What would be the appropriate intravenous dose?

LN is 84 YOM who is in hospital for a back surgery. His height is 5 feet and 4 inches, weight 85 kg and NKDA.

His past medical history includes hypertension, diabetes mellitus, major depression, hypothyroidism and chronic back pain. Post-op day 1, LN’s medication includes Dexamethasone 8mg iv q6h with taper dosing, Ondansetron 4mg iv q6h prn for N/V, Levothyroxine 0.075mg po daily, Lisinopril 10mg po daily, Citalopram 20mg po daily, Docusate sodium / Senna 1 tab po twice a day, Bisacodyl 10mg suppository daily prn for constipation, Famotidine 20mg iv q12hr, Metoclopramide 10mg iv q6h, Metformin 500mg po bid, D51/2NS with 20K at 125mls/hour and Hydromorphone PCA at 0.2mg/hour of basal rate, demand dose 0.1mg. lock­out every 6min, one hour limit 2.2mg/hour. Pertinent morning labs includes serum creatinine 1.4mg/dl, Mg 1.5mg/dl, K 5.0mmol/L, Na 135mmol/L. The bioavailability of levothyroxine is roughly 50%.

The physician requests you for a dose recommendation to convert her home dose of 75mcg po daily to intravenous.

What would be the appropriate intravenous dose?

A. 37.5mcg

B. 75mcg

C. 75mg

D. 150mcg

E. 37.5mg

View Answer

Answer: A

Explanation:

Since the bioavailability of levothyroxine is roughly 50% (given in the question). To convert the home dose to intravenous, it would be 50% of the oral dose. So 50% of oral 75 mcg would be 37.5 mcg intravenously.