Population pharmacokinetics and association between A77 1726 plasma concentrations and disease activity measures following administration of leflunomide to people with rheumatoid arthritis

AIMS

To investigate the concentration-effect relationship and pharmacokinetics of leflunomide in patients with rheumatoid arthritis (RA).

METHODS

Data were collected from 23 RA patients on leflunomide therapy (as sole disease modifying antirheumatic drug (DMARD)) for at least 3 months. Main measures were A77 1726 (active metabolite of leflunomide) plasma concentrations and disease activity measures including pain, duration/intensity of morning stiffness, and SF-36 survey. A population estimate was sought for apparent clearance (CL/F) and volume of distribution was fixed (0.155 l kg(-1)). Factors screened for influence on CL/F were weight, age, gender and estimated creatinine clearance.

RESULTS

Significantly higher A77 1726 concentrations were seen in patients with less swollen joints and with higher SF-36 mental summary scores than in those with measures indicating more active disease (P < 0.05); concentration-effect trends were seen with five other disease activity measures. Statistical analysis of all disease activity measures showed that mean A77 1726 concentrations in groups with greater control of disease activity were significantly higher than those in whom the measures indicated less desirable control (P < 0.05). There was large between subject variability in the dose-concentration relationship. A steady-state infusion model best described the pharmacokinetic data. Inclusion of age as a covariate decreased interindividual variability (P < 0.01), but this would not be clinically important in terms of dosage changes. Final parameter estimate (% CV interindividual variability) for CL/F was 0.0184 l h(-1) (50%) (95% CI 0.0146, 0.0222). Residual (unexplained) variability (% CV) was 8.5%.

CONCLUSIONS

This study of leflunomide in patients using the drug clinically indicated a concentration-effect relationship. From our data, a plasma A77 1726 concentration of 50 mg l(-1) is more likely to indicate someone with less active disease than is a concentration around 30 mg l(-1). The marked variability in pharmacokinetics suggests a place for individualized dosing of leflunomide in RA therapy.

Drug utilization review across jurisdictions – a reality or still a distant dream?

OBJECTIVE

There is a perception that many drug usage evaluations do not widely influence prescribing behaviour. The aim of this study was to critically evaluate recent journal articles which fit the Medline definition for Drug Utilization Review (DUR) and which also cover multiple healthcare sites.

METHODS

PubMed (National Library of Medicine, NLM) (2003, 2004) was searched using the MeSH topic 'drug utilization'. Retrieved studies were evaluated to ascertain those describing a DUR (measuring drug use against specific criteria). These were subdivided according to whether the DUR was conducted at one site or across many. The multi-centre DURs were critically reviewed, including evaluating whether all phases of a quality cycle were completed and determining aspects of design such as whether the study was prospective or retrospective, any interventions conducted and provision of feedback.

RESULTS

A total of 646 unique articles were retrieved. Of these, 495 (77%) did not meet the definition for DUR, while 151 (23%) articles did. Thirty-five (5%) described English language multi-centre DURs; ethics approval was obtained in ten of these and 18 were carried out retrospectively. In all 35 studies some comparator or standard was used, but only eight conducted an intervention and only three provided feedback to the prescribers.

CONCLUSION

Most DURs were not conducted across a number of centres. Of the recent published multi-centre DURs most presented only an initial audit and did not complete the quality cycle with feedback, intervention and re-audit. To widely influence prescribing behaviour, the full cycle is required with involvement of as many sites as possible to achieve improvements across many jurisdictions.

Changes in use of disease-modifying anti-rheumatic drugs in Australia over the period 1992–2004

PURPOSE

Evidence is growing that early use of disease-modifying anti-rheumatic drugs (DMARDs) and combinations of these drugs provide optimal care for people with rheumatoid arthirits. The aim of this study was to describe objectively the pattern of consumption of DMARDs in the Australian community (community-based prescribing, specialist and general practitioner) 1992-2004, and to compare this with prescribing patterns reported in other countries.

METHOD

Dispensing statistics from the Pharmaceutical Benefit Scheme (PBS-Australia's universal prescription subsidy scheme) were analysed and temporal trends evaluated. Drug consumption was calculated as the number of dispensed defined daily doses (DDD)/1000 inhabitants/day (WHO ATC/DDD classification 2005).

RESULTS

The consumption of DMARDs in the Australian community increased steadily from 2.6 DDD/1000 inhabitants/day in 1992 to 5.5 DDD/1000 inhabitants/day. Over the period 1992-2004, methotrexate (MTX) was the most commonly used DMARD (from 0.6 to 3.0 DDD/1000 inhabitants/day). Consumption of gold (parenteral and oral) and penicillamine declined during this time. The inclusion of leflunomide on the PBS in 2000 contributed to the increase in DMARD usage.

CONCLUSION

Use of DMARDs within the Australian community has increased in recent years, coinciding with the change in guidelines for therapy for rheumatoid arthritis (RA) to earlier use of DMARDs and the more common use of combinations. This study used DDD methodology to quantify trends for DMARD consumption and these trends are broadly consistent with international prescribing patterns assessed using different methodologies.

