Impact of gavage dosing procedure and gastric content on adverse respiratory effects and mortality in rat toxicity studies.

Unscheduled mortality preceded by adverse respiratory clinical signs in rats dosed by oral gavage may not only be caused by technical gavage error or systemic toxicity but may also be caused by gastro-esophageal reflux and subsequent aspiration of high concentrations of drug formulation. In a 3 week oral gavage rat toxicity study for an early drug development compound, preterminal deaths (approximately 20% of animals) at high doses (≥1000 mg kg(-1) ) and concentrations (≥60 mg ml(-1) ) were preceded by recurrent dyspnea, rales or excessive salivation, without evidence of accidental intrapulmonary gavage error. Histological evaluation revealed extensive necrosis and inflammatory changes in the upper respiratory tract, especially in the nasal turbinates and/or nasopharynx. The presence of food particles in inflammatory exudates suggested a retrograde aspiration of stomach content with test formulation via the nasopharyngeal duct into the posterior region of the nose. In contrast, no mortality or adverse respiratory effects were observed in rats following 2 week intravenous administration at comparable exposures or oral gavage administration at lower concentrations (≤20 mg ml(-1) ). In a pharmacology study, the compound caused a dose-dependent increase in gastric content (partly due to inhibition of gastric emptying), providing a pharmacological basis for the suspected gavage-mediated gastroesophageal reflux. Reducing the dose volume and dosing fasted animals substantially reduced or eliminated the respiratory effects and mortality at the high test article concentrations, demonstrating that the adverse effects are related to the gavage method.

Attentional performance of (C57BL/6Jx129Sv)F2 mice in the five-choice serial reaction time task.

Impaired attention is evident in several neurological and psychiatric disorders. In the present study, attentional capabilities were measured in the operant five-choice serial reaction time task (5-CSRTT) in male (C57BL/6Jx129Sv)F2 hybrid (B6129F2) mice. Main aims were to validate and standardize the test in these mice: to setup procedures, measure potential beneficial effects of sub-chronic nicotine in degraded versions of the 5-CSRTT (by decreasing stimulus duration, inducing white noise and making the stimuli unpredictable) and study disruptive effects of additional administration of the muscarinic antagonist scopolamine. During the baseline pre-nicotine sessions, the B6129F2 mice attained a very good performance in the test (95% accuracy). As stimulus duration was reduced from 2 s to 1 s, response accuracy of the mice decreased. Mice treated with nicotine (0.16 mg/kg) attained significantly higher response accuracy and had a lower percentage of incorrect responses in comparison with the solvent-treated animals. No further beneficial effects of nicotine were found. Reduced response accuracy was also obtained when stimulus duration was reduced from 1 s to 0.5 s and when a variable intertrial interval was introduced. Noise interpolation between trials did not impair performance. Finally, scopolamine (0.16 mg/kg) disrupted attentional functioning. Although most studies have been performed in rats, these results add to the existing evidence that the 5-CSRTT can also be used to assess attentional performance in mice. This offers the opportunity to test transgenic and knockout mice with similar background as the B6129F2 as animal models of psychiatric and neurological diseases.

Preclinical assessment of the feasibility of applying controlled release oral drug delivery to a lead series of atypical antipsychotics.

In this paper, we present a preclinical approach for evaluating the feasibility of applying controlled-release (CR) oral drug delivery to increase the duration of exposure and lower the C(max) of compounds in a lead series of short half-life atypical antipsychotics. Three lead compounds in the series had demonstrated potential pharmacological benefits for the treatment of psychosis, in preclinical studies. However, the compounds showed evidence of insufficient half-lives to enable a once-a-day (QD) product using immediate-release (IR) oral delivery. To evaluate and compare the potential for oral CR delivery to extend the duration of action and thereby enable QD administration, the in vitro solubility and permeability, and the duodenal and colonic absorption of three compounds in the series were measured. Based on the results, one candidate was selected for advancement that showed moderate in vitro solubility, but had the highest in vitro permeability and ratio of colonic to duodenal bioavailability (0.9) in the rat. The results from this study provided evidence that a CR drug delivery system could be used to extend the duration of exposure of the compounds in the series and a scientific basis for selecting one of the three compounds as a candidate.

