Population pharmacokinetics of levodopa in patients with Parkinson's disease treated with tolcapone

Comparability of Foslevodopa/Foscarbidopa Pharmacokinetics in Healthy Asian and White Participants

This phase 1 study assessed the safety, tolerability, and pharmacokinetics of a single 24-hour continuous subcutaneous dose of foslevodopa/foscarbidopa in healthy adult Japanese (N = 24), Han Chinese (N = 8), and White (N = 24) participants. Three doses of foslevodopa/foscarbidopa were evaluated in healthy participants for this study: 480/24, 960/48, and 1440/72 mg/day. Serial blood samples for measurement of levodopa, carbidopa, foslevodopa, foscarbidopa, and 3-O-methyldopa concentrations were collected for 48 hours after foslevodopa/foscarbidopa administration. Safety and tolerability were assessed throughout the study. Point estimates for ratios of central values indicated that the exposure difference between Japanese and White participants was <10%. The maximum concentration and area under the plasma concentration-time curve for both LD and CD following foslevodopa/foscarbidopa continuous subcutaneous infusion were comparable between Han Chinese and White participants. Point estimates for ratios of central values indicated that the exposure difference between Han Chinese and White participants was <14%. The regimens tested were generally well tolerated, and no new safety issues were identified in this study. There were no clinically meaningful differences in LD and CD exposures or pharmacokinetics following administration of foslevodopa/foscarbidopa among White, Japanese, and Han Chinese participants.

Population pharmacokinetics of levodopa gel infusion in Parkinson's disease: effects of entacapone infusion and genetic polymorphism

Levodopa-entacapone-carbidopa intestinal gel (LECIG) provides continuous drug delivery through intrajejunal infusion. The aim of this study was to characterize the population pharmacokinetics of levodopa following LECIG and levodopa-carbidopa intestinal gel (LCIG) infusion to investigate suitable translation of dose from LCIG to LECIG treatment, and the impact of common variations in the dopa-decarboxylase (DDC) and catechol-O-methyltransferase (COMT) genes on levodopa pharmacokinetics. A non-linear mixed-effects model of levodopa pharmacokinetics was developed using plasma concentration data from a double-blind, cross-over study of LCIG compared with LECIG in patients with advanced Parkinson’s disease (n = 11). All patients were genotyped for rs4680 (polymorphism of the COMT gene), rs921451 and rs3837091 (polymorphisms of the DDC gene). The final model was a one compartment model with a high fixed absorption rate constant, and a first order elimination, with estimated apparent clearances (CL/F), of 27.9 L/h/70 kg for LCIG versus 17.5 L/h/70 kg for LECIG, and apparent volume of distribution of 74.4 L/70 kg. Our results thus suggest that the continuous maintenance dose of LECIG, on a population level, should be decreased by approximately 35%, to achieve similar drug exposure as with LCIG. An effect from entacapone was identified on all individuals, regardless of COMT rs4680 genotype. The individuals with higher DDC and COMT enzyme activity showed tendencies towards higher levodopa CL/F. The simultaneous administration of entacapone to LCIG administration results in a 36.5% lower apparent levodopa clearance, and there is a need for lower continuous maintenance doses, regardless of patients’ COMT genotype.

Population pharmacokinetics of levodopa/carbidopa microtablets in healthy subjects and Parkinson's disease patients

OBJECTIVES

Low dose, dispersible, levodopa/carbidopa microtablets with an automatic dose dispenser have been developed to facilitate individualized levodopa treatment. The aim of this study was to characterize the pharmacokinetics (PK) of levodopa and carbidopa after microtablet administration, and evaluate the impact of potential covariates.

METHODS

The population PK analysis involved data from 18 healthy subjects and 18 Parkinson's disease patients included in two single-dose, open-label levodopa/carbidopa microtablet studies. The analysis was carried out using non-linear mixed effects modeling. Bodyweight was included on all disposition parameters according to allometric scaling. Potential influence of additional covariates was investigated using graphical evaluation and adjusted adaptive least absolute shrinkage and selection operator.

