Changes in prescribed drug doses after market introduction

How the EMERGE guideline on medication adherence can improve the quality of clinical trials

Medication adherence in drug trials is suboptimal, affecting the quality of these studies and adding significant costs. Nonadherence in this setting can lead to null findings, unduly large sample sizes and the need for dose modification after a drug has been approved. Despite these drawbacks, adherence behaviours are not consistently measured, analysed or reported appropriately in trial settings. The ESPACOMP Medication Adherence Reporting Guideline (EMERGE) offers a solution by facilitating a sound protocol design that takes this crucial factor into account. This article summarises key evidence on traditional and newer measurements of adherence, discusses implementation in clinical trial settings and makes recommendations about the analysis and interpretation of adherence data. Given the potential benefits of this approach, the authors call on regulators and the pharmaceutical industry to endorse the EMERGE guideline.

Lower-dose prescriptions in the post-marketing situation and the influencing factors thereon

The dosage of pharmaceuticals is determined through the process of clinical development and approval review based on clinical trial results; however, the information obtained from clinical trials before approval is limited. Some pharmaceutical products are used at doses lower than those approved for post-marketing use. The aim of this study was to reveal the actual state of lower-dose prescriptions for post-marketing clinical use of pharmaceuticals. We investigated the factors related to the deviation based on therapeutic area, detailed statement of the approved dosage, clinical data package, and post-marketing requirement. Among the new molecular entities approved in Japan between January 2005 and December 2014, we identified products that are orally administered and have the same daily dose for different indications, if any. For these products, we collected information on the actual daily dose from the medical information databases of Medical Data Vision Co., LTD. and JammNet Co., LTD. Products whose dose was lower than the approved dose (maintenance dose excluding the initial dose) in ≥ 30% prescriptions in 2015 were defined here as “lower-dose prescription drugs.” We identified 27 lower-dose prescription drugs out of 113 products investigated. The results of the multivariate analysis revealed that factors related to the Anatomical Therapeutic Chemical classification and the detailed statement of the approved dosage significantly influenced the occurrence of lower-dose prescription, whereas the factors related to clinical data package and post-marketing requirements did not. These results suggest the limitation in determining an optimal dosage for the actual clinical use of a drug based on the information obtained from clinical trials conducted before approval, emphasizing the importance of reexamining the optimal dosage that is applicable to a greater number of patients after marketing, if necessary. We believe that the utilization of real-world data could be of help in this regard.

Dose optimisation with simultaneous pharmacokinetic estimation in adaptive clinical trials

Determination of the optimal dose is a critical objective in the drug developmental process. An optimal dose prevents over- and under-exposure to the treatment drug thereby facilitating superior patient experience and reduced costs to the healthcare system. In this paper, we present a method for model-based dose optimisation with simultaneous pharmacokinetic estimation of the model parameters. Multiple doses of the drug are considered and the objective is to maintain the blood concentration of the drug around a pre-decided target concentration. We consider an adaptive setting wherein the model parameters are estimated from the blood samples collected at D-optimal time points from all subjects enrolled so far in the trial. The estimated parameters are then used to determine the optimal dose regimen for the next cohort. This procedure continues until the condition of a pre-decided stopping rule is met. Simulation studies and sensitivity analysis are undertaken to validate the methodology. We also evaluate the performance of the methodology when carried out in a non-adaptive setting. A two-stage design is then presented which combines the advantages of the adaptive as well as the non-adaptive approach. We demonstrate that our methodology enables pharmacokinetic estimation and dose regimen optimisation simultaneously in an ethical and cost-effective manner protecting the subjects from the ill-effects of suboptimal dose regimens and economising the number of subjects required in the trial.

Analysis of Global Drug Development Pathways and Postmarketing Safety in Japan: Local Studies May Reduce Drug-Related Deaths

Recent International Conference on Harmonization (ICH) guidelines provide pharmaceutical companies with regulatory justifications to pursue various global drug‐development pathways, in some of which “local” dose‐ranging and/or pivotal phase III studies are skipped. We examined the association between the clinical development pathway and postmarketing safety in Japan for 177 new molecular entities approved between 2004 and 2013 focusing on dose setting histories for each drug. The risk of drug‐related deaths was higher when companies did not conduct local (i.e., Japanese) dose‐ranging studies and/or pivotal studies. Even when local dose‐ranging studies were conducted, the risk remained higher in some drugs for which the approved dose in Japan was set equal to that in the United States. Drugs developed under a bridging strategy tended to show lower risks. These results suggested that local clinical studies may play a substantial role in achieving optimization of postmarketing drug use in each local target population.

