Posted in Pharmacology

Nitroglycerin is a really interesting medication because it comes in seven distinctly different forms requiring vastly different methods of administration. In this post we’ll talk about what it’s used for, what it does physiologically, precautions to take when giving it, and the assessments you’ll conduct with nitroglycerin administration.

What is nitroglycerin? 

Nitroglycerin is an explosive compound used in dynamite, but a form of it is used medically as a potent vasodilator. And before you get nervous about administering an explosive to your patients, don’t worry…nitroglycerin used for medical purposes will not combust (this article explains it well). The short version is that medical nitroglycerin is at different concentrations and diluted to neutralize any unstable effects. Whew! Makes for good trivia, though!

What is nitroglycerin used for and how does it work??

Nitroglycerin is used for two purposes: mainly it is used to alleviate angina, but in some cases it can also be used to reduce blood pressure. Angina is chest pain that occurs when the heart doesn’t get quite enough oxygen. There are all kinds of angina, and it’s a topic worth of an entire post all its own. The short version is that in most patients, much of the time, it can be relieved with nitroglycerin. Like I said, you may also see it used as an antihypertensive medication in certain patients…when you see how it works you’ll understand why it does such a great job at both relieving angina pain and lowering blood pressure.

Remember, nitroglycerin is a potent vasodilator. Vaso simply means “vessel”, so this means it could dilate arteries, veins or both. At low doses, nitro (as you may hear it called) dilates the veins, and at high doses it dilates both veins and arteries. See, I told you it was interesting! But wait…there’s more!

When it’s dilating the veins, nitro reduces preload, giving the heart less blood volume to pump. With less blood volume to pump around, the heart doesn’t have to work as hard. In essence, we have “reduced the workload of the heart” a phrase you may hear pretty often in the clinical setting. When workload is reduced, oxygen demands are also reduced, so you may also hear clinicians say that something has “reduced oxygen demand.” 

Another important concept to understand with nitroglycerin administration is ventricular transmural pressure. You know those coronary arteries running all around the heart? When the heart is pumping less strenuously, the muscle itself is exerting less pressure against those coronary arteries. What do you think happens to them with less pressure on them? They fill more easily, bringing more blood flow to the heart. Keep reading…it just keeps getting better.

Now at higher doses, nitro vasodilates both veins and arteries. So now with the arteries dilated, think about afterload for a moment. (I’ll pause here so you can ponder it). Did your very smart brain say, “I think afterload would be reduced?” DING-DING-DING, we have a winner, folks! With reduced afterload, the heart can now more efficiently pump blood into the system. 

So when we look at the total picture, we see something glorious. Nitro gets more blood flow to the heart, gives it a little bit of a break so it doesn’t have to work so hard, and makes it more efficient at pumping blood around the body. Basically we have reduced the workload of the heart, reduced the oxygen demands of the heart and improved oxygen delivery at the same time…beautiful, isn’t it?

What are the different forms of nitroglycerin and how are they administered?

Nitroglycerin administration is so interesting because it is available in so many forms… it comes in a paste that’s administered as an ointment, a patch, sublingual tablets, extended release tablets, buccal tablets, sublingual/translingual spray and in IV form. The first thing to consider when choosing a form of nitroglycerin is what it is being used for…chronic treatment or prevention of angina, acute treatment of angina or to lower blood pressure? We’ll talk about these as we go through the various types and routes.

Transdermal nitroglycerin administration

Transdermal nitroglycerin comes in two forms…as a paste or ointment and a patch. Transdermanal nitro is used for long-term, chronic management and prevention of angina pectoris. A common ointment preparation is Nitro-Bid, though you may hear people simpley say “nitro paste” as a generic term for any nitroglycerin in ointment form.

There are a few important things to know about the paste form of nitroglycerin administration. For starters, you do NOT want to get this on your hands or any other part of your body. Since it is absorbed transdermally, you would be dosing yourself with nitroglycerin causing hypotension and something called a “nitro headache” that results when those vessels in the brain dilate. You do not want that, trust me on this. In fact, the nitro headache is something your patients may complain about when first starting the medication, though it does subside after the patient gets acclimated to it.

Secondly, it is important to know that it is dosed in INCHES…as in 1 inch Nitro-Bid q 8 hours. The medication comes in a tube or a single use small packet (smaller than a mayonnaise packet) and a pad of waxy paper that’s about the size of a credit card. On one side, that paper has a small ruler so you can see how many inches to dispense from the packet. You measure out the prescribed amount of ointment, place the paper on the patient with the ointment side down, and write the date, time and your initials on the other side. 

