Lesson
Map the Dermatophyte Niche
Dermatophytes live in keratinized skin, hair, and nail. Diagnosis, anatomic depth, organism, growth rate, and host determine whether topical or systemic exposure is useful.
- Trichophyton
- Microsporum
- Epidermophyton
- Keratin growth
- Diagnostic specimen
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Locate the infection
Dermatophytes invade nonliving keratin in stratum corneum, hair shafts, and nails. Scalp follicles and nail matrix are not reliably treated by a topical product applied to the surface.
Confirm before prolonged therapy
Nail dystrophy can reflect trauma, psoriasis, eczema, yeast, or nondermatophyte mold. Microscopy, culture, histology, or validated molecular testing can protect patients from unnecessary systemic exposure.
Use growth as a clinical clock
Suppression of fungal activity can precede visible cure. Healthy nail or hair must replace damaged keratin, so distal abnormal tissue can remain after a successful drug course.
Separate site systems
Limited skin disease, tinea capitis, inflammatory kerion, fingernail disease, and toenail disease have different penetration, drug, duration, source-control, and recurrence needs.
Quick check
Lesson
Interrupt Squalene Processing
Terbinafine is a lipophilic allylamine that inhibits fungal squalene epoxidase, depletes ergosterol, and allows toxic squalene accumulation.
- Allylamine
- Squalene epoxidase
- Ergosterol
- Squalene
- Fungicidal activity
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Read the scaffold
The synthetic allylamine contains a tertiary amine and extended hydrophobic regions. Lipophilicity supports distribution into sebum and keratinized tissue but also requires formulation and hepatic exposure to remain visible.
Block the upstream enzyme
Squalene epoxidase converts squalene toward lanosterol and ergosterol. Terbinafine acts upstream of the azole CYP51 target, so the two classes must not be described as molecular equivalents.
Create two pressures
Ergosterol depletion disrupts membrane construction while intracellular squalene accumulation contributes to fungal injury. Susceptible dermatophytes are generally killed at clinically relevant tissue concentrations.
Keep selectivity honest
Preferential fungal enzyme inhibition explains therapeutic selectivity, not complete safety. Human hepatic metabolism, interactions, and idiosyncratic toxicity still determine whether oral exposure is appropriate.
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Lesson
Follow Exposure into Keratin
Oral terbinafine distributes into sebum, stratum corneum, hair, and nail, undergoes multi-enzyme hepatic metabolism, and inhibits CYP2D6.
- Keratin deposition
- Sebum
- Multiple CYP pathways
- CYP2D6 inhibition
- Persistent interaction
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Track tissue persistence
Terbinafine reaches lipid-rich and keratinized compartments and can remain after dosing ends. Persistence helps explain delayed clinical improvement, but it does not authorize a different course without evidence.
Avoid the single-enzyme myth
CYP2C9, CYP1A2, CYP3A4, CYP2C8, and CYP2C19 contribute to metabolism. Metabolites are eliminated largely in urine, so the disposition system is broader than one pathway.
Protect CYP2D6 substrates
Terbinafine can increase exposure to CYP2D6-dependent antidepressants, beta blockers, and class 1C antiarrhythmics and can affect activation of selected prodrugs. Clinical effects may persist after terbinafine stops.
Retire an unsupported shortcut
RxPrep describes weak or moderate CYP3A4 induction, but current official labeling does not support teaching a blanket CYP3A4 inducer rule. Verify the exact drug interaction rather than preserving a broad historical simplification.
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Lesson
Match Product to Site
Topical and oral terbinafine solve different exposure problems. Oral labeling uses a site-specific course for confirmed dermatophyte nail infection.
- Topical skin therapy
- Oral nail therapy
- 250 mg daily
- Six weeks
- Twelve weeks
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Separate local from systemic use
Topical terbinafine can treat appropriate limited superficial skin disease. Oral exposure is needed for selected nail and follicular disease but carries a much larger hepatic, sensory, interaction, and monitoring burden.