Consumer involvement in Quality Use of Medicines (QUM) projects - lessons from Australia

Background

It is essential that knowledge gained through health services research is collated and made available for evaluation, for policy purposes and to enable collaboration between people working in similar areas (capacity building). The Australian Quality Use of Medicine (QUM) on-line, web-based project database, known as the QUMmap, was designed to meet these needs for a specific sub-section of health services research related to improving the use of medicines. Australia's National Strategy for Quality Use of Medicines identifies the primacy of consumers as a major principle for quality use of medicines, and aims to support consumer led research. The aim of this study was to determine how consumers as a group have been represented in QUM projects in Australia. A secondary aim was to investigate how the projects with consumer involvement fit into Australia's QUM policy framework.

Method

Using the web-based QUMmap, all projects which claimed consumer involvement were identified and stratified into four categories, projects undertaken by; (a) consumers for consumers, (b) health professionals for consumers, (c) health professionals for health professionals, and (d) other. Projects in the first two categories were then classified according to the policy 'building blocks' considered necessary to achieve QUM.

Results

Of the 143 'consumer' projects identified, the majority stated to be 'for consumers' were either actually by health professionals for health professionals (c) or by health professionals for consumers (b) (47% and 40% respectively). Only 12 projects (9%) were directly undertaken by consumers or consumer groups for consumers (a). The majority of the health professionals for consumers (b) projects were directed at the provision of services and interventions, but were not focusing on the education, training or skill development of consumers.

Conclusion

Health services research relating to QUM is active in Australia and the projects are collated and searchable on the web-based interactive QUMmap. Healthcare professionals appear to be dominating nominally 'consumer focussed' research, with less than half of these projects actively involving the consumers or directly benefiting consumers. The QUMmap provides a valuable tool for policy analysis and for provision of future directions through identification of QUM initiatives.

Impact of mycophenolate mofetil loading on drug exposure in the early posttransplant period

Achieving adequate therapeutic levels of immunosuppressive medications is important in rejection prevention. This study examined exposure to mycophenolic acid (MPA) in kidney transplant patients within the first 5 days posttransplantation.

METHODS

This single-center, nonrandomized study of first solitary kidney allograft recipients receiving cyclosporine (n = 116) or tacrolimus (n = 50) included patients who received either 1 g or 1.5 g of mycophenolate mofetil twice daily starting postoperatively. Exposure to MPA was measured at days 3 and 5 posttransplant using published limited sampling time equations.

RESULTS

There were no significant differences in exposure in the cyclosporine-treated patients receiving 3-g (n = 22) compared to 2-g (n = 94) daily doses (AUC([0-12]) 33.8 +/- 10.0 mg*h/L versus 30.1 +/- 9.7 mg*h/L, P = .20, respectively). About half the patients in both groups had AUC([0-12]) <30 mg*h/L on days 3 and 5 posttransplant. On the other hand, there was significantly greater exposure on day 3 in the tacrolimus-treated patients receiving 3 g (n = 21) compared to 2 g (n = 29) daily (AUC([0-12]) 43.1 +/- 9.0 mg*h/L versus 36.8 +/- 11.1 mg*h/L, P = .016, respectively). On day 3 one (4.8%) patient receiving 3 g had an AUC([0-12]) of <30 mg*h/L; whereas, eight (27.5%) receiving 2 g were below this level (P = .068). The AUC([0-12]) levels were not different on day 5.

CONCLUSIONS

Loading with higher doses of mycophenolate mofetil results in greater exposure and a trend toward more patients in the therapeutic window within the first week for tacrolimus- but not for cyclosporine-treated patients.

Motivations and perceived influences on rural and urban general practitioners when prescribing conventional non-steroidal anti-inflammatory drugs or COX-2 inhibitors

BACKGROUND AND OBJECTIVE

Prescribers in rural and remote locations perceive that there are different influences on their prescribing compared with those experienced by urban prescribers. The aim of this study was to compare the motivations and perceived influences on general practitioners (GPs) when prescribing COX-2 inhibitors rather than conventional non-steroidal anti-inflammatory drugs (NSAIDs) between rural and urban-based GPs in Queensland, Australia.

METHODS

A questionnaire was administered to two geographically distinct groups of GPs, one urban (n=67) and one rural (n=67), investigating the reasons that the GP would prescribe a COX-2 inhibitor rather than a conventional NSAID or vice versa and also focusing on patients requesting a prescription for a COX-2 inhibitor.

RESULTS AND DISCUSSION

A 51% response rate (n=68) was achieved. The difference between the rural and the urban GPs was that the urban GPs were more likely to perceive that they were influenced to prescribe COX-2 inhibitors by their patients' knowledge of these new (at the time) drugs. GPs in both the rural and urban areas perceived the COX-2 selective inhibitors to be safer than conventional NSAIDs, and that there was little difference in terms of efficacy between the two drug classes. However, GPs from both of the study areas stated that conventional NSAIDs were preferred over COX-2 selective inhibitors, primarily due to their expense, if their patients were not at risk for developing a GI bleed.