The atypical antipsychotics risperidone, clozapine and olanzapine differ regarding their sedative potency in rats.

The atypical antipsychotics risperidone, clozapine and olanzapine were studied for their ability to antagonise apomorphine-induced stereotypy and to affect electroencephalographic (EEG) activity in rats. The compounds antagonised apomorphine-induced stereotypy with ED(50)s of 0.15 mg/kg s.c. for risperidone, 0.42 mg/kg s.c. for olanzapine and 1.3 mg/kg s.c. for clozapine. At a dose close to that required for apomorphine antagonism (0.16 mg/kg s.c.), risperidone induced only minor changes in EEG power spectral activity. At a higher dosage (0.63 mg/kg s.c.) it increased the power density in the high frequency range (9.8-18.6 Hz), characteristic of a sedative-like effect. Olanzapine and clozapine caused a dose-dependent increase in power density in all frequency bands. These effects were already present at doses (0.04 and 0.16 mg/kg s.c., respectively) 10 times below those required for apomorphine antagonism. The effects increased dose-dependently and were pronounced at the doses required for apomorphine antagonism. These results in rats are in agreement with the clinical observation that risperidone has less propensity for inducing sedation at therapeutic dose levels than olanzapine and clozapine.

A randomised controlled trial of joint consultations with general practitioners and cardiologists in primary care.

BACKGROUND: Joint consultation sessions of a small group of general practitioners (GPs) and a specialist in orthopaedics proved to be an effective way of decreasing the referral rate of orthopaedic patients. Cardiac complaints comprise an important category of health problems with high referral rates. AIMS: To study the effects of joint consultation on the quality of care and referrals for patients with cardiac complaints. DESIGN OF STUDY: Randomised controlled trial. SETTING: Forty-nine GPs participated in 16 consultation groups, each with one of 13 cardiologists, in monthly joint consultations over a period of about 18 months. METHOD: The GPs selected patients about whom they were uncertain, and those needing urgent referral were excluded. Patients were randomly assigned to joint consultation or to usual care. After a follow-up period all patients had a joint consultation for outcome assessment. Referral data were provided by two regional health insurance companies and questionnaires were given to the patients, GPs, and cardiologists to gauge their opinion of the trial. RESULTS: One hundred and forty-eight patients in the intervention group and 158 patients in the control group fulfilled the whole protocol. The quality of care was similar in both groups. In the intervention group, 34% of the patients were referred, compared with 55% in the control group (P = 0.001), and fewer patients underwent further diagnostic procedures (7% compared with 16%, P = 0.013). Referrals to cardiology as a proportion of all referrals decreased in the practices of the participating GPs, compared with their reference districts (P = 0.024). CONCLUSION: Joint consultation is an effective method that provides a quality of care that at least equals usual care and that contributes to a better selection of patients who need specialist care.

Patients at the outpatient rheumatology clinic: do they really need to be there?

BACKGROUND: The workload at many outpatient clinics within the Dutch health care system has been growing relentlessly, resulting in unacceptable waiting lists and reduced accessibility. Assessing streams of patients and introducing a method of accelerated referral of patients back to the general practitioner (GP) under specialist guidance could help to alleviate these problems. METHODS: Seventeen GPs collaborated with rheumatologists during a 2-year period in a 'joint consultation' model in which GPs and rheumatologists discussed patients together. All patient charts belonging to patients who had been referred to the outpatient clinic by these 17 GPs were identified. Rheumatologists assessed whether or not these patients could be referred back to the participating GPs under the guidance of the specialist in the joint consultation model. RESULTS: Of 276 eligible patients, 121 were discharged from the outpatient clinic. Eighty-seven patients required specialist follow-up, 22 patients refused to participate, and six patients were not entered into the study by the rheumatologist. Some 21 patients eventually entered the study, 18 of whom were referred back to the GP. CONCLUSION: The role of joint consultation appears to be limited. Improving the referral behavior of GPs should take precedence over transferring follow-up from the outpatient clinic to the primary care level.

