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St. John's wort does not interfere with therapeutic drug monitoring of 12 commonly monitored drugs using immunoassays.

St. John's wort, a popular herbal remedy for depression, is known to interact with many Western drugs because of the ability of its components to induce liver enzymes. Lower concentrations of various drugs due to increased clearance have been reported. Because immunoassays are commonly used in clinical laboratories for therapeutic drug monitoring, we studied the potential interference of St. John's wort with commonly monitored therapeutic drugs. Drug-free serum pools were supplemented with St. John's wort to achieve in vitro St. John's wort concentrations mimicking in vivo concentrations after both recommended use and overdose. Concentrations of digoxin, tricyclic antidepressants (TCAs), phenytoin, carbamazepine, theophylline, valproic acid, quinidine, phenobarbital, procainamide, and N-acetyl procainamide were measured in serum. Pooled serum specimens from patients who were taking a particular drug were also supplemented in vitro with concentrations of St. John's wort to investigate whether observed concentrations changed after supplementation with St. John's wort. The effect of St. John's wort on cyclosporine and tacrolimus (FK 506) was studied in whole blood. We found no significant interference from St. John's wort with any assay studied. Moreover, when drug-free serum was supplemented with very high concentrations of hypericin (2 microg/mL) and hyperforin (2 microg/mL) pure standard, we observed no apparent drug level with any immunoassay. The presence of both hypericin and hyperforin was also confirmed by thin layer chromatography (TLC) in both preparations of St. John's wort. We conclude that immunoassays may be used to measure levels of therapeutic drugs in patients who self-medicate with St. John's wort.

Antidepressive Agents, Tricyclic↗

Stepwise binary gradient high-performance liquid chromatographic system for routine drug monitoring.

Drug therapy is usually optimized by concentration measurement in patient serum. High-performance liquid chromatography (HPLC) is one of the most important analytical techniques used for therapeutic drug monitoring (TDM) of drugs for which no immunoassay kits are available. HPLC has been frequently used for screening purposes in toxicology, too. The Merck Tox Screening System (MTSS) has been developed for the identification of substances by a combination of gradient HPLC with diode-array detection and identification with a database system. For routine TDM an isocratic HPLC system is more suitable because of shorter analysis time, better reproducibility of retention index and better precision of results. Therefore we defined a set of methods in steps of 10% of the two MTSS eluents. Three examples are shown: Amiodarone, Indometacine and Thiopental. New applications to test for other substances can be transferred to an isocratic system after a complete MTSS gradient run.

Amiodarone↗

Problems in therapeutic drug monitoring: free drug level monitoring.

Historically, it has been assumed that only free drug concentration is the pharmacologically active species. This article reviews the theoretical pharmacological and pharmacokinetic justifications for monitoring free drug levels. The determinants likely to influence plasma protein binding and the free concentrations of drugs are delineated. The different methods which can be used for determining free drug level are presented. Their advantages and drawbacks as well as their reliability and suitability for routine clinical practice are discussed. Currently, antiepileptic drugs such as valproic acid, phenytoin, carbamazepine and a few antiarrhythmic drugs meet the theoretical criteria justifying free drug level monitoring. Conditions causing alteration in free concentrations of these drugs are reported. But, for all these drugs, there is a considerable lack of data establishing the correlations between therapeutic or toxic response and free concentration. Presently, our capability to interpret correctly the free drug level data is still limited. In the future, much more effort must be devoted in order to provide sufficient information on the clinical relevance of free drug concentration.

Anti-Arrhythmia Agents↗

Therapeutic drug monitoring: antiarrhythmic drugs.