Dose-Finding Studies Among Orphan Drugs Approved in the EU: A Retrospective Analysis

In the development process for new drugs, dose‐finding studies are of major importance. Absence of these studies may lead to failed phase 3 trials and delayed marketing authorization. In our study we investigated to what extent dose‐finding studies are performed in the case of orphan drugs for metabolic and oncologic indications. We identified all orphan drugs that were authorized until August 1, 2017. European Public Assessment Reports were used to extract the final dose used in the summary of product characteristics, involvement of healthy volunteers, study type, end points used, number of patients, number of doses, studies in special populations, and dose used for phase 3 studies. Each drug was checked for major objections and dose changes postmarketing. We included 49 orphan drugs, of which 28 were indicated for metabolic disorders and 21 for oncologic indications. Dose‐finding studies were performed in 32 orphan drugs, and studies in healthy volunteers in 26. The absence of dose‐finding studies was mostly due to the rarity of the disease. In this case the dose was determined based on factors such as animal studies or clinical experience. Dose‐related major objections were raised for 9 orphan drugs. Postmarketing dose‐finding studies were conducted in 18 orphan drugs, but dose changes were applied in only 2 drugs. In conclusion, dose‐finding studies in the case of metabolic and oncologic orphan drugs were conducted in the development programs of two thirds of orphan drugs. Dose‐finding studies performed postmarketing suggest that registered doses are not always optimal. It is thus important to perform more robust dose‐finding studies both pre‐ and postmarketing.

The pharmacodynamic and clinical trial evidence for statin dose

Statin doses around estimated effective dose 50 (ED50) can reduce myocardial infarction by over 25% and mortality by around 10%. Being a competitive enzyme inhibitor, statin efficacy plateaus at doses that are multiples above the ED50, whilst on- and off-target adverse events increase in number and severity with increasing dose. For example, myopathy has been shown to increase by up to 29-fold and liver dysfunction by up to nine-fold as statin dose is increased. Doses of up to 40-fold ED50 have been promoted, but above five-fold ED50, for example 10 mg of atorvastatin, there is no randomized controlled clinical trial evidence that coronary mortality is lowered, or that survival is increased.

Exploratory Analysis of Associations Between Postmarketing Safety Events and Approved Doses of New Drugs in Japan

While efficient and less onerous for the industry, the globalization of clinical drug development may lead to limited efforts to optimize drugs for regional conditions. We examined the association between clinical development pathways, approved doses, and postmarketing safety risks in Japan for 135 new molecular entities approved between 2004 and 2011. The risk of drug‐related deaths seemed higher when pharmaceutical companies chose exactly the same dose as in the United States, even after conducting Japanese dose‐ranging studies. We also found a positive association with drug‐related deaths when the review process was expedited and when Japanese dose‐ranging studies were not conducted for nonexpedited drugs. Our findings suggest that the decisions on regional dose settings and the choice of global clinical development pathways are associated in ways that may influence the postmarketing outcomes in the target populations.

Pharmacology-based toxicity assessment: towards quantitative risk prediction in humans

Despite ongoing efforts to better understand the mechanisms underlying safety and toxicity, ~30% of the attrition in drug discovery and development is still due to safety concerns. Changes in current practice regarding the assessment of safety and toxicity are required to reduce late stage attrition and enable effective development of novel medicines. This review focuses on the implications of empirical evidence generation for the evaluation of safety and toxicity during drug development. A shift in paradigm is needed to (i) ensure that pharmacological concepts are incorporated into the evaluation of safety and toxicity; (ii) facilitate the integration of historical evidence and thereby the translation of findings across species as well as between in vitro and in vivo experiments and (iii) promote the use of experimental protocols tailored to address specific safety and toxicity questions. Based on historical examples, we highlight the challenges for the early characterisation of the safety profile of a new molecule and discuss how model-based methodologies can be applied for the design and analysis of experimental protocols. Issues relative to the scientific rationale are categorised and presented as a hierarchical tree describing the decision-making process. Focus is given to four different areas, namely, optimisation, translation, analytical construct and decision criteria. From a methodological perspective, the relevance of quantitative methods for estimation and extrapolation of risk from toxicology and safety pharmacology experimental protocols, such as points of departure and potency, is discussed in light of advancements in population and Bayesian modelling techniques (e.g. non-linear mixed effects modelling). Their use in the evaluation of pharmacokinetics (PK) and pharmacokinetic-pharmacodynamic relationships (PKPD) has enabled great insight into the dose rationale for medicines in humans, both in terms of efficacy and adverse events. Comparable benefits can be anticipated for the assessment of safety and toxicity profile of novel molecules.

