extended hours.1 Miller et al2 found that the concentration of lithium was between 1.2- and 4.6-fold in forearm sweat compared with serum levels, with the implication that heat-induced sweating may lower lithium levels. Jefferson et al3 studied 4 athletes after a 20-km race and found that all had become dehydrated but had a decrease in the serum lithium level. This is contrary to the widely held belief that excessive sweating predisposes to lithium toxicity.
BD is among the more lethal psychiatric disorders, and lithium is among the few medications shown to mitigate suicidal behavior.4 As with any medication, lithium is not without risk, and there is a clear need for informed medical management. Any notable change in health status or physical activity in a patient taking lithium is worthy of review, with recommendations based on knowledge of the patient and medical science.