Comparison of haemodynamic- and electroencephalographic-monitored effects evoked by four combinations of effect-site concentrations of propofol and remifentanil, yielding a predicted tolerance to laryngoscopy of 90.

This prospective study evaluates haemodynamic and electroencephalographic effects observed when administering four combinations of effect-site concentrations of propofol (CePROP) and remifentanil (CeREMI), all yielding a single predicted probability of tolerance of laryngoscopy of 90% (PTOL = 90%) according to the Bouillon interaction model. We aimed to identify combinations of CePROP and CeREMI along a single isobole of PTOL that result in favourable hypnotic and haemodynamic conditions. This knowledge could be of advantage in the development of drug advisory monitoring technology. 80 patients (18-90 years of age, ASA I-III) were randomized into four groups and titrated towards CePROP (Schnider model, ug⋅ml-1) and CeREMI (Minto model, ng⋅ml-1) of respectively 8.6 and 1, 5.9 and 2, 3.6 and 4 and 2.0 and 8. After eleven minutes of equilibration, baseline measurements of haemodynamic endpoints and bispectral index were compared with three minutes of responsiveness measurements after laryngoscopy. Before laryngoscopy, bispectral index differed significantly (p < 0.0001) between groups in concordance with CePROP. Heart rate decreased with increasing CeREMI (p = 0.001). The haemodynamic and arousal responses evoked by laryngoscopy were not significantly different between groups, but CePROP = 3.6 µg⋅ml-1 and CeREMI = 4 ng⋅ml-1 evoked the lowest median value for ∆HR and ∆SAP after laryngoscopy. This study provides clinical insight on the haemodynamic and hypnotic consequences, when a model based predicted PTOL is used as a target for combined effect-site controlled target- controlled infusion of propofol and remifentanil. Heart rate and bispectral index were significantly different between groups despite a theoretical equipotency for PTOL, suggesting that each component of the anaesthetic state (immobility, analgesia, and hypnotic drug effect) should be considered as independent neurophysiological and pharmacological phenomena. However, claims of (in)accuracy of the predicted PTOL must be considered preliminary because larger numbers of observations are required for that goal.

Pharmacokinetic Modeling and Limited Sampling Strategies Based on Healthy Volunteers for Monitoring of Ertapenem in Patients with Multidrug-Resistant Tuberculosis.

Ertapenem is a broad-spectrum carbapenem antibiotic whose activity against Mycobacterium tuberculosis is being explored. Carbapenems have antibacterial activity when the plasma concentration exceeds the MIC at least 40% of the time (40% TMIC). To assess the 40% TMIC in multidrug-resistant tuberculosis (MDR-TB) patients, a limited sampling strategy was developed using a population pharmacokinetic model based on data for healthy volunteers. A two-compartment population pharmacokinetic model was developed with data for 42 healthy volunteers using an iterative two-stage Bayesian method. External validation was performed by Bayesian fitting of the model developed with data for volunteers to the data for individual MDR-TB patients (in which the fitted values of the area under the concentration-time curve from 0 to 24 h [AUC0-24, fit values] were used) using the population model developed for volunteers as a prior. A Monte Carlo simulation (n = 1,000) was used to evaluate limited sampling strategies. Additionally, the 40% TMIC with the free fraction (f 40% TMIC) of ertapenem in MDR-TB patients was estimated with the population pharmacokinetic model. The population pharmacokinetic model that was developed was shown to overestimate the area under the concentration-time curve from 0 to 24 h (AUC0-24) in MDR-TB patients by 6.8% (range, -17.2 to 30.7%). The best-performing limited sampling strategy, which had a time restriction of 0 to 6 h, was found to be sampling at 1 and 5 h (r2 = 0.78, mean prediction error = -0.33%, root mean square error = 5.5%). Drug exposure was overestimated by a mean percentage of 4.2% (range, -15.2 to 23.6%). When a free fraction of 5% was considered and the MIC was set at 0.5 mg/liter, the minimum f 40% TMIC would have been exceeded in 9 out of 12 patients. A population pharmacokinetic model and limited sampling strategy, developed using data from healthy volunteers, were shown to be adequate to predict ertapenem exposure in MDR-TB patients.

Pharmacokinetic and pharmacodynamic interactions in anaesthesia. A review of current knowledge and how it can be used to optimize anaesthetic drug administration.

