Dread and Risk Elimination Premium for the Value of a Statistical Life.

The value of a statistical life (VSL) is a widely used measure for the value of mortality risk reduction. As VSL should reflect preferences and attitudes to risk, there are reasons to believe that it varies depending on the type of risk involved. It has been argued that cancer should be considered a "dread disease," which supports the use of a "cancer premium." The objective of this study is to investigate the existence of a cancer premium (for pancreatic cancer and multiple myeloma) in relation to road traffic accidents, sudden cardiac arrest, and amyotrophic lateral sclerosis (ALS). Data were collected from 500 individuals in the Swedish general population of 50-74-year olds using a web-based questionnaire. Preferences were elicited using the contingent valuation method, and a split-sample design was applied to test scale sensitivity. VSL differs significantly between contexts, being highest for ALS and lowest for road traffic accidents. A premium (92-113%) for cancer was found in relation to road traffic accidents. The premium was higher for cancer with a shorter time from diagnosis to death. A premium was also found for sudden cardiac arrest (73%) and ALS (118%) in relation to road traffic accidents. Eliminating risk was associated with a premium of around 20%. This study provides additional evidence that there exist a dread premium and risk elimination premium. These factors should be considered when searching for an appropriate value for economic evaluation and health technology assessment.

Burden and costs of migraine in a Swedish defined patient population - a questionnaire-based study.

BACKGROUND: Migraine is a disabling, chronic neurological disease leading to severe headache episodes affecting 13.2% of the Swedish population. Migraine leads to an extensive socio-economic burden in terms of healthcare costs, reduced workforce and quality of life (QoL) but studies of the health-economic consequences in a Swedish context are lacking. The objective of this study is to map the health-economic consequences of migraine in a defined patient population in terms of healthcare consumption, production loss and QoL in Sweden. METHODS: The study is based on data from a web-based survey to members in the Swedish patients' association suffering from migraine. The survey was conducted in May 2018 and included people with migraine aged 18 years or older. The survey included questions on health resource consumption, lost production resulting from migraine-related absenteeism and presenteeism, and QoL as measured by the EuroQol 5 dimensions questionnaire (EQ-5D-5 L) and the Headache Impact Test (HIT-6). The results are presented in yearly costs per patient and losses in quality adjusted life years (QALYs). RESULTS: The results are based on answers from 630 individuals with migraine and are presented by number of migraine days per month. The total cost per patient and year increased with the number of migraine days per month (p < 0.001) and varied between approximately €5000 for those with less than 3 migraine days per month and €24,000 per year for those with 21-28 migraine days per month. Production loss represented the main part of the costs, approximately 80%. The average loss in QALYs per year also increased with the monthly number of migraine days (p = 0.023). CONCLUSIONS: Migraine leads to significant societal costs and loss of quality of life. There appears to be an unmet need and a potential for both cost savings and QoL benefits connected with a reduction in the number of migraine days.

Treatment Preferences for Acute Allergic Reactions: A Discrete Choice Experiment.

Background: Timely treatment of acute allergic reactions (AARs) is important to minimize reaction severity. Corticosteroid tablets dissolved in water are commonly used in mainstay treatment. A new oral film that dissolves on the tongue provides a faster and less cumbersome alternative to tablets for corticosteroid administration during AARs. This study evaluated patients' preferences for attributes related to administration mode of corticosteroids in AARs. Methods: A web-based survey was sent to a sample from the adult Swedish population (≥18 years) with experience of corticosteroid treatment for AAR. We assessed the willingness to pay (WTP) for attributes related to corticosteroid treatment by applying a discrete choice experiment (DCE) approach. DCE attributes were administration mode, time to symptom relief, and price. The WTP for each attribute was derived using the attribute's coefficient in a logistic regression analysis. We specified a forced choice (FC) and an unforced choice (UC) model. In the FC model, the respondents chose between 2 hypothetical treatments and in the UC model, between any of 2 hypothetical treatments and their current treatment. Results: The final study population included 348 subjects, of which 80% were women. All the evaluated DCE attributes were significant predictors for the treatment choice (p<.001). In the FC model, the incremental WTP for an oral film compared with tablets was 409 Swedish kronor (SEK [≈€36.7]), with no other factors considered. In the UC model, the incremental WTP for the oral film compared with tablets was 574 SEK (≈€51.7). After considering the value of the respondents' current treatment, the WTP for the oral film decreased to 336 SEK (≈€30.3). The total WTP was reduced by 17 SEK (≈€1.5) per minute of shorter time to symptom relief. Subgroup analyses showed that people with circulatory symptoms and experience of swallowing difficulties related to allergy medication had higher WTP for the oral film than the average respondent. Conclusion: The findings show a substantial economic benefit of the oral film vs tablets for patients with AARs in Sweden. This result remained also after compensation for the full value of the patients' current treatment.