Role of 5-HT(2) receptors in the tryptamine-induced 5-HT syndrome in rats.

We distinguished the functions of the different 5-hydroxytryptamine-2 (5-HT(2)) receptor (5-HT(2)R) subtypes in the tryptamine-induced 5-HT syndrome in rats using (1) the 5-HT(2A)R antagonist R93274 (N-[(3-p-fluorophenyl-1-propyl)-4-methyl-4-piperidinyl]-4-amino-5-iodo-2-methoxybenzamide), the 5-HT(2A/C)R antagonist R99647 (2-(dimethylaminomethyl)2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine), the 5-HT(2B/C)R antagonist SB-242084 (6-chloro-5-methyl-1-[[2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-indoline), and several 5-HT(2)R antagonists (ketanserin, risperidone, pipamperone and mianserin); and (2) chronic 5-HT(2)R activation by 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). In contrast to SB-242084, the selective 5-HT(2A)R antagonist R93274 as well as the non-selective 5-HT(2A)R antagonists (R99647, ketanserin, risperidone, pipamperone and mianserin) significantly inhibited tryptamine-induced forepaw treading and tremors, and reversed peripherally mediated cyanosis into hyperaemia; only the 5-HT(2A/C)R antagonists R99647 and mianserin inhibited the tryptamine-induced hunched back. Intermittent DOM administration (intravenously every 48 h for 12 days) did not change the centrally mediated tryptamine-induced forepaw treading, tremors and hunched back at 1, 4 or 7 days after the last DOM pretreatment. The DOM-induced head twitch response, measured immediately after every DOM injection, was not affected. In contrast, peripherally mediated cyanosis was reversed into hyperaemia in 75, 11 and 20% of all pretreated rats at 1, 4 and 7 days, respectively, after the last DOM administration. Taken together, these finding suggest that central 5-HT(2A)Rs mediate tryptamine-induced forepaw treading and tremors, that peripheral 5-HT Rs mediate tryptamine-induced cyanosis, and that 5-HT(2A)Rs mediate tryptamine-induced hunched back. Peripheral 5-HT(2C)Rs are more sensitive to desensitization after intermittent treatment with an agonist than central 5-HT(2A)Rs.

The differential effects of atypical antipsychotics on prolactin elevation are explained by their differential blood-brain disposition: a pharmacological analysis in rats.

All atypical antipsychotics avoid extrapyramidal side-effects yet differ in their propensity to cause other side-effects, like prolactin elevation. We proposed that the atypical antipsychotics with a propensity for prolactin elevation would show a higher pituitary versus striatal D2 receptor occupancy. To investigate this hypothesis, we tested four atypical antipsychotics, two that are commonly associated with prolactin elevation (amisulpride and risperidone) and two that are less frequently associated (quetiapine and olanzapine). In particular, we calculated their ED(50) values to increase plasma prolactin and block peripheral pituitary D2 receptors to their ED(50) values to antagonize apomorphine-induced stereotypy and occupy central striatal D2 receptors. All antipsychotics dose dependently increased prolactin levels and antagonized apomorphine-induced stereotypy. However, the central to peripheral potency (ED(50) for apomorphine antagonism to ED(50) for prolactin elevation) differed remarkably across these drugs: amisulpride (21764), risperidone (14), quetiapine (10), and olanzapine (1.7). Compounds displaying a higher peripheral potency brought about higher prolactin levels for a given level of functional central antagonism. This dissociation between central and peripheral effects was explained by the differential occupancy of D2 receptors in the striatum versus in the pituitary [ratio of striatal/pituitary ED(50) values (milligram per kilogram) for D2 occupancy): amisulpride (17/0.026 = 654), risperidone (0.89/0.081 = 14), quetiapine (24/4.1 = 6), olanzapine (0.30/0.43 = 0.7). These results indicate that dissociation between central and peripheral D2 receptor occupancy is a major determinant of the degree of prolactin elevation observed at therapeutic doses.