This review describes the basics of pharmacokinetic and pharmacodynamic drug interactions and methodological points of particular interest when designing drug interaction studies. It also provides an overview of the available literature concerning interactions, with emphasis on graphic representation of interactions using isoboles and response surface models. It gives examples on how to transform this knowledge into clinically and educationally applicable (bedside) tools.

A pharmacokinetic-pharmacodynamic model for intrathecal baclofen in patients with severe spasticity.

AIMS: Intrathecal baclofen (ITB) has proven to be an effective and safe treatment for severe spasticity. However, although ITB is used extensively, clinical decisions are based on very scarce pharmacokinetic-pharmacodynamic (PKPD) data. The aim of this study was to measure baclofen CSF concentrations and clinical effects after administration of various ITB boluses in patients with spasticity and to create a PKPD model for ITB. METHODS: Twelve patients with severe spasticity received four different bolus doses of ITB (0, 25, 50, 75 µg and an optional dose of 100 µg), administered via a catheter with the tip at thoracic level (Th) 10. After each bolus, 10 CSF samples were taken at fixed time intervals, using a catheter with the tip located at Th12. Clinical effect was assessed by measuring spasticity with the Modified Ashworth Scale (MAS). These data were used to develop a PKPD model. RESULTS: All patients achieved an adequate spasmolytic effect with ITB doses varying from 50 to 100 µg. No serious side effects were observed. CSF baclofen concentrations, as well as the clinical effects, correlated significantly with ITB doses. The PK model predicted a steep spinal concentration gradient of ITB along the spinal axis. The clinical effect could be predicted using a delayed-effect model. CONCLUSIONS: ITB is an effective and safe therapy with, however, a steep concentration gradient along the spinal axis. This means that the administered baclofen is staying mainly around the catheter tip, which stresses the importance to position the ITB catheter tip closely to the targeted spinal level.

Probability to tolerate laryngoscopy and noxious stimulation response index as general indicators of the anaesthetic potency of sevoflurane, propofol, and remifentanil.

BACKGROUND: The probability to tolerate laryngoscopy (PTOL) and its derivative, the noxious stimulation response index (NSRI), have been proposed as measures of potency of a propofol-remifentanil drug combination. This study aims at developing a triple drug interaction model to estimate the combined potency of sevoflurane, propofol, and remifentanil in terms of PTOL. We compare the predictive performance of PTOL and the NSRI with various anaesthetic depth monitors. METHODS: Data from three previous studies (n=120) were pooled and reanalysed. Movement response after laryngoscopy was observed with different combinations of propofol-remifentanil, sevoflurane-propofol, and sevoflurane-remifentanil. A triple interaction model to estimate PTOL was developed. The NSRI was derived from PTOL. The ability of PTOL and the NSRI to predict observed tolerance of laryngoscopy (TOL) was compared with the following other measures: (i) effect-site concentrations of sevoflurane, propofol, and remifentanil (CeSEVO, CePROP, and CeREMI); (ii) bispectral index; (iii) two measures of spectral entropy; (iv) composite variability index; and (v) surgical pleth index. RESULTS: Sevoflurane and propofol interact additively, whereas remifentanil interacts in a strongly synergistic manner. The effect-site concentrations of sevoflurane and propofol at a PTOL of 50% (Ce50; se) were 2.59 (0.13) vol % and 7.58 (0.49) µg ml(-1). A CeREMI of 1.36 (0.15) ng ml(-1) reduced the Ce50 of sevoflurane and propofol by 50%. The common slope factor was 5.22 (0.52). The PTOL and NSRI predict the movement response to laryngoscopy best. CONCLUSIONS: The triple interaction model estimates the potency of any combination of sevoflurane, propofol, and remifentanil expressed as either PTOL or NSRI.

Long-term exposure to circulating platinum is associated with late effects of treatment in testicular cancer survivors.

