Making the rheumatologist aware of patients' non-adherence does not improve medication adherence in patients with rheumatoid arthritis.

OBJECTIVES: We have developed an instrument that provides the physician structured information about medication use and patients' (non-)adherence. This study aimed to determine the effectiveness of this instrument on adherence and medication beliefs in outpatients with rheumatoid arthritis (RA). METHODS: In this within-subject controlled prospective cohort study, 50 outpatients were assessed during three consecutive visits to their rheumatologist. At these three points in time, patients' adherence, medication beliefs, satisfaction about information about medication, and physical functioning were measured using validated self-report questionnaires. An intervention was scheduled during the second visit. The intervention consisted of a written report informing the physician about medication use and adherence to medication for each patient. The effectiveness of the intervention was evaluated by comparing outcome measures at the third visit to the same measures assessed prior to the intervention. RESULTS: At baseline, 30% of the patients (n = 50) were non-adherent. No significant changes in adherence were found between the first and second visit prior to the intervention. Adherence did not change after the intervention, compared to both of the adherence assessments prior to the intervention. Beliefs about medication, patients' satisfaction about information on medication, and physical functioning were also not significantly altered. CONCLUSION: Supplying the rheumatologist a report with information about medication use and adherence did not change adherence or patients' beliefs about medication. Further research is necessary to ensure effective support for adherence for individual patients with RA.

Sustained effect after lowering high-dose infliximab in patients with rheumatoid arthritis: a prospective dose titration study.

OBJECTIVES: In clinical trials only a small subset of patients with rheumatoid arthritis (RA) benefits from higher than standard dose of infliximab (>3 mg/kg/8 weeks). However, dose escalation of infliximab is frequently applied in clinical practice. Individual adjustment of infliximab treatment based on actual disease activity, instead of subjective clinical judgement, could prevent possible unwarranted dose escalation. METHODS: The infliximab dose of all patients with RA treated at our centre was decreased from 5 mg/kg to 3 mg/kg, leaving dosing intervals unaltered. Subsequently patients were followed for at least three infusions. At every visit, 28-joint Disease Activity Score (DAS28), infliximab serum trough levels and anti-infliximab antibody levels were assessed. Inversed European League Against Rheumatism (EULAR) criteria (flare criteria) were used as the endpoint. RESULTS: A total of 18 patients were included in the study. Mean (SD) DAS28 scores before dose reduction and after first and second low dose were 3.2 (1.2), 3.2 (1.8) and 3.3 (1.2), respectively (values not significant). One patient (6%, 95% CI 0% to 17%) developed a persistent flare that subsided after increasing infliximab doses and one patient stopped infliximab because of a lupus-like reaction. In all other patients (n=16) lowering infliximab resulted in unaltered disease activity. Infliximab levels showed that most patients had either low- (<1 mg/litre) or high (>5 mg/litre) serum trough levels. Anti-infliximab antibodies were detected in four patients. CONCLUSION: Infliximab dosages of 5 mg/kg can be lowered in the majority of patients with RA using DAS28-guided dose titration without increase of disease activity. Lowering the dose of infliximab should be considered in every patient receiving higher doses infliximab.

Cost-effectiveness of add-on lamotrigine therapy in clinical practice.

OBJECTIVE: This retrospective study addresses the cost-effectiveness of add-on therapy with lamotrigine in clinical practice. METHODS: Two years' observational data of 165 patients were used. Seizure frequency, adverse effects and direct medical costs were recorded for the year before and the year after the start of lamotrigine add-on therapy. Therapy effectiveness was measured by: (1) reduction in seizure frequency and (2) retention time. The incremental cost-effectiveness ratio expressed the direct medical cost per patient treated effectively with lamotrigine. RESULTS: The cost of medication was 492 (95% CI: 399-583) higher after the start of lamotrigine therapy. The extra cost of lamotrigine therapy (622) was partly offset by a reduction of the cost of co-medication (-130; 95% CI: -210 to -50). Overall, the total medical cost was 453 higher in the first year of lamotrigine therapy than in the year before the start of lamotrigine. Lamotrigine was effective in 47% of all the patients, making the resultant incremental cost-effectiveness ratio 954 per year. DISCUSSION: Add-on therapy of lamotrigine for patients with uncontrolled epilepsy offers improved health outcomes. Lamotrigine therapy is associated with increased cost (453) and an annual incremental cost-effectiveness ratio of 954. These data, together with utility data published in the literature, support the notion that lamotrigine should be considered as an add-on therapy in for patients with refractory epilepsy.