Effects of gliclazide dose escalation on postprandial hyperglycemia in type 2 diabetes mellitus: A prospective, open-label, case-controlled, dose-escalation study

OBJECTIVES

The aims of this study were to determine the effects of increasing doses of gliclazide on postprandial glucose excursions after a standardized breakfast and lunch, and to clarify the relationship between gliclazide dose and glucose response.

METHODS

This prospective, open-label, case-controlled, dose-escalation study was conducted at the Addington Hospital Diabetes Clinic, eThekwini/Durban, KwaZulu-Natal, South Africa. Male and female patients aged ≥18 years with type 2 diabetes mellitus (DM) and postprandial hyperglycemia (2-hour postprandial blood glucose [PPBG2 h] level, ≥11.1 mmol/L [≥200 mg/dL]) and receiving an oral hypoglycemic agent were eligible. After a 1-week washout period during which patients were asked to discontinue treatment with all oral hypoglycemic agents, baseline glycemic measurements were performed (fasting blood glucose, PPBG2 h, 6-hour postprandial blood glucose [PPBG6 h], mean blood glucose [MBG], plasma insulin, fasting serum fructosamine, and glycosylated hemoglobin). All patients subsequently received 2 weeks of oral treatment with each of 3 doses of gliclazide: 40, 80, and 160 mg/d. Glycemic parameters were measured at the end of each dosing interval. Adverse-effect monitoring included direct reporting of untoward effects to the resident medical practitioner, clinical examination, monitoring of home blood glucose records, hematology, and liver and kidney function tests. Compliance was assessed using pill counts, examination of diary entries, and patient interview.

RESULTS

Thirty-three patients were screened; 14 entered the dose-escalation phase. Thirteen patients completed the study (7 women, 6 men; mean [SD] age, 52.0 [11.1] years); 1 was withdrawn because of poor compliance. Dose escalation from 40 to 80 mg/d was associated with a significant change only in MBG (mean [SD], 11.3 [4.2] vs 10.0 [3.9] mmol/L [203.6 (75.7) vs 180.1 (70.3) mg/dL]; P<0.001). Dose escalation from 80 to 160 mg/d was associated with a significant change only in PPBG6 h (9.5 [4.2] vs 10.3 [4.1] mmol/L [171.1 (75.7) vs 185.6 (73.9) mg/dL]; P=0.018). No other significant changes in glycemic parameters between doses were found throughout the treatment period. No adverse effects were reported.

CONCLUSIONS

In this small study of gliclazide dose escalation in patients with type 2 DM and postprandial hyperglycemia, gliclazide 80 mg/d was associated with a reduction in postprandial hyperglycemia. Dose escalation from 80 to 160 mg/d was not found to be associated with additional clinical benefit. Based on these results, we recommend that gliclazide dose escalation to the maximum dose recommended by the manufacturer be guided by measures of glycemia. All doses were well tolerated.

Lower-dose prescribing: minimizing "side effects" of pharmaceuticals on society and the environment

The prescribed use of pharmaceuticals can result in unintended, unwelcomed, and potentially adverse consequences for the environment and for those not initially targeted for treatment. Medication usage frequently results in the collateral introduction to the environment (via excretion and bathing) of active pharmaceutical ingredients (APIs), bioactive metabolites, and reversible conjugates. Imprudent prescribing and non-compliant patient behavior drive the accumulation of unused medications, which pose major public health risks from diversion as well as risks for the environment from unsound disposal, such as flushing to sewers. The prescriber has the unique wherewithal to reduce each of these risks by modifying various aspects of the practice of prescribing. By incorporating consideration of the potential for adverse environmental impacts into the practice of prescribing, patient care also could possibly be improved and public health better protected. Although excretion of an API is governed by its characteristic pharmacokinetics, this variable can be somewhat controlled by the prescriber in selecting APIs possessing environment-friendly excretion profiles and in selecting the lowest effective dose. This paper presents the first critical examination of the multi-faceted role of drug dose in reducing the ambient levels of APIs in the environment and in reducing the incidence of drug wastage, which ultimately necessitates disposal of leftovers. Historically, drug dose has been actively excluded from consideration in risk mitigation strategies for reducing ambient API levels in the environment. Personalized adjustment of drug dose also holds the potential for enhancing therapeutic outcomes while simultaneously reducing the incidence of adverse drug events and in lowering patient healthcare costs. Optimizing drug dose is a major factor in improving the sustainability of health care. The prescriber needs to be cognizant that the "patient" encompasses the environment and other "bystanders," and that prescribed treatments can have unanticipated, collateral impacts that reach far beyond the healthcare setting.

