Well, hello again, and welcome back to the Straight A Nursing Podcast. I'm Nursing Mo, and as always, really jazzed to be here with you today. We're going to be talking about pharmacology.
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So in this episode, we're talking about isoniazid, a medication that is pretty common, most likely will show up on a nursing school exam at some point. So I mentioned this medication in episode 218. So if you're interested in some exponential learning, make sure you go back and listen to that episode as well. So what I'm going to be teaching you are the key things to know about isoniazid, and we will be using the straight A nursing drugs framework. So let's get started.
The first letter is a D. And with that, I like to talk a bit about the drug class. So what drug class is isoniazid?
So isoniazid, you will often see abbreviated as INH. And it goes by a brand name of isotamine. I never hear it called that.
I just hear it called either INH or isoniazid. But you could see it as its brand name. And it is one of those medications that has two classifications, a therapeutic class and a pharmacologic class. Now, in the therapeutic class, it is considered an anti-tubercular.
And in the pharmacologic class, it is considered a mycolic acid inhibitor. So isoniazid is very selective for mycobacteria. And it works.
by inhibiting the synthesis of mycolic acid, and this disrupts the cell wall. It also disrupts the synthesis of DNA and other key components in the mycobacterium. A couple other key things to know about this medication, when we're just kind of looking at it from this global view of its drug class and how it works, is that it has a peak concentration that comes on pretty quickly, one to two hours after dosing. But the absorption can be delayed by both foods and antacids. So your patient will be taking this medication on an empty stomach.
Isoniazid has a special distinction of easily crossing the blood-brain barrier. And this means that CSF levels of the drug can be equal to those found in the serum. It also crosses into the placenta and breast milk and safe. Safety around its usage has not been firmly established in pregnant and lactating women.
However, note that it may be used to treat tuberculosis in pregnant women and lactating women where the benefit outweighs the risk. Okay, so now let's move on to the letter R. What routes are utilized to administer isoniazid? So isoniazid can be given PO as tablet or as a liquid, and I believe it comes in orange and raspberry flavor. Not that that will be on an exam, but you may see it in clinical, as well as via intramuscular injection, IM.
Again, make sure your patient takes the medication on an empty stomach so that they achieve the appropriate absorption. Now, when you are injecting isoniazid, note that it can cause some discomfort for the patient at that injection site. So you want to make sure that you're rotating injection sites and your instructions may state to massage that site after each administration. In addition, like some other medications that are out there, this one can form crystals at low temperatures. So when you pull that vial, you need to look at it.
And make sure there are no crystals in that vial. And if there are, you just simply let it warm to room temperature. Recheck for any remaining crystals before giving the medication.
And to be extra safe, anytime you're concerned about crystals or any kind of debris that could be in your vial, like maybe a glass vial that you open, you're going to use a filter needle to draw up the medication. And then that filter needle... is removed and exchanged for the injection needle for administration. Now, it's very important to note that isoniazid may not be FDA approved for IV administration at this time, but you may see it ordered as IV.
If your patient has isoniazid ordered IV and you're uncomfortable with that in any way, shape, or form, you can always clarify that with the prescribing physician and with the pharmacist. So there is another R in the drugs framework. It's drugs, I guess, if you want to say it like Tony the Tiger. But what is the regular dose range for isoniazid?
So isoniazid dosing can be complex, and it can vary based on its usage. And honestly, I always hate it when nursing school professors want you to memorize specific doses, because again, it can vary. And I Ideally, at the bedside, you've got a drug guide handy, either a paper drug guide or, of course, on the intranet at the facility where you work.
Where I work on the MAR, there's a spot where I can just click and get right to my facility's drug guide and look things up. So memorizing specific doses is, I don't know, it's just it's a pet peeve of mine. But I want you to know a bit about the dose range because you may have exam questions about this.
So isoniazidosing, again, it can vary based on its usage and it can be a bit complex. But for the easiest reference, note that it has a max dose of 300 milligrams if it's given daily. So 300 milligrams a day and 900 milligrams if it's given two to three times a week. Okay. So 300 milligrams when daily or 900 milligrams when two or three times per week.
Now let's move on to the U. What conditions is isoniazid used to treat? Well, isoniazid is used to treat both latent and active tuberculosis.
It is often used in combination with other medications. And again, if you want to learn more about tuberculosis, I want you to go back and listen to that episode. And that was episode 218. So in general, active infection is going to be treated more aggressively and with more medications, like a combo drug approach, than what you would see with latent TB. A typical multi-drug regimen for active infection is a two-month initial phase followed by a continuation phase of four to seven months.
So it's very long drug therapy. Because isoniazid, again, easily crosses the blood. brain barrier. It is the first-line treatment in tuberculosis meningitis.
This very destructive neurological form of extrapulmonary tuberculosis has a high mortality rate. It ranges from, I want to say, 20 to 69 percent, so pretty high, even with standard therapies. So having a medication that easily crosses the blood-brain barrier is absolutely vital.