Effectiveness of lamotrigine in clinical practice: results of a retrospective population-based study.

OBJECTIVE: Evaluation of the effectiveness of lamotrigine in a population-based cohort of epilepsy patients. METHODS: Medical charts of 360 patients treated in 37 centres in The Netherlands were reviewed. Effectiveness of lamotrigine therapy was assessed during the first year of use, with patients serving as their own controls. Effectiveness was measured by reduction in seizure frequency and retention time. RESULTS: Effectiveness could only be assessed in 165 patients; assessment in remaining patients was not possible due to various reasons, such as insufficient medical chart information. Lamotrigine was effective in 40% of patients who had been prescribed lamotrigine because of insufficient seizure control (n=112), and 14% of these 112 patients became seizure free. Duration of epilepsy, baseline seizure frequency, valproate use, drug load and number of antiepileptic drugs (AED) used were related to effectiveness of lamotrigine. In this group, 36% continued lamotrigine (LTG) throughout the first year without experiencing a >50% seizure reduction. Lamotrigine was effective in 63% of patients who received the drug because of poor tolerability of other antiepileptic drugs (n=53). DISCUSSION: Lamotrigine is an effective drug in clinical practice. Use of retention time measures only may not correctly reflect the efficacy of antiepileptic drugs.

Pharmacokinetic study of tenofovir disoproxil fumarate combined with rifampin in healthy volunteers.

Tenofovir disoproxil fumarate (tenofovir DF) was studied in combination with rifampin in 24 healthy subjects in a multiple-dose, open-label, single-group, two-period study. All subjects were given tenofovir DF at 300 mg once a day (QD) from days 1 to 10 (period 1). From days 11 to 20 the subjects received tenofovir DF at 300 mg combined with rifampin at 600 mg QD (period 2). The multiple-dose pharmacokinetics of tenofovir (day 10 and 20) and rifampin (day 20) were assessed. The drug-related adverse events (AEs) experienced during this study were mostly mild. Only one grade 3 AE possibly or probably related to the treatment (raised liver enzyme levels) occurred during period 2; the subject was withdrawn from the study. Pharmacokinetic data for 23 subjects were thus evaluable. Point estimates for the mean ratios of tenofovir with rifampin versus tenofovir alone for the area under the concentration-time curve from time zero to 24 h (AUC(0-24)), the maximum concentration of drug in plasma (C(max)), and the minimum concentration of drug in plasma (C(min)) were 0.88, 0.84, and 0.85, respectively. The 90% classical confidence intervals for AUC(0-24), C(max), and C(min) were 0.84 to 0.92, 0.78 to 0.90, and 0.80 to 0.91, respectively, thus suggesting pharmacokinetic equivalence. Similarly, coadministration of rifampin and tenofovir DF did not result in changes in the values of the tenofovir pharmacokinetic parameters. For rifampin, the values of the pharmacokinetic parameters found in this study were comparable to those found in the literature, indicating that tenofovir DF has no effect on the pharmacokinetics of rifampin. In conclusion, adaptation of either the rifampin or the tenofovir DF dose for the simultaneous treatment of tuberculosis and human immunodeficiency virus (HIV) infection in HIV-infected patients is probably not required.

Recruitment of a cohort of lamotrigine users through community pharmacists: differences between patients who gave informed consent and those who did not.