Pharmacological profile of (2R-trans)-4-[1-[3,5-bis(trifluoromethyl)benzoyl]-2-(phenylmethyl)-4-piperidinyl]-N-(2,6-dimethylphenyl)-1-acetamide (S)-Hydroxybutanedioate (R116301), an orally and centrally active neurokinin-1 receptor antagonist.

In comparison with a series of reference compounds, (2R-trans)-4-[1-[3,5-bis(trifluoromethyl)benzoyl]-2-(phenylmethyl)-4-piperidinyl]-N-(2,6-dimethylphenyl)-1-acetamide (S)-Hydroxybutanedioate (R116301) was characterized as a specific, orally, and centrally active neurokinin-1 (NK(1)) receptor antagonist with subnanomolar affinity for the human NK(1) receptor (K(i): 0.45 nM) and over 200-fold selectivity toward NK(2) and NK(3) receptors. R116301 inhibited substance P (SP)-induced peripheral effects (skin reactions and plasma extravasation in guinea pigs) and a central effect (thumping in gerbils) at low doses (0.08-0.16 mg/kg, s.c. or i.p.), reflecting its high potency as an NK(1) receptor antagonist and excellent brain disposition. Higher doses blocked various emetic stimuli in ferrets, cats, and dogs (ED(50) values: 3.2 mg/kg, s.c.; 0.72-2.5 mg/kg, p.o.). Even higher doses (11-25 mg/kg, s.c.) were required in mice (capsaicin-induced ear edema) and rats (SP-induced extravasation and salivation), consistent with lower affinity for the rodent NK(1) receptor and known species differences in NK(1) receptor interactions. R116301 inhibited the ocular discharge (0.034 mg/kg) but not the dyspnoea, lethality, or cough (>40 mg/kg, s.c.) induced by [betaALA(8)]-neurokinin A (NKA) (4-10) in guinea pigs, attesting to NK(1) over NK(2) selectivity. R116301 did not affect senktide-induced miosis (>5 mg/kg, s.c.) in rabbits, confirming the absence of an interaction with the NK(3) receptor. R116301 was inactive in guinea pigs against skin reactions induced by histamine, platelet-aggregating factor, bradykinin, or Ascaris allergens (>10 mg/kg, s.c.). In all species, R116301 showed excellent oral over parenteral activity (ratio, 0.22-2.7) and a relatively long duration (6.5-16 h, p.o.). The data attest to the specificity and sensitivity of the animal models and support a role of NK(1) receptors in various diseases.

Measurement of upper extremity volume in women after axillary dissection for breast cancer.

OBJECTIVE: To determine if 2 methods of calculating upper extremity volume (using arm circumferences) can substitute for water displacement volumetry. DESIGN: Interrater and test-retest reliability and limits of agreement for volume measures. SETTING: University. PARTICIPANTS: Twenty-five women at risk for lymphedema who had undergone axillary lymph node dissection surgery for breast cancer. INTERVENTIONS: Circumference and volume measurements of both upper extremities were taken by 2 physical therapists at an initial visit and by 1 of the therapists 1 week later. MAIN OUTCOME MEASURES: Intraclass correlation coefficients (ICCs) were calculated to analyze measurement reliability. Pearson's product-moment correlation coefficient (r) was used to evaluate the relationship between volumetry and calculated truncated cone volumes. Limits of agreement were calculated to determine the level of agreement between the 2 measurement methods. RESULTS: Interrater and test-retest reliability ICCs for circumferential and volumetric data were .99 and .99, respectively. Pearson's r values were .93 and .97 for the single truncated cone and the summed truncated cone volume calculations, respectively. Limits of agreement (mean +/- 2 standard deviations) were -52 +/- 334mL and -40 +/- 234mL, respectively, between volumetry and the single truncated cone and summed truncated cone calculations. CONCLUSIONS: Calculated and volumetric measurements in this population are both reliable and closely related, but do not agree with each another, and thus should not be used interchangeably.