Antiarrhythmic agents are traditionally classified according to Vaughan Williams into four classes of action. Class I antiarrhythmic agents include most of the drugs traditionally thought of as antiarrhythmics, and have as a common action, blockade of the fast-inward sodium channel on myocardium. These agents have a very significant toxicity, and while they are being used less, therapeutic drug monitoring (TDM) does significantly increase the safety with which they can be administered. Class II agents are antisympathetic drugs, particularly the b-adrenoceptor blockers. These are generally safe agents which do not normally require TDM. Class III antiarrhythmic agents include sotalol and amiodarone. TDM can be useful in the case of amiodarone to monitor compliance and toxicity but is generally of little value for sotalol. Class IV antiarrhythmic drugs are the calcium channel blockers verapamil and diltiazem. These are normally monitored by haemodynamic effects, rather than using TDM. Other agents which do not fall neatly into the Vaughan Williams classification include digoxin and perhexiline. TDM is very useful for monitoring the administration (and particularly the safety) of both of these agents.

Anti-Arrhythmia Agents↗

Therapeutic drug monitoring: antiarrhythmic drugs.

Antiarrhythmic agents are traditionally classified according to Vaughan Williams into four classes of action. Class I antiarrhythmic agents include most of the drugs traditionally thought of as antiarrhythmics, and have as a common action, blockade of the fast-inward sodium channel on myocardium. These agents have a very significant toxicity, and while they are being used less, therapeutic drug monitoring (TDM) does significantly increase the safety with which they can be administered. Class II agents are antisympathetic drugs, particularly the beta-adrenoceptor blockers. These are generally safe agents which do not normally require TDM. Class III antiarrhythmic agents include sotalol and amiodarone. TDM can be useful in the case of amiodarone to monitor compliance and toxicity but is generally of little value for sotalol. Class IV antiarrhythmic drugs are the calcium channel blockers verapamil and diltiazem. These are normally monitored by haemodynamic effects, rather than using TDM. Other agents which do not fall neatly into the Vaughan Williams classification include digoxin and perhexiline. TDM is very useful for monitoring the administration (and particularly the safety) of both of these agents.

Adrenergic beta-Antagonists↗

Neonatal drug monitoring and drug delivery systems.

The problems associated with drug delivery and achievement of therapeutic blood levels in neonates are reviewed, using chloramphenicol as an example. Administration of small volumes, concentrated solutions and intravenous line filter chambers greatly affect the final dose delivered to the infant. Once delivered, variability in drug elimination caused by changing hepatic and renal function and protein binding necessitate careful drug monitoring and pharmacokinetic analysis especially with drugs like chloramphenicol that have a narrow therapeutic range. If one uses a team approach involving nurses, clinical chemists and clinical pharmacologists, optimal doses of chloramphenicol in the newborn are achieved more consistently.

Chloramphenicol↗

Therapeutic drug monitoring in drug overdose.

The treatment of poisoned patients is still largely defined by history, clinical assessment and interpretation of ancillary investigations. Measurement of drug concentrations is clinically important for relatively few compounds. Most measurements form an adjunct to and should not be considered a substitute for clinical assessment. Drug concentrations are particularly important for those compounds where the concentration is predictive of serious toxicity in an otherwise asymptomatic patient.

Acetaminophen↗

Therapeutic drug monitoring in drug overdose.

The treatment of poisoned patients is still largely defined by history, clinical assessment and interpretation of ancillary investigations. Measurement of drug concentrations is clinically important for relatively few compounds. Most measurements form an adjunct to and should not be considered a substitute for clinical assessment. Drug concentrations are particularly important for those compounds where the concentration is predictive of serious toxicity in an otherwise asymptomatic patient.

Acetaminophen↗

Appropriateness of requests for therapeutic drug monitoring of antiepileptic drugs: the experience in southwestern Saudi Arabia.

The purpose of this study was to evaluate request forms of therapeutic drug monitoring of antiepileptic drugs for appropriateness criteria according to published data. Request forms received by the laboratory were sampled as all requests in one day per week on an alternating basis. Drugs monitored were phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ) and valproic acid (VPA). A total of 420 request forms were collected. Age, gender and weight were provided in 95.5%, 97.1% and 56.9% of request forms, respectively. The diagnosis, seizure type and the indication for therapeutic drug monitoring were provided in 81.6%, 3.2% and 55.5%, respectively. Sampling times were provided in 45% and were considered appropriate in 25.2% of the request forms. The indications for therapeutic drug-monitoring were considered appropriate in 28.6% of the request forms, and only 19.2% of these were appropriately sampled. Only 37.9% of all samples were drawn at steady-state. Serum albumin and creatinine concentrations were lacking in 93.6% and 53.3% of requests, respectively. The potential for drug-drug interactions was detected in 28.6% of all requests. Thus, the information needed for the proper interpretation of therapeutic drug monitoring results and that was provided in the request forms was surprisingly scarce. Most of the appropriateness criteria for therapeutic drug monitoring were not met.