Disease burden and unmet need for acute allergic reactions - A patient perspective.

Background: Acute allergic reactions (AARs) occur shortly after exposure to an allergen, and the severity is on a continuum. Systemic corticosteroids (CS) are mainstay treatment of moderate to severe AARs, whereas those at risk of the most severe AARs (ie, anaphylaxis) are also recommended prescription of epinephrine autoinjectors. There is limited research on the impact of AARs not fulfilling the criteria for anaphylaxis. We have characterized a sample with a history of moderate to severe AARs and evaluated their self-reported disease burden (ie, daily life impact, anxiety, and treatment impediments). Methods: Survey study of adults with experience of AARs treated with CS. Participants recruited from a web-based panel and using social media were asked to complete a questionnaire related to their allergy and experience of AARs. The results were summarized for the whole sample and across subgroups with and without prescription of epinephrine. Results: The final study sample included 387 participants (80% women, mean age 41), of which 129 (33%) had at some point been prescribed epinephrine. The most common symptoms were respiratory (80%) and skin (78%) manifestations, and the mean (standard deviation, SD) self-rated severity score (scale from 0 [very mild] to 10 [very severe]) of the most recent AAR was 6.1 (2.0). More than 80% had experience of AARs interrupting daily activities and 50% of AARs that had limited work/studies or participation in leisure activities. Most of the respondents reported some degree of anxiety related to AARs and 43% had feared for their lives. Moreover, difficulties swallowing allergy medicine at an AAR was experienced by 26% and not having the medicine available when needed by 66%. Participants with prescription of epinephrine experienced more severe AARs than those without such prescription (mean [SD] severity 6.8 [2.1] vs 5.8 [1.8], p < 0.0001); however, also those without epinephrine prescription reported considerable anxiety and impact on daily life and to a similar degree as those with prescription. Conclusions: In this sample, subjects with experience of AARs treated with CS showed a considerable disease burden with anxiety and interruption on daily life, as well as problems related to access to, and swallowing of, medication. Although respondents with epinephrine prescription had more severe disease, a high disease burden was also evident among those without epinephrine. The study increases the knowledge of people with moderate to severe AARs, a patient population that has previously been underrepresented in the research literature.

Acceptance and application of a broad population health perspective when evaluating vaccine.

The traditional health economic analysis is limited to estimating the impact on the treated patient. As vaccines are usually aimed at preventing infectious diseases, they may be associated with additional values for the non-treated wider population. Although there are valid reasons for treating vaccines differently, and a wide support for a broader perspective in the literature (i.e., beyond the net costs and health gain related to the outcome for the vaccinated individual), it remains unclear to what extent the Health Technology Assessment (HTA) agencies accept and apply a broader perspective. The purpose of this study is to examine and discuss what type of consequences are relevant for a health economic analysis of vaccines and which consequences are considered by HTA agencies. The study includes a strategic review of literature and HTA decisions in Sweden and other countries, online round-table discussions with stakeholders in Sweden, and a basic estimation of the value of a COVID-19 vaccination in Sweden. The study shows that, other than herd effect, broader economic consequences for the population are generally not included in the economic evaluation of vaccines. Also, all economic consequences for the treated patient (production loss) and caregiver (health loss) are not always considered. The perspective chosen can have a major impact on the outcome of the analysis. A vaccine for COVID-19 is estimated to provide a value of €744-€956 per dose when using a societal perspective including broader consequences for the population. Providing a complete and appropriate picture of the value of vaccination is of importance to allocate resources efficiently, to provide incentives for vaccine development, and to show the cost of delaying decisions to implement a new vaccine.

The impact on quality of life of diet restrictions and disease symptoms associated with phenylketonuria: a time trade-off and discrete choice experiment study.

