Monday, December 3, 2012

Low vs Standard Dose Diltiazem


A few days ago I read a few tweets about evidence versus eminence-based medicine and the ensuing discussions.  I started to think of a number of examples of eminence based medicine I practice; but not out of old habits, or limited knowledge – but because there’s simply a lack of evidence.

Diltiazem dosing for AFIB rate control was one of them.  So sayeth the drug reference; the initial weight based diltiazem dose for rate control is 0.25mg/kg. If that didn’t control a patients rate, you could repeat a dose of 0.35mg/kg. Those large doses could drop a patient’s blood pressure, and a particular concern for patients with borderline blood pressure in the neighborhood of 90-100 systolic. Clinically, the dose could be empirically lowered in this case to say 0.15mg/kg to try to minimize the drop in SBP. But what’s the evidence?

Old data existed comparing standard dose diltiazem to various other rate control treatments: digoxin, amiodarone, metoprolol, etc. But until recently, evidence to suggest the effects of using a normal vs low dose diltiazem did not exist.

Now, I’m certain this article has been reviewed elsewhere, so I’ll try to summarize the meat of it briefly. The tagline of the study was low-dose diltiazem (0.14mg/kg ± 0.04) was as good as standard dose diltiazem (0.24mg/kg ± 0.02) and high dose (0.34 mg/kg ± 0.02) at achieving a positive therapeutic response (30 min post administration - reduction of the ventricular response rate to < 100 OR > 20% reduction from baseline).  Not surprisingly, there was a lower incidence of hypotension (but no clinically significant events as a result of the hypotension) in the low dose arm compared to standard and high dose.[1]

Although it wasn’t the most robust study, and no slam-dunk, it did finally provide some evidence to support using a lower dose in situations. More importantly, the ethos of this study was what I enjoyed the most – challenging what we think we know and putting our clinical habits to the test. Hopefully, this will inspire others to challenge their eminence-based practices. I know it has for me.

[1] J. Lee et al. Low-dose diltiazem in atrial fibrillation with rapid ventricular response. American Journal of Emergency Medicine (2011) 29, 849–854