Adolescent↗

Therapeutic drug monitoring--antiepileptic drugs.

AIMS: To provide a brief critical review of the basis and contemporary practice of monitoring the concentrations of antiepileptic drugs in biological fluids. METHODS: The review is based on literature data and observations from clinical practice. RESULTS: As experience has accumulated, monitoring of antiepileptic drug concentrations has come to be applied mainly to certain of the drugs when present in whole plasma. For these drugs there is a reasonably established relationship between drug concentrations and biological effects, but attention still needs to be paid to issues such as the timing of the measurements in relation to drug intake, the presence or absence of steady-state conditions, the presence in plasma of active metabolites and possible nonlinear pharmacokinetics of particular agents e.g. phenytoin. CONCLUSIONS: Plasma antiepileptic drug concentration monitoring is coming to be used in a more thoughtful and critical manner. Lack of adequate knowledge of matters such as the relationship between the plasma concentrations and antiepileptic and toxic effects of the drugs, not only the newer, but also the longer established ones, in particular clinical situations, remains more important than deficiencies in analytical methodology in limiting the clinical usefulness of antiepileptic drug concentration monitoring.

Anticonvulsants↗

Therapeutic drug monitoring--antiepileptic drugs.

AIMS: To provide a brief critical review of the basis and contemporary practice of monitoring the concentrations of antiepileptic drugs in biological fluids. METHODS: The review is based on literature data and observations from clinical practice. RESULTS: As experience has accumulated, monitoring of antiepileptic drug concentrations has come to be applied mainly to certain of the drugs when present in whole plasma. For these drugs there is a reasonably established relationship between drug concentrations and biological effects, but attention still needs to be paid to issues such as the timing of the measurements in relation to drug intake, the presence or absence of steady-state conditions, the presence in plasma of active metabolites and possible nonlinear pharmacokinetics of particular agents, e.g. phenytoin. CONCLUSIONS: Plasma antiepileptic drug concentration monitoring is coming to be used in a more thoughtful and critical manner. Lack of adequate knowledge of matters such as the relationship between the plasma concentrations and antiepileptic and toxic effects of the drugs, not only the newer, but also the longer established ones, in particular clinical situations, remains more important than deficiencies in analytical methodology in limiting the clinical usefulness of antiepileptic drug concentration monitoring.

Anticonvulsants↗

Current opinions on therapeutic drug monitoring of immunosuppressive drugs.

The pharmacokinetics of the immunosuppressive drugs cyclosporine, tacrolimus, mycophenolate mofetil (MMF), and sirolimus are complex and unpredictable. A narrow therapeutic index unique to each patient, as well as variable absorption, distribution, and elimination, are characteristics of these drugs. Therapeutic drug monitoring plays a key role in helping clinicians maintain blood and plasma levels of immunosuppressive drugs within their respective therapeutic ranges. Variation in concentrations outside the narrow therapeutic ranges can result in adverse clinical outcomes. Therapeutic drug monitoring ensures that concentrations are not too high or too low, thereby reducing the risks of toxicity or rejection, respectively. Therapeutic monitoring of immunosuppressive drugs has been based on several choices of assay and biologic fluid (i.e., whole blood, plasma) appropriate for a particular drug. High-performance liquid chromatography (HPLC) remains the gold standard among assay methods used to monitor immunosuppressive drugs. Although HPLC is the assay of choice for cyclosporine, newer monoclonal assays are suitable as well for routine monitoring. HPLC is also widely used for therapeutic drug monitoring of mycophenolic acid, the active metabolite of MMF, and an immunoassay (used in European centers) has been developed. Therapeutic drug monitoring of tacrolimus has been improved with the recent development of assays with greater sensitivity and specificity for tacrolimus than those previously available. No commercial assays are currently available for the therapeutic monitoring of sirolimus. It is also important to identify a specific pharmacokinetic parameter for each individual drug, whether it is trough or area under the concentration-time curve, that may be most useful as a tool for optimal therapeutic drug monitoring in clinical practice. With an increased understanding of the pharmacokinetics of immunosuppressive drugs, therapeutic drug monitoring guidelines will be more clearly defined to ensure the safe and effective management of transplant recipients.