OBJECTIVE: Community pharmacists may function as intermediaries in the recruitment of a population-based cohort of patients using specific drugs. In this study, baseline characteristics and the retention rate of patients that gave informed consent, refused and did not answer were compared. METHODS: A total of 1819 patients using the new antiepileptic drug (AED) lamotrigine were asked to provide informed consent for a retrospective chart study via their individual pharmacist. Four possible reactions resulted from the consent question: active consent, active refusal, passive refusal and non-informed. Patient characteristics and lamotrigine retention rate of the different groups were compared. RESULTS: Pharmacists did not inform a total of 183 patients (10%). Of the remaining patients, a total of 968 (59%) gave consent; 101 (6%) actively refused and 567 (35%) did not respond. Age, burden of illness, psychotropic co-medication and continuation of lamotrigine therapy were related to active consent. Lamotrigine retention rate in patients that gave consent was higher than in other patients. CONCLUSIONS: Patient recruitment with community pharmacists as intermediaries for observational studies on the effects of (new) drugs is feasible, and allows access to a broad population of patients. The recruitment procedure, however, may lead to selection bias.

Diffusion of the new antiepileptic drug lamotrigine in Dutch clinical practice.

INTRODUCTION: Lamotrigine is one of the recently introduced antiepileptic drugs (AEDs) licensed in the Netherlands in 1995. The objective of this study was to examine the diffusion of lamotrigine into clinical practice. Three different aspects of this diffusion process were examined: incidence of use, patient characteristics and changes in prescription patterns in the first 5 years following its introduction. METHODS: A retrospective follow-up study has been conducted using drug prescription data from the database of the Dutch Drug Information Project (GIP database). Patients were included who started with lamotrigine, carbamazepine, phenytoin or valproate in the period between January 1996 and December 2000. Incidence of use was calculated for the four drugs. Multiple logistic regression analysis was used to determine differences in baseline characteristics. The Chi-square test was used to analyse changes in the usage patterns of lamotrigine. RESULTS: The study population consisted of a total of 29,718 patients who were prescribed carbamazepine, phenytoin, valproate or lamotrigine for the first time in the study period. Carbamazepine and valproate accounted for the majority of all new prescriptions; the incidence of lamotrigine use remained stable with 4.4 patients per 100,000 per year. Baseline characteristics of lamotrigine differed depending on the patient's age and gender (OR 3.7, 95% CI 3.3-4.2; OR 1.4, 95% CI 1.3-1.5) relative to the conventional AEDs. In a large majority of cases, lamotrigine was used as a second-line or third-line AED. Physicians prescribing lamotrigine were predominantly neurologists, in contrast to prescribers of conventional AEDs. The prevalence of psychotropic medication and migraine-abortive drugs was significantly lower in users of lamotrigine than in users of conventional AEDs. During follow-up, several significant trends were noticed in the prescribing of lamotrigine with regard to age groups, gender, antiepileptic history and off-label use. DISCUSSION: Lamotrigine is prescribed to a population different from that using conventional AEDs. The uptake of lamotrigine in clinical practice is slow, for reasons probably related to characteristics of the drug itself and the prescribers. During the observation period, lamotrigine diffused gradually towards more first-line use as an AED and more off-label use.

Effect of efavirenz treatment on the pharmacokinetics of nelfinavir boosted by ritonavir in healthy volunteers.

AIMS: A once-daily (q.d.) nucleoside-sparing regimen can prevent mitochondrial toxicity, overcome viral resistance and improve compliance. In the present study the effect of efavirenz on the pharmacokinetics and tolerability of once-daily nelfinavir/ritonavir was evaluated in healthy subjects. METHODS: This was a multiple-dose, open-label, single-group, two-period study in 24 healthy subjects. Each received from days 1-10 (period 1): 1875 mg nelfinavir plus 200 mg ritonavir q.d. with a 300-kcal snack. During days 11-20 (period 2) efavirenz 600 mg q.d. was added to the regimen. Blood samples were collected up to 24 h after dosing on days 10 (period 1) and 20 (period 2). High-performance liquid chromatography methods were used for the determination of the concentrations of all compounds. The main pharmacokinetic parameters were calculated using noncompartmental methods. RESULTS: All subjects completed the study. After the first period mean nelfinavir AUC(0-24 h), C(max) and C(24) were 49.6 mg h(-1) l(-1), 5.0 mg l(-1) and 0.37 mg l(-1), and the sum of nelfinavir plus its active metabolite M8 C(24) was 0.83 mg l(-1). The relative bioavailability, expressed as a geometric mean ratio (90% confidence interval) for nelfinavir AUC(0-24 h), C(max) and C(24) of period 2 compared with period 1 was: 1.30 (1.21, 1.40), 1.29 (1.19, 1.40) and 1.48 (1.32, 1.66). The sum of nelfinavir and M8 C(24) in period 2 was 0.99 mg l(-1), an increase of 19%. No serious adverse events occurred. CONCLUSIONS: The studied regimens were well tolerated. Nelfinavir/ritonavir given together with efavirenz resulted in a 48% higher mean C(24) concentration for nelfinavir, and the sum of nelfinavir and M8 C(24) concentrations was 0.99 mg l(-1). Efavirenz exposure in this study was similar to that reported previously, and therefore can be used effectively in combination with ritonavir and nelfinavir.