CONCLUSION

The motivations and perceived influences to prescribe a COX-2 inhibitor in rural and in urban areas of Queensland, Australia were very similar. Almost all surveyed GPs in rural and urban areas had patients request a prescription, or enquire about the COX-2 inhibitors. Urban GPs were more likely to feel pressured to prescribe a COX-2 inhibitor than their rural counterparts, agreeing with other research which found that patient pressure to prescribe appears to be greater in urban general practice.

Population pharmacokinetics of mycophenolic acid during the first week after renal transplantation

OBJECTIVE

To investigate the population pharmacokinetics of mycophenolic acid (MPA) in adult kidney transplant recipients during the crucial first week after transplantation.

METHODS

Data were collected from 117 patients. MPA plasma concentrations were determined at t=0, 1, 2, 3 and 4 h after mycophenolate mofetil dosing on days 3, 5 and 7. Population analysis was performed using NONMEM. Covariates screened were sex, age, body weight, serum creatinine, creatinine clearance, serum albumin, days of therapy, diabetes mellitus, organ source (live or cadaveric) and co-therapy (tacrolimus or cyclosporine). Final model validity was evaluated using 200 boot strapped samples from the original data. Bias and precision were determined through comparison of observed and predicted concentrations.

RESULTS

Individual concentration-time profiles showed evidence of an absorption lag time and enterohepatic recirculation of MPA in some patients on some occasions. The best base model had bi-exponential elimination with a typical population (SE%) apparent clearance (CL/F) of 29 l/h (5%) and apparent volume of the central compartment of 65 l (7%). CL/F decreased significantly with increasing serum albumin (1.42 l/h reduction in total plasma CL/F with each 1 g/l increase in albumin) and was 27% greater in patients receiving cyclosporine than in those receiving tacrolimus. Evaluation of the final model showed close agreement between pairs of boot strapped and final model parameter estimates (all differences <7%). Predictions were non-biased (0.11 mg/l) but imprecise (2.8 mg/l).

CONCLUSION

Population pharmacokinetic parameters for MPA were determined. These can be used to achieve specific target MPA concentrations or areas under the concentration-time curve.

Quantifying the use of the statin antilipemic drugs: comparisons and contrasts between Nova Scotia, Canada, and Queensland, Australia

BACKGROUND

Jurisdictions are developing public drug insurance systems to improve access to pharmaceuticals, cost-effective prescribing, and patient health and well-being. We compared 2 jurisdictions with different pharmaceutical policies to determine prescribing patterns for 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (ie, statins).

OBJECTIVE

The aim of this work was to investigate the feasibility of using available prescription administrative databases to compare the use of statins in Queensland, Australia, and in Nova Scotia, Canada.

METHODS

Data from the Nova Scotia Pharmacare Program and the Health Insurance Commission in Australia were used to obtain dispensing data. Utilization was compared for the 5-year period from 1997 through 2001, using the World Health Organization anatomic therapeutic chemical/defined daily dose (DDD) system.

RESULTS

In the year 2001, there were 177,000 beneficiaries in the public drug plan in Nova Scotia (62% aged > or = 65 years old) and 960,000 concession beneficiaries (pensioners and social security recipients, 61 aged > or = 65 years) in Queensland. These 2 groups were comparable. The overall utilization of statin medications increased steadily in both areas over the study period, from 50 to 205 DDD/1000 beneficiaries per day. Comparison of the 2 growth lines showed no statistically significant differences in overall statin use despite differences in brand availabilities and policies about prescribing. In the year 2001, atorvastatin was the most commonly prescribed statin in both areas, comprising 46% of statin use in Nova Scotia and 51% in Queensland. Mean doses of each statin prescribed were slightly above the DDDs. Expenditure on statins per 1000 beneficiaries and per DDD were similar in each jurisdiction, being slightly higher in Nova Scotia.

CONCLUSIONS

Despite differences in pharmaceutical reimbursement systems, use of the statins was similar in Nova Scotia and Queensland. The feasibility of the methodology was demonstrated. Future studies, including comparisons of drug utilization for other classes of drugs for which drug policies may be divergent (eg, different pricing structures or prior authorization requirements), or for which less evidence for appropriate use is available, may be useful.

Mycophenolic acid pharmacokinetics and related outcomes early after renal transplant

AIMS

The pharmacokinetics of mycophenolic acid and its glucuronide are complex. This study investigated the pharmacokinetics, pharmacodynamics and protein binding of mycophenolic acid and its glucuronide metabolite, early post-transplant in renal allograft recipients.

METHODS

Forty-two de novo renal transplant recipients receiving mycophenolate mofetil and concomitant cyclosporin (n = 32) or tacrolimus (n = 10) participated in the study. Blood samples were taken on day 5 post-transplant for measurement of free and total concentrations of mycophenolic acid, mycophenolic acid glucuronide and relevant biochemistry. Associations between free fraction and biochemistry were investigated. Free and total 6-h area under the concentration-time curve (AUC0-6) of mycophenolic acid was assessed relative to clinical outcomes in the first month post-transplant.

