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Overview of Use of PK-PD in Streamlining Drug Development

Overview of Use of PK-PD in Streamlining Drug Development. William A. Craig Professor of Medicine University of Wisconsin. Why Interest in Pharmacodynamics?. Always occurs when there is narrow difference between MICs and obtainable drug concentrations

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Overview of Use of PK-PD in Streamlining Drug Development

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  1. Overview of Use of PK-PD in Streamlining Drug Development William A. Craig Professor of Medicine University of Wisconsin

  2. Why Interest in Pharmacodynamics? • Always occurs when there is narrow difference between MICs and obtainable drug concentrations - early days of penicillin in 1940s (low doses used) - appearance of Pseudomonas infections in 1960s and 1970s (high MICs) - appearance of resistant Streptococcus pneumoniae and other bacteria in 1990s

  3. Applications of PK-PD • Optimize dosage regimens - once-daily dosing of aminoglycosides - prolonged or continuous infusion of beta-lactams • Establish susceptibility breakpoints - new NCCLS breakpoints with oral beta-lactams and with ceftriaxone/cefotaxime for pneumococci • Preventing the emergence of resistance - with fluoroquinolones and gram-negative bacilli

  4. PK/PD Parameters versus Emergence of Resistance for Fluoroquinolones Resistance Developed 24-Hr AUC/MICP. aeruginosaOther GNB <100 - Monotherapy 80% 100% >100 – Monotherapy 33% 10% Combinations 11% 0% 25% 12% Thomas et al. AAC 42:521, 1998

  5. Applications of PK-PD • Guideline development - CDC guidelines for pneumonia and otitis media - Sinus and Allergy Health Partnership guidelines for sinusitis • Formulary decisions - based on local or regional susceptibility data

  6. Application of PK-PD for New Drug Development • Dose Selection for Phase 2/3 Studies - in vitro and animal studies to identify PK-PD target for efficacy - phase 1 studies to determine which doses reach target with high probability - mostly with antibacterials; rarely with antifungals • Susceptibility Breakpoint Selection - required by NCCLS by M23 (1 of 4 parameters used for breakpoint selection) - FDA – variable use

  7. Application of PK-PD for New Drug Development • PK-PD studies in phase 2/3 clinical trials - optimal sampling techniques - interest in including “time to events” - statistical strategies to model both clinical and microbiological outcomes - bacteriologic cure usually harder to obtain than clinical cure

  8. Relationship Between 24-Hr AUC/MIC and Efficacy of Ciprofloxacin in 64 Patients with Serious Bacterial Infections Forrest et al. AAC 37:1073, 1993

  9. PK-PD Studies in Phase 2/3 Clinical Trials • Increases complexity of study • Increases cost • No established benefit with regulatory agencies Can such studies reduce the number of patients needed for efficacy trials ? - used for a fluoroquinolone to reduce number of cases for inclusion of penicillin-resistant pneumococci in label

  10. Dose Selection • What is the PK-PD indice that best determines efficacy? Requires in vitro or animal models • What is the magnitude of the PK-PD indice required for efficacy? Should be based on free drug levels and linked to survival in animal models • How do neutrophils effect the magnitude of the PK-PD indice? • Does the magnitude vary with different organisms especially resistant strains? • Does the magnitude vary with different sites of infection

  11. Correlation of Serum Concentrations with Sites of Infection Good Interstitial fluid Fluid Collections (sinusitis, AOM) Abscess ELF ( macrolides; vanco, dapto) CSF Intracellular fluid Urine Serum Poor

  12. Dose Selection • What is the magnitude of the PK-PD indice required to prevent the emergence of resistance? • Can nontoxic doses of the drug in humans reach the magnitude of the PK-PD indice required for efficacy and for prevention of resistance with a high probability? Should be based on free drug concentrations

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