Third, it’s important to know how to remove it correctly. When removing the nitro paste, you want to wipe it off the patient. Don’t just remove the paper, leaving a bunch of ointment behind…be sure to wipe it off. If your patient becomes hypotensive while wearing nitro paste (or a patch) one of the very first things you’ll do is remove the medication from the patient. And always, always remove the prior patch before placing a new one. Common site for nitro ointment is the chest or deltoid. 

And fourth, you need to know that repeated exposure to the medication decreases the body’s sensitivity to it, making it less effective. So, it will likely be ordered to be worn only 12-14 hours per day, giving the patient a “nitro holiday” so that tolerance does not build up (I guarantee this will be a test question!). While we’re at it, please rotate application sites to avoid any issues with skin irritation.

The other transdermal application is administered via a patch. A common brand name is Nitro-Dur and it is typically dosed at 0.2mg/hr to 0.8mg/hr, with the patch releasing the medication slowly into the system. Like the paste, the patch must be removed daily in order for the medication to remain effective. Patches can be applied to any hair-less area, but you’ll want to avoid the distal extremities, and definitely don’t place over any skin abnormality such as a callous, rash, cut or wound. 

And here’s a very important safety precaution with any medication patch…always remove it prior to defibrillation or cardioversion to prevent burns. And, never ever cut the patch to achieve a smaller dose. If you have 0.6 patches, and the doc has changed the order to 0.4, then get the proper patch from the pharmacy! Also, your patient may ask if they can shower or bathe while wearing the patch and the answer is YES!

PO nitroglycerin administration

Another route of nitroglycerin administration for chronic and prophylactic management of angina is by mouth in the form of extended-release tablets. Some common brand names you may see are NitroglynE-R, Nitrong and Nitro-Time. PO nitro is usually given on an empty stomach, so this would either be 1 hour before eating or 2 hours after. As is the case with ANY sustained-release meds, do not crush, chew or break the tablets...this would negate the slow release mechanism causing a dangerous and fast influx of nitroglycerin into the system. So, for example, let’s say you have a patient who is acutely ill and has a nasogastric tube while they’re on a ventilator. The MD re-starts his home medications which include NitroglynE-R. You absolutely would NOT crush this medication and administer via the feeding tube. You’d call the MD and ask for an alternate route…this patient would possibly be a good candidate for transdermal administration.

Buccal nitroglycerin administration

For patients who cannot swallow pills or who aren’t good candidates for transdermal administration because of issues with their skin, there are extended-release buccal tablets available. As with the transdermal route, buccal administration avoids first-pass metabolism as the medication is absorbed directly into the bloodstream without taking a detour to the liver the way PO medications do. 

For buccal nitroglycerin administration, the patient holds the tablet between the cheek and gum or underneath the upper lip. Advise the patient to avoid chewing the tablet, drinking hot liquids or touching it with their tongue as this increases absorption too quickly. 

Nitroglycerin used for acute angina

What if your patient is having a painful attack of angina right now? He needs relief and so does his heart! That’s where sublingual and translingual nitroglycerin come into play. 

Sublingual nitroglycerin administration

Nitrostat is a common sublingual form of nitroglycerin that comes in a small bottle containing a whole bunch of tiny little dissolvable tablets. Be aware that each dose is ONE of those tiny tablets, NOT one vial of tablets! Each tablets contains a set dose, commonly 0.3, 0.4 or 0.6 mg, so read the orders carefully to ensure you give the right dose in the correct number of tablets. Administration is easy…simply place under the patient’s tongue and wait for it to dissolve. Advise the patient to avoid drinking, eating, smoking, chewing gum or doing anything else with their mouth while the tablet is dissolving. 

You also need to instruct the patient to leave the medication in the original glass vial and no other medications should be stored in the vial (this causes the tablets to lose potency). Tablets also need to avoid exposure to heat, moisture and air…so don’t store them in the bathroom, don’t open the vial unnecessarily, and don’t keep in a shirt pocket or in the car (too warm!). Once opened, the tablets have a shelf life of 6 months, according to Davis’ Drug Guide, so patients need to replace them at that time to be sure they get optimally potent medication.

