Pharmacy Consult: Nitroglycerin Paste to IV Conversion
While I’m not a huge fan of nitroglycerin paste, I understand it’s clinical usefulness. The ability to slap on an inch of paste to relieve chest discomfort is certainly non-invasive and can achieve effective results. With this simplicity, a degree of randomness exists with regard to the ability to titrate the dose. If the desired clinical effect is not achieved, how much more can we apply safely? Conversely, if hypotension results, how long will the effects last after the paste is wiped off?
Though more invasive, IV nitroglycerin provides greater control and titratability and one study suggests a dose conversion between the dosage forms. (Am J Crit Care. 1998 Mar;7(2):123-30)
The conversion from IV to PASTE is relatively straightforward. Apply the appropriate amount of PASTE, and then stop the infusion of nitroglycerin 30 minutes later. (see table below for conversions)
Converting from PASTE to IV is a little more difficult (and has not been studied). After removal of the Nitropaste, the duration of the effect of nitroglycerin is anywhere from 2 hours to 12 hours. So titration to IV will be more difficult and require close attention. It would, therefore, make more sense to target the lower end of the conversion range. For example, if 1 inch was applied and the conversion range is 10-39 mcg/min, the IV rate should be started at 10 mcg/min about 1 hour after the paste is removed and subsequently titrated.
Of course, if the decision to convert to IV was because the paste is not achieving the desired effect, the infusion could be started earlier, but still targeting the lower dose range.
| PASTE | IV |
| 0.5″ | 5 mcg/min |
| 1.0″ | 10 – 39 mcg/min |
| 1.5″ | 40 – 59 mcg/min |
| 2.0″ | 60 – 100 mcg/min |
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Thanks for this! I too am not a fan of nitro paste (my question is always, “Why? We have SL and IV which are a lot easier to titrate and offer consistent dosing…) but never had a handy guide for how to relate inch-based dosing to the IV-standard.
Do you have a source from where you got that conversion information from?
The study cited above (Am J Crit Care. 1998 Mar;7(2):123-30). Being a clinical outcomes study, while not an exact conversion, the above topical doses yielded the same clinical effects as the associated IV infusion rate.
[…] Nitroglycerin comes in a plethora of dosage forms. For ADHF, the more commonly used preparations are the IV dosage form and paste. If a patient doesn’t have IV access, nitroglycerin paste could be used. However, caution should be taken since if the patient’s blood pressure drops, or are highly dependent on venous return, getting IV access and subsequent fluid/norepinephrine/epinephrine would be extremely challenging. I highly caution this application since, as described above, nitroglycerin is not a mortality benefiting intervention. With that said, if paste is selected, it’s useful to have an idea of how much it roughly converts to in IV dose. The application of 1.0 inches of paste converts to approximately 10-40 mcg/min, correspondingly, 2.0 inches converts to 60-100 mcg/min. For more on this, see this Classic EM PharmD post. […]