Plasma antipsychotic concentration and receptor occupancy, with special focus on risperidone long-acting injectable

Risperidone ISM as a New Option in the Clinical Management of Schizophrenia: A Narrative Review

Antipsychotics are the cornerstone of schizophrenia treatment. Lack of treatment adherence encouraged the development of injectable long-acting antipsychotics. However, second-generation or atypical antipsychotics require a loading dose at the start of treatment and eventually oral supplementation to achieve therapeutic plasma levels. This review discusses the evidence emerging from studies evaluating the pharmacokinetics, efficacy and safety of the intramuscular formulation of risperidone based on in situ microparticles (ISM). ISM® technology applied to risperidone allows therapeutic levels of the active moiety to be achieved within 2 h of intramuscular administration without the need for loading doses or oral supplementation, leading to a constant release over the whole dosing period. Risperidone ISM showed significant antipsychotic efficacy versus placebo in the Positive and Negative Syndrome Scale (PANSS) total score (p < 0.0001) and on the subscales of positive symptoms after 8 days, negative symptoms in 8 weeks, and general psychopathology during the 12 weeks of treatment. The improvement was also statistically significant (p < 0.0001) against placebo in the Clinical Global Impressions-Severity of Illness scale (CGI-S) score at the end of the treatment. Risperidone ISM was generally well tolerated and the most frequently reported adverse events were similar to those observed with other risperidone formulations. There is clinical evidence that these results are maintained in the long term. In conclusion, four-weekly risperidone ISM (75 mg and 100 mg) is an adequate antipsychotic for treating schizophrenia, both in the short term when an exacerbation has recently occurred and for long-term maintenance, since it provides rapid onset of action and sustained efficacy, as well as being safe and well tolerated.

Current and emerging long-acting antipsychotics for the treatment of schizophrenia

Introduction: In this review, the authors discuss the role of long-acting injectable antipsychotics (LAIs) for schizophrenia, focusing on the effectiveness and new perspectives introduced by such treatment strategy. Despite their promising pharmacokinetic features and their potential advantages in medication adherence, clinical outcomes, and medical costs, LAIs are not habitually presented as an option for patients, especially in the early phase of schizophrenia.Areas covered: This review explores the panorama of available LAIs for the treatment of schizophrenia, first-episode of psychosis, approved indications, medical costs, medication adherence, side effects, effectiveness and differences between first-generation (FGA)-LAIs and second-generation (SGA)-LAIs.Expert Opinion: LAIs differ in terms of specific indications, approved injection sites, needle size, injection volume, injection interval as well as potential drug-drug interactions, and commonly reported adverse reactions. The approved indications have expanded beyond schizophrenia to include bipolar and schizoaffective disorder. SGA-LAIs are often preferred to FGA-LAIs. FGA-LAIs although are less chosen in new patients due to the induction of cognitive and extrapyramidal side effects, even if, on the other hand, many SGA-LAIs are burden by hyperprolactinemia and weight gain. After a review of the available evidence, insight is provided into the potential and current therapeutic opportunities offered by LAI antipsychotic formulations.

Therapeutic Drug Monitoring of Long-Acting Injectable Antipsychotic Drugs

BACKGROUND

The use of therapeutic drug monitoring (TDM) to guide treatment with long-acting injectable (LAI) antipsychotics, which are increasingly prescribed, remains a matter of debate. The aim of this review was to provide a practical framework for the integration of TDM when switching from an oral formulation to the LAI counterpart, and in maintenance treatment.

METHODS

The authors critically reviewed 3 types of data: (1) positron emission tomography data evaluating dopamine (D2/D3) receptor occupancy related to antipsychotic concentrations in serum or plasma; D2/D3 receptors are embraced as target sites in the brain for antipsychotic efficacy and tolerability, (2) pharmacokinetic studies evaluating the switch from oral to LAI antipsychotics, and (3) pharmacokinetic data for LAI formulations. Based on these data, indications for TDM and therapeutic reference ranges were considered for LAI antipsychotics.

