Many EMS services around the world carry topical nitroglycerin for use on acutely ill patients. How effective is topical nitroglycerin in this setting, and what should every provider know?
1. Topical Nitroglycerin is Not Effective for Treatment of Acute Symptoms
The onset of topical nitroglycerin is not exact but ranges from 30 minutes – one hour for the desired effect to be achieved. For many EMS providers, transport time to the closest emergency department is less than 30 minutes. More importantly, can a patient with acute pulmonary edema really afford to wait 30 minutes for this treatment to take effect? Probably not.
2. One Inch (2.5cm) of Topical Nitroglycerin Contains 15 mg of Nitroglycerin
2% Nitroglycerin ointment (Nitro-Bid) contains a whopping 15mg of nitroglycerin per inch applied. While a 15 mg bolus of NTG would likely devastate the vascular tone of a patient, in the topical form, it does not. This brings us to our next key item, the rate of delivery.
3. The Actual Rate of Nitroglycerin Delivered Over a Specified Amount of Time is Unknown
That’s right, you will have no idea exactly how much NTG your patient is actually receiving. Even when using sublingual nitroglycerin, we can estimate that the patient is receiving roughly 60-80 mcg/min, but this is not possible with nitro-paste. Studies have shown that a single application of topical nitroglycerin can have clinical effects for up to 7 hours. However, even if the delivery is exquisitely consistent over those 7 hours, a patient with one inch applied would receive a maximum of 36 mcg/min. Even if you were to apply a two inch dose (30 mg), the topical route still has a 30-minute onset, and even then seems unlikely to be as effective as sublingual or intravenous NTG.
4. Delivery of Nitroglycerin Will Continue for an Additional 30 minutes – One Hour After Removal
If the fact that it takes 30 minutes or more to start working was irritating, you will be thrilled to know that it takes just as long to STOP working. This is presumably due to the many nitroglycerin molecules that, prior to removal, started their voyage through the epithelial jungle but have not yet reached the systemic circulation.
5. Topical Nitroglycerin May Be Useful for Difficult IV Initiations
Somewhere in between all of these undesirable properties of topical nitroglycerin, surely there must be something good, right? Well, here it is! Topical nitroglycerin MAY be useful in starting peripheral IVs. A small amount of NTG applied to the site where you wish to gain IV access, may cause enough vasodilation to make that difficult stick, a little less difficult. Of course, this is not likely to be included in your protocols, and I am in no way recommending this. In all reality, improving your tourniquet technique will probably have more significant, and faster results.
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DailyMed – NITRO-BID- nitroglycerin ointment. U.S. National Library of Medicine. [accessed 2017 Mar 24]. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e464e9bb-48e8-4b9f-9fff-e220cfbac0c5