Cyclosporine↗

Position paper on therapeutic drug monitoring of antiretroviral agents.

Monitoring drug concentrations in humans to optimize efficacy and reduce toxicity is not a new concept in clinical pharmacology. It has been successfully applied to many different classes of drugs. As a result of considerable concentration and response data, the concept of therapeutic drug monitoring (TDM) has been expanded to certain antiretroviral compounds. In particular, protease inhibitors and nonnucleoside reverse transcriptase inhibitors may be viable candidates for TDM, and limited clinical trial data suggest monitoring plasma concentrations of these agents may indeed clinically benefit patients with HIV infection. A primary distinction between TDM of antiretroviral drugs compared with other drugs is that multiple agents are concomitantly used to treat HIV infection. As with all illnesses that require self-administered drug therapy, poor adherence is a major impediment to success. However, in the treatment of HIV infection, inadequate drug concentrations will result in the appearance or evolution of drug resistance mutations that can endanger present and future drug treatment options. Procedures for sample collection, cross-validation of analytical procedures, and interpretation of assay results should be standardized. More clinical data are needed to confirm this approach and methods of implementing TDM should be further explored. This position paper offers guidelines to aid clinicians who choose to incorporate TDM into the routine care of their patients.

Anti-HIV Agents↗

Therapeutic drug monitoring of immunosuppressive drugs in kidney transplantation.

PURPOSE OF REVIEW: Drug monitoring has become an accepted adjunct to optimizing therapy with immunosuppressive drugs. This review assesses publications that relate to the analytical techniques used to measure cyclosporin, tacrolimus, mycophenolic acid, sirolimus and everolimus, as well as the clinical data obtained for these drugs. For all of these drugs there has been a substantial and continuing investment in assessing the clinical value of drug monitoring. RECENT FINDINGS: Fundamental controversies still persist regarding which time point to use for monitoring. The most significant single development has been the move towards using a timed blood sample 2 h after drug administration (C2) to monitor cyclosporin therapy with the Neoral formulation. The favourable clinical results obtained with this approach have had an impact on reevaluating monitoring data for some of the other drugs. The newest drugs to reach clinical evaluation, sirolimus and everolimus, have been studied in the context of concentration-controlled dosing and there is a good rationale for their measurement. There have also been developments in the analytical techniques used, mostly to improve the selectivity of the assays or to adapt them to new monitoring strategies. SUMMARY: Interpretation of drug concentration data is becoming ever more complex in this field as the number of potential drug combinations expands. The relatively narrow therapeutic index of these agents and the ever-present risk of clinically significant pharmacokinetic drug interactions makes drug monitoring an important aspect of their prescription.

Animals↗

[Problems and possible errors in monitoring drug side effects at the hospital (author's transl)].

Special problems and possible errors in drug monitoring were discussed by analyzing three cases of hospital treated patients. The first one showed how easily side effects of drug can be falsely diagnosed and treated as a drug independent complicating disease. Furthermore, the active principle of the drug had to be differentiated from several potentially inducing substances. In the second case, the wrong diagnosis of a drug induced illness caused an intermission of a vital basic therapy. The lateron developing signs were interpreted as symptoms of the primary disease but they might also have been caused by drugs given later. For the third case it should be pointed out that side effects can be provoked during long- or short-term treatment by changing the diet. For drug monitoring it is therefore equally necessary to watch the drugs as well as the living circumstances.

Adult↗