RESULTS

Kinetic variability of free and total mycophenolic acid and its glucuronide was greater in patients on cyclosporin (12- to 18-fold variation) than on tacrolimus (four- to fivefold) cotherapy. Cyclosporin-treated patients also had significantly lower predose total mycophenolic acid concentrations than tacrolimus-treated patients (median 0.8 mg l(-1) and 1.6 mg l(-1), respectively, P = 0.002). Mycophenolic acid glucuronide predose concentration correlated positively with mycophenolic acid glucuronide AUC0-6 (r > 0.95). Mycophenolic acid free fraction varied 11-fold, from 1.6% to 18.3%, whilst the glucuronide free fraction varied threefold, from 17.4% to 54.1%. Urea and creatinine concentrations correlated positively (r > 0.46), whilst albumin correlated negatively (r = -0.54) with free fraction of mycophenolic acid. Similar relationships were found for the free fraction of mycophenolic acid glucuronide. Mycophenolic acid free fraction was on average 70% higher in patients with albumin concentrations below a specified albumin cut-off concentration of 31 g l(-1)[free fraction = 7 +/- 4% for lower albumin and 4 +/- 3% for higher albumin, respectively; P = 0.001; 95% confidence interval (CI) for the difference 1.9, 4.2]. Neither free nor total mycophenolic acid AUC0-6 was related to rejection (P > 0.07). Free AUC0-6 was significantly higher in those patients with thrombocytopenic, leukopenic and/or infectious outcomes than in those without (mean +/- SD 1.9 +/- 0.3 mg h(-1) l(-1) and 1.1 +/- 0.1 mg h(-1) l(-1), P = 0.0043; 95% CI for the difference 0.3, 1.4).

CONCLUSIONS

The marked variability in mycophenolic acid/glucuronide pharmacokinetics occurring early post-transplant during the current study was greater in cyclosporin (12-18-fold) than in tacrolimus (four- to fivefold) treated patients. Concomitant cyclosporin was associated with total mycophenolic acid concentrations approximately half that of tacrolimus. Patients with marked renal impairment had the highest free fractions reported to date. The exposure to unbound mycophenolic acid was significantly related to infections and haematological toxicity.

Medication management reviews for people from the former Yugoslavia now resident in Australia

AIM

The objective of this prospective study was to conduct medication management reviews (MMR) in people from a non-English speaking background (NESB) (Bosnian/Serbian/Croatian, from former Yugoslavia, currently residing in Australia) in their native language in order to identify medication-related problems (needs analysis) and implement appropriate therapeutic interventions, in collaboration with their general practitioners (GPs).

METHODS

Twenty-five participants entered the study. Each was interviewed and medication-related issues were identified by the health care team.

RESULTS

Various interventions (over 150 for the whole group, an average of 6 per participant), based on actual and potential medication-related problems, were designed to improve the use of medicines. The MMRs introduced effective changes into the participants' health care. Psychological (e.g., feeling depressed) and sociological factors (e.g., costs of medicines, not understanding labels written in English) were identified as having significant impacts on medication management.

CONCLUSIONS

These data confirmed there are avoidable medication-related problems in people from a NESB. GPs and pharmacists working in health care teams with a trained interpreter could greatly improve medication use through regular review and a team approach to problem identification and solving.

Original Article. Do rural consumers expect a prescription from their GP visit? Investigation of patients' expectations for a prescription and doctors' prescribing decisions in rural Australia

OBJECTIVE

To assess patients' expectation for receiving a prescription and GPs' perceptions of patient expectation for a prescription.

DESIGN

Matched questionnaire study completed by patients and GPs.

SETTING

Seven general practices in rural Queensland, Australia.

SUBJECTS

The subjects were 481 patients consulting 17 GPs.

MAIN OUTCOME MEASURES

Patients' expectation for receiving a prescription and GPs' perceptions of patients' expectation.

RESULTS

Ideal expectation (hope) for a prescription was expressed by 57% (274/481) of patients. Sixty-six per cent (313/481) thought it was likely that the doctor would actually give them a prescription. Doctors accurately predicted hope or lack of hope for a prescription in 65% (314/481) of consultations, but were inaccurate in 19% (93/481). A prescription was written in 55% of consultations. No increase in patients' expectation, doctors' perceptions of expectation, or decision to prescribe were detected for patients living a greater distance from the doctors.

CONCLUSIONS

Rural patients demonstrated similar rates of hope for a prescription to those found in previous urban studies. Rural doctors seem to be similarly 'accurate' and 'inaccurate' in determining patients' expectations. Rates of prescribing were comparable to urban rates. Distance was not found to increase the level of patient expectation, affect the doctors' perception or to influence the decision to prescribe.

Uptake of new drugs in rural and urban areas of Queensland, Australia: the example of COX-2 inhibitors

OBJECTIVE

This study compared the changes over time in the volume of prescriptions of COX-2 selective inhibitors between rural and urban Queensland to reveal any difference in the uptake of the prescribing of these new drugs between two geographically distinct areas.