Sexual origins of placental dysfunction.

Severe placental dysfunction is much more common in pregnancies with a male than with a female fetus. Furthermore, the birthweight/placental weight ratio is increased in these pregnancies, consistent with fetal growth restriction, and is higher with a male fetus than with a female fetus. These observations of placental insufficiency may underlie the increased in-utero loss rate of male fetuses.

New 2-substituted 1,2,3,4-tetrahydrobenzofuro[3,2-c]pyridine having highly active and potent central alpha 2-antagonistic activity as potential antidepressants.

The synthesis and biological activity of a series of benzofuro[3,2-c]pyridines and a benzothieno[3,2-c]pyridine are described. These compounds exhibit high affinity for the alpha 2-adrenoceptor, with high selectivity versus the alpha 1-receptor. Compound 1 also shows potent in vivo central activity and has been selected for further biological and clinical evaluation.

Humanization of mouse 5-hydroxytryptamine1B receptor gene by homologous recombination: in vitro and in vivo characterization.

We replaced the coding region of the murine 5-hydroxytryptamine (5-HT)1B receptor by the human 5-HT1B receptor using homologous recombination in embryonic stem cells and generated and characterized homozygous transgenic mice that express only the human (h) 5-HT1B receptor. The distribution patterns of h5-HT1B and murine (m) 5-HT1B receptor mRNA and binding sites in brain sections of transgenic and wild-type mice were identical as measured by in situ hybridization histochemistry and radioligand receptor autoradiography. When measured in parallel under identical conditions, the h5-HT1B receptor expressed in mouse brain had the same pharmacological characteristics as that in human brain. Stimulation by 5-HT1B agonists of [35S]guanosine-5'-O-(3-thio)triphosphate binding in brain sections demonstrated the functional coupling of the h5-HT1B receptor to G proteins in mouse brain. In tissue slices from various brain regions, electrically stimulated [3H]5-HT release was not modified by 5-HT1B agonists in tissue from either transgenic and wild-type mice; a 5-HT1B antagonist enhanced electrically stimulated [3H]5-HT release in wild-type mouse brain, but was ineffective in the transgenics. The centrally active 5-HT1A/5-HT1B agonist RU24969 induced hypothermia but did not increase locomotor activity in the transgenic mice. The ineffectiveness of RU24969 in the transgenic mice could be due to the lower affinity of the compound for the h5-HT1B receptor compared with the m5-HT1B receptor. The present study demonstrates a complete replacement of the mouse receptor by its human receptor homolog and a functional coupling to G proteins. However, modulation of [3H]5-HT release could not be shown. Furthermore, behavioral effects were not clearly observed, which may be due to a lack of appropriate tools.

Physical therapist management of lymphedema following treatment for breast cancer: a critical review of its effectiveness.

The purpose of this review is to analyze the research literature that has examined the effectiveness of physical therapy in the management of lymphedema following treatment for breast cancer. Thirteen studies met the criteria for experimental research, which were then categorized according to Sackett's levels of evidence. One study was graded at level II, 5 studies were graded at level III, and the remaining 7 studies were graded at level V. One grade B recommendation and 6 grade C recommendations were developed from the levels of evidence. The 13 selected studies were also graded according to 6 criteria to evaluate scientific rigor. Clinical recommendations and future research directions are provided.

Comparison of the analgesic and intestinal effects of fentanyl and morphine in rats.

