Page 716 - Basic _ Clinical Pharmacology ( PDFDrive )

702 SECTION VII Endocrine Drugs

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Subclinical Hypothyroidism and Hyperthyroidism The Effects of Drugs on Thyroid Function
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C ASE STUD Y ANSWER

The initial methimazole treatment was appropriate and to start. However, her elevated TSH level indicates inad-
preferable to propylthiouracil because of its longer duration equate levothyroxine replacement which may be related
of action allowing once daily dosing and its improved safety to nonadherence, or concomitant calcium and omeprazole
profile. JP presents with the typical signs and symptoms co-administration. For optimal absorption, levothyroxine
of hypothyroidism following RAI despite levothyroxine should be taken orally 60 minutes before meals on an
replacement. Either radioactive iodine or thyroidectomy empty stomach or at bedtime, and separated by 4 hours
are reasonable and effective strategies for definitive treat- from her calcium administration. Lower thyroxine doses
ment of her hyperthyroidism, especially before becoming may also be sufficient if her omeprazole is stopped. Once
pregnant to avoid an acute hyperthyroid exacerbation weekly thyroxine injections may be effective in those with
during pregnancy or following delivery. Her hypothy- ongoing nonadherence. Thyroid function tests should be
roid symptoms should have been easily corrected by the monitored after 6–8 weeks of therapy, obtained before
addition of levothyroxine dosed correctly at 1.7 mcg/kg/ thyroxine administration to avoid transient hormone alter-
day or 100 mcg daily. Because she is young and has no ations, and the dosage adjusted to achieve a normal TSH
cardiac disease, full replacement doses were appropriate level and resolution of hypothyroid symptoms.