METHODS

This study used data from an administrative claims database. Dispensing data were obtained for celecoxib and rofecoxib in two areas, one rural and one urban, defined by postcodes. The numbers of consumers in these areas were similar and they were served by similar numbers of general practitioners. The number of defined daily doses (DDDs) of celecoxib and rofecoxib dispensed at specific times was calculated.

RESULTS

Statistical analysis revealed no significant difference between the total numbers of DDDs of COX-2-selective non-steroidal anti-inflammatory drugs dispensed in the rural and urban groups over the period August 2000 to December 2002 (P=0.81). The rate of uptake of usage was also clearly similar between the urban and the rural groups. Total usage peaked in August 2000 in both groups (urban 39 DDD/1,000 people per day; rural 37 DDD/1,000 people per day), coinciding with the pharmaceutical benefits scheme (subsidized) listing of celecoxib. The number of DDDs declined dramatically in the following month, and then peaked again in May 2002 (urban 34, rural 36). The number of DDDs then steadily decreased in both areas after October 2002.

CONCLUSION

The results suggest that the marketing of the new COX-2 inhibitors and the patients' anticipation of a safe and effective treatment have overcome the geographical boundaries of Queensland. Both areas had very high rates of uptake of the prescribing of these new drugs.

Pharmacokinetic Considerations Relating to Tacrolimus Dosing in the Elderly

Relaxation of the upper age limits for solid organ transplantation coupled with improvements in post-transplant survival have resulted in greater numbers of elderly patients receiving immunosuppressant drugs such as tacrolimus. Tacrolimus is a potent agent with a narrow therapeutic window and large inter- and intraindividual pharmacokinetic variability. Numerous physiological changes occur with aging that could potentially affect the pharmacokinetics of tacrolimus and, hence, patient dosage requirements. Tacrolimus is primarily metabolised by cytochrome P450 (CYP) 3A enzymes in the gut wall and liver. It is also a substrate for P-glycoprotein, which counter-transports diffused tacrolimus out of intestinal cells and back into the gut lumen. Age-associated alterations in CYP 3A and P-glycoprotein expression and/or activity, along with liver mass and body composition changes, would be expected to affect the pharmacokinetics of tacrolimus in the elderly. However, interindividual variation in these processes may mask any changes caused by aging. More investigation is needed into the impact aging has on CYP and P-glycoprotein activity and expression. No single-dose, intense blood-sampling study has specifically compared the pharmacokinetics of tacrolimus across different patient age groups. However, five population pharmacokinetic studies, one in kidney, one in bone marrow and three in liver transplant recipients, have investigated age as a co-variate. None found a significant influence for age on tacrolimus bioavailability, volume of distribution or clearance. The number of elderly patients included in each study, however, was not documented and may have been only small. It is likely that inter- and intraindividual pharmacokinetic variability associated with tacrolimus increase in elderly populations. In addition to pharmacokinetic differences, donor organ viability, multiple co-morbidity, polypharmacy and immunological changes need to be considered when using tacrolimus in the elderly. Aging is associated with decreased immunoresponsiveness, a slower body repair process and increased drug adverse effects. Elderly liver and kidney transplant recipients are more likely to develop new-onset diabetes mellitus than younger patients. Elderly transplant recipients exhibit higher mortality from infectious and cardiovascular causes than younger patients but may be less likely to develop acute rejection. Elderly kidney recipients have a higher potential for chronic allograft nephropathy, and a single rejection episode can be more devastating. There is a paucity of information on optimal tacrolimus dosage and target trough concentration in the elderly. The therapeutic window for tacrolimus concentrations may be narrower. Further integrated pharmacokinetic-pharmacodynamic studies of tacrolimus are required. It would appear reasonable, based on current knowledge, to commence tacrolimus at similar doses as those used in younger patients. Maintenance dose requirements over the longer term may be lower in the elderly, but the increased variability in kinetics and the variety of factors that impact on dosage suggest that patient care needs to be based around more frequent monitoring in this age group.

Perceptions around concordance--focus groups and semi-structured interviews conducted with consumers, pharmacists and general practitioners

BACKGROUND

Achieving concordance by identifying beliefs about illness, treatment and medicine-taking should impact positively on behaviour and consumer satisfaction with respect to treatment, and health outcomes may be improved.

OBJECTIVE

To explore, in the Australian context, beliefs and expectations of general practitioners (GPs), consumers and pharmacists in relation to concordance to allow further exploration of the implementation of principles of concordance in Australia.

DESIGN

Qualitative analysis of focus group and semi-structured interview data.

SETTING AND PARTICIPANTS

Focus groups were held with seven consumers and nine pharmacists and, in-depth, semi-structured interviews were held with 10 GPs between February and May 2003, in Brisbane (Australia).

RESULTS

This explorative study identified a variety of issues. Consumers expressed the need for more input from health professionals - being given more information on their treatments and conditions, more time spent in discussion, and establishing a system where harmonious relationships between health professionals could take place, which would result in a more consumer-friendly health care system. The main issues voiced by the pharmacists were about the idea of organizing the health care system in a way that would accommodate more quality information sharing between all partners. GPs' issues included better and unlimited information-sharing, having more time to promote quality in health care and receiving remuneration for increased verbal contact with other health care professionals. Suggestions were made about ways to achieve concordance by improved information-sharing and shared decision-making.