Clinical studies report a low incidence of intestinal side effects with transdermally administered fentanyl (TTS-fentanyl) in comparison with oral morphine. To support these clinical data, analgesic and intestinal effects of both opioids were compared in rats. After subcutaneous injection, analgesia in the tail withdrawal reaction test was obtained at a peak effect dose of 0.032 mg/kg with fentanyl and 8.0 mg/kg with morphine. This analgesic dose exceeded the ED50 for inhibition of castor oil-induced diarrhea only slightly (1.1 x) in the case of fentanyl (0.028 mg/kg) but markedly (36 x) in the case of morphine (0.22 mg/kg). To reverse completely the antidiarrheal effect of equivalent analgesic doses of the opioids (their ED50S for analgesia lasting 2 hours), much more naloxone was required in the case of morphine (5.4 mg/kg) than in the case of fentanyl (0.19 mg/kg). After oral administration, the difference between both opioids was less pronounced. Analgesia was obtained at 0.85 mg/kg with fentanyl and 32 mg/kg with morphine. This analgesic dose only slightly (1.7 x) exceeded the antidiarrheal dose in the case of fentanyl (0.49 mg/kg) but significantly (6.2 x) in the case of morphine (5.2 mg/ kg). To reverse completely the antidiarrheal effect of equivalent analgesic oral doses of the opioids (their ED50S for analgesia lasting 2 hours), more naloxone was required in the case of morphine (11 mg/kg) than in the case of fentanyl (2.0 mg/kg). Rapid penetration of fentanyl into the brain is thought to be responsible for small dissociation between the analgesic and intestinal effect of this lipophilic opioid. The present data provide preclinical evidence to support the relatively low incidence of intestinal side effects observed clinically with the use of TTS-fentanyl in comparison with orally administered morphine.

Effectiveness of joint consultation sessions of general practitioners and orthopaedic surgeons for locomotor-system disorders.

Joint consultation sessions between general practitioners (GPs) and specialists to examine patients for whom decisions about referral are difficult are thought to be helpful, but their effects have not been evaluated. In a randomised, controlled trial we studied the effects of joint sessions of GPs and orthopaedic surgeons on referral and intervention rates. During 1.5 years, 12 GPs (in groups of three) held monthly joint consultation sessions with four participating orthopaedic surgeons: patients were seen by one orthopaedic surgeon in the presence of three GPs. Patients were included in the trial if the GP was uncertain about the diagnostic or therapeutic management and if referral was considered; and excluded if referral was urgently necessary or if there was some other clear indication for referral. By a randomised consent design, patients were assigned to joint consultation sessions (n = 144) or a usual-care control group (n = 128). A year later the patients were examined by an independent orthopaedic surgeon. There were significantly fewer referrals (51/144 [35%] vs 87/128 [68%], p < 0.01) and diagnostic actions in the intervention group than in the control group, without negative effects on health or functional status. More patients in the intervention group were symptom-free at 1 year (35% vs 24%, p < 0.05). Joint consultation sessions of GPs and orthopaedic surgeons within the framework of general practice resulted in more efficient care, with better targeted examination, treatment, and referrals.

Risperidone: a novel antipsychotic with balanced serotonin-dopamine antagonism, receptor occupancy profile, and pharmacologic activity.