Protect the nail regimen
Current oral labeling uses 250 mg once daily for six weeks for fingernail onychomycosis and twelve weeks for toenail onychomycosis. Confirm dermatophyte infection before starting.
Set the right expectation
Clinical benefit may continue after the tablets end because new clear nail must grow forward. Track proximal healthy growth, symptoms, adherence, and recurrence rather than expecting immediate cosmetic normalization.
Audit failure before repeating
Recheck diagnosis, organism, specimen quality, adherence, interactions, absorption, tinea pedis reservoir, footwear, nail care, host factors, and reinfection before another systemic course.
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Lesson
Recognize Systemic Toxicity Early
Oral terbinafine can cause severe liver injury, sensory loss, neutropenia, severe skin or hypersensitivity reactions, depression, lupus exacerbation, and thrombotic microangiopathy.
- Liver injury
- Taste and smell
- ANC threshold
- Severe skin reaction
- Thrombotic microangiopathy
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Protect the liver
Chronic or active liver disease is a contraindication. Obtain pretreatment transaminases, monitor as clinically appropriate, and stop for jaundice, dark urine, pale stools, anorexia, nausea, fatigue, or right-upper-quadrant pain.
Take sensory loss seriously
Taste or smell disturbance can be severe, prolonged, or permanent and can cause reduced intake, weight loss, anxiety, or depression. Clinically significant loss warrants discontinuation and evaluation.
Respond to infection symptoms
Severe neutropenia is rare. Fever, sore throat, or oral ulcers should prompt assessment and CBC when indicated. Current labeling directs discontinuation when ANC is 1000 cells per cubic millimeter or less.
Escalate systemic findings
Progressive rash, mucosal injury, hypersensitivity, lupus symptoms, mood change, purpura, anemia, thrombocytopenia, kidney injury, or neurologic findings can signal a serious reaction and require prompt withdrawal and evaluation.
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Lesson
Translate Interactions into Monitoring
Terbinafine is both a victim of selected metabolic interactions and a perpetrator through CYP2D6 inhibition. Each alert needs an exposure direction and clinical endpoint.
- CYP2D6 substrates
- Rifampin
- Cimetidine
- Fluconazole
- Patient counseling
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Review sensitive substrates
CYP2D6-dependent antidepressants, beta blockers, class 1C antiarrhythmics, and selected prodrugs require a purpose-built plan. Monitor the therapeutic endpoint and toxicity rather than merely recording an alert.
Read opposite perpetrators
Rifampin increases terbinafine clearance and can lower exposure. Cimetidine decreases clearance and can raise exposure. Direction matters when deciding whether to monitor, adjust, or avoid.
Use combination antifungals deliberately
Fluconazole can increase terbinafine exposure through inhibition of contributing pathways. Combining antifungals requires a clinical purpose plus liver, sensory, and interaction surveillance.
Make the patient part of monitoring
Teach stop and contact thresholds for liver symptoms, sensory loss, rash or mucosal injury, fever, mood change, and purpura. Confirm who will review new medications and follow laboratory or symptom results.
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Lesson
Protect New Keratin
Griseofulvin is a fungistatic dermatophyte agent that disrupts mitosis, deposits in keratin precursor cells, and binds newly formed keratin.
- Microtubules
- Mitotic spindle
- Keratin precursor
- Fungistatic activity
- Tinea capitis
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Interrupt fungal division
Griseofulvin has a colchicine-like effect on fungal mitosis and spindle function. It does not inhibit CYP51 or glucan synthase and should not be grouped with azoles or echinocandins by target.
Bind the replacement tissue
After oral absorption, griseofulvin deposits in keratin precursor cells and binds new keratin. The protected tissue becomes resistant to fungal invasion as infected keratin is shed or grows out.
Respect the spectrum
Activity is directed toward susceptible Microsporum, Epidermophyton, and Trichophyton. It does not treat bacteria or every fungal genus, so organism and syndrome remain decisive.