Phenylketonuria (PKU) is a metabolic disorder leading to a deficiency in the metabolism of phenylalanine (Phe). Elevated Phe levels in the blood, tissue and brain may lead to emotional, cognitive, and physical symptoms in adults. To control blood Phe levels, most individuals with PKU need to follow a strict, life-long Phe-restricted diet. The main objective of this study was to estimate the impact of PKU-related disease symptoms and dietary restrictions on health-related quality of life (HRQoL). This study was designed as a web-based survey using the methods of Time Trade-Off (TTO) and Discrete Choice Experiment with duration (DCETTO) in a survey of the Swedish general population and population with PKU. Data were collected using questionnaires for TTO diet (n = 509), TTO symptoms (n = 507), and DCETTO (n = 1117). The disutility of diet restrictions ranged from 0.050 for a partially restricted diet without medical food to 0.193 for a fully restricted diet with medical food in the TTO (DCE: 0.043-0.108). The disutility of experiencing symptoms (emotional, cognitive and physical) ranged from 0.148 for mild symptoms to 0.593 for severe symptoms in the TTO (DCE: 0.122-1.522). The study shows that both diet and symptoms have a significant negative impact on HRQoL in PKU and that utility estimates are largely consistent across methods and samples.

Optimizing drug exposure to minimize selection of antibiotic resistance.

The worldwide increase in antibiotic resistance is a concern for public health. The fact that the choice of dose and treatment duration can affect the selection of antibiotic-resistant mutants is becoming more evident, and an increased number of studies have used pharmacodynamic models to describe the drug exposure and pharmacodynamic breakpoints needed to minimize and predict the development of resistance. However, there remains a lack of sufficient data, and future work is needed to fully characterize these target drug concentrations. More knowledge is also needed of drug pharmacodynamics versus bacteria with different resistance mutations and susceptibility levels. The dosing regimens should exhibit high efficacy not only against susceptible wild-type bacteria but, preferably, also against mutated bacteria that may exist in low numbers in "susceptible" populations. Thus, to prolong the life span of existing and new antibiotics, it is important that dosing regimens be carefully selected on the basis of pharmacokinetic and pharmacodynamic properties that prevent emergence of preexisting and newly formed mutants.

Glioblastoma Cell Malignancy and Drug Sensitivity Are Affected by the Cell of Origin.

The identity of the glioblastoma (GBM) cell of origin and its contributions to disease progression and treatment response remain largely unknown. We have analyzed how the phenotypic state of the initially transformed cell affects mouse GBM development and essential GBM cell (GC) properties. We find that GBM induced in neural stem-cell-like glial fibrillary acidic protein (GFAP)-expressing cells in the subventricular zone of adult mice shows accelerated tumor development and produces more malignant GCs (mGC1GFAP) that are less resistant to cancer drugs, compared with those originating from more differentiated nestin- (mGC2NES) or 2,'3'-cyclic nucleotide 3'-phosphodiesterase (mGC3CNP)-expressing cells. Transcriptome analysis of mouse GCs identified a 196 mouse cell origin (MCO) gene signature that was used to partition 61 patient-derived GC lines. Human GC lines that clustered with the mGC1GFAP cells were also significantly more self-renewing, tumorigenic, and sensitive to cancer drugs compared with those that clustered with mouse GCs of more differentiated origin.

Preferences for improvements in attributes associated with basal insulin: a time trade-off and willingness-to-pay survey of a diabetic and non-diabetic population in Sweden.

OBJECTIVE: Apart from improved health outcomes, treatment convenience per se may have a value to individuals. This is sometimes referred to as process utility and can be estimated in terms of willingness-to-pay (WTP) or quality-adjusted life-years (QALYs). Previous research has produced multiple studies on QALY gains and WTP estimates of insulin-related attributes. There are, however, significant variations between studies, and it is not clear to what extent the value is a reflection of the true preferences or a consequence of the methodological approach. The aim of this study is to estimate the preferences for treatment attributes associated with basal insulin (administration frequency, administration flexibility, and treatment-induced weight gain) using both QALYs-elicited using time trade-off (TTO) and WTP-among a sample of the Swedish general population and among a sample of the Swedish diabetes population. METHODS: Data was collected using web-based surveys which were distributed to members of internet panels. The WTP survey presented five hypothetical scenarios with an offer to pay the incremental cost to receive basal insulin with improved attributes. The TTO survey presented six hypothetical scenarios where the respondent could choose between living for the rest of his/her life with diabetes and receiving treatment with a basal insulin with certain attributes or live for a shorter time with full health. The scenarios were combined with either a basal or a basal-bolus treatment regimen. Results from the TTO analysis were translated into monetary estimates using a threshold value of SEK500,000 per QALY. RESULTS: In total, 2012 responses were included. The ratings of the attributes were almost identical, irrespective of method for the general population, while it differed to some extent for the diabetes population. The methods produced the same value for flexibility, but the estimates generated with the TTO approach were higher for one less injection and avoided weight gain. The general population assigned a higher utility gain to convenience attributes, while the diabetes population assigned a higher utility gain to avoiding weight gain. LIMITATIONS: About a quarter of the respondents did not accept the scenario in the WTP survey, i.e. protesters. CONCLUSIONS: The ranking of the attributes was generally independent of evaluation method, but the TTO method resulted in similar or higher values compared to the WTP method.