Isoniazid is contraindicated in cases of pancreatitis, acute liver disease, and in anyone at risk for developing hepatitis from a prior usage of isoniazid. So it's going to be used cautiously in anyone with a history of liver disease, chronic alcohol use, again, because of the liver involvement. severe kidney disease, and pregnant breastfeeding women.
Now, the risk for neuropathy is increased in patients with diabetes. So you know how patients with diabetes often have diabetic neuropathy. Well, we have a higher risk for neuropathy with isoniazid if you have diabetes, and also if you have malnourishment. So it's going to be used very cautiously in those patients.
In addition, Black and Hispanic women are at higher risk for serious and lethal hepatotoxicity, liver toxicity, so it is used very cautiously in these individuals. Are you excited to get organized and ready for nursing school? I know I sure was.
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Use the link in the episode notes to learn more. See you there. Now let's move on to the guidelines. This is the G in the drugs framework. So some key guidelines around isoniazid administration.
So the first thing I want to talk with you about is medication adherence. This is probably one of the most important things. So medication adherence with tuberculosis treatment and the prevention of drug-resistant strains is reliant upon medication adherence.
That very thick mycolic acid layer that surrounds that mycobacterium, remember, this drug disrupts that, but it's very resistant to penetration. And even with the most anti-infective medications, it can take a while for all of this to work and to get all of those mycobacterium destroyed. So treatment must be consistent and persistent in order to be effective.
So to achieve this goal, and remember, that medication regimen was, what, months long, right? How many times do you hear from patients or even yourself, like you get tired of taking a medication after a while, or you start to feel better and it's so tempting to stop taking it, right? So to achieve this goal of strict medication adherence, we utilize something called directly observed therapy.
And you might see this abbreviated as DOT. So in directly observed therapy, the individual is basically directly observed taking the medication. This can occur in the inpatient setting. This can occur at an outpatient clinic.
This can even occur over a telehealth appointment. By directly observing the patient taking their medication, we get much higher levels of medication adherence. We get effective. treatment and less of the development of those drug-resistant strains.
Another key guideline around isoniazid is when to take it. Because absorption can be inhibited by the presence of food, as I mentioned earlier, you want to ensure it is taken on an empty stomach. And in general, this is one hour before a meal or two hours after a meal. Antacids can also decrease absorption. So you'll want to make sure their administration is staggered with isoniazid as well.
Now, speaking of foods, let's talk about some dietary considerations with this medication. Foods containing tyramine can cause serious adverse reactions that include tachycardia, vomiting, shortness of breath, and severe headache. Now, many foods contain tyramine. If you're studying psychopharmacology, you've already learned about this. So this is a key patient teaching area because it is in so many foods.
There are a lot, but some common ones to avoid are aged cheeses, fermented foods like sauerkraut, soy sauce, miso. You also want to teach the patient to avoid cured, smoked, and processed meats, fish sauce, chocolate, caffeine, beer, there are a lot more. So you always want to check with a reputable drug guide, with the pharmacist or the prescriber when questions arise.
Let's talk a little bit about the ongoing assessment guidelines for a patient taking isoniazid. So patients taking this medication will be assessed for the development of drug resistance prior to therapy and periodically throughout therapy. As you can probably tell, we take this idea of drug-resistant strains very, very, very seriously. The patient's hepatic function, their liver function, will also be monitored as isoniazid can cause something called drug-induced hepatitis. So the key labs that are monitored there are AST, ALT, and serum bilirubin.
In addition, you will be monitoring your patient for general signs of hepatic dysfunction. This can include abdominal pain, nausea and vomiting, weakness or malaise, jaundice. increased bruising, and facial edema.
Isoniazid can cause neurological effects, so patients should also be monitored and assessed for altered mental status, seizure activity, and peripheral neuropathy. Additionally, patients taking isoniazid should be monitored for fever, unusual bleeding, and signs of infection such as sore throat or unusual fatigue. Now let's talk a little bit more about the labs we're following.
I already mentioned AST, ALT, and bilirubin. We are also following platelets. We want to follow creatinine as well. And sputum cultures will be obtained regularly until the patient has two negative results in a row. Okay, what about pregnancy?
What are the guidelines surrounding that? So isoniazid is in pregnancy. category C.
And what pregnancy category C means is that animal studies have shown adverse effects on the fetus, but there aren't any well-controlled or adequate studies in humans. So a medication in this category could still be prescribed to a pregnant individual if the potential benefits outweigh those risks. So pregnant individuals taking isoniazid may also be prescribed pyridoxine, which is vitamin B6. And taking pyridoxine along with isoniazid helps prevent isoniazid toxicity.
And then what about renal disease? What are the guidelines around that? So patients with end-stage renal disease can still take isoniazid, but the dose should be given. after peritoneal or hemodialysis because this medication is what we call dialyzable. It dialyzes out.
In other words, it's removed by the process of dialysis. Now, because the medication is excreted by the kidneys, you will probably see reduced dosing in your patients who have renal disease. Now, let's talk a little bit about the drug interactions. Lots of drug interactions with isoniazid, but here are some of the most common ones.