Impact of dose frequency on compliance and health outcomes: a literature review (1966-2006)

In order for treatments to be effective, patients must be compliant with their medication regimens. Currently, patient compliance is seen as one of the most challenging issues in treating patients with chronic diseases. Studies in which dose frequency has been changed have been reviewed across several different diseases to examine the impact of a change in dose frequency on compliance and health outcomes, as well as efficacy and tolerability. In general, reducing dose frequency may improve medication compliance and effectiveness, and reduce adverse events, while possibly reducing healthcare costs. Suggestions for future research have been presented, including a need to measure compliance with injectable formulations and a standardized definition of compliance.

Approaches to Japanese dose evaluation in global drug development: factors that generate different dosages between Japan and the United States

Drug development in Japan is shifting from a bridging strategy to a global strategy, and the number of multiregional trials in which Japan is included is increasing every year. The Japanese drug regulatory authority requires that data be collected in Japanese populations, and therefore dose-response studies of various drugs are frequently conducted in Japan. However, the current standard for adequate dose-finding processes may sometimes hinder the timely participation of Japan in these multiregional trials. We studied the development approaches and review patterns of 99 new molecular entities (NMEs) approved in 2003-2008 and have identified some common factors that result in differences in approved dosages in Japan as compared with other countries, such as dose-response study design, pharmacokinetics, and the timing of development. The findings of our research will serve as an initial information base on which to build an efficient global drug development strategy in Japan.

The value of population pharmacokinetics and simulation for postmarketing safety evaluation of dosing guidelines for drugs with a narrow therapeutic index: buflomedil as a case study

Population pharmacokinetics and simulation techniques currently play an important role in new drug development. This paper illustrates the potential value of those methods in postmarketing safety assessment, using buflomedil in elderly patients as an example. We retrospectively assessed the risk of buflomedil overdosing associated with the latest dosing recommendations of the French Drug Agency (AFSSAPS). First, buflomedil concentrations measured in 24 elderly patients were analysed with a nonparametric population approach. Then, the pharmacokinetic model was used to perform a 1000-patient Monte Carlo simulation for the two recommended buflomedil dosage regimens. The maximum concentrations calculated after 10 days of therapy were compared with levels observed in reported cases of toxicity to assess the probability of overdosing. A three-compartment model best fit concentration data. Population predictions showed little bias (-0.14 mg/L) and good precision (8.73 mg(2) /L(2)). Overall results of the simulation study showed that the application of the two recommended dosage regimens of buflomedil was associated with overdosing (C(max) > 10 mg/L) and potential toxicity in 2.9% of geriatric patients. In patients with mild renal impairment, who may receive the higher-dosage regimen by therapeutic error, the probability of overdosing was 6.2%. Despite specific dosing recommendations in case of renal impairment, this study shows that the use of buflomedil could be associated with significant risk of overdosing in geriatric patients. Such results might have enhanced decision-making when buflomedil safety was reassessed by AFSSAPS in 2006. The retrospective case of buflomedil illustrates how these methods may be valuable in postmarketing safety evaluation of potentially toxic drugs.

Adherence to medications: insights arising from studies on the unreliable link between prescribed and actual drug dosing histories

Satisfactory adherence to aptly prescribed medications is essential for good outcomes of patient care and reliable evaluation of competing modes of drug treatment. The measure of satisfactory adherence is a dosing history that includes timely initiation of dosing plus punctual and persistent execution of the dosing regimen throughout the specified duration of treatment. Standardized terminology for initiation, execution, and persistence of drug dosing is essential for clarity of communication and scientific progress. Electronic methods for compiling drug dosing histories are now the recognized standard for quantifying adherence, the parameters of which support model-based, continuous projections of drug actions and concentrations in plasma that are confirmable by intermittent, direct measurements at single time points. The frequency of inadequate adherence is usually underestimated by pre-electronic methods and thus is clinically unrecognized as a frequent cause of failed treatment or underestimated effectiveness. Intermittent lapses in dosing are potential sources of toxicity through hazardous rebound effects or recurrent first-dose effects.