RESULTS

Dispositions of levodopa and carbidopa were best described by a two- and one-compartment model respectively. Double-peak profiles were described using two parallel absorption compartments. Levodopa apparent clearance was found to decrease with increasing carbidopa dose (15% lower with 75 compared to 50 mg of carbidopa) and disease stage (by 18% for Hoehn and Yahr 1 to 4). Carbidopa apparent clearance was found to decrease with age (28% between the age of 60 and 80 years). An external evaluation showed the model to be able to reasonably well predict levodopa concentrations following multiple-dose microtablet administration in healthy subjects.

CONCLUSIONS

The presented models adequately described the PK of levodopa and carbidopa, following microtablet administration. The developed model may in the future be combined with a pharmacokinetic-pharmacodynamic target and used for individualized dose selection, utilizing the flexibility offered by the microtablets.

Methods and strategies for assessing uncontrolled drug-drug interactions in population pharmacokinetic analyses: results from the International Society of Pharmacometrics (ISOP) Working Group

The purpose of this work was to present a consolidated set of guidelines for the analysis of uncontrolled concomitant medications (ConMed) as a covariate and potential perpetrator in population pharmacokinetic (PopPK) analyses. This white paper is the result of an industry-academia-regulatory collaboration. It is the recommendation of the working group that greater focus be given to the analysis of uncontrolled ConMeds as part of a PopPK analysis of Phase 2/3 data to ensure that the resulting outcome in the PopPK analysis can be viewed as reliable. Other recommendations include: (1) collection of start and stop date and clock time, as well as dose and frequency, in Case Report Forms regarding ConMed administration schedule; (2) prespecification of goals and the methods of analysis, (3) consideration of alternate models, other than the binary covariate model, that might more fully characterize the interaction between perpetrator and victim drug, (4) analysts should consider whether the sample size, not the percent of subjects taking a ConMed, is sufficient to detect a ConMed effect if one is present and to consider the correlation with other covariates when the analysis is conducted, (5) grouping of ConMeds should be based on mechanism (e.g., PGP-inhibitor) and not drug class (e.g., beta-blocker), and (6) when reporting the results in a publication, all details related to the ConMed analysis should be presented allowing the reader to understand the methods and be able to appropriately interpret the results.

Population pharmacokinetics of levodopa in subjects with advanced Parkinson's disease: levodopa-carbidopa intestinal gel infusion vs. oral tablets

AIMS

Levodopa-carbidopa intestinal gel (LCIG) provides continuous levodopa-carbidopa delivery through intrajejunal infusion. This study characterized the population pharmacokinetics of levodopa following a 16 h jejunal infusion of LCIG or frequent oral administration of levodopa-carbidopa tablets (LC-oral) in subjects with advanced Parkinson's disease (PD).

METHODS

A non-linear mixed-effects model of levodopa pharmacokinetics was developed using serial plasma concentrations from an LCIG phase 1 study and a phase 3 double-blind, double-dummy study of the efficacy and safety of LCIG compared with LC-oral in advanced PD patients (n = 68 for model development; 45 on LCIG and 23 on LC-oral). The final model was internally evaluated using stochastic simulations and bootstrap and externally evaluated using sparse pharmacokinetic data from 311 subjects treated in a long term safety study of LCIG.

RESULTS

The final model was a two compartment model with a transit compartment for absorption, first order elimination, bioavailability for LCIG (97%; confidence interval = 95% to 98%) relative to LC-oral, different first order transit absorption rate constants (LCIG = 9.2 h(-1) vs. LC-oral = 2.4 h(-1) ; corresponding mean absorption time of 7 min for LCIG vs. 25 min for LC-oral) and different residual (intra-subject) variability for LCIG (15% proportional error, 0.3 μg ml(-1) additive error) vs. LC-oral (29% proportional error, 0.59 μg ml(-1) additive error). Estimated oral clearance and steady-state volume of distribution for levodopa were 24.8 l h(-1) and 131 l, respectively.

CONCLUSIONS

LCIG administration results in faster absorption, comparable levodopa bioavailability and significantly reduced intra-subject variability in levodopa concentrations relative to LC-oral administration.