RESULTS

Antipsychotic concentrations in blood exhibited interindividual variability not only under oral but also under LAI formulations because these concentrations are affected by demographic characteristics such as age and sex, genetic peculiarities, and clinical variables, including comedications and comorbidities. Reported data combined with positron emission tomography evidence indicated a trend toward lower concentrations under LAI administration than under oral medications. However, the available evidence is insufficient to recommend LAI-specific therapeutic reference ranges.

CONCLUSIONS

Although TDM evidence for newer LAI formulations is limited, this review suggests the use of TDM when switching an antipsychotic from oral to its LAI formulation. The application of TDM practice is more accurate for dose selection than the use of dose equivalents as it accounts more precisely for individual characteristics.

Influence of cytochrome P450 2D6 polymorphism on hippocampal white matter and treatment response in schizophrenia

Cytochrome P450 2D6 (CYP2D6) is expressed at high levels in the brain and plays a considerable role in the biotransformation and neurotransmission of dopamine. This raises the question of whether CYP2D6 variations and its impact on the brain can confer susceptibility to schizophrenia. We investigated the possible links among the CYP2D6 genotype, white matter (WM) integrity of the hippocampus, and the treatment response to antipsychotic drugs in Korean patients with schizophrenia (n = 106). Brain magnetic resonance imaging and genotyping for CYP2D6 were conducted at baseline. The severity of clinical symptoms and the treatment response were assessed using the Positive and Negative Syndrome Scale (PANSS). After genotyping, 43 participants were classified as intermediate metabolizers (IM), and the remainder (n = 63) were classified as extensive metabolizers (EM). IM participants showed significantly higher fractional anisotropy (FA) values in the right hippocampus compared to EM participants. Radial diffusivity (RD) values were significantly lower in the overlapping region of the right hippocampus in the IM group than in the EM group. After 4 weeks of antipsychotic treatment, the EM group showed more improvements in positive symptoms than the IM group. FAs and RDs in the CYP2D6-associated hippocampal WM region were significantly correlated with a reduction in the positive symptom subscale of the PANSS. Greater improvements in positive symptoms were negatively associated with FAs, and positively associated with RDs in the right hippocampal region. The findings suggest that CYP26D-associated hippocampal WM alterations could be a possible endophenotype for schizophrenia that accounts for individual differences in clinical features and treatment responses.

Haloperidol in palliative care: Indications and risks

Individual response to medication depends on several factors (age, gender, body weight, general clinical condition, genetics, diet, hydration status, comorbidities, co-administered drugs and their mode of administration, smoking, alcohol overuse, environmental factors, e.g. sunlight) that may contribute to adverse drug reactions even at therapeutic doses. Patients in palliative care are at increased risk of these reactions. Unwanted drug effects diminish the quality of life and may lead to a suboptimal dying process. Haloperidol is one of the three most commonly used drugs in palliative care and the most commonly employed typical antipsychotic. It has also been recommended for inclusion into the palliative care emergency kit of home care teams. As such, it is important to be fully conversant with the indications, benefits, and risks of haloperidol, especially in the context of palliative care.

Discrepancy in Taiwanese psychiatrists' preferences for long-acting injectable antipsychotics across facilities: a nationwide questionnaire survey

BACKGROUND

Although many studies have discussed psychiatrists' attitudes toward long-acting injectable antipsychotics (LAIs), no previous study has focused on differences in preference based on the facilities in which the psychiatrists practiced.

MATERIALS AND METHODS

A pilot survey was conducted in a medical center in northern Taiwan, and a questionnaire was then distributed at the annual conference of the Taiwanese Society of Psychiatry in 2013. The questionnaire included general demographic data and preferences for the use of LAIs in different situations.

RESULTS

A total of 142 psychiatrists were included in our study. Among them, 114 were male (80.3%), and most practiced in general hospitals (n=110, 77.5%). We found that general hospital psychiatrists were more likely to prescribe LAIs for patients in the acute stage and with positive symptoms than were psychiatric hospital psychiatrists. General hospital psychiatrists also tended to prescribe LAIs at every time point of the disease.

CONCLUSION

General hospital psychiatrists were more likely to prescribe LAIs than those in psychiatric hospitals. Knowing the factors affecting psychiatrists' preferences may help us to develop a further study to explore "why" psychiatrists consider or do not consider LAIs in different facilities.