CONCLUSION

The data from this study will lead to the development of models to explore and attempt to incorporate principles of concordance in Australian pharmacy and medical practice.

Vancomycin pharmacokinetics in critically ill patients receiving continuous venovenous haemodiafiltration

AIMS

To investigate the pharmacokinetics of vancomycin in critically ill patients on continuous venovenous haemodiafiltration (CVVHDF), a continuous renal replacement therapy (CRRT) and to see if routine measures approximate vancomycin clearance.

METHODS

Pharmacokinetic profiles (15) of initial and steady-state doses of 750 mg twice daily intravenous vancomycin were obtained from blood and ultrafiltrate samples from 10 critically ill patients in the intensive care unit, with acute renal failure on CVVHDF (1 l h(-1) dialysate plus 2 l h(-1) filtration solution; 3 l h(-1) effluent; extracorporeal blood flow 200 ml min(-1)).

RESULTS

CVVHDF clearance of vancomycin was 1.8 +/- 0.4 l h(-1) (30 +/- 6.7 ml min(-1)). This was 1.3-7.2 times that reported previously for vancomycin using other forms of CRRT. Total vancomycin body clearance was 2.5 +/- 0.7 l h(-1) (41.7 +/- 11.7 ml min(-1)). The clearance of vancomycin by CVVHDF was 76 +/- 16.5% of the total body clearance. CVVHDF removed approximately half the vancomycin dose during the 12-h period (A(CVVHDF) = 413 mg). The fraction eliminated by all routes was 60%. The sieving coefficient for vancomycin was 0.7 +/- 0.1 and for urea was 0.8 +/- 0.06.

CONCLUSIONS

Vancomycin is cleared effectively by CVVHDF. Clearance was faster than other forms of CRRT, therefore doses need to be relatively high. Urea clearance slightly overestimates vancomycin clearance. The administered doses of 750 mg every 12 h were too high and accumulation occurred, as only approximately 60% of a dose was cleared over this period. The maintenance dose required to achieve a target average steady-state plasma concentration of 15 mg l(-1) can be calculated as 450 mg every 12 h.

Sampling Times for Monitoring Tacrolimus in Stable Adult Liver Transplant Recipients

The aim of this study was to determine the most informative sampling time(s) providing a precise prediction of tacrolimus area under the concentration-time curve (AUC). Fifty-four concentration-time profiles of tacrolimus from 31 adult liver transplant recipients were analyzed. Each profile contained 5 tacrolimus whole-blood concentrations (predose and 1, 2, 4, and 6 or 8 hours postdose), measured using liquid chromatography-tandem mass spectrometry. The concentration at 6 hours was interpolated for each profile, and 54 values of AUC(0-6) were calculated using the trapezoidal rule. The best sampling times were then determined using limited sampling strategies and sensitivity analysis. Linear mixed-effects modeling was performed to estimate regression coefficients of equations incorporating each concentration-time point (C0, C1, C2, C4, interpolated C5, and interpolated C6) as a predictor of AUC(0-6). Predictive performance was evaluated by assessment of the mean error (ME) and root mean square error (RMSE). Limited sampling strategy (LSS) equations with C2, C4, and C5 provided similar results for prediction of AUC(0-6) (R2 = 0.869, 0.844, and 0.832, respectively). These 3 time points were superior to C0 in the prediction of AUC. The ME was similar for all time points; the RMSE was smallest for C2, C4, and C5. The highest sensitivity index was determined to be 4.9 hours postdose at steady state, suggesting that this time point provides the most information about the AUC(0-12). The results from limited sampling strategies and sensitivity analysis supported the use of a single blood sample at 5 hours postdose as a predictor of both AUC(0-6) and AUC(0-12). A jackknife procedure was used to evaluate the predictive performance of the model, and this demonstrated that collecting a sample at 5 hours after dosing could be considered as the optimal sampling time for predicting AUC(0-6).

Clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplantation

The aim of this review is to analyse critically the recent literature on the clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplant recipients. Dosage and target concentration recommendations for tacrolimus vary from centre to centre, and large pharmacokinetic variability makes it difficult to predict what concentration will be achieved with a particular dose or dosage change. Therapeutic ranges have not been based on statistical approaches. The majority of pharmacokinetic studies have involved intense blood sampling in small homogeneous groups in the immediate post-transplant period. Most have used nonspecific immunoassays and provide little information on pharmacokinetic variability. Demographic investigations seeking correlations between pharmacokinetic parameters and patient factors have generally looked at one covariate at a time and have involved small patient numbers. Factors reported to influence the pharmacokinetics of tacrolimus include the patient group studied, hepatic dysfunction, hepatitis C status, time after transplantation, patient age, donor liver characteristics, recipient race, haematocrit and albumin concentrations, diurnal rhythm, food administration, corticosteroid dosage, diarrhoea and cytochrome P450 (CYP) isoenzyme and P-glycoprotein expression. Population analyses are adding to our understanding of the pharmacokinetics of tacrolimus, but such investigations are still in their infancy. A significant proportion of model variability remains unexplained. Population modelling and Bayesian forecasting may be improved if CYP isoenzymes and/or P-glycoprotein expression could be considered as covariates. Reports have been conflicting as to whether low tacrolimus trough concentrations are related to rejection. Several studies have demonstrated a correlation between high trough concentrations and toxicity, particularly nephrotoxicity. The best predictor of pharmacological effect may be drug concentrations in the transplanted organ itself. Researchers have started to question current reliance on trough measurement during therapeutic drug monitoring, with instances of toxicity and rejection occurring when trough concentrations are within 'acceptable' ranges. The correlation between blood concentration and drug exposure can be improved by use of non-trough timepoints. However, controversy exists as to whether this will provide any great benefit, given the added complexity in monitoring. Investigators are now attempting to quantify the pharmacological effects of tacrolimus on immune cells through assays that measure in vivo calcineurin inhibition and markers of immunosuppression such as cytokine concentration. To date, no studies have correlated pharmacodynamic marker assay results with immunosuppressive efficacy, as determined by allograft outcome, or investigated the relationship between calcineurin inhibition and drug adverse effects. Little is known about the magnitude of the pharmacodynamic variability of tacrolimus.

Free Mycophenolic Acid Should Be Monitored in Renal Transplant Recipients with Hypoalbuminemia

The current approach for therapeutic drug monitoring in renal transplant recipients receiving mycophenolate mofetil (MMF) is measurement of total mycophenolic acid (MPA) concentration. Because MPA is highly bound, during hypoalbuminemia the total concentration no longer reflects the free (pharmacologically active) concentration. The authors investigated what degree of hypoalbuminemia causes a significant change in protein binding and thus percentage free MPA. Forty-two renal transplant recipients were recruited for the study. Free and total concentrations of MPA (predose, and 1, 3, and 6 hours post-MMF dose samples) and plasma albumin concentrations were determined on day 5 posttransplantation. Six-hour area under the concentration-time curve (AUC(0-6)) values were calculated for free and total MPA, and percentage free MPA was determined for each patient. The authors found a significant relationship between low albumin concentrations and increased percentage free MPA (Spearman correlation = -0.54, P < 0.0001). Receiver operating characteristic (ROC) curve analysis was performed on the albumin versus percentage free MPA data. The cutoff value of albumin determined from the ROC analysis that differentiated normal from elevated percentage free MPA (defined as > or = 3%) in this patient population was 31 g/L. At this cutoff value albumin was found to be a good predictor of altered free MPA percentage, with a sensitivity and specificity of 0.75 and 0.80, respectively, and an area under the ROC curve of 0.79. To rationalize MMF dosing regimens in hypoalbuminemic patients (plasma albumin < or = 31 g/L), clinicians should consider monitoring the free MPA concentration.

Rapid determination of the active leflunomide metabolite A77 1726 in human plasma by high-performance liquid chromatography

A simple method for the measurement of the active leflunomide metabolite A77 1726 in human plasma by HPLC is presented. The sample workup was simple, using acetonitrile for protein precipitation. Chromatographic separation of A77 1726 and the internal standard, alpha-phenylcinnamic acid, was achieved using a C(18) column with UV detection at 305 nm. The assay displayed reproducible linearity for A77 1726 with determination coefficients (r2) > 0.997 over the concentration range 0.5-60.0 microg/ml. The reproducibility (%CV) for intra- and inter-day assays of spiked controls was <5%. The limit of quantification was 0.8 microg/ml. The average absolute recovery was approximately 100%. This assay is suitable for the determination of A77 1726 in plasma of patients taking leflunomide, and is simpler to use than other HPLC methods reported previously.

A pharmacodynamic investigation of tacrolimus in pediatric liver transplantation

Although monitoring of tacrolimus blood concentrations is standard clinical practice following liver transplantation, a greater understanding of the relationship between trough concentrations and clinical outcome is required. The aim of this study was to perform a pharmacodynamic investigation of tacrolimus in pediatric liver transplant recipients. A retrospective analysis was performed on 35 pediatric liver recipients who received oral tacrolimus as the primary immunosuppressant. Outcome data were recorded corresponding to the times that tacrolimus trough concentrations had been determined (using a validated high-performance liquid chromatography-tandem mass spectrometry assay). A Mann-Whitney rank sum test was used to investigate differences between median concentrations at which drug toxicity, infection, and organ rejection did and did not occur. Outcome data and trough concentrations were recorded from the immediate post-transplant time to over 3 years (656 concentration-effect measures). Seventy one percent of data was obtained after the first 90 days post-transplant. Patients were identified as having experienced hypomagnesemia (20), hypertension (14), hyperkalemia (12), infection (11), nephrotoxicity (8), diarrhea (6), hyperglycemia (3), neurotoxicity(3), and rejection (3) during retrospective follow-up. Median trough concentrations were significantly higher (P <.05) at times patients experienced tacrolimus toxicity compared to no toxicity for nephrotoxicity (11.8 vs. 6.1 ng/mL) and neurotoxicity (15.1 vs. 6.2 ng/mL) and at times when patients suffered from diarrhea (8.9 vs. 6.0 ng/mL). No significant difference could be found between median trough concentrations at which hypertension, hyperkalemia, hyperglycemia, infection and organ rejection did and did not occur. A statistically significant relationship exists between some tacrolimus toxicities and tacrolimus trough concentrations. To minimize toxicity in the later post-transplant period, we propose a target trough tacrolimus concentration of 6 ng/mL.

