Chapter 83: Laxatives

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You know, you've got a massive pharmacology exam coming up and well, today we are your study guides.

Exactly.

We are deep diving into Lane's Pharmacology for Nursing Care, specifically chapter 83.

Right, the laxatives chapter.

And I know it's a dense one.

It really is.

So our mission today is to translate all that dense drug info into a plain English, student -friendly format.

And we are going to cover the material in the exact order it appears right there in your textbook.

Which is the best way to study it, honestly.

But before we even get into the specific drugs, we have to establish a baseline.

We have to define the difference between a laxative effect and catharsis.

Because, you know, they are very different things clinically.

Absolutely.

People use the terms interchangeably, but they shouldn't.

Right.

So a laxative effect refers to the production of a soft form stool over a period of one or more days.

It's gentle.

It's relatively slow.

Catharsis, on the other hand, is a prompt, intense fluid evacuation of the bowel.

I mean, it is fast and aggressive.

It's the clear the room kind of situation.

Exactly.

And to understand how these drugs trigger either of those effects, we first need to look at what the colon is actually doing all day.

Right.

So let's talk about the colon's job.

I always picture the colon like this long conveyor belt in a factory.

That's a great analogy.

Thanks.

So the material is moving down the belt, and along the way, little robotic arms, which are the intestinal lining,

are siphoning water out of it.

And they siphon a lot of water.

The colon's main function is absorbing water and electrolytes.

About 1 ,500 milliliters of fluid enters the colon daily, and it absorbs like 90 percent of it.

Wow, 90 percent.

So if the conveyor belt moves at the right speed, the perfect amount of water gets removed.

The stool is soft and passes easily.

Right.

But what if the belt moves too slowly?

Then those little robotic arms just keep pulling water out over and over.

Yeah.

And the result is this hard dehydrated stool.

Which is classic constipation.

But wait.

So what actually counts as a normal frequency?

Is the conveyor belt supposed to drop a shipment once a day?

See, that is the biggest myth we have to debump right now.

There is no universal once a day rule.

Normal varies so widely.

For some people, it's three times a day, and for others, it's twice a week.

Right.

So we can't just look at the clock or the calendar.

Exactly.

In table 83 .1, the textbook introduces the Rome IV criteria.

This tells us that constipation is defined by symptoms, not just frequency.

Things like stool consistency, excessive straining, a prolonged effort to go, or a feeling of incomplete evacuation.

If a patient only goes twice a week, but it's soft and easy, they are not constipated.

That makes total sense.

Now, before we reach for the medication card, the textbook emphasizes diet, right?

Oh, absolutely.

Dietary fiber is huge.

Especially bran.

You want to aim for 20 to 60 grams a day.

Because fiber acts like a sponge on that conveyor belt, right?

Exactly.

It absorbs water to increase the stool mass, and it also feeds the colonic bacteria, which increases the mass even more.

Okay, so that's diet.

But let's look at the person -centered care across the lifespan chart in the book, because you're going to see patients of all ages who need actual pharmacological help.

Let's run through it.

For ancients, things like docu -set, lactulose, and glycerin suppositories are generally safe.

Good to know.

What about during pregnancy?

This is a massive caution area.

You have to be so careful with pregnant patients.

Because of the GI stimulation?

Yes, exactly.

The uterus and the GI tract are so close together.

If you use a strong laxative that violently stimulates the gut, that agitation can actually cross over and induce labor.

Oh, wow.

That is a serious risk.

And for breastfeeding.

Sena is considered safe, but you want to use caution with PEG or polyethylene glycol, because the data is just limited.

Right.

Okay, so moving on to indications and contraindications.

Why are we giving these drugs and when should we absolutely never give them?

Well, a huge valid indication is reducing strain.

Think about a cardiovascular patient, maybe someone who just had a heart attack.

Right, if they strain on the toilet, their blood pressure spikes.

Exactly, and that could trigger another cardiac event.

So we give them a gentle laxative just to keep things moving effortlessly.

We also use them for anthelmintic therapy.

To flush out dead parasites.

You got it.

But the contraindications, these are critical for your exam.

Never, ever use a laxative if a patient has undiagnosed abdominal pain, nausea, cramps, or symptoms of appendicitis.

