NR 568 Week 6 Hyponatremia Adverse Effect Write-Up Example

Adverse Effect Write-Up: A Sodium of 126 and New Confusion Six Weeks After Chlorthalidone Was Raised, Traced to a Drug Already Prescribed and Handled Without Leaving the Blood Pressure Untreated

Student Name

College of Nursing, Chamberlain University

NR 568: Advanced Pharmacology for the Adult-Gerontology Primary Care Nurse Practitioner

Instructor Name

Month Day, Year

Adverse Effect Write-Up: A Sodium of 126 and New Confusion Six Weeks After Chlorthalidone Was Raised, Traced to a Drug Already Prescribed and Handled Without Leaving the Blood Pressure Untreated

The Event

In late November, the patient's spouse called the practice to say that the patient had been confused for two days, could not follow a television program and had nearly fallen in the kitchen. At a same-day visit, the patient was alert but disoriented to date, with no focal neurological signs. Serum sodium was 126 mmol/L, compared with 137 mmol/L in August. Potassium was 3.3 mmol/L. Glucose, calcium and thyroid tests were normal. Urine osmolality was inappropriately concentrated, consistent with impaired water excretion.

The Interval, Stated

The interval is the key fact. Chlorthalidone was increased from 12.5 mg to 25 mg on 7 October, when doxazosin was being tapered and the blood pressure was expected to rise. The confusion began on 20 November, about six weeks later. Thiazide-associated hyponatremia usually develops within the first weeks after starting or increasing the dose, though it can appear later, and older age, female sex, low body weight and other drugs that affect sodium increase the risk (Leung et al., 2011). A six-week interval fits that pattern.

The other candidate is citalopram, a selective serotonin reuptake inhibitor that can make the body hold on to water by raising antidiuretic hormone activity. But citalopram was reduced from 40 mg to 20 mg in September, not increased, and the patient has taken it for six years without hyponatremia. Antidepressant-associated hyponatremia is most common in the first weeks of treatment (Leth-Møller et al., 2016). The timing therefore points to chlorthalidone, with citalopram as a contributing background factor.

Does It Track the Dose?

The effect tracks the dose. The patient took chlorthalidone 12.5 mg for two years with sodium values between 135 and 139 mmol/L. The sodium fell only after the dose doubled. Thiazide effects on sodium and potassium are dose-related, and the potassium fell at the same time, which supports a diuretic cause.

Other Causes Considered

The write-up does not argue about alternatives at length, but it records that they were checked: no vomiting, diarrhea or new fluid intake pattern; no new medicines besides the chlorthalidone change; normal glucose and thyroid function; no signs of heart failure or liver disease. The patient had started drinking more water in October on advice to prevent dizziness, which could add to the problem by increasing free water intake while the kidney's ability to excrete it was impaired.

What Actually Came Off

Chlorthalidone was stopped on 22 November. Because the sodium was 126 with moderate symptoms, the patient was admitted overnight for monitoring, fluid restriction to 1 liter a day and potassium replacement. Sodium rose to 131 the next day and 134 by day three, a rate of correction within safe limits. The patient's confusion cleared by the second day. Citalopram was continued at 20 mg, with a sodium check planned, because stopping it as well would make it impossible to know which drug was responsible and would risk a relapse of depression.

The Condition Left Behind

Removing chlorthalidone left the blood pressure less controlled, with sitting readings around 148/84 a week later. The condition it treated cannot simply be left. Amlodipine 2.5 mg daily was started, a calcium channel blocker that does not affect sodium, with a plan to increase to 5 mg in four weeks if needed. The patient's lisinopril 40 mg continued. Amlodipine can cause ankle swelling, which is a known effect and should not lead to a diuretic being added back, a prescribing cascade the practice will watch for.

What the Patient Was Told

The patient and spouse were told that the water pill had lowered the salt in the blood, causing the confusion; that it has been stopped permanently and should be recorded as an intolerance; that a different blood pressure pill has replaced it; and that drinking large amounts of water is no longer advised. They were told to call for any return of confusion, headache, nausea or unsteadiness.

Lessons for the Practice

Two lessons follow from the event. First, a thiazide dose was raised in a 79-year-old, low-weight patient already taking a selective serotonin reuptake inhibitor, without a sodium check scheduled in the following weeks. Both drugs are known to lower sodium, and the combination raises the risk. Second, the advice to drink more water for dizziness, given informally, added free water at the same time. The practice has added a standing order for sodium and potassium two to four weeks after any thiazide start or increase in patients over 75, and a reminder that advice about fluid intake should be checked against the medication list.

Why Chlorthalidone Is Not Restarted at a Lower Dose

Restarting chlorthalidone at 12.5 mg was considered, since the patient tolerated that dose for two years. It was rejected because the patient's age, weight and citalopram make recurrence likely, and amlodipine provides an alternative that does not affect sodium. Rechallenge after a hospital admission for hyponatremia would need a strong reason, and none exists here.

Monitoring

Sodium and potassium at one week and four weeks after discharge, and again if any new drug affecting sodium is considered. Home blood pressure twice daily for two weeks.

How the Practice Will Recognize It Next Time

The episode is added to the practice's teaching file as an example of a common, preventable reaction. Hyponatremia in older adults often presents as confusion, unsteadiness or falls rather than as anything that points to the kidney, and it is easily attributed to dementia or to a new infection. Checking sodium in any older patient on a thiazide or a selective serotonin reuptake inhibitor who becomes confused is a simple rule that would have shortened this patient's two days of confusion. The practice nurse who took the spouse's call is commended for arranging a same-day visit rather than waiting.

Reportable or Not

The event is a serious adverse drug reaction because it led to hospital admission, and the geriatric prescribing criteria already flag both diuretics and serotonin reuptake inhibitors as drugs to use with caution because of sodium (American Geriatrics Society Beers Criteria Update Expert Panel, 2023). It was entered in the patient's allergy and intolerance record as chlorthalidone, hyponatremia, and reported to the Food and Drug Administration's MedWatch program by the practice, as hospital admissions from known drug effects are still useful for surveillance. The case was also reviewed at the practice's monthly safety meeting to consider sodium checks two to four weeks after any thiazide dose increase in patients over 75.

References

American Geriatrics Society Beers Criteria Update Expert Panel. (2023). American Geriatrics Society 2023 updated AGS Beers Criteria for potentially inappropriate medication use in older adults. Journal of the American Geriatrics Society, 71(7), 2052-2081. https://doi.org/10.1111/jgs.18372

Leth-Møller, K. B., Hansen, A. H., Torstensson, M., Andersen, S. E., Ødum, L., Gislasson, G., Torp-Pedersen, C., & Holm, E. A. (2016). Antidepressants and the risk of hyponatremia: A Danish register-based population study. BMJ Open, 6(5), e011200. https://doi.org/10.1136/bmjopen-2016-011200

Leung, A. A., Wright, A., Pazo, V., Karson, A., & Bates, D. W. (2011). Risk of thiazide-induced hyponatremia in patients with hypertension. The American Journal of Medicine, 124(11), 1064-1072. https://doi.org/10.1016/j.amjmed.2011.06.031