Chapter 44: Antibiotics Part 2 – Aminoglycosides & Fluoroquinolones

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Welcome to the Deep Dive.

Today, we're diving into a really specific but absolutely vital part of pharmacology.

We're talking about the heavy hitters.

These are the powerful antibiotics.

The ones kept in reserve for the really serious, stubborn infections.

The kind where your first -line drugs just aren't cutting it.

These are definitely the high -stakes medications.

If you're learning about healthcare practice, you absolutely need to grasp these, not just what they are, but why we reach for them, and crucially, the serious toxicities.

They demand really constant, careful monitoring.

Absolutely.

Our mission for this deep dive is pretty straightforward.

Quickly unpack the key stuff, how they work, their special uses, those unique toxicities we mentioned, and the really non -negotiable safety checks for patients.

Right.

We'll cover three main groups.

The amyglycosides, the fluoroquinolones, and then several specialized miscellaneous drugs.

And the whole backdrop for this chapter, the reason these drugs are so critical, it boils down to one huge global issue.

Multi -drug -resistant organisms.

How do you do?

MDROs.

Zucker bugs?

Exactly.

There are four main culprits driving the need for these kinds of aggressive treatments.

You've got MRSA, that's methicillin -resistant staph aureus, then VRE, vancomycin -resistant, and terracoccus.

Okay.

Also, organisms that produce ESBL's extended -spectrum beta -lactamuses.

And the one that's really causing concern lately, KPC, Klebsiella pneumonia, Carbapinemaeus.

KPC, yeah.

Heard about that one.

When resistance gets to that level, well, you're forced to turn to these high -risk, but hopefully high -reward drugs we're about to discuss.

Okay.

Let's jump right in then.

First group, the aminoglycosides, thinking gentamicin, tobromycin, amicusin here.

Yep.

Those are the main ones.

These are, like you said, potent, bactericidal.

And mostly given IV or IM, right, because they don't absorb well if you take them by mouth.

That's correct.

Poor oral absorption.

Their power comes from how they attack bacteria.

They latch on to the bacterial 30S ribosome.

The protein factory.

Exactly.

They essentially jam up the works, preventing protein synthesis.

But what's really interesting is how they often work best with another antibiotic, Synergy.

Synergy, okay.

Yeah.

Like combining forces.

Precisely.

They're often paired with beta -lactams, like penicillins.

But here's the crucial part.

You have to give the beta -lactam first.

Okay, wait.

Why first?

What's the logic there?

Think of the beta -lactam as like a demolition crew.

It breaks down the bacteria's tough outer cell wall.

Ah, okay.

It breaches the defenses.

Right.

It punches holes in the wall, essentially opening the door so the amino glycoside can get inside the cell to reach that ribosome target.

You got to break down the door before the amino glycoside can get in and shut down the factory.

That makes total sense.

And you mentioned something about how they kill differently.

This trips students up sometimes.

Oh, absolutely.

It's a key concept.

See, most antibiotics work by time -dependent killing.

That means the drug level needs to stay above a certain minimum concentration, the MIC, for a good chunk of time.

Right.

Keep it steady.

But amino glycosides, they're different.

They primarily use concentration -dependent killing.

What matters most is hitting a really high peak concentration in the blood, even if it's just for a short time.

That massive spike gives you the most effective bacterial kill.

So a big initial hit is better than keeping it level.

For these drugs, yes.

And that understanding completely changed how we dose them.

We used to give them, you know, three times a day.

Yeah, I remember that.

Now, the standard is often a high dose once -daily regimen, usually around five to seven milligrams per kilogram per day.

This maximizes that peak concentration, gets better killing, and maybe surprisingly, it can actually reduce the risk of toxicity compared to the older regimens.

How does giving more at once reduce toxicity?

Because the patient gets a longer period where the drug level is very low or even zero, allowing the kidneys, for example, some recovery time.

Plus, we benefit from the post -antibiotic effect, or PAE.

PAE.

Yeah, the bacteria stay suppressed for a while, even after the drug concentration drops below that minimum inhibitory level.

It's like they're stunned.

OK, so high dose once a day makes sense for efficacy and maybe even safety.

But we have to talk about the toxicities.

You said monitoring is key.

The double threat.

The double threat, absolutely.

Nephrotoxicity and autotoxicity.

Nephrotoxicity means kidney damage.

It can happen in maybe five to 25 % of patients.

Wow, that's quite a range.

It is.

You'll see signs like urinary cast, protein spilling into the urine, and those kidney function markers, BUN and creatinine, starting to rise.

The good news, relatively speaking, is that this kidney damage is usually reversible if you catch it and stop the drug.

Usually reversible.

OK, but the other threat, autotoxicity.

That sounds worse.

It often is.