Oh, and ulcerative colitis too, right?

Or any bowel obstruction or fecal impaction.

Yes, because think about it.

If there is a physical blockage or a severely inflamed appendix and you give a drug that violently increases peristalsis.

You're forcing the gut to contract against a wall.

Right, and the bowel can literally perforate, it will rupture, and that is a life -threatening emergency.

Okay, so safety first.

Now let's talk about how we organize these drugs in our heads.

The textbook gives us two classification schemes.

Yes, the how and the when.

Table 83 .2 classifies them by mechanism of action.

You have your four main buckets, bulk -forming, surfactant, stimulant, and osmotic.

But then, table 83 .3 classifies them by therapeutic response, which is, well, a much more clinical way to think about it.

It is.

It's based on the time of onset and the stool consistency.

So group I agents, they act fast, in two to six hours, and produce a watery stool.

You use these for colonoscopy prep.

Then you have group II agents.

These act in six to 12 hours and produce a semi -fluid stool.

And we'll talk about this later, but this is the group that gets abused the most.

And finally, group III agents.

These take one to three days to act, and they produce a soft but formed stool.

This is what you use for chronic constipation.

So let's dive right into those group III agents.

Specifically, the bulk -forming and surfactant laxatives.

Perfect.

Bulk -forming agents include methylcellulose, psyllium, and polycarpophyll.

They basically act just like dietary fiber.

Meaning they aren't absorbed, right?

Exactly.

They are non -absorbable.

They sit in the gut, and when they come into contact with water, they swell up to form this viscous gel.

OK, wait.

I have to push back on this, because this always confused me as a student.

If a patient is backed up, right,

why are we giving them a medication that creates more mass in their gut?

It seems counterintuitive, I know.

Right.

Doesn't that just make the traffic jam worse?

It would, if the gut were just a rigid, static pipe.

But it's not.

The gut is muscle.

When you increase the fecal mass with these swelling agents, that bulk stretches the intestinal wall.

Oh, OK.

And that stretching is the exact mechanical trigger the body needs to stimulate peristalsis.

It tells the muscle, hey, wake up, it's time to push.

That makes so much sense now.

But because they swell up, there is a huge nursing implication here.

Patients absolutely must take these with a full glass of water or juice.

Yes.

This is non -negotiable.

If they swallow that powder with just a tiny sip of fluid, it can start swelling while it's still in the esophagus.

Which causes an esophageal obstruction.

Literally a choking hazard.

Exactly.

Now, the other group three agents are the surfactant laxatives.

The big one here is docucate, either docucate sodium or docucate calcium.

Oh, docucate.

You see this ordered all the time.

All the time.

And these work by altering stool consistency.

They lower the surface tension of the stool, which basically breaks down its waterproof outer layer.

So it allows water to actually penetrate the feces and soften it up.

Yes.

And it also inhibits fluid absorption in the gut wall, leaving more water in the lumen.

But again, you have to administer docucate with a full glass of water for it to work properly.

Right.

You need the water there to do the softening.

OK.

Moving on to section four in the book,

the stimulant laxatives.

These are mostly your group two agents.

And these are widely used, but also massively abused.

Their legitimate uses are actually pretty narrow, right?

Very narrow.

We're primarily talking about treating opioid induced constipation or constipation from slow intestinal transit.

So what's the mechanism here?

They directly irritate and stimulate the intestinal motility.

They also increase the amount of water and electrolytes secreted into the intestinal lumen.

Basically, they force the issue.

Let's look at the specific drugs here.

First up is bisacodil, often known as dulcalex.

Right.

Bisacodil is an interesting cause you can give it orally, which takes about six to twelve hours or as a suppository, which is super fast, like 15 to 60 minutes.

For the oral tablets,

patient teaching is critical here.

These tablets are enteric -coated.

Which means they're designed to survive the stomach acid and only dissolve in the intestines.

Exactly.

So patients must swallow them intact.

No crushing, no chewing.

But there's a huge drug interaction here too, right?

Yes.

They have to wait at least one hour after drinking milk or taking antacids before taking oral bisacodil.

Cause milk and antacids lower the stomach acidity, right?

Exactly.

They make the stomach more alkaline.

So if the enteric coating hits that alkaline environment, it thinks it's already in the intestines and it dissolves prematurely right there in the stomach.

