Study design and efficacy results for tinea pedis clinical trials
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Study Design and Efficacy Results for Tinea Pedis Clinical Trials. Kathleen Fritsch, Ph.D. Division of Biometrics III, FDA. Part I: Clinical Trial Design for Tinea Pedis Trials. Trial Characteristics. Trial Design Randomized, double-blind, vehicle controlled, multicenter Indications

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Study Design and Efficacy Results for Tinea Pedis Clinical Trials

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Study design and efficacy results for tinea pedis clinical trials

Study Design and Efficacy Results for Tinea Pedis Clinical Trials

Kathleen Fritsch, Ph.D.

Division of Biometrics III, FDA


Part i clinical trial design for tinea pedis trials

Part I: Clinical Trial Design for Tinea Pedis Trials


Trial characteristics

Trial Characteristics

  • Trial Design

    • Randomized, double-blind, vehicle controlled, multicenter

  • Indications

    • tinea pedis (athlete’s foot)

      • evaluate “all-comers” or multiple sub-types

    • interdigital tinea pedis (athlete’s foot between the toes)

      • evaluate interdigital variant only


Patient populations

Patient Populations

  • Randomized & treated population

    • positive KOH

    • clinical signs and symptoms

  • Efficacy analysis population (MITT)

    • must also have positive baseline culture

      (cultures take up to 4 weeks—treatment may be completed before baseline culture results are known)

    • only ~2/3 of randomized patients have positive baseline culture


3 nested efficacy endpoints involving mycological clinical outcomes

3 Nested Efficacy EndpointsInvolving Mycological & Clinical Outcomes


Efficacy endpoints

Efficacy Endpoints

  • Negative Mycology

    • negative KOH & culture

  • Effective Treatment (Sometimes Primary)

    • negative KOH & culture + mild or no signs & symptoms (typically at most mild erythema and scaling, but definition varies)

  • Complete Cure (Often Primary)

    • negative KOH & culture + no signs & symptoms

      Signs and symptoms: at a minimum--erythema, pruritus, scaling (may include others)


Study phases

Study Phases

  • Treatment period

    • Typical treatment duration is 1-4 weeks

  • Post-treatment follow-up

    Primary timepoint for efficacy evaluation at least 2 weeks after completing treatment

    • 5 to 8 weeks post-treatment for 1 week Tx

    • 2 to 4 weeks post-treatment for 4 week Tx

    • In both cases, primary timepoint is 6 to 9 weeks after starting treatment


Why is efficacy assessed during post treatment follow up

Why is efficacy assessed during post-treatment follow-up?

  • epidermal turnover may take several weeks

  • may not expect clearance of some signs until at least 6 weeks after start of treatment, even if fungus is eradicated

    →May be significant time lag (weeks or months) between end of treatment and assessment of cure


Part ii data presentation

Part II: Data Presentation

Efficacy results from selected clinical trials


Selected drug products

Selected Drug Products

Criteria for dataset selection:

  • NDA reviews available (oldest from 1988)

  • vehicle controlled trials

    The 9 products/formulations/regimens identified represent:

  • 6 active ingredients

  • 4 Rx and 5 OTC products/regimens

  • 4 one-week and 5 four-week regimens

  • 7 “interdigital tinea pedis” and 2 “tinea pedis”


Sample sizes

Sample Sizes

*Data from 2 studies


Caution

CAUTION!

  • Data do NOT represent head-to-head comparisons of products!

  • Success rates are influenced by

    • Patient populations (e.g. concomitant disease, baseline severity)

    • Clinical study procedures (e.g. sample collection, timing)

    • Endpoint definitions (e.g. assessment scales, evaluations)

      which can vary substantially from trial to trial


Efficacy outcomes 9 drug products

Efficacy Outcomes (9 Drug Products)

Negative Mycology

Effective Treatment

Complete Cure


Negative mycology end of treatment

Negative Mycology(End of Treatment)


Negative mycology primary timepoint week 6 9

Negative Mycology(Primary Timepoint – Week 6-9)


Effective treatment end of treatment

Effective Treatment(End of Treatment)


Effective treatment primary timepoint week 6 9

Effective Treatment(Primary Timepoint – Week 6-9)


Complete cure end of treatment

Complete Cure(End of Treatment)


Complete cure primary timepoint week 6 9

Complete Cure(Primary Timepoint – Week 6-9)


Clearance of signs and symptoms over time 2 drug products

Clearance of Signs and Symptoms over Time (2 Drug Products)

Erythema

Scaling

Pruritus


Erythema percent of subjects clear

Erythema(Percent of Subjects Clear)


Scaling percent of subjects clear

Scaling(Percent of Subjects Clear)


Pruritus percent of subjects clear

Pruritus(Percent of Subjects Clear)


Summary of efficacy results

Summary of Efficacy Results

  • May be a time lag of several weeks between end of treatment and clearance of signs and symptoms (particularly for 1-week products)

  • Most subjects have some signs and symptoms remaining post-treatment

  • Typical cure rates at primary post-treatment timepoint (Week 6-9) are

    Complete cure: 20%

    Effective Treatment: 50%

    Negative Mycology: 70%


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