Autotoxicity affects the eighth cranial nerve, the auditory nerve.

It happens in maybe three to 14 % of patients.

And here's the scary part.

It's often not reversible.

Not reversible.

Yeah.

It can show up in two main ways.

There's cochlear damage, that means hearing loss, potentially permanent, or that awful ringing in the ears, tinnitus, that just won't quit.

Or it can hit the vestibular system, that causes intense vertigo, dizziness, problems with balance at taxia.

Patients literally can't walk straight.

It's debilitating.

OK, so given those risks, the monitoring,

you mentioned trough levels.

How does that work with once daily dosing?

Right.

With once daily dosing, we typically skip measuring the peak level.

What's absolutely critical is the trough level.

That's the lowest point the drug concentration reaches right before the next doses do.

We usually draw that blood sample about 30 minutes before hanging the next bag.

What's the target number?

The goal is to have that trough level at or below one microgram per milliliter, MCGML.

OK, A1.

Exactly.

If that trough starts creeping up, especially if it hits two mcgml or higher, well, that's a red flag.

The risk for both that irreversible hearing damage and the kidney damage goes way up.

Time to adjust the dose or maybe stop the drug altogether.

And there are specific populations we need to be extra careful with.

Absolutely.

Major caution in pregnancy.

There have been reports of irreversible deafness in babies whose mothers received aminoglycosides, so generally contraindicated.

And you need extreme caution in neonates.

Their kidneys and nervous systems are still immature, much more vulnerable to damage.

Makes sense.

And drug interactions.

What should we workshop for?

Big ones are combining them with other drugs that can harm the kidneys of other nephrotoxic agents.

Think vancomycin, cyclosporine, that just multiplies the risk.

OK, avoid doubling up on kidney -harming drugs.

Right.

And also, combining aminoglycosides with loop diuretics, like furosemide, that significantly increases the risk of ototoxicity, the hearing damage.

Got it.

OK, let's shift gears.

Second major class.

The quinolones or floroquinolones,

drugs like ciprofloxane, levofloxane.

Chipper and levokane, yeah.

Common ones.

These are also potent, broad -spectrum, bactericidal.

And a big plus is their oral absorption, right?

Sometimes it's almost as good as 5V.

Exactly.

Excellent oral bioavailability makes them very convenient.

Their mechanism is pretty neat, too.

They mess with bacterial DNA replication by targeting two enzymes, DNA gyrase and tippoizomerase V.

Enzymes bacteria needs, but humans don't rely on it the same way.

Precisely.

So they disrupt bacterial DNA without harming ours.

They cover a lot of bugs, especially gram negatives.

And since they're mostly eliminated unchanged by the kidneys, they're a go -to for complicated UTIs.

OK, but here comes the big patient safety alert.

The one Health Canada flags prominently.

The black box warning.

Yes, this is absolutely critical for counseling.

Increased risk of tendonitis and worse,

actual tendon rupture.

Not just a little soreness, but rupture.

Full rupture.

It most commonly affects the Achilles tendon like 95 % of cases.

You must tell patients.

If you feel any pain, swelling or inflammation in a tendon or joint, stop taking the drug immediately and call your provider.

Immediately.

And are certain people more at risk?

Yes.

The risk is highest in older adults, people with existing kidney failure, and crucially anyone also taking glucocorticoid steroids like prednisone.

Steroids plus a quinolone equals much higher risk.

Much higher.

That combination really elevates the danger.

OK, beyond tendons, any other major concerns?

Cardiac maybe?

Yes, cardiac risk is another one.

Quinolones can cause prolongation of the QT interval on an electrocardiogram.

Which is bad because?

Because a prolonged QT interval increases the risk of potentially fatal heart rhythm problems.

Specifically, a type called torsons de pointes.

Very dangerous.

That's why you avoid using them with certain heart rhythm drugs like class IA or class III antirhythmics, which also prolong the QT.

The combined effect is just too risky.

Gotcha.

And any important interactions we need to teach patients about, especially with food or supplements?

Definitely.

This is key for oral dosing.

Things like antacids or supplements containing calcium, magnesium, iron, zinc, even dairy products.

They can significantly slash the amount of quinolone absorbed.

So taking your super with milk is a bad idea.

A very bad idea.

You need to tell patients to separate taking the quinolone from any of those products by at least one hour before or two hours after.

Give the drug time to absorb on its own.

Good practical tip.

And what about sun exposure?

Ah yes, photosensitivity.

They need to avoid strong sunlight and tanning beds.

They can get some nasty sunburns really easily.

Okay.

Tendon pain, QT prolongation, separate from minerals, stay out of the sun.

Got it.

Let's move to the third section.

The miscellaneous antibiotics.

Kind of a mixed bag of specialized agents.

Exactly.