Treat the follicle systemically
Tinea capitis requires a systemic agent because surface products do not adequately reach infected hair follicles. Adjunctive shampoo can reduce shedding but does not provide cure alone.
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Lesson
Verify the Formulation Before the Dose
Microsize and ultramicrosize griseofulvin have different absorption efficiency and milligram requirements. Food, weight, concentration, and site complete the calculation.
- Microsize
- Ultramicrosize
- Fatty meal
- mg per kg
- Site duration
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Do not substitute equal milligrams
Ultramicrosize absorption is about one and one-half times conventional microsize absorption. Current labeling describes roughly two-thirds as much ultramicrosize oral drug, but clinical decisions must use the exact product label.
Use food intentionally
Microsize griseofulvin is poorly water soluble, and absorption improves with a fatty meal. Balance this administration principle with nutrition, nausea, malabsorption, and adherence.
Calculate in kilograms
For a 44 lb child, divide by 2.2 to obtain 20 kg. Multiply kilograms by the current formulation-specific mg/kg/day range, then verify product concentration, practical volume, frequency, and maximum.
Let the site set the timeline
Skin and scalp courses are shorter than nail replacement courses, and toenails can require the longest exposure. Continue through organism control and healthy keratin replacement under current guidance.
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Lesson
Build a Longitudinal Safety Plan
Griseofulvin combines reproductive, hepatic, hematologic, photosensitivity, alcohol, enzyme-induction, and hypersensitivity concerns across often prolonged treatment.
- Pregnancy contraindication
- Porphyria
- Warfarin
- Hormonal contraception
- Photosensitivity
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Exclude major contraindications
Current labeling contraindicates griseofulvin in pregnancy, porphyria, and hepatocellular failure. Use current pregnancy and lactation narrative information instead of obsolete letter categories.
Plan enzyme-induction consequences
Griseofulvin can reduce warfarin-type anticoagulant activity and estrogen contraceptive effectiveness. Arrange INR monitoring and additional nonhormonal contraception during the relevant exposure window.
Prevent exposure-related harm
Counsel patients to avoid intense natural or artificial UV exposure and to avoid alcohol, which can produce flushing and tachycardia. Discuss dizziness or impaired performance when relevant.
Monitor long courses
Use periodic hepatic, renal, and hematopoietic assessment according to duration and risk. Stop and evaluate severe skin or hepatic events, granulocytopenia, progressive hypersensitivity, or lupus-like findings.
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Lesson
Close the Dermatophyte Loop
A safe plan connects diagnosis, organism, site, product, formulation, dose, duration, interactions, toxicity, keratin growth, recurrence prevention, and follow-up ownership.
- Diagnosis
- Agent selection
- Monitoring
- Reinfection control
- Ownership
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Keep organism, site, product, exposure, toxicity, outgrowth, and ownership connected.
Choose by biology
Terbinafine is central to many confirmed dermatophyte nail infections. Griseofulvin remains useful in selected hair and skin syndromes, particularly when organism, age, formulation, and evidence support it.
Protect reproductive decisions
Document pregnancy, lactation, conception plans, contraceptive method, and alternatives. Griseofulvin has an explicit pregnancy contraindication and can reduce hormonal contraceptive effectiveness.
Control reservoirs
Treat concurrent tinea pedis when appropriate, keep feet dry, rotate or disinfect footwear, avoid shared grooming tools, assess household or pet sources, and address reinfection before repeating systemic exposure.
Assign the next action
Record the product, dose, course, symptom stops, laboratory plan, response checkpoint, pending specimen, recurrence strategy, and clinician responsible for each result. Educational examples never replace individualized prescribing.
Quick check
Module test
Check the connections.
Each attempt draws 10 questions from the complete 176 question bank.
Each attempt draws a fresh set and rearranges the answer choices.
References
Current clinical foundation.
Lecture material was synthesized with the following contemporary guidance. Verify local policy and current guidance before applying clinical information.