Empirical and semi-mechanistic modelling of double-peaked pharmacokinetic profile phenomenon due to gastric emptying

Models have been developed to explain double-peaked plasma concentration-time profiles using mechanisms such as variable absorption and enterohepatic recirculation. Interruption of gastric emptying has also been shown to produce double-peaks, and this work proposes models for analysis of such data. In the presence of levodopa, gastric emptying is interrupted at times associated with double-peaks in pharmacokinetic profiles. Data from a simultaneous scintigraphy and paracetamol absorption study with levodopa was obtained, and models with compartments for stomach, intestine, central and peripheral tissue were developed to describe levodopa and paracetamol pharmacokinetics, including the double-peak phenomenon. The empirical model uses two gastric emptying parameter rates which are applied over separate time periods to describe the varying gastric emptying rate. The semi-mechanistic model uses a feedback mechanism acting via an effect compartment to link the plasma concentration of levodopa to the rate of gastric emptying, allowing levodopa pharmacokinetics to vary the rate of gastric emptying and give rise to a multiple-peaked plasma pharmacokinetic profile. The models were applied to plasma levodopa and paracetamol pharmacokinetic data with and without simultaneous analysis of scintigraphy data, in both cases giving a good fit and in the absence of scintigraphy data adequately predicting the stomach profile. For the semi-mechanistic model, the first-order constant governing gastric emptying was shown to switch between fast and slow values at a critical levodopa effect compartment concentration. New models have thus been proposed for analysis of plasma concentration profiles that exhibit double-peak phenomenon and applied successfully to levodopa data.

Effect of opicapone and entacapone upon levodopa pharmacokinetics during three daily levodopa administrations

BACKGROUND AND OBJECTIVES

Opicapone is a novel third generation catechol-O-methyltransferase (COMT) inhibitor. The purpose of this study was to compare the levodopa pharmacokinetic profile throughout a day driven by the COMT inhibition either following repeated doses of opicapone or concomitant administration with entacapone.

METHODS

A randomized, double-blind, gender-balanced, parallel-group study was performed in 4 groups of 20 healthy subjects each. Four subjects in each group received placebo during the entire study. Sixteen subjects in one group received placebo once daily for 11 days and on day 12, 200 mg entacapone concomitantly with each levodopa/carbidopa dose (three times separated by a 5-h interval). Sixteen subjects in each of the remaining three groups received respectively 25, 50, and 75 mg opicapone once daily for 11 days and on day 12, placebo concomitantly with each levodopa/carbidopa dose.

RESULTS

Levodopa minimum plasma concentration (Cmin) for each levodopa/carbidopa dose and for the mean of all levodopa/carbidopa doses increased substantially with all active treatments (entacapone and opicapone) when compared to the control group (placebo), with values ranging from 1.7-fold (200 mg entacapone) to 3.3-fold (75 mg opicapone). No statistical difference was found for levodopa peak of systemic exposure (as assessed by maximum observed plasma concentration (Cmax)) between all active treatments and placebo. A significant increase in the levodopa extent of systemic exposure (as assessed by concentration-time curve (AUC)) occurred with all opicapone treatments in relation to placebo. No statistical difference was found for levodopa AUC when entacapone was compared to placebo. When compared to entacapone, both 50 and 75 mg opicapone presented a significant increase for the levodopa AUC. All active treatments significantly inhibited both peak (as assessed by Emax) and extent (as assessed by effect-time curve (AUEC)) of the COMT activity in relation to placebo. When compared to entacapone, all opicapone treatments significantly decreased the extent (AUEC) of the COMT activity due to a long-lasting and sustained effect. The tolerability profile was favorable for all active treatments.

CONCLUSION

Opicapone, a novel third generation COMT inhibitor, when compared to entacapone, provides a superior response upon the bioavailability of levodopa associated to more pronounced, long-lasting, and sustained COMT inhibition. The tolerability profile was favorable. On the basis of the results presented in this study and along with the earlier pharmacology studies, it is anticipated that opicapone adjunct therapy at the dosages of 25 and 50 mg will provide an enhancement in levodopa availability that will translate into clinical benefit for Parkinson's disease patients.