[A patient with lessened sensitivity to acenocoumarol during a period of enteral feeding]. / Een patiënt met verminderde gevoeligheid voor acenocoumarol tijdens gebruik van sondevoeding.

A 69-year-old man was operated on for a subdural haematoma which had developed during the use of acenocoumarol. Directly after the operation the patient was started on enteral feeding. The acenocoumarol was restarted at a later stage. The dose of acenocoumarol needed for an appropriate level of blood-dilution was twice as high during the period of enteral feeding than it had been preoperatively. After the transition from enteral feeding to oral feeding it was possible to lower the dose of acenocoumarol. The need for a higher dose was probably due to enhanced binding of the proteins in the enteral feeding. The patient was admitted to a nursing home. The combination of acenocoumarol and enteral feeding occurs frequently in patients being rehabilitated. It is important to monitor the blood-dilution when starting and stopping enteral feeding.

Patterns of lamotrigine use in daily clinical practice during the first 5 years after introduction in the Netherlands.

OBJECTIVE: Follow-up data on the long-term effectiveness (efficacy and tolerability) of lamotrigine are limited. A useful though crude measure for effectiveness in daily clinical practice is the treatment retention rate determined from drug dispensing data. This study describes the baseline characteristics, the usage patterns and the retention rate of this antiepileptic drug (AED) in a population-based cohort of lamotrigine users in the Netherlands during the first 5 years after its registration in 1995. Data from this cohort are compared with those from the initial randomized clinical trials (RCTs) in patients with refractory epilepsy. METHODS: This retrospective cohort study used dispensing data from community pharmacies. Baseline characteristics and usage patterns were evaluated for first time users of lamotrigine in this study. Usage patterns were characterized as continued, add-on or discontinued use during the patient observation time window. Cox regression analysis was used to explore possible relationships between baseline characteristics and specific usage patterns defined. The baseline characteristics and discontinuation rates in this cohort study were compared with RCT data reported in medical literature. RESULTS: A total of 3598 lamotrigine users were identified. The mean age of the population was 39 years and 54% were female. On average, patients used two other AEDs at the start of lamotrigine therapy and approximately 6% of the patients had no history of prior AED use. The discontinuation rate was 25% after 1 year, and approximately 32% at the end of the 5-year study. Addition of another drug or discontinuation was seen in more than half of the population 3 years after the start of therapy. Concurrent use of valproic acid was associated with a better retention rate. Absence of AED history, use of antidepressants, or use of migraine abortive drugs resulted in an increased likelihood of discontinuing lamotrigine. The population from RCTs differed from the study cohort with respect to age, concurrent use of AEDs and length of follow-up. CONCLUSION: Data from RCTs cannot easily be extrapolated to daily clinical practice. In this large, observational study, lamotrigine therapy failed in a considerable number of patients, although the mean retention rate was better than previously reported by others. Population-based linkage of health care records can be used to further clarify the effectiveness of lamotrigine.

Pharmacokinetics of adjusted-dose lopinavir-ritonavir combined with rifampin in healthy volunteers.

