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Welcome to the Deep Dive.
Today we're really getting into some core clinical knowledge.
Chapter 13, focusing on fungal, viral, and bacterial infections of the skin.
Whether you're cramming for a farm exam or you're already seeing patients, well this Deep Dive is all about boiling down those essential diagnostic clues and the treatment pathways you just can't afford to get wrong.
And you know, the urgency is real here.
Skin infections seem common, maybe minor sometimes, but they cover such a huge spectrum of risk.
We absolutely need rapid, appropriate management.
I mean, bacterial infections can escalate incredibly quickly.
Think necrotizing fasciitis, that's a true emergency.
And then on the flip side, non -bacterial treatments, like for fungal infections, they often need specific drugs, sometimes for long durations, and those bring their own systemic risks.
Okay, so our plan for today isn't just like a topic list, it's more of a clinical risk strategy.
We're kicking off with bacteria, where resistance and speed are key.
Then we'll shift to fungi, where the challenge is maybe less about immediate death and more about systemic toxicity and treatment length.
Good way to put it.
And finally, viruses.
Focusing on that critical timing for effective treatment, especially with something like shingles.
Alright, let's jump straight into it.
Bacterial scene infections, the usual suspects,
right?
Staphylococcus aureus and those beta hemolytic streps like Streptococcus pyogenes GAS.
Yep, those are the big players.
But the factor that completely flips the script on treatment, even before you think about specific drugs, is methicillin -resistant S -aureus, MRSA.
That is the absolute game changer, because MRSA just laughs off our standard workhorses, penicillins, most cephalosporins, they just don't work.
Clinically, if you see a purulent infection, like an abscess, even without culture results back yet, you almost have to assume MRSA is in the mix, or at least consider it strongly, especially if there are risk factors.
Okay, so let's quickly break down the common types based on how deep they go.
Pedigo, everyone knows that one.
Superficial, super contagious, those classic honey -colored crusts.
Right, the textbook picture.
But when it goes deeper into the subcutaneous tissue cellulitis, how do we tell standard cellulitis from, you know, something worse just by looking and feeling?
Well, with cellulitis, it's usually diffuse, the edges aren't sharp, the skin itself often has that pitting edema, sometimes you hear it called orange peel texture or peau d 'orange, and because it's deeper, there's that potential for systemic spread.
So, systemic antibiotics are needed, usually right away.
Now, there's a really critical point in the chapter about managing purulent infections, abscesses, carbuncles, mostly SREs, often MRSA, right?
Correct.
The book stresses IND, incision and drainage,
but why do we still sometimes see antibiotics thrown at a simple localized abscess first?
It's, well, it might be an old habit or maybe uncertainty, but the chapter's algorithm is crystal clear.
For any localized abscess, the number one priority is IND.
Drain the pus.
Drain first.
Drain first.
Antibiotics, they're secondary, really only needed if the patient has systemic signs of fever, chills, or if the infection is huge, spreading fast, or maybe if IND alone doesn't seem to be enough.
But the antibiotics don't replace drainage.
Got it.
And then the other end of the spectrum.
Wow.
The one that makes everyone nervous.
Necrotizing fasciitis,
NF.
Yeah.
Life and limb threatening.
Subcutaneous tissue, fascia, demands emergency surgery, debridement, and really heavy hitting antibiotics.
What's the clinical clue that screams, this isn't just bad cellulitis, this is NF?
There are a couple things, but the big one described is the feel of the tissue.
It spreads incredibly fast, often way faster than you'd expect from how it looks initially.
But critically on exam, the subcutaneous tissue feel, well the book says, wooden hard.
Wooden hard, okay.
That really firm, unyielding texture tells you the destruction is deep, hitting the fascia.
That patient needs the OR, like, now.
Right, let's put it to the drugs.
Empiric treatment.
We need to cover both GAS and regular S -oreas, the penicillinase producers.
What are our reliable first line oral options?
So you need something that gets around that penicillinase enzyme.
Amoxicillin clavulin is a mainstay, the clavulin it protects the amoxicillin.
The beta -lactamates inhibitor.
Exactly.
Dicloxacillin is another solid penicillinase resistant choice.
And then first gen cephalosporins, like cephalexin or cephasolin, they cover both GAS and MSSA pretty well.
Good standard choices.
But we have to mention the general antibiotic risks, right?
Oh, absolutely.
Always.
Beyond the common stuff like GI upset or maybe a rash, you have to counsel about Clostridium difficile, C.
diff, that pseudomembranous colitis can be incredibly severe, even fatal.
It's a crucial warning.
And it underlines the basic principle.
Use the shortest effective duration possible.
Minimize exposure, reduce risk, fight resistance.
Okay.