Societal cost of subcutaneous and intravenous trastuzumab for HER2-positive breast cancer - An observational study prospectively recording resource utilization in a Swedish healthcare setting.

INTRODUCTION: Trastuzumab is part of the standard treatment for HER2-positive breast cancer. The aim of this study was to estimate the societal value of trastuzumab administered through subcutaneous (SC) injection compared to intravenous (IV) infusion. METHODS: Female patients with HER2-positive breast cancer receiving SC or IV trastuzumab were consecutively enrolled from five Swedish oncology clinics from 2013 to 2015. Data on time and resource utilization was collected prospectively using patient and nurse questionnaires. Societal costs were calculated by multiplying the resource use by its corresponding unit price, including direct medical costs (pharmaceuticals, materials, nurse time, etc.), direct non-medical costs (transportation) and indirect costs (production loss, lost leisure time). Costs were reported separately for patients receiving trastuzumab for the first time and non-first time ("subsequent treatment"). RESULTS: In total, 101 IV and 94 SC patients were included in the study. The societal costs were lower with SC administration. For subsequent treatments the cost difference was €117 (IV €2099; SC €1983), partly explained by a higher time consumption both for nurses (14 min) and patients (23 min) with IV administration. Four IV and 16 SC patients received trastuzumab for the first time and were analysed separately, resulting in a difference in societal costs of €897 per treatment. A majority of patients preferred SC to IV administration. CONCLUSION: SC administration resulted in both less direct medical costs and indirect costs, and was consequently less costly than IV administration from a societal perspective in a Swedish setting.

Willingness to pay for a new drug delivery in Parkinson patients.

OBJECTIVE: The Swedish reimbursement system operates a system where prices are set based on the expected value to the consumer. This value can be measured using willingness to pay (WTP). AIM: To assess Parkinson's disease (PD) patients' WTP for newly developed microtablets of levodopa in combination with a drug-delivering electronic device (M/E) compared to standard treatment with levodopa in combination with the COMT (catechol-O-methyl transferase)-inhibitor entacapone (L/e). METHOD: A total of 2,000 randomly included PD patients had a postal questionnaire covering demographics, disease-specific issues, views on medication and WTP in different hypothetical scenarios. The first scenario was M/E with no change in effects or side effects; the second scenario was M/E with same effect and less side effects; and the third scenario was M/E with improved effect and less side effects. These scenarios were coupled to different costs to choose from. RESULTS: A total of 999 patients (50%) responded, mean age of 71 years and a mean PD duration of 9 years. Of all respondents, 50% preferred M/E before L/e in scenario one with increasing preference to scenario three. The average monthly WTP among all respondents in scenario one was SEK 230 and SEK 226 in L/e, both with an almost longitudinal doubling up to scenario three. Duration of PD-related symptoms, high education, and high medication intake implied a higher WTP in all scenarios in contrast to age, sex, and extra doses of levodopa. CONCLUSION: WTP for M/E increased gradually with high medication intake and education as well as with expected increased reduction of PD symptoms.

Mutant prevention concentrations of pradofloxacin for susceptible and mutant strains of Escherichia coli with reduced fluoroquinolone susceptibility.

Pharmacodynamic and mutant prevention properties of the fluoroquinolone pradofloxacin (PRA) were measured against a set of 17 Escherichia coli strains carrying no, one or two known mutations conferring reduced fluoroquinolone susceptibility. The strains included susceptible wild-types, isogenic constructed mutants, isogenic selected mutants and clinical isolates. The effectiveness of PRA was determined with regard to preventing the selection of resistant mutants, using static and changing concentrations of drug. Ciprofloxacin was used as a reference drug. Minimum inhibitory concentrations (MICs) and mutant prevention concentrations (MPCs) of PRA for the susceptible wild-type strains were in the range 0.012-0.016mg/L and 0.2-0.3mg/L, respectively, giving a mean±standard deviation mutant prevention index (MPI=MPC/MIC) of 17.7±1.1. The mean MPI PRA of the 14 mutant strains was 19.2±12, and the mean MPI across all 17 strains was 18.9±10.8. In an in vitro kinetic model in which PRA was diluted with a half-life of 7h to mimic in vivo conditions, an initial concentration of PRA of 1.6-2.4mg/L (8-10× MPC), giving a PRA AUC/MPC ratio of 73-92, and a T>MPC of 21-23h was sufficient to prevent the selection of resistant mutants from the three susceptible wild-type strains. Dosing to reduce selection for antibiotic resistance in veterinary therapy has a role in reducing the reservoir of resistant mutants. We conclude that a level of dosing that prevents the selection of resistant mutants during therapy should be achievable in vivo.