Bridging the efficacy-effectiveness gap: a regulator's perspective on addressing variability of drug response

Drug regulatory agencies should ensure that the benefits of drugs outweigh their risks, but licensed medicines sometimes do not perform as expected in everyday clinical practice. Failure may relate to lower than anticipated efficacy or a higher than anticipated incidence or severity of adverse effects. Here we show that the problem of benefit-risk is to a considerable degree a problem of variability in drug response. We describe biological and behavioural sources of variability and how these contribute to the long-known efficacy-effectiveness gap. In this context, efficacy describes how a drug performs under conditions of clinical trials, whereas effectiveness describes how it performs under conditions of everyday clinical practice. We argue that a broad range of pre- and post-licensing technologies will need to be harnessed to bridge the efficacy-effectiveness gap. Successful approaches will not be limited to the current notion of pharmacogenomics-based personalized medicines, but will also entail the wider use of electronic health-care tools to improve drug prescribing and patient adherence.

Discrepancies between prescribed and defined daily doses: a matter of patients or drug classes?

Purpose

Defined daily doses (DDD) are used for the measurement of drug utilisation. The aim of the study was to analyse whether differences between DDD and prescribed daily doses (PDD) exist for relevant drug classes such as antihypertensive drugs and, if so, whether they primarily depend on drug classes or patient-related factors.

Methods

Using the data of a large German statutory health insurance scheme, we analysed continuous prescriptions for the following antihypertensive drug classes: thiazide diuretics, beta-blockers, dihydropyridine calcium channel blockers (CCBs), angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin-II receptor blockers (ARBs). We summed the doses of all dispensed drugs per person during a defined time frame. We calculated the PDD (= total dose divided by the number of days) and expressed them as the PDD:DDD ratio (= amount of DDD per day and person).

Results

During the study period, 149,704 patients continuously received an antihypertensive medication. The average PDD:DDD ratio ranged from 0.84 (beta-blockers) to 1.88 (ARBs) and 2.17 (ACEIs). The average prescribed dosage of each drug class remained unchanged, even if the patients had previously received another antihypertensive drug with another PDD:DDD ratio. For example, if patients were switched from a beta-blocker to an ACEI, the PDD:DDD ratio increased, on average, from 0.79 to 2.17. Vice versa, the ratio decreased for patients with a drug change from an ACEI to a beta-blocker from 2.06 to 0.75.

Conclusions

Even large differences between DDD and PDD seem to be a matter of drug classes and not primarily of patient characteristics.

Superior efficacy of new medicines?

Purpose

To provide an overview of and discuss newly authorised medicines with an improved efficacy.

Methods

This analysis focussed on new medicines with an improved efficacy based on the results of randomised active control trials. Information on comparative efficacy was obtained from the European Medicines Agency European Public Assessment Reports.

Results

Between 1999 and 2005 we identified 122 new medicines with a new active substance. Of these, 13 (10%) were shown to be superior to already available medicines in terms a statistically significant difference in primary clinical endpoints.

Conclusions

A proven advantage in efficacy at an early stage of drug development is the exception rather than the rule. The absence of evidence demonstrating differences between medicines does not necessarily mean that there are no actual differences. Optimal pharmacotherapy would benefit from more comparative research in the development of new medicines. The results of comparative trials need to be critically evaluated for their specific value in clinical practice. To this end, prescription data may be helpful.

Coping with changes in the Defined Daily Dose in a longitudinal drug consumption database

OBJECTIVE

To illustrate the best approach to accurate representation of temporal evolution of drug consumption, when confronted with changes over time in the Defined Daily Dose (DDD) measurement unit.

METHOD

As an example, drug consumption (2001-2005) at the University Hospital Rijeka was expressed with the corresponding DDD in each year; and with the DDD value of the last year of the observation time window. By visual appraisal, results with both methods were compared with the graph of drug consumption trends expressed in physical units (mg, IU, etc.).

RESULTS

Of 20 drugs for which the DDD value has changed in the 5 year period, 5 were used in Rijeka hospital: erythropoietin parenteral, budesonide nasal spray, repaglinide oral, amoxicillin with clavulanic acid parenteral, and fentanyl transdermal. Graphs for individual drugs with the year by year method showed artificial jerks in the years proceeding the year of DDD change. Representation of total hospital consumption did not differ notably with the two methods.

CONCLUSION

Drug consumption data should be calculated with the latest DDD value in the time window. The policy of the World Health Organisation to keep changes to the system of DDD to a minimum should be continued.

Choice of comparator in active control trials of new drugs

BACKGROUND

When choosing the active control group in a randomized trial, it is important to maintain standard treatment for the therapeutic indication for which a medicine is studied. This choice is relevant not only for demonstrating the efficacy and safety of a new drug, but also for assessing its place in therapy in comparison with existing medicines. Comparative information is important for decisions on prescribing and reimbursement. However, choosing the most suitable comparator is difficult when recommendations on drugs of first choice vary depending on clinical settings and times.