Translingual nitroglycerin administration

This form of nitroglycerin, known by the brand names NitroMist or Nitrolingual, is simply a spray that is administered under or on the tongue. It’s a pretty common form for patients to have at home because it’s so easy to administer…no fumbling open a vial, taking out a tiny tablet, spilling half of them on the floor where they get eaten by the kids or the dog…you get the idea. Note that NitroMist can be given under or on the tonuge, while Nitrolingual is only sprayed under the tongue. 

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Nitroglycerin used for hypertension

After an MI or CHF that resulted from an MI, nitroglycerin can decrease the workload of the heart and improve oxygen delivery while keeping blood pressure copacetic. It’s also used in surgery as a blood pressuring lowering agent, but if that’s the case, it’s going to be the anesthesiologist who is administering it and not your awesome self (unless you become a CRNA!). And, you may also see it used to treat dangerously high hypertension when the patient also has pulmonary edema, as this study discusses. IV nitroglycerin is going to be titrated (increased or lowered) to achieve a certain therapeutic effect…typically a BP parameter identified by the MD. 

The main things you need to know about IV nitroglycerin is that it must be administered via special tubing (you may hear it called “nitro tubing”). This is because standard tubing can absorb a substantial amount of the medication. 

There is one more form of nitroglycerin used for an entirely different purpose. You may see it ordered as a rectal ointment to treat the pain of chronic anal fissures. We’re not going to get into that here, but just know it’s something you could see. 

What assessments are needed with nitroglycerin?

  • Blood pressure: Hypotension can result from the use of any blood pressure-lowering medication.
  • Orthostatic hypotension: This occurs when your patient changes position from lying down to sitting or from sitting to standing. Be sure to instruct patients to SIT DOWN before taking their at-home doses! They should also be instructed to change positions slowly…from lying down to seated, lying down to standing, or seated to standing. They need to GOOOOOOO SLOOOOOOOOOW.
  • Pain: Nitro is often used to treat angina, so it’s important to know if symptoms resolve. Patients can also get a headache with nitroglycerin, but this typically reduces as therapy continues. 
  • Heart rate and ECG: Nitroglycerin can cause bradycardia, so check the heart rate before and after administration. However, it can also cause what’s called “reflex tachycardia” which is an increase in heart rate in response to the lowered blood pressure. Patients receiving IV infusions of nitro must be on continuous ECG monitoring so this patient will likely be in ICU.
  • Monitor for signs of methemoglobinemia, which can occur with high doses of nitroglycerin, especially IV administration. Methemoglobinemia is a blood disorder where the body produces excessive amounts of methemoglobin, which replaces hemoglobin in red blood cells and is unable to participate in gas exchange. Common signs are a bluish tinge to the skin, headache, altered mental status, fatigue and shortness of breath. Untreated, it can be fatal.
  • Knowledge: Assess if your patient understands how to take the medication, when to take it, how much to take, how to store it and how to prevent orthostatic hypotension.

So there you go! One of THE most interesting and varied medications you’ll learn about in nursing school. What other pharm guidance are you looking for? Let me know in the comments below!

Get this on audio in episode 63 of the Straight A Nursing Podcast.

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References

Deglin, J. H., & Vallerand, A. H. (2007). Davis’s drug guide for nurses(11th ed.). Philadelphia, PA: F. A. Davis Company.

Ferreira, J. C. B., & Mochly-Rosen, D. (2012). Nitroglycerin Use in Myocardial Infarction Patients: Risks and Benefits. Circulation Journal : Official Journal of the Japanese Circulation Society, 76(1), 15–21.

Holland, N., & Adams, M. P. (2007). Core Concepts in Pharmacology(2nd ed.). Upper Saddle River, NJ: Pearson Prentice Hall.

Holley, J. L. (2017, September 18). Muscle cramps in dialysis patients. Retrieved from UpToDate website: https://www.uptodate.com/contents/muscle-cramps-in-dialysis-patients#H10

Nitro-Dur (Nitroglycerin): Side Effects, Interactions, Warning, Dosage & Uses. (n.d.). Retrieved July 21, 2019, from RxList website: https://www.rxlist.com/nitro-dur-drug.htm

Woo, T. M., & Robinson, M. V. (2016). Pharmacotherapeutics for Advanced Practice Nurse Prescribers(Fourth Edition). Philadelphia: F. A. Davis Company.