Unique drugs for specific, often tough situations, especially resistance.

Let's start with a big one.

Vancomycin hydrochloride.

Vank.

The go -to for MRSA for a long time.

Still is in many cases.

It's a natural antibiotic, bactericidal, structurally different from others.

It also works by inhibiting cell wall synthesis, just at a different step than penicillins.

Prime choice for MRSA and lots of other resistant gram -positive infections.

And the root is really important here, right?

4V versus oral.

Absolutely.

Critical distinction.

RV vancomycin is for systemic infections, bloodstream, bone, joint, pneumonia, that sort of thing.

Okay.

The oral form is basically not absorbed.

It stays in the gut.

So we only use oral vancomycin to treat infections inside the GI tract itself, most notably C.

difficile colitis.

Because it stays locally in the gut to kill the C.

diffs.

Precisely.

It doesn't get into the bloodstream from the gut.

Okay.

And like the amino glycosides, then it carries those same risks for toxicity and ogotoxicity.

So we monitor levels.

Yes.

Same risks.

We routinely monitor trough levels for IV vancomycin, aiming for a range of 10 -20 mcgmL.

We used to measure peaks too, but that's generally not done anymore.

Trough is key.

Got it.

But Vanek has its own unique adverse effect, that infusion reaction.

Ah.

Yes.

The vancomycin infusion reaction used to be called Redman syndrome.

Redman syndrome.

Right.

What does that look like?

It's an infusion rate -dependent reaction.

The patient gets flushed, itchy, develops redness, erythema, usually on the face, neck, upper torso.

It can also cause a drop in blood pressure.

It looks alarming.

And what causes it?

Giving the IV infusion too fast.

The simple prevention, and the fix if it happens, is to slow the infusion down.

Standard practice is to infuse each dose over at least 60 minutes.

Some larger doses might need 90 minutes or more.

So if your patient turns red while getting Vanek, first step, slow the infusion.

Exactly.

Slow it right down.

Okay.

Next up, clindamycin.

Why does this one make clinicians a bit nervous sometimes?

Clindamycin.

It's useful often for anaerobic infections or chronic things like bone infections, some skin infections,

but the big caution, the thing everyone worries about, is its strong association with pseudomembranous colitis.

Which is?

Basically a severe C.

difficile infection.

Clindamycin is notorious for wiping out the normal gut bacteria, which then allows C.

diff to overgrow and release toxins, causing really bad, potentially life -threatening diarrhea.

Okay.

So C.

diff risk is high with clindamycin.

Good to know.

How about linazolid?

That's a newer one, relatively speaking.

Linazolid, yeah.

First in its class, the oxazolidinones.

Its big claim to fame was being developed specifically to treat VRE, vancomycin -resistant, and turococcus.

Ah, filling a gap there.

Exactly.

It also hits MRSA effectively.

And a major plus, as we mentioned earlier, is its fantastic oral absorption.

Almost 100%.

That's huge for letting patients with serious infections finish treatment at home.

That's a big advantage.

But outpatient therapy means the patient needs to be really careful about interactions, right?

Absolutely crucial.

Two big ones with linazolid.

First, it's a weak MAOI monoamine oxidase inhibitor.

So if you take it with other drugs that boost serotonin, like SSRI antidepressants.

Prozac or Zoloft?

Right.

You run the risk of serotonin syndrome, which can be fatal.

That's a serious drug interaction.

Okay, serotonin syndrome.

What's the second one?

Food interactions.

Because it's an MAOI, patients must avoid foods high in tiramine.

It's tiramine.

Like what kinds of foods?

Aged cheeses, smoked or cured meats, salami, pepperoni, some beers, red wine, that kind of thing.

Eating those while on linazolid can cause a sudden dangerous spike in blood pressure, a hypertensive crisis.

Wow.

Okay, so strict diet is necessary.

No aged cheese and wine with linazolid.

Definitely not.

Strict adherence is key.

Got it.

Let's move to metronidazole, often called flagell.

Metronidazole, great drug for anaerobic bacteria, the ones that don't like oxygen.

So common in treating intra -abdominal infections, gynecological infections, and it's also a first -line oral treatment for C.

difficile.

Okay, and the absolute must -know warning for metronidazole.

The alcohol rule.

Non -negotiable.

Cannot be stressed enough.

Why happens?

Metronidazole blocks an enzyme needed to break down alcohol.

So if a patient drinks alcohol while taking it, or even shortly before or after, they get what's called a disulfiram -like reaction.

Intense nausea, vomiting, flushing, pounding headache, feeling awful.

Like the reaction some drugs cause to deter drinking.

Exactly like that.

So patients must avoid all alcohol, including hidden sources, like some cough syrups or mouth washes, for 24 hours before starting metronidazole during the entire course and for at least 36 hours after the very last dose.