Now, what if we do suspect MRSA, but it seems mild,
maybe treatable outpatient?
Oral options.
We're thinking sulfamethoxazole, trimethoprim, SMXTMP, or maybe doxycycline, minocycline.
Those are the main oral players for community -acquired MRSA, yes.
But there's a huge asterisk, a really important one, SMXTMP.
It doesn't reliably cover streptococcus pyogenes, GAS.
So if you're treating something like cellulitis, where strep is a very likely culprit alongside potential MRSA, SMXTMP alone might not cut it.
So you might need to add something else.
You often need to pair it maybe with amoxicillin or cephalexin to make sure you've got that strep covered too.
It's a common pitfall.
Good point.
Okay.
Stepping up the severity.
Hospitalized patient, severe cellulitis, definitely concerned about MRSA, 4V therapy.
We're pulling out the big guns now.
Right.
Vancomycin is still the workhorse, the IV drug of choice for suspected or confirmed severe MRSA.
The standard.
Yep.
Alternatives include daptomycin, linazolid.
But you know what's really interesting are the newer agents, delbovancin and ordovancin.
That's special about them.
Their pharmacokinetics are just wild.
Extremely long half -lives.
We're talking single dose or dose.
Yeah.
Incredible convenience, especially for finishing treatment outpatient.
But of course, they come with a high cost and are often reserved for specific situations or infectious disease specialists.
It's that constant balancing act.
That definitely sets the bacterial scene.
Okay.
Let's switch gears completely.
Fungal skin infections.
Here the battle feels different.
Less about rapid systemic collapse, maybe more about structure penetration and drug toxicity.
That's a great way to think about it.
The underlying pathology is different.
We're mostly talking dermatophytes.
They cause tinea and candida albicans.
And dermatophytes, remember, they're kind of limited.
They only infect that dead keratinized top layer, the stratum corneum.
They can invade living tissue.
Correct.
Which influences how we treat.
And the naming for tinea is thankfully pretty straightforward.
It's all about location.
It is tinea capitis head, tinea pedis feet, athlete's foot, tinea corporeis body, classic ringworm.
And then the really stubborn one, tinea ungium ongomycosis.
Nails.
Nails.
Yeah.
Notoriously tough.
Diagnosis wise, the gold standard is fungal culture, but it's slow, right?
Takes weeks sometimes.
Up to two weeks, yeah, can be frustrating.
So why does the chapter recommend waiting for that culture before jumping to systemic antifungals, especially with that delay?
It really comes down to the drugs themselves.
Systemic antifungals aren't benign.
They have significant potential side effects, toxicity risks.
Right.
So before you commit someone to say 12 weeks of an oral antifungal for toenails, you really want to be sure it's actually a fungus causing the problem.
Confirming the diagnosis avoids unnecessary drug exposure.
Quick tests like a woodlamp only pick up certain species like microsporum.
So they aren't definitive.
Makes sense.
So where's the dividing line?
When we say, okay, topicals aren't enough, we absolutely need to go systemic.
Generally, if the infection is just on the surface skin, tinea corporis, pedis, caress, topical creams or solutions like azoles or aliamines usually work quite well.
But if the fungus has gotten into the hair follicles, like in tinea capitis, or deep into the nail plate in ongomycosis, systemic therapy is pretty much mandatory.
Topicals just can't penetrate deep enough into those structures to clear the infection.
Okay, systemic it is for hair and nails.
Let's talk agents.
Turbinifine is a big one, an elamine.
It messes with fungal cell membranes by inhibiting squally epoxidase.
Right, leads to fungal cell death.
And the dose for toenails is significant.
250 milligrams daily for 12 weeks.
That's a long time.
What are the major warnings, the things you absolutely have to discuss beforehand?
The chapter highlights two big ones.
First, liver function.
You need to check LFT's liver enzymes before starting and probably periodically during therapy because of potential hepatotoxicity.
Okay, monitor the liver.
But the one that requires immediate discontinuation, no questions asked, is the potential for permanent changes in taste or smell.
If a patient reports any change, food tasting weird, can't smell things properly, stop the drug immediately.
That's a non -negotiable.
Wow, permanent.
That's serious.
It is.
Definitely needs careful counseling.
All right, moving to the systemic azoles
Itraconazole.
Fluconazole.
Now we're talking CYP450 inhibition.
Yep.
Different mechanism.
They block ergosterol synthesis in the fungus by inhibiting fungal CYP450 enzymes.
But that interaction with CYP systems is also the source of their main problems.
Drug interactions and safety.
Exactly.
Systemic azoles can prolong the QTC interval on an EKG.
So they are absolutely contraindicated with other drugs that also prolong QTC and are metabolized by CYP3A4, think erythromycin, some antipsychotics, others.
