PK/PD of Antibiotics in relation to resistance Otto Cars MD Department of Medical Sciences Infectious diseases Uppsala University Sweden

Question: Can the PK/PD and dosage of antibiotics influence the emergence of antibiotic resistance ?

What is resistance? Genotype The bacteria carry certain resistance elements Phenotype The bacteria has an increased MIC in comparison with the wild type Clinical The bacteria are able to multiply in humans in the presence of drug concentrations achievable during therapy

Ecological compartments Oropharyngeal Skin Peri-urethral Faecal Intracellular

Infecting bacterial population Antibiotic exposure Clinical failure and/or bacterial persistance Infecting bacterial population Selection of resistant bacterial subpopulations R Normal microflora Gradual change in susceptibility

Bactericidal activity of two enoxacin regimens against K.pneumoniae Blaser et.al. AAC 1987

Killing of P.aeruginosa at three different dosage regimens of ciprofloxacin Marchbanks et. Al. AAC 1993

Lomefloxacin Therapy for Pseudomonas Sepsis in Neutropenic Rats: Effect of Dose Fractionation (N=50/Group) Drusano GL, et al. Antimicrob Agents Chemother. 1993;37:483-490.

Major risk factors for emergence of antibiotic resistance during therapy Mutation frequency / size of inoculum Biological fitness cost and cost compensation Selective antibiotic concentrations

Major risk factors for emergence of antibiotic resistance during therapy Mutation frequency / size of inoculum Biological fitness cost and cost compensation Selective antibiotic concentrations

Mutant Preventive Concentration (MPC) Mutant Selective Window (MSW)

MIC MPC MIC and MPC in theory Antibiotic concentration that prevents the growth of susceptible bacteria A measure of the Majority of the Population MPC Antibiotic concentration that prevents the growth of single-step resistant mutant A measure of the Most Resistant Part of the Population

Dong, Zhao, Domagala, Drlica MIC and MPC in practice MIC (Etest) Cells 0.5 McFarland 16-18 hrs, 37ºC MIC MPC Dong, Zhao, Domagala, Drlica AAC, 43: 1756-1758, 1999 0.1 µg/ml 0.3 µg/ml 0.5 µg/ml Cells 1010 48 hrs, 37ºC

22 Sensitive Clinical UTI E.coli isolates Marcusson et al , JAC, accepted for publication MIC MPC MIC Mutants Clinical UTI Strains

MPC The concept has similarities to agar dilution MICs. Both are measured at static concentrations The last decade has clearly shown that the MIC alone is not predictive for outcome. MIC has to be related to dosing regimens, pk and PK/PD indices It is not logical to use the MPC as a primary parameter

The concept of Mutant Selective Window Time post-administration MIC MPC Serum or tissue drug concentration Mutant Selection Window Cmax

PD and resistance: Endpoints Regrowth of the population- increase in MICs Change in the number of resistant bacteria during the experiment e.g. time zero vs time X (culture on antibiotic containing plates) AUC of the population analysis profile (serial plating on antibiotic plates during the experiments) Specific measuring of the susceptible and resistant population (competition assay using selective markers)

T> MPC TMSW AUCMSW Cmax /MIC Cmax/MPC AUC/MIC AUC/MPC Pharmacodyamic indices used in resistance studies T> MPC TMSW AUCMSW Cmax /MIC Cmax/MPC AUC/MIC AUC/MPC

Firsov et al

Firsov et al

Pharmacodynamics and MPC : Prevention of emergance of resistance in E.coli vs ciprofloxacin Resistance Prevention of resistance Olofsson et al, to be publ.

