Pharmacology Flashcards: Thyroid Drugs, Corticosteroid Therapy, Osteoporosis Medications

Levothyroxine is a synthetic form of the thyroid hormone T4 used to treat hypothyroidism and thyroid hormone replacement after thyroidectomy. It is the most prescribed medication in the United States. Levothyroxine should be taken on an empty stomach, 30 to 60 minutes before breakfast, with a full glass of water. Many substances reduce its absorption, including calcium supplements, iron supplements, antacids, and proton pump inhibitors, which should be taken at least four hours apart. Thyroid-stimulating hormone, or TSH, levels are monitored every six to eight weeks after dose changes.

Methimazole is an antithyroid medication used to treat hyperthyroidism, most commonly Graves disease. It works by inhibiting thyroid peroxidase, the enzyme that incorporates iodine into thyroid hormones, thereby reducing the production of T3 and T4. Methimazole is preferred over propylthiouracil for most patients because of its longer duration of action and lower risk of liver damage. The most serious adverse effect is agranulocytosis, a dangerous drop in white blood cells that occurs in less than 1 percent of patients.

Bisphosphonates like alendronate, risedronate, and zoledronic acid are first-line medications for osteoporosis that work by inhibiting osteoclast activity, reducing bone resorption, and increasing bone mineral density. Oral bisphosphonates must be taken first thing in the morning on an empty stomach with a full glass of plain water, and the patient must remain upright for at least 30 minutes to prevent esophageal erosion and ulceration. Long-term use beyond five years is associated with rare but serious adverse effects including osteonecrosis of the jaw and atypical femoral fractures.

Cushing syndrome from exogenous corticosteroid use presents with a characteristic constellation of signs including central obesity with a round "moon face" and fat deposits on the upper back called a "buffalo hump," thin fragile skin with easy bruising and purple striae, muscle weakness especially in the proximal limbs, hyperglycemia, hypertension, osteoporosis, mood changes, and immunosuppression with increased infection risk. These features develop gradually with chronic corticosteroid therapy at supraphysiologic doses.

Adrenal crisis, or acute adrenal insufficiency, is a life-threatening emergency that occurs when the body cannot produce enough cortisol to meet physiological demands. Chronic corticosteroid therapy suppresses the hypothalamic-pituitary-adrenal axis through negative feedback, causing adrenal atrophy. If corticosteroids are stopped abruptly, the atrophied adrenal glands cannot produce adequate cortisol, leading to severe hypotension, shock, hyponatremia, hyperkalemia, hypoglycemia, and potentially death. ---