Pharmacologic Options for Treatment of Levodopa-Associated ``Wearing Off''

Levodopa remains the gold standard drug for the treatment of Parkinson's disease, but the combination of disease progression and prolonged treatment can lead to ``wearing-off'' problems in the majority of patients. This constitutes the onset of motor fluctuations which includes nonmotor sensory, psychiatric, and autonomic ``off '' symptoms. There are several pharmacologic options to minimize the ``wearing-off'' phenomenon, including adjustment of levodopa treatment, the use of long-acting dopamine agonists, monoamine oxidase type B inhibition, or catechol-O-methyl-transferase inhibition in combination with levodopa. Dopamine agonists may reduce levodopa requirements. Monoamine oxidase type B inhibition can increase dopamine availability by preventing its metabolism. Similarly catechol-O-methyl-transferase inhibitors can increase the half-life of levodopa and the amount available to cross the blood-brain barrier by preventing its breakdown. The selection of a treatment for the management of ``wearing off'' should consider the relief of symptoms and also the potential adverse effects of adjunctive therapy.

Importance of within subject variation in levodopa pharmacokinetics: a 4 year cohort study in Parkinson's disease

The purpose of the study was to describe the population pharmacokinetics of levodopa in patients with Parkinson's disease studied in 5 trials (10 occasions) over 4 years. Twenty previously untreated Parkinsonian patients were investigated. Each trial consisted of a 2-hr IV infusion of levodopa (1 mg/kg/h) with concomitant oral carbidopa given on two occasions separated by 72 hr with no levodopa in between. This trial design was repeated at 6, 12, 24 and 48 months. A two-compartment pharmacokinetic model with central volume (V1), peripheral volume (V2), clearance (CL) and inter-compartmental clearance (CL(ic)) was used to fit plasma levodopa concentrations. The model accounted for levodopa dosing prior to each trial and endogenous levodopa synthesis. Population parameter estimates (geometric mean) and population parameter variability (PPV; SD of normal distribution) were V1 11.4 l/70 kg (0.44), CL 30.9 l/h/70 kg (0.25), V2 27.3 l/70 kg (0.27), and CL(ic) 34.6 l/h/70 kg (0.48). PPV was partitioned into between subject variability (BSV) which was 0.12 V1, 0.13 CL, 0.15 V(2), 0.28 CL(ic), within trial variability (WTV) which was 0.16 V1, 0.13 CL, 0.08 V2, 0.18 CL(ic) and between trial variability (BTV) which was 0.40 V1, 0.17 CL, 0.21 V2, 0.34 CL(ic.) Neither structural nor random levodopa pharmacokinetic parameters were associated with the time course of development of fluctuation in motor response. Variability in levodopa pharmacokinetic parameters (particularly V1) may result in variability in plasma levodopa concentrations that could contribute to fluctuations in motor response.