Oh, and that would cause severe gastric irritation and cramping.

Terrible cramping.

And as a quick note on the suppositories, long -term use can cause a burning sensation and even proctitis, which is inflammation of the rectum.

Definitely something to warn patients about.

Now the second stimulant is Senna.

This one is plant -derived.

Yes.

And the main patient teaching point for Senna is a harmless but a very alarming side effect.

It can turn their urine a yellowish -brown or pink color.

Oh yeah.

You definitely want to warn them about that.

Or they'll think they're bleeding internally.

Right.

And then we have the big exception in the stimulant category, castor oil.

Yes.

Massive clinical warning right here.

Cause, castor oil is the only stimulant laxative that acts on the small intestine.

Which means it's a powerful Group I agent.

It doesn't take 6 to 12 hours.

It causes a watery evacuation in 2 to 6 hours.

It just flushes the whole system.

Completely.

Which is why its clinical use is strictly for rapid evacuation, like prep for a radiology procedure.

So you never give it at bedtime.

Oh, absolutely not.

Unless you want them up all night.

And it tastes awful, so mix it with chilled juice to mask the taste.

Good tip.

Section 5, osmotic laxatives and the other agents.

So osmotic laxatives include osmotic salts like magnesium hydroxide and sodium phosphate.

How do these work?

They are poorly absorbed salts.

Their mechanism is pure osmosis.

Because they sit in the intestinal lumen, they draw water out of the body tissues and into the gut.

And all that extra water softens the stool, swells it up, and triggers the stretch response for peristalsis.

You got it.

And there's a direct dosing connection here.

At low doses, these salts give you a group 2 effect semi -fluid stool in 6 to 12 hours.

But at high doses?

High dose gives you a group I effect, that rapid watery evacuation in 2 to 6 hours.

But wait, pulling all that water and using these heavy duty salts, there have to be systemic safety issues, right?

Major issues.

Let's look at magnesium first.

Magnesium is totally contraindicated in patients with kidney disease.

Because if the kidneys can't filter it out, the magnesium just builds up in the blood.

Exactly.

It can accumulate to toxic levels.

Now, what about sodium phosphate?

Well, with sodium phosphate, you're dealing with a huge sodium load.

And water always follows sodium.

Which leads to fluid retention.

So sodium phosphate is completely contraindicated in patients with heart failure, hypertension, or ADHERA.

It's just too much fluid volume for their system to handle.

And it can cause acute renal failure too, right?

Yes.

So we have to be very careful.

This is why polyethylene glycol, or Mirallax, is so popular.

Right.

Mirallax.

It's a non -absorbable compound, so it doesn't have the same salt toxicity risks.

It takes about 2 to 4 days to work, and it's dosed at 17 grams, dissolved in 4 to 8 ounces of liquid.

And the textbook says it's superior to Lactulose for chronic constipation.

Which brings us to Lactulose, of this one.

The physiology is so cool.

It really is.

Lactulose is metabolized by colonic bacteria into acids, which causes a mild osmotic effect.

But the key nursing pearl here isn't even about constipation, is it?

No, it's about the liver.

We use Lactulose extensively for patients with severe liver disease, specifically hepatic encephalopathy.

Right.

Cause a failing liver lets toxic ammonia build up in the blood, which causes brain fog and confusion.

Exactly.

And when Lactulose breaks down into acids in the gut, it creates an environment that actually pulls ammonia out of the blood and traps it in the intestines.

And then the laxative effect just flushes the ammonia completely out of the body.

You're using a laxative to clear brain toxins.

I just, I love that connection.

It's a brilliant mechanism.

Now, the book also lists a few other agents in table 83 .4.

Like glycerin suppositories.

Yes.

Glycerin simply softens hardened or inspicated feces.

It works in about 30 minutes.

Very straightforward.

And then there's Lubiprostone.

Right.

Lubiprostone is a chloride channel activator.

It basically opens up chloride channels in the gut, which secretes a chloride -rich fluid into the intestinal lumen.

It's used for opioid -induced constipation, chronic idiopathic constipation, and IBS with constipation.

You do need to take it with food.

And it has a really strange side effect.

Patients can get this transient chest tightness or difficulty breathing right after taking it.