OBJECTIVE

To evaluate the choice of comparator in premarketing randomized active control trials (RaCTs) in comparison with recommendations for standard treatment.

METHODS

We evaluated drugs that were authorized for use in the European Union market between 1999 and 2005. Information on active comparators in RaCTs was extracted from the European Public Assessment Reports and information on recommendations regarding standard treatment was retrieved from the annual editions of the Dutch reference book on pharmacotherapy. Data on prescribing and indications at the time of authorization and 3 years before authorization were included. The comparator was considered to be in line with standard treatment if there was a similarity in both active substance or therapeutic class and the dosage.

RESULTS

For 58 new medications identified, treatment in the active control group was in line with the recommended standard treatment in 108 of 153 (71%) RaCTs at the time of the drug's authorization; 47 (81%) of the new drugs had been compared with the recommended standard treatment in at least one trial. When dissimilarities occurred, none of the comparators had been recommended as standard treatment 3 years earlier (the supposed time of defining the trials' protocol).

CONCLUSIONS

Most comparators in the premarketing RaCTs of new medicines were in line with the recommended standard treatment at the moment of marketing authorization. In view of this similarity, most of these trials are also fit for postmarketing decision-making on prescribing and on inclusion in clinical guidelines and reimbursement systems.

Polymorphic cytochrome P450 enzymes and post-marketing drug dosage revisions: clinical relevance to dermatologic therapies

The therapeutic drug resources available to dermatologists have expanded and encompass off-label use of other drugs as well. As these new resources are employed, it is important to remain vigilant of possible drug interactions and toxicities contingent upon inter-individual variability of plasma drug levels. This article reviews the biochemistry of CYP enzymes and the clinical implications of genetic polymorphisms as relating to certain dermatologic drugs. In addition, we discuss the potential clinical function of cutaneous CYP enzymes.

Preventing postmarketing changes in recommended doses and marketing withdrawals

Recent market withdrawals of prescription drug products have brought attention to premarketing safety research. Less known but related to some drug withdrawals are postmarketing dosage changes of newly marketed drugs, including both dosage reductions and increases. These events have serious effects on patients, manufacturers, and regulatory authorities. Most of these harmful events could be avoided by intensive employment of targeted clinical pharmacology investigations to optimize dosage prior to phase III testing and regulatory approval. In this paper, the frequency and implications of postmarketing dosing changes and market withdrawals are considered in light of approaches to preventing them.

Current issues relating to drug safety especially with regard to the use of biomarkers: a meeting report and progress update

An expert group met in Leiden to review the state-of-the-art in detecting drug-related safety problems and to review the role of biomarkers and modelling techniques. It was clear that new drugs are not necessarily safer than old drugs, despite much larger clinical trial programs. Larger or longer clinical trials may be unfeasible and postmarketing surveillance is not being undertaken systematically enough to ensure safety. Biomarkers could improve drug safety by detecting drug-related signals early but determining whether the biomarker is on the causal pathway to toxicity is difficult. The maturity and utility of safety-related biomarkers varies among target organ systems. A consortium approach to assimilate a large amount of biomarker-related safety signals incorporating this information into mechanism-based models may provide a useful way forward. However no techniques will ensure that drugs are perfectly safe and communication with the public is required to achieve mutual understanding of benefit risk/balance assessments.

Can pharmacogenetics help rescue drugs withdrawn from the market?

Observations over the later half of the last century have suggested that genetic factors may be the prime determinant of drug response, at least for some drugs. Retrospectively gathered data have provided further support to the notion that genotype-based prescribing will improve the overall efficacy rates and minimize adverse drug reactions (ADRs), making personalized medicine a reality. During the last 16 years, 38 drugs have been withdrawn from major markets due to safety concerns. Inevitably, a question arises as to whether it might be possible to 'rescue' some of these drugs by promoting genotype-based prescribing. However, ironically pharmacogenetics has not perceptibly improved the risk/benefit of a large number of genetically susceptible drugs that are already in wide clinical use and are associated with serious ADRs. Drug-induced hepatotoxicity and QT interval prolongation (with or without torsade de pointes) account for 24 (63%) of these 38 drug withdrawals. In terms of the number of drugs implicated, both these toxicities are on the increase. Many others have had to be withdrawn due to their inappropriate use. This paper discusses the criteria that a drug would need to fulfill, and summarizes the likely regulatory requirements, before its pharmacogenetic rescue can be considered to be realistic. One drug that fulfils these criteria is perhexiline (withdrawn worldwide in 1988) and is discussed in some detail. For the majority of these 38 drugs there are, at present, no candidates for genetic traits to which the toxicity that led to their withdrawal may be linked. For a few other drugs where a potential candidate for a genetic trait might explain the toxicity of concern, the majority of patients who experienced the index toxicity had easily managed nongenetic risk factors. It may be possible to rescue these drugs simply by careful attention to their dose, interaction potential and prescribing patterns, but without the need for any pharmacogenetic test. In addition, the pharmacogenetic rescue of drugs might not be as effective as anticipated as hardly any pharmacogenetic test is known to have the required test efficiency to promote individualized therapy. Multiple pathways of drug elimination, contribution to toxicity by metabolites as well as the parent drug, gene-gene interactions, multiple mechanisms of toxicity and inadequate characterization of phenotype account for this lack of highly predictive tests. The clinical use of tests that lack the required efficiency carries the risks of over- or under-dosing some patients, denying the drug to others and decreasing physician vigilance of patients. Above all, at present, prescribing physicians lack an adequate understanding of pharmacogenetics and its limitations. It is also questionable whether their prescribing will comply with the requirements for pretreatment pharmacogenetic tests to make pharmacogenetic rescue a realistic goal.

