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Expert calls for paradigm shift in lab monitoring of some dermatology drugs




The clinical use of regularly monitoring potassium levels in young women taking spironolactone for acne has also been questioned. The drug has been linked to an increased risk for hyperkalemia, but the prevalence is unclear. “I got a lot of normal potassium levels in these patients [when] I was in training and I really questioned, ‘Why am I doing this? What is the rationale?’ ” Dr. Kirby said.

In a study that informed her own practice, researchers reviewed the rate of hyperkalemia in 974 healthy young women taking spironolactone for acne or for an endocrine disorder with associated acne between Dec. 1, 2000, and March 31, 2014 (JAMA Dermatol. 2015 Sep;151[9]:941-4). Of the total of 1,802 serum potassium measurements taken during treatment, 13 (0.72%) were mildly elevated levels and none of the patients had a potassium level above 5.5 mEq/L. Retesting within 1 to 3 weeks in 6 of 13 patients with elevated levels found that potassium levels were normal. “The recommendation for spironolactone in healthy women is not to check the potassium level,” Dr. Kirby said, adding that she does counsel patients about the risk of breast tenderness (which can occur 5% to 40% of the time) and spotting (which can occur in 10% to 20% of patients). Gynecomastia can occur in 10% to 30% of men, which is one of the reasons she does not use spironolactone in male patients.

TB testing and biologics

Whether or not to test for TB in patients with psoriasis taking biologic therapies represents another conundrum, she continued. Patients taking biologics are at risk of reactivation of latent TB infection, but in her experience, package inserts contain language like “perform TB testing at baseline, then periodically,” or “use at baseline, then with active TB symptoms,” and “after treatment is discontinued.”

“What the inserts didn’t recommend was to perform TB testing every year, which is what my routine had been,” Dr. Kirby said. “In the United States, thankfully we don’t have a lot of TB.” In a study that informed her own practice, researchers at a single academic medical center retrospectively reviewed the TB seroconversion rate among 316 patients treated with second-generation biologics (J Am Acad Dermatol. 2020 Oct 1;S0190-9622[20]32676-1. doi: 10.1016/j.jaad.2020.09.075). It found that only six patients (2%) converted and had a positive TB test later during treatment with the biologic. “Of these six people, all had grown up outside the U.S., had traveled outside of the U.S., or were in a group living situation,” said Dr. Kirby, who was not affiliated with the study.

“This informs our rationale for how we can do this testing. If insurance requires it every year, fine. But if they don’t, I ask patients about travel, about their living situation, and how they’re feeling. If everything’s going great, I don’t order TB testing. I do favor the interferon-gamma release assays because they’re a lot more effective than PPDs [purified protein derivative skin tests]. Also, PPDs are difficult for patients who have a low rate of returning to have that test read.”

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