You have to do a thorough medication reconciliation.
Critical check.
And Itraconazole specifically has a weird absorption issue, doesn't it?
Oh, it's notoriously finicky.
The capsules need food and acid in the stomach to be absorbed properly, but the liquid suspension needs an empty stomach.
Opposite requirements.
Completely opposite.
And crucially, the capsule and suspension forms are not interchangeable dose for dose because of differences.
It's complex.
Definitely tricky.
And quickly, grizofulvin,
an older drug.
Yeah, it works by depositing in new keratin cells, making them resistant, still used sometimes, especially for tinea, capitis in kids.
But the huge flag is pregnancy category X, absolutely contraindicated in pregnancy.
Got it.
Category X.
Okay.
Final section.
Viral cellular infections,
mostly herpes viruses and HPV, the cause of warts.
The key concept here is different.
It's latency, right?
Precisely.
Herpes viruses, HSV1, HSV2, VZV, which causes chicken pox and shingles, they're DNA viruses.
They set up shop permanently in the sensory nerve ganglia.
Meaning you never truly clear them.
Never fully eradicated.
Treatment goals are about reducing symptoms, shortening duration, stopping viral shedding, managing pain, but not cure.
They can always reactivate.
The chapter uses the case of BH,
the 72 year old man with that painful rash just on one side of his trunk.
Classic shingles presentation.
VZV reactivation.
Textbook herpes zoster.
Unilateral fall is a dermatome that nerve distribution and it's typically those painful vesicles, often preceded by nerve pain, the neuralgia.
And for older patients like BH, what's the big complication we're trying to head off?
The main concern is pusturpedic neuralgia, or PHN.
That's persistent nerve pain that lasts for weeks, months, even years, defined usually as pain lasting more than six weeks after the rash itself heals.
It can be debilitating.
So treatment involves systemic antivirals.
Cyclover, Femciclover, Valliciclover.
Any preferences there?
And what's the absolute rule for start of them?
Femciclover and Valliciclover generally have better oral bioavailability than a cyclover, meaning more convenient dosing.
Salicyclover, one gram, three times a day for seven days is a common shingles regimen.
But the absolute critical factor is timing.
Treatment is most effective significantly so if you start it within 72 hours of the rash appearing.
Or maybe if new lesions are still actively forming.
Three days.
That's a tight window.
Very tight.
Miss that window.
And the benefit in terms of preventing PHN drops off dramatically.
Early diagnosis and treatment are key.
Okay.
And finally, warts.
Ferrucce, caused by human papillomavirus, HPV.
Usually self -limiting, people want them gone for cosmetic reasons or if they're painful.
What's the first line?
Do it yourself treatment.
For common warts, not on the face or genitals, the go -to is over -the -counter salicylic acid.
It's a keratolytic and it dissolves keratin.
Various ways.
There's the liquid collodion, usually 17%, or plasters that are often stronger, maybe 40%.
You apply it regularly, it slowly breaks down the warty tissue.
Simple enough.
But who absolutely should not use salicylic acid, especially on feet or hands?
Big contraindication for patients with diabetes or anyone with poor peripheral circulation.
Why is that?
Because the acid irritates and breaks down skin.
In someone with poor circulation or sensation, like in diabetic neuropathy, that irritation could lead to a non -healing ulcer or infection.
The risk is just too high.
Okay.
That makes perfect sense.
Wow.
We've covered a lot of ground bacteria, fungi, viruses.
If we boil it down to core takeaways for bacterial stuff, it's that split between needing IND first for pus versus antibiotics for cellulitis and always having MRSA in the back of your mind.
Exactly.
And for fungi, remember, location dictates systemic versus topical hair and nails means systemic therapy.
But systemic means you accept those risks, monitoring LFTs for turbinifine, washing QTC and interactions with azoles.
And viruses, especially shingles, that 72 -hour clock is ticking for antiviral effectiveness to prevent that nasty, posterpetic neuralgia.
Couldn't summarize it better.
And from the pharmacist's view, patient education is huge here, making sure people finish antibiotic courses, no allergy signs, manage hygiene.
And for us, remembering dose adjustments for kidney function with many of these agents, penicillin, cephalosporins, antivirals.
Right.
So let's leave everyone with maybe one final thought.
Yeah.
We have these amazing tools now, like Oreadavancin or Dalbovancin single IV dose treatments.
Incredible convenience.
But does that incredible convenience often at high cost and usually needing specialist oversight always represent the best path?
Or does leaning on these powerful, convenient options risk accelerating resistance against our last lines of defense?
It's that constant tension in modern medicine balancing effectiveness, cost, compliance, and the huge global challenge of resistance.
A very relevant point to ponder.
Thank you for joining us for this deep dive, tackling these complex decisions together.