A six month randomized controlled trial of long acting injectable risperidone 50 and 100mg in treatment resistant schizophrenia

It has been suggested that atypical antipsychotic drugs (A-APDs) other than clozapine may be effective to improve positive symptoms in some patients with treatment resistant schizophrenia (TRS), if both the dose is higher, and the duration of the trial longer, than those which have been ineffective in non-TRS (NTRS) patients. This hypothesis was tested with long acting injectable risperidone (Risperdal Consta®, RLAI). One hundred sixty TRS patients selected for persistent moderate-severe delusions or hallucinations, or both, were randomized to RLAI, 50 or 100mg biweekly, in a six month, outpatient, double-blind, multicenter trial. We hypothesized that RLAI, 100mg, would be more effective than RLAI, 50mg. However, both doses produced clinically significant and equivalent improvement in PANSS Total, Positive, and Negative subscale scores, as well as key cognitive, global and functional measures, with increasing response during the course of the study, confirming the value of longer clinical trial duration for patients with TRS, but not superiority of the higher dose. The overall response rate was comparable to that previously reported for clozapine and high dose olanzapine, another A-APD, in TRS. Both doses of RLAI were equally well tolerated, producing minimal extrapyramidal side effects and few drop outs. Plasma levels of the active moiety, risperidone+9-hydroxyrisperidone, during treatment with RLAI 100mg, were comparable to those for 6-8 mg/day oral risperidone, which have not been effective in TRS. Further study of RLAI, ≥ 50-100mg biweekly, should compare it with clozapine and oral risperidone in TRS, with duration of treatment ≥ six months.

Therapeutic drug monitoring of common antipsychotics

The aim of this review is to provide information for interpreting outcome results from monitoring of antipsychotics in biological samples. A brief overview of the working mechanisms, pharmacological effects, drug interactions, and analytical methods of classical and atypical antipsychotics is given. Nineteen antipsychotics were selected based on their importance in the worldwide market as follows: amisulpride, aripiprazole, asenapine, bromperidol, clozapine, flupenthixol, haloperidol, iloperidone, lurasidone, olanzapine, paliperidone, perphenazine, pimozide, pipamperone, quetiapine, risperidone, sertindole, sulpiride, and zuclopenthixol. A straightforward relationship between administered dose, plasma or serum concentration, clinical outcome, or adverse effects is often lacking. Nowadays, focus lies on therapeutic drug monitoring and individualized therapy to find adequate treatment, to explain treatment failure or nonresponse, and to check patient compliance. However, extensive research in this field is still mandatory.

Interactions and monitoring of antipsychotic drugs

As a consequence of individualized antipsychotic pharmacotherapy, many patients need more than a single drug, since they do not respond sufficiently to monotherapy. Other patients suffer from comorbid diseases and therefore require additional drugs from other pharmacological classes. Drug combinations, however, can give rise to pharmacokinetic and/or pharmacodynamic drug-drug interactions. Evaluation of pharmacokinetic interactions with antipsychotic drugs must consider substrate, inhibitor, and inducer properties for the cytochrome P450 (CYP) isoenzymes of all combined drugs. For consideration of pharmacodynamic interactions, special attention must be given to effects on dopamine D(2), histamine H(1), and acetylcholine M(1) receptors and on cardiac potassium channels. Additive pharmacological actions of combined drugs on these target structures can induce adverse reactions such as extrapyramidal symptoms, drowsiness, metabolic disturbances leading to weight gain and cardiac problems, cognitive impairment, delirium, or ventricular arrhythmia. Measuring plasma concentrations, i.e., therapeutic drug monitoring (TDM), is valuable to adjust antipsychotic medication when drug combinations contain inhibitors or inducers that alter plasma concentrations of the antipsychotic drugs. Amalgamating the broad knowledge on drug-drug interactions and using appropriately the option to monitor plasma concentrations in blood will help to apply complex combination therapies with antipsychotic drugs with maximal efficiency and safety.

Comparative pharmacology of antipsychotics possessing combined dopamine D2 and serotonin 5-HT1A receptor properties

RATIONALE

There is increasing interest in antipsychotics intended to manage positive symptoms via D(2) receptor blockade and improve negative symptoms and cognitive deficits via 5-HT(1A) activation. Such a strategy reduces side-effects such as the extrapyramidal syndrome (EPS), weight gain, and autonomic disturbance liability.