BACKGROUND: The success of cisplatin-based (Platinol, Bristol-Myers Squibb Company, New York, NY, USA) chemotherapy for testicular cancer comes at the price of long-term and late effects related to healthy tissue damage. We assessed and modelled serum platinum (Pt) decay after chemotherapy and determined relationships between long-term circulating Pt levels and known late effects. PATIENTS AND METHODS: In 99 testicular cancer survivors, treated with cisplatin-based chemotherapy, serum and 24-h urine samples were collected during follow-up (1-13 years after treatment). To build a population pharmacokinetic model, measured Pt data were simultaneously analysed, together with cisplatin dose, age, weight and height using the NONMEM software. Based on this model, area under the curve between 1 and 3 years after treatment (Pt AUC1-3 years) was calculated for each patient. Predicted long-term Pt exposure was related to renal function and to late effects of treatment assessed median 9 (3-15) years after chemotherapy. RESULTS: Decay of Pt was best described by a two-compartment model. Mean terminal T1/2 was 3.7 (range 2.5-5.2) years. Pt AUC1-3 years correlated with cumulative cisplatin dose, and creatinine clearance before and 1 year after treatment. Patients with paraesthesia had higher Pt AUC1-3 years (30.9 versus 27.0 µg/l month) compared with those without paraesthesia (P = 0.021). Patients with hypogonadism, elevated LDL-cholesterol levels or hypertension also had higher Pt AUC1-3 years. CONCLUSIONS: Renal function before and after cisplatin treatment is an important determinant of long-term Pt exposure. Known long-term effects of testicular cancer treatment, such as paraesthesia, hypogonadism, hypercholesterolaemia and hypertension, are associated with long-term circulating Pt exposure.

Pharmacokinetics of clomipramine during pregnancy.

PURPOSE: Clomipramine is one of the drugs for depression during pregnancy; however, pharmacokinetic data of clomipramine and its active metabolite desmethylclomipramine in this vulnerable period are lacking. In this study, we describe clomipramine and desmethylclomipramine concentrations including their ratios during pregnancy. Second, we describe Center for Epidemiologic Studies Depression scale (CES-D) scores during pregnancy. METHODS: During 13 pregnancies, every trimester and 3 months after pregnancy, the clomipramine and desmethylclomipramine concentrations were measured with LC-MSMS and the severity of depression was assessed by taking the CES-D score. All concentrations used in our calculations were in fact the ratio between actual plasma concentration (µg/l) and the actual dose (mg). We compared differences in ratios between trimesters by using the Friedman test. RESULTS: Studying 12 women and 13 pregnancies, we found no changes in mean clomipramine concentrations, a statistically significant decrease in mean desmethylclomipramine concentrations (p = 0.014) and a significant decrease in the ratio of desmethylclomipramine/clomipramine mean concentrations during pregnancy (p = 0.014) compared to the post-partum period. Sub-therapeutic concentrations of clomipramine and desmethylclomipramine were found in three patients during whole pregnancy. CONCLUSIONS: The mean concentrations of the pharmacologically active metabolite of clomipramine and desmethylclomipramine changes during pregnancy, where a decrease in mean concentrations was found during pregnancy. In case of recurrent disease, we recommend to control clomipramine and its metabolite concentrations, while both are active.

Is time to peak effect of neuromuscular blocking agents dependent on dose? Testing the concept of buffered diffusion.

BACKGROUND AND OBJECTIVES: For neuromuscular blocking agents, an inverse relationship between potency and time to peak effect has been observed. To test the hypothesis that this relationship is due to buffered diffusion, we investigated the influence of dose on time to peak effect. Pharmacokinetic-pharmacodynamic simulations were performed to support the expected relationships between potency, dose, peak effect and time to peak effect. METHODS: Pigs (20-28 kg body weight) were anaesthetized with ketamine and midazolam, followed by pentobarbital and fentanyl intravenously. Neuromuscular block was measured by stimulating the peroneal nerve supramaximally at 0.1 Hz and measuring the response of the tibialis anterior muscle mechanomyographically. After an initial dose to establish the individual ED90 of a neuromuscular blocking agent (rocuronium, vecuronium, pipecuronium or d-tubocurarine), five different doses of the same compound were administered to each animal, aiming at 20%, 40%, 60%, 75% or 90% block, in a random order. Doses were given 45 min after complete recovery of the twitch response. RESULTS: For rocuronium and pipecuronium, time to peak effect increased with dose, whereas dose did not affect time to peak effect of vecuronium and d-tubocurarine. Simulations predict that time to peak effect decreases with dose if buffered diffusion is taken into account. CONCLUSIONS: The results suggest that buffered diffusion does not play a dominant role in the time to peak effect of neuromuscular blocking agents. Therefore it is unlikely that the observed inverse relationship between potency and time to peak effect of neuromuscular blocking agents in the clinical range is due to buffered diffusion.

Validation of limited sampling models (LSM) for estimating AUC in therapeutic drug monitoring--is a separate validation group required?