Pharmacodynamics of Penicillin G vs S.pneumoniae with different suceptibility for penicillin T>MIC PSP 46% PIP 6% PRP 0% Odenholt et al AAC 47,518,2003

T>MIC PSP 75% PIP 38% PRP 0% T>MIC PSP 100% PIP 100% PRP 48%

In vivo experimental pneumonia model in rabbits Five pneumococcal strains with variable susceptibility to fluoroquinolones Simulated human kinetics of gatifloxacin TMSW and AUCMSW significantly correlated with emergence of resistance mutants Croiser at al JAC 2004, 54:640

Retrospective, including 4 earlier studies 107 acutely ill patients, 128 pathogens, 5 antimicrobial regimens. PK and MICs for every individual patient Pharmacodynamic (PD) models probability of developing bacterial resistance. Thomas et al, AAC 1998 42:521

Overall, in 32 of 128 (25%) resistance developed during therapy. AUC[0-24]/MIC was as a significant predictor. This relationship was observed across all treatments and within all organism groupings, with the exception of beta-lactamase-producing gram- negative organisms Thomas et al, AAC 1998 42:521

Beta-lact. Prod. Thomas et al, AAC 1998 42:521

Pneumococci Bacteriologic Failures vs. MIC to Penicillin. Otitis Media (double tap studies) (N=78) 4/5 80 10 20 30 40 50 60 70 80 90 Cefuroxime axetil Cefaclor 3/7 43 2/6 Failure rate (%) 33 3/13 23 2/22 1/25 9 4 MIC <0.1 0.125 - 0.25 0.38 - 1.0 Chi-square for linear trend in proportion, P < 0.001

Ratiao of aminopenicillins:cephaalosporins Relationship between shift in the use of aminopenicillins–cephalosporins and emergence of penicillin resistance in S. pneumoniae 30 6 25 5 20 4 Ratiao of aminopenicillins:cephaalosporins % of resistant strains 15 3 10 2 5 1 84 85 86 87 88 89 90 91 92 93 Year Ratio of aminopenicillins:cephalosporins per 1000 inhabitants in France Penicillin resistance in S. pneumoniae Baquero. JAC 1996; 38(Suppl A):117–132

New macrolides may be ‘driving’ selection of macrolide resistance in S New macrolides may be ‘driving’ selection of macrolide resistance in S. pneumoniae 5 4.5 R=0.896 4 3.5 Short half-life macrolides Long half-life macrolides 3 Prescriptions / 1000 2.5 2 R=0.099 1.5 1 0.5 10 20 30 40 50 % macrolide resistance The Alexander Project 1992–1996 IMS data 1992–1996

Erythromycin-Resistant Streptococcus pneumoniae and Consumption of Erythromycin and Azithromycin, Denmark, 1994-2002 Source: DANMAP, 2003 in EPI-NEWS 2004,3. Available from: URL: ww.ssi.dk

Resistance to levofloxacin and failure of treatment of pneumococcal pneumonia First step mutations in parC occurs approx in one out of 107 pneumococci. Total load of pneumococci in an infected lung 1012-1014 Low D, CID 2004:38,suppl4, 357 Increased used of levofloxacin,specifically, as opposed to other fluoroquinolones was associated with increases in the MIC. A failure of levofloxacin to achieve a highprobability of PK-PD target attainment may be an important contributing factor Bhavani et al Diagn Micr and INf Dis 2005,51:31-37

Resistance to levofloxacin and failure of treatment of pneumococcal pneumonia Clinical failures in pneumonia caused by S.pneumoniae resistant to levofloxacin confirm that resistance is becoming clinically relevant for agents with marginal PD indices. Davidson et al NEJM 346:747, 2002 Urban et al J Inf Dis 184 : 794, 2001 To maximize the pharmacodynamic properties of levofloxacin, A dosing regimen of 750 mg once daily seems more appropriate, in adult patients than the current dosage of 500 mg. Ferrara , Infection 2005,33:106

resistance will vary due to the infectious site, Conclusions Certain dosage regimens are clearly associated with a risk for selective enrichment of a resistant subpopulation The selective pressure varies between bacterial species, antibiotics, and resistance mechanisms The pharmacdynamic indices to minimize resistance will vary due to the infectious site, bacterial species, antibiotics, and resistance mechanisms

Potential clinical implications Avoid monotherapy with drugs where Cmax does not reach the MPC or where the MSW is very long Adjust dosages regimens (dose, dose interval) to reduce the TMSW Include studies on prevention of resistance early in drug development Preferred properties: - Low mutation rate - High fitness cost of mutants - Narrow MSW