So phenytoin has a drug-to-drug interaction with isoniazid. It can cause increased levels of phenytoin to occur in the bloodstream, which is a common medication that you'll see used to treat seizure disorder in your patients. Theophylline, there's also an interaction here. asthma medication may have reduced elimination when taken with isoniazid, and this can lead to theophylline toxicity. Another one is the antacids that contain aluminum.
This can cause that decreased absorption. So again, you want to stagger the administration of aluminum-containing antacids with the isoniazid so they're not taken together. Carbamazepine can cause it.
An increased risk of hepatotoxicity when taken with isoniazid and carbamazepine is a pretty common anticonvulsant medication. And then taking isoniazid with warfarin could inhibit the metabolism of warfarin, leading to increased risk of bleeding. Disulfiram, this is a medication that's used as a deterrent for alcohol consumption.
So taking isoniazid along with disulfiram can cause psychosis reactions and ataxia. And then in general, any medication that can cause hepatotoxicity is going to increase the risk of hepatotoxicity when taking isoniazid. It's like you're kicking the liver and we're going to kick it even more with another hepatotoxic drug. So this includes other anti-tubercular medications and even something as common as aceta. Menopin.
Another key guideline is the patient teaching. There's a lot of patient teaching around isoniazid. Some key elements you want to make sure that your patient understands are, number one, that long-term medication adherence.
That's absolutely critical for preventing drug-resistant strains. And that directly observed therapy is what's going to help with that. You want to make sure your patient understands that they need to continue their medication, even if they start to feel better, until their doctor tells them it's time to stop taking it.
And you also want to make sure they understand that DOT or directly observed therapy is not punitive. They're not being singled out. It's just how we give isoniazid and other medications to treat tuberculosis.
You also want to teach your patient to monitor for side effects. and how to recognize isoniazid toxicity. So some common signs of that they should be aware of are nausea and vomiting, a rash, ataxia, altered mental status, slurred speech, dizziness, and fever.
You also want to make sure your patient knows they need to avoid alcohol while taking this medication as alcohol. is going to increase the risk for that hepatotoxicity or liver impairment. Teach your patient to take the medication on an empty stomach and to avoid those tyramine-containing foods because consuming them can cause a serious reaction that is very unpleasant and could be very dangerous.
And make sure your patient, of course, understands how to avoid the spread of tuberculosis. You can learn more about tuberculosis in that episode I mentioned earlier. That was episode 218. And then, of course, teaching the patient just in general what the adverse effects of isoniazid are, which ones to expect, and which ones warrant a call to their physician.
So let's talk about those adverse effects. The S in the drugs framework is for side effects. What are the side effects of isoniazid?
So central nervous system and neuro side effects include peripheral neuropathy. That's probably the most common neurological effect. There is a heightened risk of neuropathy in patients with renal failure, nutritional deficiencies, chronic alcohol use, pregnancy, and diabetes.
A lot of times you'll see patients concurrently prescribed. pyridoxine, which is vitamin B6, as it can help prevent neuropathy from occurring. Isoniazid competes with B6 as a cofactor when the body makes synaptic neurotransmitters. So by supplementing with vitamin B6, the hope is that we counteract these effects.
Other less common neurological effects are ataxia, seizure, and psychosis. Let's look at some GI side effects. Isoniazid can cause that hepatic impairment. We've talked about that quite a bit. Can also cause nausea, vomiting, and life-threatening pancreatitis.
So hepatic toxicity is typically observed in the first couple months of treatment and is going to be more likely in individuals using alcohol or taking other medications with the hepatotoxic profile. Mild cases of hepatic toxicity may not mean that the patient's medication is going to be discontinued, but they will definitely be monitored very, very closely. Now, when we look at something like isoniazid hepatitis, this is a severe form of liver injury that can be fatal.
Signs of serious hepatic or liver injury are fatigue, anorexia, jaundice, nausea, and vomiting. right upper quadrant pain, dark urine, and clay-colored stool. So all those signs of basically liver failure.
Dermatologic side effects include a rash, and you can also have some very severe side effects, including toxic epidermal necrolysis, Stevens-Johnson syndrome, and DRESS, D-R-E-S-S, which is drug reaction with eosinophilia and systemic symptoms. So again, that was a rash being probably the most common dermatologic side effect, but there are also some very serious ones. Toxic epidermal necrolysis. Stevens-Johnson syndrome and duress drug reaction with eosinophilia and systemic symptoms.
Other adverse effects that are just kind of general include fever, visual disturbances, anemia, and drug-induced lupus erythematosus. Isoniazid toxicity or isoniazid poisoning occurs most generally in cases of vitamin B6 deficiency or GABA deficiency. So some key signs of the isoniazid toxicity, again, nausea, vomiting, rash, ataxia, altered mental status, slurred speech, dizziness, and fever. It can also cause seizures and even status epilepticus. The seizures with isoniazid toxicity often do not respond to monotherapy with benzodiazepines.
So the treatment is often benzodiazepines. plus that vitamin B6, that pyridoxine. So I hope this review of isoniazid helps you understand this common medication used in the treatment of tuberculosis.
In our next episode, we will be jumping into fundamentals and going through neurological assessment, one of the most difficult and important assessments to master. Hope to see you then. Bye for now.
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