OBJECTIVE

This study aims to review pharmacological literature on compounds interacting at both 5-HT(1A) and D(2) receptors (as well as at other receptors), including aripiprazole, perospirone, ziprasidone, bifeprunox, lurasidone and cariprazine, PF-217830, adoprazine, SSR181507, and F15063.

METHODS

We examine data on in vitro binding and agonism and in vivo tests related to (1) positive symptoms (e.g., psychostimulant-induced hyperactivity or prepulse inhibition deficit), (2) negative symptoms (e.g., phencyclidine-induced social interaction deficits and cortical dopamine release), and (3) cognitive deficits (e.g., phencyclidine or scopolamine-induced memory deficits). EPS liability is assessed by measuring catalepsy and neuroendocrine impact by determining plasma prolactin, glucose, and corticosterone levels.

RESULTS

Compounds possessing "balanced" 5-HT(1A) receptor agonism and D(2) antagonism (or weak partial agonism) and, in some cases, combined with other beneficial properties, such as 5-HT(2A) receptor antagonism, are efficacious in a broad range of rodent pharmacological models yet have a lower propensity to elicit EPS or metabolic dysfunction.

CONCLUSIONS

Recent compounds exhibiting combined 5-HT(1A)/D(2) properties may be effective in treating a broader range of symptoms of schizophrenia and be better tolerated than existing antipsychotics. Nevertheless, further investigations are necessary to evaluate recent compounds, notably in view of their differing levels of 5-HT(1A) affinity and efficacy, which can markedly influence activity and side-effect profiles.

Induction of Drug Transporters Alters Disposition of Risperidone - A Study in Mice

Pharmacokinetic interactions, e.g. modulation of drug transporters like P-glycoprotein at the blood-brain barrier, can be a reason for treatment non-response. This study focuses on the influence of induction of drug transporters on the disposition of the antipsychotic drugs risperidone and 9-hydroxyrisperidone. Brain and serum concentrations of risperidone and its active metabolite 9-hydroxyrisperidone, which are known P-glycoprotein substrates, were measured after drug transporter induction with rifampicin, dexamethasone or 5-pregnene-3beta-ol-20-on-16alpha-carbonitrile using high performance liquid chromatography. Disposition of risperidone and 9-hydroxyrisperidone was dramatically decreased in mouse brain and serum after drug transporter induction. The metabolism of risperidone was also affected.

Experience with injectable long-acting risperidone in long-term therapy after an acute episode of schizophrenia: the SPHERE Study

BACKGROUND

Risperidone long-acting injectable (RLAI) is the first long-acting formulation of an atypical antipsychotic introduced into clinical practice. RLAI combines the benefits of atypical antipsychotic agents with an extended duration of activity and is intended for long-term management of schizophrenia. This study evaluated the use of RLAI as part of a long-term management strategy in patients with an acute episode of schizophrenia.

OBJECTIVES

The primary objective was to determine clinicians' approaches to the use of RLAI in patients with an acute exacerbation of schizophrenia by examining the prescribing patterns of antipsychotic and other psychotropic medications. Other objectives were to evaluate the overall safety of switching patients to RLAI from previous antipsychotic therapy and to determine patients', caregivers' and relatives' attitudes towards RLAI treatment.

METHODS

The Safety and Profile of Handling and Employing of Risperdal Consta in Emergency/Acute Care Settings (SPHERE) study was an observational, non-interventional, multicenter, retrospective study involving a large cohort of patients with acute psychotic exacerbation who attended Spanish emergency/acute care facilities (between August and December 2003) and were treated with RLAI during hospitalization.

RESULTS

A total of 1232 patients (70% men; mean age 37 years; median of 8 months since most recent admission) were included in the analyses; 79% had been receiving antipsychotic therapy prior to admission. All patients received RLAI post-stabilization. The main reasons for initiating RLAI were the need for long-term treatment (76%) and a low adherence to previous treatment (71%). RLAI doses administered during hospitalization were: 25 (26%), 37.5 (29%), 50 (42%) and 75-100 mg (3%). The mean number of injections per patient (2 +/- 1) and mean hospitalization time (25 +/- 16 days) indicated that RLAI was administered every 2 weeks as per the manufacturer's recommendations. All patients were discharged on RLAI treatment; 62% were prescribed concomitant therapy, mainly oral risperidone (39%), anxiolytics (25%), antiparkinsonians (15%), hypnotics (11%) and anticonvulsants (11%). Only 5.7% of patients reported adverse events, most commonly extrapyramidal symptoms (1.1%) and somnolence (0.9%).

