COMPARISON OF EFFECTIVENESS OF THYROTROPIN-SUPPRESSIVE DOSES OF D-THYROXINE AND L-THYROXINE IN TREATMENT OF HYPERCHOLESTEROLEMIA

To compare the cholesterol-lowering effects of equivalent doses of D- and L-thyroxine, 10 euthyroid, hypercholesterolemic subjects were treated with graded doses of each medication in a cross-over design using TSH suppression following TRH administration as the end-point. The mean TSH-suppressive dose of D-thyroxine was 2.4 .+-. 0.66 mg/day, which resulted in mean reductions of 10% in total plasma cholesterol, 10% in plasma low-density lipoprotein cholesterol, and 11% in plasma high-density lipoprotein cholesterol. The mean TSH-suppressive dose of L-thyroxine was 135 .+-. 46 .mu.g/day, which resulted in mean reductions of 7% in total plasma cholesterol, 6% in plasma low-density lipoprotein cholesterol, and 14% in plasma high-density lipoprotein cholesterol. The reductions in total, low-density, and high-density cholesterol achieved with D-thyroxine were not significantly different from those achieved with L-thyroxine. Neither medication produced a significant increase in heart rate or ventricular ectopy as determined by Holter monitoring. D-thyroxine apparently does not have a preferential cholesterol-lowering effect in humans when compared with equivalent doses of L-thyroxine. Both D- and L-thyroxine reduced plasma high-density lipoprotein cholesterol.