Therapeutics and Drugs Briefs
Therapeutics and Drugs Briefs
Treating Hypothyroidism Isn’t Always as Simple as it Seems
Source: Singh N, et al. JAMA 2000;283:2822-2825.
The effect of calcium carbohydrate on the absorption of levothyroxine is important since many postmenopausal women may be taking this combination of medications.
This study involved 20 hypothyroid patients (age range, 27-78 years; n = 11 men). All subjects had normal free T4 and thyrotropin levels before beginning the study. The subjects were instructed to take 1200 mg/d of elemental calcium carbonate along with their thyroxine for three months.
Levels of free T4, total T4, total triiodothyronine (T3), and thyrotropin were taken at baseline before taking calcium carbonate, at two and three months while taking calcium carbonate with their thyroxine, and two months after discontinuing the calcium carbonate.
Mean free T4 and total T4 levels were significantly reduced during the calcium carbonate period and increased when the calcium carbonate was discontinued. Mean free T4 levels were 1.3 ng/dL at baseline, 1.2 ng/dL during the calcium carbonate period, and 1.4 ng/dL after calcium carbonate was discontinued.
Total T4 levels followed a similar pattern. Mean thyrotropin levels increased significantly from 1.6 mL U/L at baseline to 2.7 mlU/L during the calcium carbonate period and decreased to 1.4 mL U/L after calcium discontinuation. Twenty percent of the patients had thyrotropin levels during the calcium carbonate period; the highest level was 7.8 mL/L. Mean T3 levels did not change.
The conclusion of the study was that calcium carbonate reduces T4 absorption and increases thyrotropin levels.
Comment by Ralph R. Hall, MD, FACP
Singh and colleagues also note that other drugs have been shown to interfere with the absorption of levothyroxin. These include sulfate, sucralfate, bile acid sequestrants, and aluminum hydroxide. High-fiber diets have also been shown to impair thyroxine absorption. Other drugs such as phenytoin (Dilantin), carbamazepine (Tegretol), and sertraline (Zoloft) may accelerate disposal.
It would have been interesting to see if thyroid function would continue to worsen had the calcium carbonate been given over a longer period of time. The liklihood is that there would have continued to be a worsening of the status of her thyroid function.
It behooves us to monitor all patients who are taking other medications with their thyroxine a little more often. Polypharmacy is complicated.
Dr. Hall is Emeritus Professor of Medicine, University of Missouri-Kansas City School of Medicine.
As-Needed Use of Fluticasone Proprionate Nasal Spray Reduces Symptoms of Seasonal Allergic Rhinitis
Source: Jen A, et al. J Allergy Clin Immunol 2000;105:732-738.
It is likely that most clinicians anticipate chronic daily administration of nasal steroid therapy (NS) for many of their patients who are established as sufferers of seasonal allergic rhinitis. On the other hand, since NS pathophysiologically prevents inflammation from developing, prevents allergic priming, and blocks the late allergic response, dose administration for mild disease may have a somewhat durable effect. In contrast, antihistamines block only the immediate allergic response and have less effect as allergy season becomes more established and the late allergic response more activated. This placebo controlled study evaluated the use of fluticasone nasal spray (FNS) taken as needed for allergic rhinitis symptoms during allergy season (n = 56).
Over the course of 28 days, as-needed dosing resulted in an average of 14-16 dose administrations (placebo or FNS). Symptom scores among active drug recipients were dramatically lower (mean = 4.5) than placebo recipients (mean = 8.5), despite the fact that active medication was administered on only approximately half of the study days.
Jen and associates point out that it is likely that many patients administer NS less often than directed, or on an as-needed basis. This study suggests that even as-needed NS provides substantial relief to allergic rhinitis sufferers.
This Therapeutics & Drug Brief was written by Louis Kuritzky, MD, Clinical Assistant Professor, University of Florida, Gainesville, Fla.
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