Estimation of dosing strategies aiming at maximizing utility or responder probability, using oxybutynin as an example drug

Methods for optimizing dosing strategies for individualization with a limited number of discrete doses, in terms of maximizing the expected utility of treatment or responder probability, are presented. The optimality criteria require models for both beneficial and adverse effects that are part of the utility definition and published population models describing those effects for oxybutynin (urge urinary incontinence episodes per week and severity of dry mouth, respectively) were used for illustration. Dosing strategies with two dosing categories were defined in terms of sizes of the daily doses (low and high dose) and the proportion of patients that can be expected to be preferentially treated at the low dose level. Utility and responder definitions were varied to investigate the influence on the resulting dosing strategy. By minimizing a risk function, describing the seriousness of deviations from the predefined target, optimal dosing strategies were estimated using mixture models in NONMEM. The estimated dose ranges for oxybutynin were similar to those recommended. The optimal individualization conditions were dependent on the definitions of responder and utility. The predicted gain of individualization given utility and responder definitions used was greater, when a responder criteria was maximized compared with maximizing utility.

Changes in the defined daily dose; CYP2D6/CYP3A metabolism as an indicator for dose-setting problems

OBJECTIVE

Interindividual variability is common at all stages of drug absorption, distribution, pharmacodynamics, metabolism and elimination. In this study, we focused on two enzymes involved in phase-I drug metabolism as markers of pharmacological variability: the CYP3A and CYP2D6 subsystems of cytochrome P450. The main aim of our study was to determine whether substrate drugs for CYP2D6 and/or CYP3A enzymes, showing high interindividual matabolic variability, are more prone to postmarketing adjustments of defined daily dose (DDD).

METHODS

A case-control design was used. We identified all DDD changes between 1982 and May 2004 through the website of the WHO Collaborating Centre for Drug Statistics Methodology. Cases were drugs with a DDD change and controls were other drugs with unchanged DDDs. Information about metabolism pathway, introduction year, literature exposure and administration route was retrieved.

RESULTS

We included 88 cases and 176 controls. Of the 88 cases, 51 were dosage decreases (58.0%). Overall, DDD changes were not associated with CYP2D6/CYP3A metabolism (OR 1.92; 95%CI 0.78-4.72). However, DDD decreases were associated with CYP2D6/CYP3A metabolism (OR 3.21; 95%CI 1.25-8.26). Adjusting for introduction year weakened this effect (OR 2.78; 95%CI 0.98-7.90).

CONCLUSION

Our study indicates that CYP2D6 and CYP3A substrates are more likely to require a DDD decrease after granting of market authorisation. However, this effect was diminished by adjusting for period of introduction. The implication of this finding is that variability indicators, as is demonstrated in this study for CYP2D6/CYP3A metabolism, can exert their influence on a wide variety of drug measures, such as the DDD.

Beyond the Evidence of the New Hypertension Guidelines. Blood pressure measurement - is it good enough for accurate diagnosis of hypertension? Time might be in, for a paradigm shift (I)

Despite widespread availability of a large body of evidence in the area of hypertension, the translation of that evidence into viable recommendations aimed at improving the quality of health care is very difficult, sometimes to the point of questionable acceptability and overall credibility of the guidelines advocating those recommendations.