Effect of treatment with natalizumab on ability to work in people with multiple sclerosis: productivity gain based on direct measurement of work capacity before and after 1 year of treatment.

BACKGROUND: Sweden is a high endemic region for multiple sclerosis (MS), a neurologic disorder characterized by repeated inflammatory episodes affecting the CNS. The disease has its peak age of onset at approximately 30 years and affects women twice as often as men. The young age of onset makes MS one of the major causes of reduced capacity to work due to neurologic disease in Western society. Natalizumab (Tysabri®) is among the new generation of biologic drugs for the treatment of MS. Clinical studies have demonstrated that natalizumab is an effective treatment for preventing relapses and inflammatory activity. OBJECTIVE: The aim of the study was to estimate the monetary value of treatment with natalizumab on the ability to work in patients with MS in Sweden, based on a direct measurement of weekly hours worked before and after 1 year of treatment with natalizumab. METHODS: A sample of patients, consisting of all patients who had started treatment with natalizumab during the period June 2007-May 2008, was identified through the Swedish Multiple Sclerosis Register (SMSreg). Data about sex, age, disease severity, and disease duration were collected from the register. Data about type of work and work capacity (number of hours worked per week) were collected retrospectively through a postal questionnaire. The average hours worked per week was estimated at baseline (2 weeks before treatment started) and at follow-up (50 weeks after treatment started), and the change was assigned an economic value using the human capital approach. RESULTS: This study showed that after 50 weeks of treatment with natalizumab, people with MS increased their productivity by 3.3 hours per week on average (p < 0.01), which corresponded to an economic value of &U20AC;3216 per person per year (year 2007 values). A shorter duration of illness or being 25-35 years old was significantly associated with a greater productivity gain (p = 0.025 and p = 0.002, respectively). CONCLUSION: A shorter duration of illness and a lower age at the start of treatment were significantly associated with a greater productivity gain after 50 weeks of treatment with natalizumab, which indicates that it is more beneficial to initiate efficient therapy early in patients with MS.

Dose-related selection of fluoroquinolone-resistant Escherichia coli.

OBJECTIVES: To investigate the effects of clinically used doses of norfloxacin, ciprofloxacin and moxifloxacin on survival and selection in Escherichia coli populations containing fluoroquinolone-resistant subpopulations and to measure the value of the pharmacodynamic index AUC/mutant prevention concentration (MPC) that prevents the growth of pre-existing resistant mutants. METHODS: Mixed cultures of susceptible wild-type and isogenic single (gyrA S83L) or double (gyrA S83L, Delta marR) fluoroquinolone-resistant mutants were exposed to fluoroquinolones for 24 h in an in vitro kinetic model. Antibiotic concentrations modelled pharmacokinetics attained with clinical doses. RESULTS: All tested doses eradicated the susceptible wild-type strain. Norfloxacin 200 mg administered twice daily selected for both single and double mutants. Ciprofloxacin 250 mg administered twice daily eradicated the single mutant, but not the double mutant. For that, 750 mg administered twice daily was required. Moxifloxacin 400 mg once daily eliminated the single mutant, but did not completely remove the double mutant. The MPC of ciprofloxacin was determined and based on those dose simulations that eradicated mutant subpopulations, an AUC/MPC(wild-type) of 35 prevented selection of the single mutant, whereas an AUC/MPC(single mutant) of 14 (equivalent to an AUC/MPC(wild-type) of 105) prevented selection of the double mutant. CONCLUSIONS: All tested clinical dosing regimens were effective in eradicating susceptible bacteria, but ciprofloxacin 750 mg twice daily was the only dose that prevented the selection of single- and double-resistant E. coli mutants. Thus, among approved fluoroquinolone dosing regimens, some are significantly more effective than others in exceeding the mutant selection window and preventing the enrichment of resistant mutants.

Selection of ciprofloxacin resistance in Escherichia coli in an in vitro kinetic model: relation between drug exposure and mutant prevention concentration.