36 hours after.

Wow, okay.

Crucial teaching point.

Now specifically for UTIs, there's nitroferroctoine.

Right, nitroferroctoine, often macrobid.

Its use is pretty much restricted only to urinary tract infections.

Why only UTIs?

Because it gets filtered by the kidneys and concentrates really highly in the urine, right where you need it for a UTI, but it doesn't reach good levels elsewhere in the body.

Makes sense.

Any major cautions?

Yes.

Big one.

It's contraindicated if the patient has significant kidney impairment, because if the kidneys aren't working well, the drug can't concentrate in the urine effectively, and it might build up systemically.

Okay, need good kidney function.

Other potential issues include peripheral neuropathy, nerve damage in the hands and feet, which can sometimes be irreversible and, rarely, liver toxicity.

Oh, and tell patients it can turn their urine a dark brown or rust color.

That's normal, not harmful.

Good to warn them so they don't panic.

Last one in this miscellaneous group, and it really highlights the resistance crisis.

Cholestimethasodium or Cholestin?

Cholestin.

Yeah, this is an old drug, a polypeptide antibiotic.

It was actually shelved for decades because it was known to be pretty toxic.

So why are we using it now?

Desperation, basically.

Because of the rise of these incredibly resistant bacteria, particularly the KPC -producing organisms,

Cholestin is one of the very few antibiotics left that still has activity against some of these nightmare bugs.

It's truly a last resort.

Last resort.

And the toxicity that shelved it before.

Still a concern.

Oh, absolutely.

Serious adverse effects are common.

Kidney failure is a major risk.

And neurotoxicity, things like tingling or numbness around the mouth, paresthesia, dizziness, vertigo.

It's a tough drug to use, requires very careful monitoring.

Really underscores the threat of resistance when we're dusting off old toxic drugs.

OK, so we've covered these high alert meds.

Let's wrap up by connecting this back to the nursing process.

What are the universal responsibilities?

Well, for all these drugs, assessment is paramount.

You need baseline labs before you start liver function tests like AST, ALT, kidney function like BUN, creatinine, neurological status baseline too.

And getting those cultures before the first dose.

Critically important whenever possible.

Culture and sensitivity results guide therapy.

You also need to constantly assess for signs of super infection, things that happen when antibiotic wipes out good bacteria,

like crevue white patches in the mouth suggesting thrush or maybe perineal itching indicating a yeast infection.

OK, baseline assessment cultures monitor for super infection.

What about implementation?

Anything general we should be doing?

A simple but important one is encouraging fluid intake.

Unless there's a reason not to, like heart failure, aiming for up to three liters, three thousand milliliters per day can help flush the kidneys and might minimize the risk of nephrotoxicity, especially with drugs like Vanakik or aminoglycosides.

Good hydration helps protect the kidneys.

Makes sense.

And let's quickly recap the absolute must -remember safety points for patients for the big categories.

OK, quick hits.

Aminoglycosides.

Tell patients to report any ringing in the ears, tinnitus, feelings of fullness in the ears, or any dizziness or unsteadiness immediately.

That could be irreversible odor toxicity starting.

Quinolones.

Report any joint or tendon pain right away and stay out of the sun or use strong protection.

Vancomycin.

Make sure that Avi infuses slowly over at least 60 minutes to prevent the infusion reaction and stress the need for follow -up blood tests to check those trough levels.

Linazolid and metronidazole.

Strict assist adherence to those dietary restrictions.

No tiramine with linazolid.

Absolutely no alcohol with metronidazole.

Those are life -saving instructions.

Definitely.

And it all comes back to resistance, doesn't it?

We're using these powerful, risky, last -line drugs because of MDROs, MRSA, VRE, ESBL, KPC.

What's the single most effective thing we can all do?

It sounds almost too simple, but it's fundamental.

Rigorous, proper hand hygiene.

Washing hands effectively, using sanitizer correctly.

It's the number one way all healthcare providers, caregivers, everyone, can help prevent the spread of these dangerous organisms in the first place.

Stop the spread before we even need these heavy hitters.

That's the ultimate goal.

We've covered a lot of these high alert antibiotics.

Unique ideas like concentration -dependent killing, the critical side effects needing monitoring like kidney and hearing damage, tendon rupture.

Hopefully this leaves you better prepared to handle these complex drugs safely.

So thinking about all this, knowing the serious consequences tied to relying on these last resort antibiotics.

What kind of public health strategies, maybe beyond just hand washing, do you think we urgently need to tackle the spread of bugs like KPC, where our treatment options are genuinely dwindling?

Something to think about.

Definitely something to think about.

Thank you for joining us on this deep dive.

We appreciate you committing the time to stay informed about this incredibly serious challenge of antibiotic resistance.