OBJECTIVE: Limited sampling models (LSM) for estimating AUC in therapeutic drug monitoring are usually validated in a separate group of patients, according to published guidelines. The aim of this study is to evaluate the validation of LSM by comparing independent validation with cross-validation using the patient data from the development group. METHODS: The design of the Monte Carlo simulation study was similar to a study described in the literature, i.e. a development group of 20 patients receiving cyclosporine orally every 12 h. Blood samples were taken at 10 fixed time points. In total 20,000 patient data sets were generated by Monte Carlo simulation, taking into account interindividual variability and measurement errors. Accuracy (mean error, ME) and precision (root mean squared error, RMSE) were calculated for evaluation of the validation procedures, varying the time points of the samples used for the estimation of AUC to identify the optimal sampling time points. In addition, the influence of the number of samples and the number of subjects was investigated. RESULTS: Cross-validation resulted in values for ME and RMSE almost identical to values using a separate validation group with the same number of subjects as the development group. CONCLUSION: A separate validation group is not needed. The most efficient method is to use all patient data for the development of the LSM, and to assess the accuracy and precision by cross-validation.

Limited sampling strategies for therapeutic drug monitoring of amikacin and kanamycin in patients with multidrug-resistant tuberculosis.

Amikacin and kanamycin are considered important and effective drugs in the treatment of multidrug-resistant tuberculosis (MDR-TB). Unfortunately, the incidence of toxicity is high and is related to elevated drug exposure. In order to achieve a balance between efficacy and toxicity, a population pharmacokinetic (PPK) model may help to optimise drug exposure. Patients with MDR-TB who had received amikacin or kanamycin as part of their treatment and who had routinely received therapeutic drug monitoring were evaluated. A PPK model was developed and subsequently validated. Using this model, a limited sampling model was developed. Eleven patients receiving amikacin and nine patients receiving kanamycin were included in this study. The median observed 24-h area under the concentration-time curve (AUC0-24h) was 77.2 mg h/L [interquartile range (IQR) 64.7-96.2 mg h/L] for amikacin and 64.1 mg h/L (IQR 55.6-92.1 mg h/L) for kanamycin. The PPK model was developed and validated using n-1 cross-validation. A robust population model was developed that is suitable for predicting the AUC0-24h of amikacin and kanamycin. This model, in combination with the limited sampling strategy developed, can be used in daily routine to guide dosing but also to assess AUC0-24h in phase 3 studies.

Pharmacokinetics and pharmacodynamics of rocuronium at the vocal cords and the adductor pollicis in humans.

The pharmacokinetic-pharmacodynamic relationship of rocuronium at the laryngeal adductor muscles and the adductor pollicis was determined in eight patients during general anesthesia. Rocuronium was administered as an infusion at a rate of 100 micrograms.kg-1.min-1 over 5 minutes. The half-life of transport between plasma and biophase (effect compartment) was significantly shorter at the adductor laryngeal muscles (2.7 +/- 0.6 minutes, mean +/- SD) than at the adductor pollicis (4.4 +/- 1.5 minutes, p = 0.003). The concentration in the effect compartment producing 50% of the maximum effect was significantly greater at the adductor laryngeal muscles (1424 +/- 148 micrograms.L-1) than at the adductor pollicis (823 +/- 157 micrograms.L-1, p = 0.0001). The shorter onset of neuromuscular blockade at the laryngeal muscles than at the adductor pollicis may be explained by a faster transfer rate at the laryngeal adductor muscles neuromuscular junction than at the adductor pollicis neuromuscular junction.

Pharmacokinetic studies in children with cancer.

We reviewed the current status of our knowledge of pharmacokinetics and pharmacodynamics of some anti-neoplastic drugs, used in the treatment of childhood cancer. Extrapolation of data from pharmacokinetic studies in adults to the paediatric population is often not feasible. Specific studies in children are needed. Of all reviewed anti-neoplastic drugs methotrexate appears to be most extensively studied. Methotrexate pharmacokinetics is correlated with toxicity and response to therapy, and it has been shown that individualized adaptive dosing of methotrexate is correlated with a better response to therapy without increasing toxicity in children with ALL and osteosarcoma. Of most of the other reviewed anti-neoplastic drugs it is demonstrated that pharmacokinetics is correlated with toxicity, and of some drugs a relationship of pharmacokinetics with response to therapy is demonstrated as well. In case of cytarabine, etoposide, and teniposide, individualized dosing also appears to be feasible. However, there is no evidence that this strategy improves response to therapy. Specifically data on pharmacokinetic and pharmacodynamic correlations and effect of pharmacokinetically guided, individualized dosing are important for the design of optimal cancer chemotherapy for individual patients. Unfortunately for a considerable number of anti-neoplastic drugs these specific data are lacking in children and future research is needed.