Coadministration of lopinavir-ritonavir, an antiretroviral protease inhibitor, at the standard dose (400/100 mg twice a day [BID]) with the antituberculous agent rifampin is contraindicated because of a significant pharmacokinetic interaction due to induction of cytochrome P450 3A by rifampin. In the present study, two adjusted-dose regimens of lopinavir-ritonavir were tested in combination with rifampin. Thirty-two healthy subjects participated in a randomized, two-arm, open-label, multiple-dose, within-subject controlled study. All subjects were treated with lopinavir-ritonavir at 400/100 mg BID from days 1 to 15. From days 16 to 24, the subjects in arm 1 received lopinavir-ritonavir at 800/200 mg BID in a dose titration, and the subjects in arm 2 received lopinavir-ritonavir at 400/400 mg BID in a dose titration. Rifampin was given at 600 mg once daily to all subjects from days 11 to 24. The multiple-dose pharmacokinetics of lopinavir, ritonavir, and rifampin were assessed. Twelve of 32 subjects withdrew from the study. For nine subjects lopinavir-ritonavir combined with rifampin resulted in liver enzyme level elevations. Pharmacokinetic data for 19 subjects were evaluable. Geometric mean ratios for the lopinavir minimum concentration in serum and the maximum concentration in serum (C(max)) on day 24 versus that on day 10 were 0.43 (90% confidence interval [CI], 0.19 to 0.96) and 1.02 (90% CI, 0.85 to 1.23), respectively, for arm 1 (n = 10) and 1.03 (90% CI, 0.68 to 1.56) and 0.93 (90% CI, 0.81 to 1.07), respectively, for arm 2 (n = 9). Ritonavir exposure increased from days 10 to 24 in both arms. The geometric mean C(max) of rifampin was 13.5 mg/liter (day 24) and was similar between the two arms. Adjusted-dose regimens of lopinavir-ritonavir in combination with therapeutic drug monitoring and monitoring of liver function may allow concomitant use of rifampin.

Selecting outcome parameters in studies aimed at improving rational use of antibiotics - practical considerations.

When designing studies of the optimal use of antimicrobial drugs, it is important to define at an early stage, which outcome parameters to use. It must be clear to which category a parameter to be measured belongs: the structure, the process or a clinical outcome. Attention must be paid to the measurement scales as well as the statistical tests to be used. The outcome measure must be sensitive, specific and reliable. Furthermore, the timeframe chosen for the performance of a study should be validated. Whether process parameters or clinical outcomes are to be preferred depends on the settings and the intended purpose. The essential point is the appropriate choice of outcome measure for the study. Examples drawn from the field of quality of use of antimicrobial drugs are discussed.

Selection criteria for the clinical use of the newer antiepileptic drugs.

In recent years, several new antiepileptic drugs (AEDs) have been licensed: felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide. These drugs have proven efficacy as add-on therapy in patients with difficult-to-treat partial epilepsy, as 20-50% of patients treated in add-on trials experienced a seizure reduction of >or=50%. Relatively few trials have been conducted to evaluate these drugs as monotherapy for patients with newly diagnosed epilepsy. In the monotherapy trials that have been conducted, the newer drugs were often as efficacious as conventional drugs, and their tolerability was often better. However, the methodology of these trials can be criticised. Because of the relative lack of robust data for the newer agents, the conventional drugs have thus far maintained their status as first-line monotherapy. However, when first-line monotherapy fails, an alternative drug has to be chosen from the available conventional and newer drugs. This article aims to give detailed background information on the newer AEDs in order to enable physicians to make a rational choice from the available drugs for individual patients. Data are provided for the different newer AEDs on mechanisms of action; efficacy in refractory partial epilepsy, newly diagnosed epilepsy in adults and generalised seizure types; adverse effects; pharmacokinetics; and use in special patient categories.

Pharmacokinetics, food intake requirements and tolerability of once-daily combinations of nelfinavir and low-dose ritonavir in healthy volunteers.