The scientific community world-wide and especially professionals interested in the topic of hypertension are witnessing currently an unprecedented debate over the issue of appropriateness of using different drugs/drug classes for the treatment of hypertension. An endless supply of recent and less recent "drug-news", some in support of, others against the current guidelines, justifying the use of selected types of drug treatment or criticising other, are coming out in the scientific literature on an almost weekly basis. The latest of such debate (at the time of writing this paper) pertains the safety profile of ARBs vs ACE inhibitors.

To great extent, the factual situation has been fuelled by the new hypertension guidelines (different for USA, Europe, New Zeeland and UK) through, apparently small inconsistencies and conflicting messages, that might have generated substantial and perpetuating confusion among both prescribing physicians and their patients, regardless of their country of origin.

The overwhelming message conveyed by most guidelines and opinion leaders is the widespread use of diuretics as first-line agents in all patients with blood pressure above a certain cut-off level and the increasingly aggressive approach towards diagnosis and treatment of hypertension. This, apparently well-justified, logical and easily comprehensible message is unfortunately miss-obeyed by most physicians, on both parts of the Atlantic.

Amazingly, the message assumes a universal simplicity of both diagnosis and treatment of hypertension, while ignoring several hypertension-specific variables, commonly known to have high level of complexity, such as:

- accuracy of recorded blood pressure and the great inter-observer variability,

- diversity in the competency and training of diagnosing physician,

- individual patient/disease profile with highly subjective preferences,

- difficulty in reaching consensus among opinion leaders,

- pharmaceutical industry's influence, and, nonetheless,

- the large variability in the efficacy and safety of the antihypertensive drugs.

The present 2-series article attempts to identify and review possible causes that might have, at least in part, generated the current healthcare anachronism (I); to highlight the current trend to account for the uncertainties related to the fixed blood pressure cut-off point and the possible solutions to improve accuracy of diagnosis and treatment of hypertension (II).

Patient adherence to prescribed antimicrobial drug dosing regimens

The aim of this article is to review current knowledge about the clinical impact of patients' variable adherence to prescribed anti-infective drug dosing regimens, with the aim of renewing interest and exploration of this important but largely neglected area of therapeutics. Central to the estimation of a patient's adherence to a prescribed drug regimen is a reliably compiled drug dosing history. Electronic monitoring methods have emerged as the virtual 'gold standard' for compiling drug dosing histories in ambulatory patients. Reliably compiled drug dosing histories are consistently downwardly skewed, with varying degrees of under-dosing. In particular, the consideration of time intervals between protease inhibitor doses has revealed that ambulatory patients' variable execution of prescribed dosing regimens is a leading source of variance in viral response. Such analyses reveal the need for a new discipline, called pharmionics, which is the study of how ambulatory patients use prescription drugs. Properly analysed, reliable data on the time-course of patients' actual intake of prescription drugs can eliminate a major source of unallocated variance in drug responses, including the non-response that occurs and is easily misinterpreted when a patient's complete non-execution of a prescribed drug regimen is unrecognized clinically. As such, reliable compilation of ambulatory patients' drug dosing histories has the promise of being a key step in reducing unallocated variance in drug response and in improving the informational yield of clinical trials. It is also the basis for sound, measurement-guided steps taken to improve a patient's execution of a prescribed dosing regimen.

Clinical Pharmacology

The dose of a drug is a major determinant of its safety, and establishing a safe dose of a novel drug is a prime objective during clinical development. The design of pre-marketing clinical trials precludes the representation of important subpopulations such as children, the elderly and people with co-morbidities. Therefore, postmarketing surveillance (PMS) activities are required to monitor the safety profile of drugs in real clinical practice. Furthermore, individual variations in pharmacogenetic profiles, the immune system, drug metabolic pathways and drug-drug interactions are also important factors in the occurrence of adverse drug reactions. Thus, the safety of a drug is a major clinical consideration before and after it is marketed. A multidisciplinary approach is required to enhance the safety profile of drugs at all stages of development, including PMS activities. Clinical pharmacology encompasses a range of disciplines and forms the backbone of drug safety consideration during clinical drug development. In this review we give an overview of the clinical drug development process and consider its limitations. We present a discussion of several aspects of clinical pharmacology and their application to enhancing drug safety. Pharmacokinetic-pharmacodynamic modelling provides a method of predicting a clinically safe dose; consideration of drug pharmacokinetics in special populations may enhance safe therapeutics in a wider spectrum of patients, while pharmacogenetics provides the possibility of genotype-specific therapeutics. Pharmacovigilance activities are also discussed. Given the complex nature and unpredictability of type B reactions, PMS activities are crucial in managing the risks drugs pose to the general population. The various aspects of clinical pharmacology discussed make a strong case for this field as the backbone of optimising and promoting safe development and use of drugs.