CONCLUSIONS

As part of a long-term management strategy aimed at improving treatment adherence in schizophrenic patients, RLAI was prescribed to a wide spectrum of patients with an acute episode of schizophrenia during hospitalization and at the time of discharge from emergency/acute care facilities. RLAI was well tolerated in the study population and the overall impression of patients, primary caregivers and relatives to RLAI therapy was positive.

Pharmacokinetics and efficacy of a direct switch from conventional depot to risperidone long-acting injection in Chinese patients with schizophrenic and schizoaffective disorders

AIMS

This 12-week open-label study was designed to investigate the pharmacokinetics and efficacy of a direct switch from a conventional depot to long-acting injectable risperidone in patients with schizophrenia and schizoaffective disorder.

METHODS

Men or women from 18 to 65 years old with a diagnosis of schizophrenia or schizoaffective disorder were eligible for participation if they had been treated with conventional depot for at least 8 weeks before study entry. Intramuscular long-acting risperidone was administered starting from 25 mg, with the dose flexibly adjusted every two weeks for 12 weeks from week 4.

RESULTS

Of the 25 patients enrolled in this study, 21 completed at least one post-baseline assessment and were thus included in the analysis. The mean serum concentration of risperidone plus 9-hydroxyrisperidone was 29.1 ng/mL at the 12th week after switching, with an average injection dose of 31.25 mg long-acting risperidone every two weeks. The levels of active moiety of risperidone seemed to be higher in Chinese patients compared to those in Caucasian patients. Positive and Negative Syndrome Scale total scores (from 67.5 to 56.4; P = 0.002), scores for negative symptoms (P = 0.006) and general symptoms (P = 0.001) were improved significantly 12 weeks after the switch. Mean Extrapyramidal Symptom Rating Scale scores were improved significantly from 20.1 to 5.5 (P < 0.001). Significantly decreased levels of cholesterol and triglyceride were found at the 12th week. The levels of fasting glucose, low-density lipoprotein, high-density lipoprotein and bodyweight remained unchanged.

CONCLUSIONS

These findings suggest that switching from conventional depot to long-acting risperidone is feasible with the advantage of symptom reduction and side-effect profile decrement.

Dosing patterns in Europe: Efficacy and safety of risperidone long-acting injectable in doses of 25, 37.5 and 50 mg

Objective. To assess the dose prescription patterns for risperidone long-acting injectable (RLAI) in patients with schizophrenia who participated in the 6-month, open-label Switch to Risperidone Microspheres (StoRMi) trial. Methods. Clinically stable patients requiring a change in medication were converted to RLAI prescribed using clinically-appropriate doses, as determined by treating clinicians. RLAI 25 mg was recommended as the starting dose, although higher initiation doses were permitted if deemed necessary. RLAI was administered intramuscularly every 2 weeks, with dosage adjustments permitted, and continued for a total of 6 months. Efficacy outcomes included Positive and Negative Syndrome Scale (PANSS) and Clinical Global Impression-Severity (CGI-S). Treatment-emergent adverse events (AEs) were monitored. Results. A total of 1,849 patients were included. Modal dose was 25 mg for 52.9% of patients. At baseline, patients treated with lower RLAI doses were more likely to be female, have shorter disease duration, milder symptoms, and be using less polypharmacy. The strongest predictors that a patient would remain on 25 mg RLAI were baseline PANSS hallucinatory behaviour item score (odds ratio [OR]=0.78), baseline CGI-S score (OR=0.69), female gender (OR=1.56), and country of residence (P<0.001 for all). Efficacy measures improved in all dose groups, with the greatest improvement seen in patients treated with lower doses. AEs were more common in patients treated with 50 mg RLAI (68 vs. 57% with lower doses; P<0.0001), although most AEs were mild to moderate in severity. Conclusion. In this study, 25 mg RLAI was the most commonly prescribed dose. RLAI was effective and well tolerated over the full range of doses.