AIMS: This study was performed to evaluate the steady-state pharmacokinetics, food intake requirements and short-term tolerability of once-daily combinations of nelfinavir and low-dose ritonavir. METHODS: Twenty-seven healthy volunteers were randomized over three groups to receive a once-daily regimen of nelfinavir/ritonavir 2,000/200 mg (group 1), 2,000/400 mg (group 2) or 2,500/200 mg (group 3) with food for 14 days. Pharmacokinetic parameters for nelfinavir and its active metabolite M8 were assessed on study days 15 and 16, after administration of the regimens with a full (610 kcal) or light (271 kcal) breakfast, respectively. RESULTS: Pharmacokinetic data were evaluable for eight volunteers in group 1, eight in group 2 and four in group 3. Administration of nelfinavir/ritonavir with a full breakfast resulted in geometric mean (GM) nelfinavir AUC(24h) values of 76.8, 51.3, and 61.9 h*mg/l in group 1, 2 and 3, respectively. GM 24-h Cmin concentrations of nelfinavir were 0.76 mg l(-1), 0.43 mg l(-1) and 0.47 mg l(-1), respectively. Co-administration of ritonavir increased M8 concentrations more than nelfinavir concentrations, resulting in GM AUC(24h) and Cmin values for nelfinavir plus M8 that were higher than or comparable to reference values for the approved regimen of nelfinavir (1,250 mg BID without ritonavir). In the 2,000/200 mg group, seven out of eight subjects had a Cmin value of nelfinavir plus M8 above a threshold of 1.0 mg l-1. Administration of the combinations with a light breakfast resulted in significant decreases in the AUC(24h) and Cmin of nelfinavir and nelfinavir plus M8, compared with intake with a full breakfast. For the Cmin of nelfinavir plus M8, the GM ratio (light/full breakfast) was 0.76 (90% confidence interval 0.67-0.86, participants from all groups combined). Short-term tolerability was satisfactory, apart from a higher than expected incidence of mild rash (12%). CONCLUSIONS: Administration of nelfinavir in a once-daily regimen appears feasible. A nelfinavir/ritonavir 2,000/200 mg combination appears appropriate for further evaluation. Once-daily nelfinavir/ritonavir should be taken with a meal containing at least 600 kcal.

Saquinavir soft-gel capsules (Fortovase) give lower exposure than expected, even after a high-fat breakfast.

BACKGROUND: The soft-gel capsule (sgc) of saquinavir has been developed in order to improve the poor oral bioavailability of the original hard-gel capsules. However, in a Dutch study population using saquinavir-sgc plasma levels were lower than expected. We hypothesised that this was caused by differences in the amount of fat in the meals of the study populations. METHODS: 8-h steady-state plasma curves after observed ingestion of 1200 mg saquinavir-sgc were recorded, concomitantly with a normal breakfast (600 kcal, 33% fat) on the first day, and a high-fat breakfast (1040 kcal, 54% fat) on the second day. Additionally, a comparison was made between saquinavir hard-gel capsules and saquinavir-sgc with or without grapefruit juice (n = 1). Furthermore, a comparison between saquinavir-sgc and ritonavir + saquinavir-sgc 400/400 mg bid was made (n = 1). RESULTS: Although saquinavir exposure was improved by fat, grapefruit juice or ritonavir, exposure to saquinavir for all recorded curves was lower than expected. A large proportion of trough concentrations was below the efficacy threshold. CONCLUSION: Intake of squinavir-sgc with high-fat meals or grapefruit juice may improve the pharmacokinetic profile. However, plasma concentrations may then still be lower than expected and insufficient for good antiviral efficacy. Probably the only way to reach adequate saquinavir concentrations is by combining saquinavir with ritonavir.

Use of fluconazole in daily practice: still room for improvement.

One hundred courses of fluconazole treatment in a university hospital and 81 courses in a non-university teaching hospital have been analysed in a prospective audit to evaluate prescribing practices. The quality of treatments was assessed by an infectious disease specialist and a pharmacist according to standard guidelines. In the non-university hospital, prescribed dosages were lower than in the university hospital, and often below the recommended dose. Mean duration of treatment for oesophageal candidosis and disseminated infections was considerably shorter in the non-university hospital compared with the university hospital, and often judged too short. Microbiological samples were examined in 75% of the cases in both hospitals. The expert reviewers agreed with the indication to use fluconazole in 58-100% of cases in the university hospital and 42-80% in the non-university hospital, depending on the type of infection. There did not appear to be a major problem with inappropriate use of fluconazole. However, important issues for improvement could be identified, such as increasing the dosage and duration of treatment in cases of serious infections, and withholding treatment from patients with colonization rather than infection.