Pharmacokinetics of pancuronium in patients undergoing coronary artery surgery with and without low dose dopamine.

Pancuronium is frequently used in coronary artery surgery, but its pharmacokinetics in these patients are still unknown. It is possible that dopamine, administered to prevent renal impairment induced by the surgery, might promote the elimination of pancuronium. Therefore, the pharmacokinetics of a bolus dose of pancuronium were studied in 2 groups of coronary artery surgery patients, with and without dopamine 2 micrograms/kg/min, administered during and after cardiopulmonary bypass. Dopamine in the administered dose did not influence the systemic haemodynamics. The pharmacokinetic variables in both groups did not differ from those found in an earlier study in healthy normothermic patients. Total renal clearance was not influenced by dopamine, due to post-bypass rebound hyperperfusion in the control group. Pancuronium was shown to be subject to considerable tubular reabsorption, and its elimination was found to be increased during hypothermia. Dopamine increases pancuronium elimination by an increase in glomerular filtration rate. The dopamine-induced decrease in tubular solute reabsorption did not enhance the elimination of pancuronium.

Pharmacokinetics and anti-HIV-1 efficacy of negatively charged human serum albumins in mice.

Negatively charged albumins (NCAs, with the prototypes succinylated human serum albumin (Suc-HSA) and aconitylated human serum albumin (Aco-HSA)), modified proteins with a potent anti-human immunodeficiency virus type 1 (anti-HIV-1) activity in vitro, were studied for their pharmacokinetic behaviour in mice and their in vivo anti-HIV-1 efficacy in an HIV-1 infection model in mice. In contrast to the saturation kinetics found in rats, intravenous injections of 10-300 mg/kg for both NCAs showed a linear correlation between the area under the curve (AUC) and the dose. The elimination t1/2 was 25 and 30 min for Suc-HSA and Aco-HSA, respectively. Preinjections of an excess of formaldehyde-treated albumin (Form-HSA) resulted in plasma levels that were 3- and 4-fold higher for Aco-HSA and Suc-HSA, respectively. These data indicate that elimination is at least partly (scavenger) receptor-mediated. Organ distribution studies 10 min after injection showed an accumulation in liver (Suc-HSA 17.3 +/- 6.6% of the dose; Aco-HSA 20.9 +/- 2.3%) and lungs (Suc-HSA 12.7 +/- 10.5%; Aco-HSA 16.0 +/- 13.6). Intraperitoneal injection of 300 mg/kg Suc-HSA resulted in a final bioavailability of about 0.45. Suc-HSA was also evaluated for its in vivo neutralizing capacity in a human-to-mouse chimeric model for HIV-1 infection. Intraperitoneal injections of 300 and 3 mg/kg Suc-HSA, given 15-30 min before the mice were challenged with the virus, sufficed to protect these mice against infection with the HIV-1 IIIB strain.

Adaptive control of drug dosage regimens using maximum a posteriori probability Bayesian fitting.

Optimal drug therapy can only be achieved if a drug is given in the right dosage regimen. Therefore the dosage regimen needs to be optimized, using the available information of the drug, the patient, and his disease. The optimization of drug therapy comprises two major steps: First, the clinician should define explicit therapeutic goals for each patient individually. Second, a strategy to achieve these goals with the greatest possible precision should be chosen. An overview of the optimization of drug therapy is presented, with special reference to maximum a posteriori probability (MAP) Bayesian fitting. Drug dosage optimization requires 1. measurement of a performance index related to the therapeutic goal, generally one or more plasma concentration measurements, 2. population pharmacokinetic parameters, including mean values, standard deviations, covariances and information on the statistical distribution, and 3. reliable software for adaptive control strategy and optimal dosage regimen calculation. The benefit of optimal drug therapy by adaptive control using MAP Bayesian fitting has been proven, resulting in improved patient outcome by improved efficacy of therapy and a reduction of adverse reactions, and in reduced costs, mainly due to a reduction of hospitalization. Newer strategies might replace the MAP Bayesian fitting procedure, if their advantage has been demonstrated convincingly, and if reliable and user-friendly software is available.