Pharmacokinetic optimisation in the treatment of Parkinson's disease : an update

Pharmacotherapy for Parkinson's disease is focused on dopaminergic drugs, mainly the dopamine precursor levodopa and dopamine receptor agonists. The elimination half-life (t(1/2)) of levodopa from plasma (in combination with a decarboxylase inhibitor) of about 1.5 hours becomes more influential as the disease progresses. The long-duration of response to levodopa, which is evident in early Parkinson's disease, diminishes and after a few years of treatment motor performance is closely correlated to the fluctuating plasma concentrations of levodopa. Absorption of levodopa in the proximal small intestine depends on gastric emptying, which is erratic and may be slowed in Parkinson's disease. The effects of levodopa on motor function are dependent on gastric emptying in patients in the advanced stages of disease. The current treatment concept is continuous dopaminergic stimulation (CDS). Sustained-release formulations of levodopa may provide more stable plasma concentrations. Oral liquid formulations shorten the time to reach peak concentration and onset of effect but do not affect plasma levodopa variability. The t(1/2) of levodopa can be prolonged by adding a catechol-O-methyltransferase inhibitor (entacapone or tolcapone), which may reduce fluctuations in plasma concentrations, although both peak and trough concentrations are increased with frequent administration. Intravenous and enteral (duodenal/jejunal) infusions of levodopa yield stable plasma levodopa concentrations and motor performance. Enteral infusion is feasible on a long-term basis in patients with severe fluctuations. Among the dopamine receptor agonists the ergot derivatives bromocriptine, cabergoline, dihydroergocryptine and pergolide, and the non-ergot derivatives piribedil, pramipexole and ropinirole, have longer t(1/2) compared with levodopa. Thus, they stimulate dopamine receptors in a less pulsatile manner, yet pharmacokinetic studies of repeated doses of dopamine receptor agonists are few. Optimisation of these drugs is often performed with standardised titration schedules. Apomorphine and lisuride have short t(1/2) and are suitable for subcutaneous infusion, with results similar to those of levodopa infusion. Transdermal administration of dopamine receptor agonists such as rotigotine might be an alternative in the future. In general, initial dopamine receptor agonist monotherapy is associated with poorer motor performance and lower incidence of motor complications compared with levodopa. Buccal administration of the monoamine oxidase-B inhibitor selegiline (deprenyl) provides better absorption and less formation of metabolites compared with standard tablets. To conclude, several new drugs, formulations and routes of administration have been introduced in the treatment of Parkinson's disease during the last decade, mainly with CDS as the aim. CDS can be approached by optimising the use of dopaminergic drugs based on pharmacokinetic data.

Pharmacokinetic-pharmacodynamic relationship of levodopa with and without tolcapone in patients with Parkinson's disease

OBJECTIVE

To investigate the effect of administration of the catechol-Omethyltransferase (COMT) inhibitor tolcapone on the concentration-effect relationship of levodopa in patients with advanced Parkinson's disease and on-off fluctuations.

DESIGN

Nonblind single-group 2-period pharmacokinetic-pharmacodynamic study.

PATIENTS AND PARTICIPANTS

12 patients, mean age 59 years, with idiopathic Parkinson's disease and response fluctuations.

METHODS

The pharmacokinetics [plasma concentrations of levodopa and 3-O-methyldopa (3-OMD)] and motor effects [global score of the Columbia University Rating Scale (CURSsigma)] of levodopa (plus the peripheral decarboxylase inhibitor benserazide 1:4) were determined for 4 consecutive dosage intervals (4 hours each, starting at 8.00am) in 12 patients before (day 1) and during (day 8) coadministration of tolcapone 100 mg 3 times daily for 7 days.

RESULTS

Under tolcapone, exposure to levodopa [area under the plasma concentration-time for the dosage interval (AUCt)] observed for the separate doses increased by 1.6- to 2.2-fold, and peak plasma drug concentrations (Cmax) increased by 1.1 - to 2.1 -fold. 3-OMD concentrations at day 8 were reduced to about 20% of the values at day 1. At baseline (day 1, before the first levodopa dose), CURSsigma averaged 40 +/- 10 points. After the first levodopa dose. CURSsigma declined to 20 +/- 9 points. At day 8. the predose CURSsigma decreased to a final score of 31 +/-13 points, and the maximal decline after the first levodopa dose was to a final score of 16 +/- 8 points. Population analysis (NONMEM) of the concentration-effect relationship of levodopa according to a sigmoidal Emax model and over all dosage intervals did not show differences in levodopa responsiveness with or without tolcapone. The population mean of the 50% effective concentration (EC50) of levodopa was 1350 microg/L with an standard error of the population parameter estimate of 18%: adding tolcapone treatment as a covariate did not significantly change the population fit. Circadian influences on levodopa respon- siveness were not evaluable by the NONMEM model due to overparametrisation, but visual inspection of plotted data did not suggest differences in the concentration-effect relationship between the 4 consecutive dosage intervals on days 1 and 8.

CONCLUSIONS

The gain in clinical improvement with levodopa under tolcapone can be fully explained by tolcapone-induced changes of peripheral levodopa pharmacokinetics. We suggest that this interaction study, performed in patients and using clinical data, excludes any central effects of tolcapone or any inhibiting effect of 3-OMD on levodopa permeation through the blood-brain barrier, which otherwise would have led to a decrease in the EC50 of levodopa.