Analysis of variation in plasma concentrations of nelfinavir and its active metabolite M8 in HIV-positive patients.

OBJECTIVE: To characterize sources of variation in plasma concentrations of nelfinavir and its active metabolite M8 and to evaluate the use of therapeutic drug monitoring for nelfinavir treatment. METHODS: Plasma samples and patient's characteristics were obtained from outpatient clinic. Differences between groups of patients were studied by comparing the observed plasma concentrations with the corresponding concentration on a pharmacokinetic population curve based on median plasma levels. RESULTS: Plasma samples (618) were available from 355 patients taking 1250 mg nelfinavir twice daily. The median ratio between M8 and nelfinavir concentrations was 0.29. This ratio appeared to be independent of the time after ingestion. Statistically significantly lower M8 concentrations were found in Black and Asian patients, or when comedication with CYP3A4 inducers was used. Coadministration of CYP2C19 inhibitors, such as omeprazole, decreased the median M8/nelfinavir ratio. Nevertheless, nelfinavir concentrations and summed concentrations of nelfinavir and M8 were only marginally affected in these patients. Diarrhoea was identified as a cause for lower nelfinavir concentrations, without changing the M8/nelfinavir ratio. In a number of patients with suspected therapy failure or intoxication, abnormal nelfinavir plasma concentrations were found. Dose adjustments based on nelfinavir plasma levels were helpful in a number of patients. CONCLUSION: This study shows that the total concentration of nelfinavir and M8 together is not significantly influenced when variation in M8 levels occurs. Consequently, measuring M8 concentrations in addition to nelfinavir concentrations is not required for the purpose of therapeutic drug monitoring for this drug.

Pyrazinamide use as a method of estimating under-reporting of tuberculosis.

OBJECTIVE: To develop a method of validating the notification of active tuberculosis by physicians in the Netherlands. METHOD: The chemotherapeutic agent pyrazinamide was used as a marker for the occurrence of tuberculosis. On the basis of defined daily doses (DDD) of pyrazinamide dispensed to out-patients, an estimate was made of the number of patients with tuberculosis in the Netherlands in the period 1994-1998. DDD is a technical unit of measurement and does not necessarily reflect the recommended or actual dose used. Usually it is based on the average dosage per day for the main indication in adults with normal organ function. The Dutch Drug Information Project (GIP) of the Health Care Insurance Board (CVZ) provided the DDD data. Based on the notification of tuberculosis patients to the Netherlands Tuberculosis Register (NTR) we calculated how much pyrazinamide (measured in DDDs) these patients would have used depending on their body weight. RESULTS: The number of DDDs prescribed according to the GIP pharmacy records differed by only 8% from the number of DDDs calculated on the basis of notification to the NTR; 6889 patients should have been registered instead of 6349. CONCLUSION: The close correlation between the use of pyrazinamide as measured by the GIP and NTR provides strong evidence that in the Netherlands tuberculosis is reported in conformity with the guidelines for notifiable diseases. The method was simple to apply and may deserve follow-up in other countries.

High-performance liquid chromatography of HIV protease inhibitors in human biological matrices.

Methods for HPLC analysis of protease inhibitors (PIs) in human biological matrices were reviewed. Assays have been developed for analysis of single PIs or for simultaneous measurement of multiple PIs in plasma-serum, saliva, cerebrospinal fluid and semen. Liquid-liquid extraction was most often applied for sample pretreatment, but solid-phase extraction and protein precipitation were used as well. Reversed-phase or ion-pair chromatography have been used to separate PIs. Detection of PIs should be sensitive enough for quantitation of plasma concentrations below trough levels of single PIs, or below proposed therapeutic thresholds for PIs. The large majority of assays employs UV detection. As the potential for interferences is large, the selectivity of every method should be evaluated properly. The available high-performance liquid chromatography (HPLC) methods have been applied in clinical pharmacokinetic studies and for therapeutic drug monitoring of PIs. Participation in an interlaboratory quality control program is recommended for every laboratory engaged in the bioanalysis of PIs.