That would be scary.

What about Plecanotide and Precalipride?

Plecanatide increases chloride and bicarbonate secretion.

Precalipride is completely different.

It's a serotonin agonist.

It triggers the release of acetylcholine to increase GI motility.

Oh, nice.

And last in the others group is good old mineral oil.

A classic lubricant.

It's really useful as an enema for treating fecal impaction.

But there's a big safety alert here in the text.

A massive one.

If a patient accidentally aspirates mineral oil, meaning they breathe a little bit of it into their lungs while swallowing, it can cause lipid pneumonia.

Because the lungs can't clear oil.

Also, if they use it too much, the mineral oil coats the gut and decreases the absorption of fat soluble vitamins.

OK, let's move to section six, bowel cleansing products for colonoscopies, table 83 .5.

Yes, colonoscopies are absolutely crucial for detecting colon cancer, but the prep is just notoriously awful for patients.

There are two main types of cleansers we need to know.

First is the PEG electrolyte solutions like Golightly.

The mechanism here is that it's isotonic with body fluids.

That means there are no massive fluid or electrolyte shift.

So it's safe for renal and cardiac patients.

Very safe.

But if it's so safe, why does everyone hate taking it?

The sheer volume.

Patients literally have to drink four liters of this stuff.

That's 250 to 300 milliliters every 10 minutes.

Oh, that is brutal.

It is.

Newer products like MoviPrep have added ascorbic acid to help, which cuts the volume down to two liters.

But it's still a lot.

Right.

Which leads us to the alternative,

sodium phosphate products like Prepelpic.

Patients love these because the volume of the actual medication is so much smaller, but the mechanism is hypertonic.

Meaning it aggressively pulls water out of the body.

Exactly.

And the danger is that it can cause massive dehydration, extreme electrolyte shifts, and severe kidney damage.

It causes hyperphosphatemia, which precipitates calcium and phosphate crystals in the renal tubules.

Wow.

So it's strictly contraindicated for patients on ACE inhibitors, ARVs, diuretics, or NSAIDs.

Yes.

The easier prep is definitely not the safer prep.

Good to remember.

All right.

Section seven, the final stretch, laxative abuse and major nursing implications.

This is a huge real world problem.

The vicious cycle of abuse.

Why do people abuse them so much?

Mostly, it's driven by two misconceptions.

First, the myth we talked about earlier, that you have to have a daily bowel movement to be healthy.

Second, the false belief that laxatives help with weight loss.

Which is physically impossible, right?

Because food is already absorbed in the small intestine before the laxative even hits the colon.

Right.

You're just losing water weight.

But this leads to a physiological trap.

How so?

A patient takes a strong laxative, it purges the entire bowel clean, now the gut is totally empty, right?

Yeah.

Well, it takes two to five days for new food to travel down and replenish the stool bulk.

Oh, I see.

So the patient goes a few days without a bowel movement.

And they think, oh no, I'm constipated again, so they take another dose, and the cycle just continues.

And eventually, that constant purging diminishes their natural defectory reflexes, and it can cause colitis.

So how does a nurse help a patient break this habit?

You have to guide them through abrupt cessation.

You just stop the laxative, and you clearly warn them, you will not have a bowel movement for several days, and that is normal.

Setting the expectation.

Exactly.

Then you focus on diet, getting that fiber and fluid up, and bowel training, teaching them to heed the natural reflex when it happens.

Awesome.

Let's do a rapid -fire synthesis of the major nursing implications from the whole chapter.

Alright.

Always take bulk -forming agents with a full glass of water.

Never give any laxative to someone with undiagnosed abdominal pain.

Check renal function before giving magnesium salts.

And always separate bisakado from milk or antacids by at least an hour.

Nailed it.

Well, that wraps up chapter 83.

But I want to leave you with a final thought to mull over.

Yeah, this is important.

When a patient comes to you complaining of constipation, remember that their definition of normal in yours might be completely different.

Exactly.

Before you reach for a pill, you have to find out what normal actually means for their body.

The cure for their constipation might not be a medication at all.

It might simply be unlearning a lifetime of bad advice.

Could not have said it better.

Good luck on your exam, and a warm thank you from the Last Minute Lecture Team for learning with us.