Long-acting risperidone improves negative symptoms in stable psychotic patients

The aim of this paper was to evaluate the efficacy of risperidone long-acting injectable (RLAI) for reducing negative symptoms of schizophrenia in patients with predominantly negative symptoms at baseline. A subanalysis was performed on data from the 6-month, open-label Switch to Risperidone Microspheres trial. Patients with Positive and Negative Syndrome Scale (PANSS) negative subscale score > or = 21, which was higher than their PANSS positive subscale score, were included in this subanalysis. Improvement in negative symptoms was measured by assessing change in the PANSS negative subscale and a negative factor score. Additional outcome variables included measures in general functioning, quality of life and patient satisfaction. A total of 842 patients were eligible for inclusion in this subanalysis. Six months of treatment was completed by 631 (74.9%) patients. Forty-three (5.1%) patients discontinued treatment due to an adverse event. Negative symptoms were significantly reduced by 6.1 +/- 6.3 points for the PANSS negative score and 6.1 +/- 6.4 points for the negative factor score (P < 0.0001 for both). Significant improvements were also noted for total PANSS and other PANSS subscale scores, general functioning, quality of life and patient satisfaction (P < 0.0001). The most common treatment-emergent adverse events (>5%) were: anxiety (6.8% of patients), exacerbation of disease (6.2%) and insomnia (5.7%). Overall, RLAI was well tolerated and associated with significant reductions in movement disorder severity. The treatment resulted in a significant improvement in negative symptom severity and was well tolerated in patients with predominantly negative symptoms, who switched from a stable antipsychotic regimen

Therapeutic drug monitoring in neuropsychopharmacology: does it hold its promises?

To produce its characteristic effects, a drug must be present in appropriate concentrations at its sites of action. The latter is not only a function of the dose administered, but also of the extent and rate of drug absorption, distribution, tissue binding, biotransformation, and excretion, which can vary markedly between individual patients due to differences in gender, age, morbidity, smoking or eating habits, differential expression of drug metabolising enzymes or drug transporters or other factors. Therefore drug concentrations in blood resulting after a given dose differ by tenfold or more between individual patients. For psychoactive drugs, animal studies have shown that plasma concentrations of psychotropic drugs correlate well with concentrations in the target organ, the brain. In the brain of patients treated with antipsychotic or antidepressant drugs clear-cut relationships were found between plasma concentrations of the drug and occupancy of dopamine receptors or serotonin uptake sites by positron emission tomography (PET). Monitoring concentrations of psychoactive drugs in plasma of patients, so called therapeutic drug monitoring (TDM), is therefore useful to adjust dosages for optimal "receptor" blockade. TDM is well established for mood stabilizers and anticonvulsant drugs. For other neuropsychiatric drugs, however, "routine" TDM is rare. Optimal target concentrations are unclear for many drugs, and the number of laboratories that use reliable methods to measure the low concentrations of the drugs within a single day is quite limited. Moreover, the use of TDM in practice is far from optimal. The TDM group of the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP see http://www.agnp.de/) has published literature-based guidelines for optimal use of TDM in psychiatry. TDM can be most informative to solve problems underlying the treatment of an individual patient. It can be clarified if suggested non-compliance or insufficient response in spite of recommended doses is due to rapid metabolism of the drug. Moreover, many drug interactions have been detected by using TDM. In conclusion, TDM is a reliable tool to optimise psychopharmacotherapy. When used adequately it is helpful for many psychiatric patients and in many situations.

The use of academic detailing to improve evidence based prescribing of risperidone long acting injection

Objective. It takes 6 weeks for plasma levels of risperidone long-acting injection (RLAI) to reach steady state, and randomised controlled trials demonstrate a flat dose-response curve. In clinical practice, the dose of RLAI is often increased rapidly at the start of treatment and many patients receive a dose above 25 mg/2 weeks. We sought to understand why and to use academic detailing as a catalyst for change. Method. (1) Semi-structured interview of and academic detailing visit to psychiatrists. (2) Number of pharmacy issues or each strength of RLAI issues before and after the academic detailing visit. Results. Understanding of the pharmacokinetics of RLAI and the flat dose-response curve were poor. After a single visit from an academic detailer, the proportion of 50-mg doses issued decreased from 44 to 31%. Conclusion. Academic detailing was effective in changing prescribing practice; patients are likely to benefit through receiving treatment that has a better risk-benefit ratio, and the healthcare organization is likely to benefit, in terms of more cost-effective prescribing.