OBJECTIVES: To evaluate the mutant prevention concentrations (MPCs) of ciprofloxacin for two susceptible and one first-step gyrA resistant mutant Escherichia coli strains in an in vitro kinetic model and to identify the pharmacodynamic index that best predicts prevention of resistance emergence. METHODS: An in vitro kinetic model was used to measure MPC with static antibiotic concentrations and to test different dosing profiles to study pharmacokinetics/pharmacodynamics indices important to prevent the growth of resistant mutants. In one set of kinetic experiments the starting concentration was equal to the MPC and the T > MPC was varied before antibiotic dilution was begun. In a second set of kinetic experiments C(max) was varied and dilution of the antibiotic was started at time zero. RESULTS: From the static experiments we calculated MPC values of 0.128 mg/L for both the susceptible strains (16x MIC) and 0.188 mg/L (4x MIC) for the first-step resistant (gyrA) strain. The kinetic experiments showed that the T > MPC needed to prevent the growth of resistant bacteria was shorter with an increased C(max). When resistance was selected, several subpopulations with different levels of susceptibility to ciprofloxacin emerged. CONCLUSIONS: Neither T > MPC nor C(max) proved to be single correlates for preventing resistance development. For the two investigated wild-type strains, an AUC/MPC ratio of > or =22 was the single pharmacodynamic index that predicted prevention of resistant mutant development.

Pharmacodynamic model to describe the concentration-dependent selection of cefotaxime-resistant Escherichia coli.

Antibiotic dosing regimens may vary in their capacity to select mutants. Our hypothesis was that selection of a more resistant bacterial subpopulation would increase with the time within a selective window (SW), i.e., when drug concentrations fall between the MICs of two strains. An in vitro kinetic model was used to study the selection of two Escherichia coli strains with different susceptibilities to cefotaxime. The bacterial mixtures were exposed to cefotaxime for 24 h and SWs of 1, 2, 4, 8, and 12 h. A mathematical model was developed that described the selection of preexisting and newborn mutants and the post-MIC effect (PME) as functions of pharmacokinetic parameters. Our main conclusions were as follows: (i) the selection between preexisting mutants increased with the time within the SW; (ii) the emergence and selection of newborn mutants increased with the time within the SW (with a short time, only 4% of the preexisting mutants were replaced by newborn mutants, compared to the longest times, where 100% were replaced); and (iii) PME increased with the area under the concentration-time curve (AUC) and was slightly more pronounced with a long elimination half-life (T(1/2)) than with a short T(1/2) situation, when AUC is fixed. We showed that, in a dynamic competition between strains with different levels of resistance, the appearance of newborn high-level resistant mutants from the parental strains and the PME can strongly affect the outcome of the selection and that pharmacodynamic models can be used to predict the outcome of resistance development.

Mutant prevention concentrations of ciprofloxacin for urinary tract infection isolates of Escherichia coli.

OBJECTIVES: To measure the mutant prevention concentration (MPC) of ciprofloxacin for a set of urinary tract infection (UTI) Escherichia coli isolates with different levels of susceptibility and determine whether MPC can be predicted from MIC. METHODS: MPC was defined as the lowest ciprofloxacin concentration that prevented the growth of resistant colonies when 10(10) bacteria were spread on solid medium and incubated for 96 h at 37 degrees C. MIC was measured by Etest. Bacteria surviving (persisting) at MPC were isolated and quantified from agar plugs taken after 96 h. The genes hipA and hipB were amplified by PCR from persisters and sequenced. RESULTS: Isolates with MICs above the NCCLS breakpoint for ciprofloxacin resistance (4 mg/L) typically have MPCs greater than 32 mg/L. Isolates with MICs below the breakpoint for ciprofloxacin susceptibility (1 mg/L) have MPCs up to 5 mg/L. MPC/MIC is approximately 16 for most susceptible isolates but there are several notable exceptions (MPC/MIC > 100). Resistant colonies arising one dilution step below MPC often had MIC > MPC. In every case tested, a proportion of cells survived (persisted), but did not grow into colonies, at MPC, without any increase in MIC. CONCLUSIONS: MPCs were determined for all ciprofloxacin-susceptible isolates. MPC is not accurately predicted from MIC. Colonies selected below MPC frequently have MIC > MPC, suggesting multiple mutations. A small fraction of cells from all strains tested survived for 96 h at MPC, without any associated increase in MIC. These survivors/persisters are not hipAB mutants.