Which of the following medication may significantly cause QT prolongation?

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 8 mg iv q6h with taper dosing, Ondansetron 4 mg iv q6h prn for N/V, Levothyroxine 0.075 mg po daily, Lisinopril 10 mg po daily, Citalopram 20 mg po daily, Docusate sodium / Senna 1 tab po twice a day, Bisacodyl 10 mg suppository daily prn for constipation, Famotidine 20 mg iv q12hr, Metoclopramide 10 mg iv q6h, Metformin 500 mg po bid, D51/2NS with 20K at 125mls/hour and Hydromorphone PCA at 0.2 mg/hour of basal rate, demand dose 0.1 mg. lock-out every 6min, one hour limit 2.2 mg/hour. Pertinent morning labs includes serum creatinine 1.4 mg/dl, Mg 1.5 mg/dl, K 5.0 mmol/L, Na 135 mmol/L.

Which of the following medication may significantly cause QT prolongation?

A. Lisinopril

B. Levothyroxine

C. Metformin

D. Hydromorphone

E. Citalopram

View Answer

Answer: E

Explanation:

Celexa causes dose-dependent QT interval prolongation, which can cause Torsades de Pointes, ventricular tachycardia, and sudden death. Celexa is not recommended for use at doses greater than 40 mg per day because such doses cause too large an effect on the QT interval and confer no additional benefit. Celexa should be discontinued in patients found to have persistent QTc measurements greater than 500 ms. Ondansetron and Famotidine may cause QT prolongation. Ondansetron may cause QT prolongation.

However, this would be dose-dependent. Doses greater than 16 mg of Ondansetron IV are no longer recommended due to an increased risk of QT prolongation. Famotidine may prolong the QT interval; this has been reported in those with renal dysfunction. There have also been reports of torsade de pointes. Use of all three medications may result in an arrhythmia occurring since both have the potential to prolong the QT interval. Therefore, close monitoring is recommended or discontinuation of one medication. The other medications listed do not have this warning/precaution.