In vitro and in vivo demonstration of risperidone implants in mice

BACKGROUND

Non-adherence with medication is a critical limitation in current long-term treatment of schizophrenia and a primary factor in poor quality-of-life outcomes. However, few treatments have addressed this shortcoming using an implantable drug delivery approach. The goal of this study was to provide in vitro and in vivo proof of concept for a long-term implantable risperidone delivery system in mice.

METHODS

Implantable formulations of risperidone were created using the biodegradable polymer Poly Lactic co Glycolic Acid (PLGA) combined with various drug loads. Implant bioactivity was tested using in vitro release and stability studies, as well as in vivo pharmacokinetic and behavioral studies in mice.

RESULTS

The pattern of risperidone release is influenced by various parameters, including polymer composition and drug load. In vitro measures demonstrate that risperidone is stable in implants under physiological conditions. Behavioral measures demonstrate the bioactivity of risperidone implants delivering 3 mg/kg/day in mice, while pharmacokinetic analyses indicate that reversibility is maintained throughout the delivery interval.

CONCLUSIONS

The current report suggests that implantable formulations are a viable approach to providing long-term delivery of antipsychotic medications based on in vivo animal studies and pharmacokinetics. Implantable medications demonstrated here can last two months or longer while maintaining coherence and removability past full release, suggesting a potential paradigm shift in the long-term treatment of schizophrenia.

F15063, a potential antipsychotic with dopamine D2/D3 antagonist, 5-HT1A agonist and D4 partial agonist properties: (IV) duration of brain D2-like receptor occupancy and antipsychotic-like activity versus plasma concentration in mice

F15063 (N-[(2,2-dimethyl-2,3-dihydro-benzofuran-7-yloxy)ethyl]-3-(cyclopent-1-enyl)-benzylamine fumarate salt) is a novel potential antipsychotic with dopamine D(2)/D(3) blocking properties and agonist activity at 5-HT(1A) and D(4) receptors. The pertinent parameter for pharmacological activity of antipsychotics appears to be central D2-like receptor occupancy. However, its duration is not necessarily correlated with drug plasma levels, on which clinical dosing regimens are often based. Thus, we compared in mice the duration of actions of F15063 and haloperidol to (1) inhibit apomorphine-induced climbing and sniffing (behavioural measures of D2-like receptor antagonism) and (2) occupy D2-like receptors in vivo in the striatum and olfactory tubercles (inhibition of [(3)H]nemonapride binding). Finally, we measured plasma levels of F15063. D2-like receptor occupancy in the striatum remained elevated at 1, 4 and 8 h postadministration, with both F15063 (ID(50): 7.1, 3.6 and 16.5 mg/kg p.o., respectively) and the typical antipsychotic, haloperidol (ID(50): 1.4, 0.52 and 0.53 mg/kg p.o., respectively). This was paralleled by a protracted inhibition of apomorphine-induced climbing (ED(50): 0.9, 2.8 and 3.6 mg/kg p.o., and 0.21, 0.37 and 0.87 mg/kg p.o., respectively, for F15063 and haloperidol). In contrast, after administration of 10 mg/kg p.o. of F15063, its plasma levels decreased rapidly: 15.2, 2.1 and 0.6 ng/ml, 1, 4 and 8 h after administration, respectively. A similar pattern of results was observed when F15063 and haloperidol were administered i.p. and s.c., respectively. To summarise, the time-course of D2-like receptor occupancy and inhibition of apomorphine-climbing (and sniffing) behaviours was similarly long lasting with F15063 and haloperidol. In addition, the durations of action of F15063 and haloperidol in a behavioural model of antipsychotic-like activity were closely correlated to their occupancy of central D2-like receptors, and much longer than their presence in plasma.