Quantification of free mycophenolic acid and its glucuronide metabolite in human plasma by liquid-chromatography using mass spectrometric and ultraviolet absorbance detection

The immunosuppressant drug mycophenolic acid (MPA) and its major metabolite, mycophenolic acid glucuronide (MPAG), are highly bound to albumin. An HPLC-tandem-MS (HPLC/MS/MS) and an HPLC-UV assay were developed to measure free (unbound) concentrations of MPA and MPAG, respectively. Ultrafiltrate was prepared from plasma (500 microl) by ultrafiltration at 3000 x g for 20 min (20 degrees C). Both MPA and MPAG were isolated from ultrafiltrate (100 microl) by acidification and C18 solid-phase extraction. Free MPA was measured by electrospray tandem mass spectrometry using selected reactant monitoring (MPA: m/z 338.2--> 206.9) in positive ionisation mode. Chromatography was performed on a PFPP column (50 mm x 2 mm, 5 microm). Total analysis time was 7 min. The assay was linear over the range 1-200 microg/l with a limit of quantification of 1 microg/l. The inter-day accuracy and imprecision of quality controls (7.5, 40, 150 microg/l) were 94-99% and < 7%, respectively. Free MPAG was chromatographed on a C18 Nova-Pak column (150 mm x 3.9 mm, 5 microm) using a binary gradient over 20 min. The eluent was monitored at 254 nm. The assay was linear over the range 1-50 mg/l with the limit of quantification at 2.5 mg/l. The inter-day accuracy and imprecision of quality controls (5, 20, 45 mg/l) was 101-107% and < 8% (n = 4), respectively. For both methods no interfering substances were found in ultrafiltrate from patients not receiving MPA. The methods described have a suitable dynamic linear range to facilitate the investigation of free MPA and MPAG pharmacokinetics in transplant patients. Further, this is the first reported HPLC-UV method to determine free MPAG concentrations.

Population pharmacokinetics of hydroxychloroquine in patients with rheumatoid arthritis

SUMMARY

Hydroxychloroquine (HCQ) is an antimalarial drug that is also used as a second-line treatment of rheumatoid arthritis (RA). Clinically, the use of HCQ is characterized by a long delay in the onset of action, and withdrawal of treatment is often a result of inefficacy rather than from toxicity. The slow onset of action can be attributed to the pharmacokinetics (PK) of HCQ, and wide interpatient variability is evident. Tentative relationships between concentration and effect have been made, but to date, no population PK model has been developed for HCQ. This study aimed to develop a population PK model including an estimation of the oral bioavailability of HCQ. In addition, the effects of the coadministration of methotrexate on the PK of HCQ were examined. Hydroxychloroquine blood concentration data were combined from previous pharmacokinetic studies in patients with rheumatoid arthritis. A total of 123 patients were studied, giving the data cohort from four previously published studies. Two groups of patients were included: 74 received hydroxychloroquine (HCQ) alone, and 49 received HCQ and methotrexate (MTX). All data analyses were carried out using the NONMEM program. A one-compartment PK model was supported, rather than a three-compartment model as previously published, probably because of the clustering of concentrations taken at the end of a dosing interval. The population estimate of bioavailability of 0.75 (0.07), n = 9, was consistent with literature values. The parameter values from the final model were: Cl = 9.9 +/- 0.4 L/h, V = 605 +/- 91 L, ka = 0.77 +/- 0.22 hours(-1), t(tag) = 0.44 +/- 0.02 hours. Clearance was not affected by the presence of MTX, and, hence, steady-state drug concentrations and maintenance dosage requirements were similar. A population PK model was successfully developed for HCQ.

A perspective on Australia's National Medicines Policy

There is international interest in Australia's health care system for prescription medicines. The issue is particularly topical in Canada with the debate following publication of the Romanow Report into the future of health care in Canada. This Report recommended a new National Drug Agency. Australia has a National Medicines Policy with four arms-quality, safety and efficacy of medicines; equity of access; a viable and responsible pharmaceutical industry; quality use of medicines. The four arms of the Policy are interlinked and interdependent for optimal functioning. In this paper, an overview of how the prescription drug system in Australia works is presented. The manuscript focuses upon specific aspects of the Policy, describing how it functions and some of the processes integral to success, from the viewpoint of the author. The discussion includes some of the advantages of Australia's system for pharmaceuticals as well as some of the problems, as these present opportunities for development and change.