Dose individualization in PharmDIS-e+.

Individualized dosage regimen calculations require knowledge on the pharmacokinetic and pharmacodynamic properties of the drug and the characteristics of the patient. A PK-PD-based dosage regimen is not easily and generally applicable, mainly because the combination of available PK parameters and therapeutic target levels may be inappropriate for the purpose of predicting a plausible dosage regimen. Within the project PharmDIS-e+, an alternative approach was chosen, and this "PK and standard dose"-based principle is well suited for computerized dosing advice. PharmDIS-e+ aims at the development of several applications for dosing regimen advice for general practitioners, hospital physicians and pharmacists.

Pharmacokinetics of Succinylated Serum Albumin in Wistar Rats and Cynomolgus Monkeys: Implications for Dosage Regimens in the Therapy of HIV Infection.

Succinylation of serum albumin produces a negatively charged protein with a potent anti-HIV-1/2 and anti-SIVmac activity. The in vitro IC50 values of Suc-HSA against the respective primate lentiviruses are in the low nanomolar concentration range. Succinylated homologous serum albumin was given intravenously at four different doses, ranging from 0.1 to 10 mg/kg to Wistar rats and Cynomolgus monkeys. Plasma samples were assayed for their drug content using iodinated proteins. The pharmacokinetics parameters were calculated by a single compartment model, taking into account a potential saturable elimination process. In rats as well as in monkeys succinylated serum albumin clearly showed dose-dependent kinetics. The rate of Suc-SSA elimination from the bloodstream in macaques could be described by a Vmax of 11.7 ± 0.2 µg/min kg-(1) and a K. of 0.40 ± 0.06 µg/mL (5.5 nM). The elimination of Suc-RSA in rats was characterized by a 10-fold higher V. of 112 ± 29 µg/min kg(-1) and a much higher K. of 25 ± 9 µg/mL (340 nM). The volume of distribution was about the plasma volume for both species. In rats, no significant differences were found between the kinetic parameters of Suc-RSA, Suc-HSA, or Suc-SSA. Histochemical staining of tissue sections obtained from the liver, spleen, kidneys, and different lymph nodes showed that endothelial cells and macrophages from the liver and spleen are involved in the clearance of the negatively charged albumins. Since replication of HIV mainly takes place in the lymphoid tissue, uptake of succinylated albumin in this system may imply an interesting therapeutic aspect of the negatively charged albumins.

MW/Pharm, an integrated software package for drug dosage regimen calculation and therapeutic drug monitoring.

The pharmacokinetic software package MW/Pharm offers an interactive, user-friendly program which gives rapid answers in clinical practice. It comprises a database with pharmacokinetic parameters of 180 drugs, a medication history database, and procedures for an individual drug dosage regimen calculation. The included curve-fitting facilities allow estimation of pharmacokinetic parameters on the basis of medication history, taking into account a varying status of the patient with respect to body weight and kidney function, optionally using a Bayesian procedure. The module KinBes performs the evaluation of bioavailability studies, including various methods, and an extensive statistical evaluation of bioequivalence.

Pharmacokinetic-pharmacodynamic modeling of severity levels of extrapyramidal side effects with markov elements.

A major problem in the treatment of schizophrenic patients with current antipsychotic drugs, mainly acting as dopamine-2 receptor antagonists, is the occurrence of side effects such as extrapyramidal symptoms (EPS). Meta-analyses of summary data of EPS occurrence, and receptor occupancies inferred from mean plasma concentrations, have shown the incidence of EPS to rise when receptor occupancy is above ~80%. In this analysis, individual longitudinal EPS data from 2,630 patients participating in one of seven different trials and treated with haloperidol, paliperidone, ziprasidone, olanzapine, JNJ-37822681, or placebo were analyzed using a continuous time probability model with Markov elements. The developed pharmacokinetic-pharmacodynamic model describes the longitudinal changes of spontaneously reported EPS-related adverse events and their severity levels rated by clinicians. Individual steady-state concentrations and occupancy levels were found to be predictors for EPS. The results confirm 80% occupancy as a level of increased EPS occurrence rates, also at the individual level.CPT: Pharmacometrics & Systems Pharmacology (2012) 1, e1; doi:10.1038/psp.2012.9; advance online publication 26 September 2012.