The interaction of risperidone, 9-hydroxyrisperidone (the principal active metabolite), and clozapine with neurotransmitter receptors was investigated in vitro using animal brain tissue homogenates and cloned human receptors expressed in cells and ex vivo using quantitative receptor autoradiography in rat and guinea pig brain sections. In vitro, risperidone and 9-hydroxyrisperidone had similar binding profiles, and their highest affinity was for 5-HT2A receptors (cloned human, Ki 0.4 nM); affinities for other 5-HT-receptor subtypes were at least 100 times lower. Risperidone bound to 5-HT2A receptors with 20 times greater affinity than clozapine and 170 times greater affinity than haloperidol. Clozapine primarily bound to histamine H1 receptors and haloperidol to dopamine D2 receptors. The binding affinity of risperidone and 9-hydroxyrisperidone for the D2 family of receptors (D2L, D2S, D3, D4) was one order of magnitude lower than their affinity for 5-HT2A receptors. Risperidone bound to D2 and D3 receptors with 50 and 20 times greater affinity than clozapine and was only 2 to 3 times less potent than haloperidol. All compounds bound with similar affinities to D4 receptors (Ki 5-9 nM), and their affinities for D1 receptors were 100 times lower than for D4 receptors. The ex vivo receptor occupancy profile of the compounds matched the in vitro receptor binding profile. A conspicuous property of risperidone, not seen for the other compounds, was the shallow occupancy curve at D2 receptors in the striatum and mesolimbic brain area. Moreover, it was observed that antagonism of strong D2-receptor stimulation by apomorphine in rats was achieved at less than 50% D2 occupancy by the antipsychotics.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional brain distribution of risperidone and its active metabolite 9-hydroxy-risperidone in the rat.

Risperidone is a new benzisoxazole antipsychotic. 9-Hydroxy-risperidone is the major plasma metabolite of risperidone. The pharmacological properties of 9-hydroxy-risperidone were studied and appeared to be comparable to those of risperidone itself, both in respect of the profile of interactions with various neurotransmitters and its potency, activity, and onset and duration of action. The absorption, plasma levels and regional brain distribution of risperidone, metabolically formed 9-hydroxy-risperidone and total radioactivity were studied in the male Wistar rat after single subcutaneous administration of radiolabelled risperidone at 0.02 mg/kg. Concentrations were determined by HPLC separation, and off-line determination of the radioactivity with liquid scintillation counting. Risperidone was well absorbed. Maximum plasma concentrations were reached at 0.5-1 h after subcutaneous administration. Plasma concentrations of 9-hydroxy-risperidone were higher than those of risperidone from 2h after dosing. In plasma, the apparent elimination half-life of risperidone was 1.0 h, and mean residence times were 1.5 h for risperidone and 2.5 h for its 9-hydroxy metabolite. Plasma levels of the radioactivity increased dose proportionally between 0.02 and 1.3 mg/kg. Risperidone was rapidly distributed to brain tissues. The elimination of the radioactivity from the frontal cortex and striatum--brain regions with high concentrations of 5-HT2 or dopamine-D2 receptors--became more gradual with decreasing dose levels. After a subcutaneous dose of 0.02 mg/kg, the ED50 for central 5-HT2 antagonism in male rats, half-lives in frontal cortex and striatum were 3-4 h for risperidone, whereas mean residence times were 4-6 h for risperidone and about 12 h for 9-hydroxy-risperidone. These half-lives and mean residence times were 3-5 times longer than in plasma and in cerebellum, a region with very low concentrations of 5-HT2 and D2 receptors. Frontal cortex and striatum to plasma concentration ratios increased during the experiment. The distribution of 9-hydroxy-risperidone to the different brain regions, including frontal cortex and striatum, was more limited than that of risperidone itself. This indicated that 9-hydroxy-risperidone contributes to the in vivo activity of risperidone, but to a smaller extent than would be predicted from plasma levels. AUCs of both active compounds in frontal cortex and striatum were 10-18 times higher than those in cerebellum. No retention of metabolites other than 9-hydroxy-risperidone was observed in any of the brain regions investigated.

Survey on the pharmacodynamics of the new antipsychotic risperidone.

This review reports on the pharmacodynamics of the new antipsychotic risperidone. The primary action of risperidone is serotonin 5-HT2 receptor blockade as shown by displacement of radioligand binding (Ki: 0.16 nM), activity on isolated tissues (EC50: 0.5 nM), and antagonism of peripherally (ED50: 0.0011 mg/kg) and centrally (ED50: 0.014 mg/kg) acting 5-HT2 receptor agonists in rats. Risperidone is at least as potent as the specific 5-HT2 receptor antagonist ritanserin in these tests. Risperidone is also a potent dopamine D2 receptor antagonist as indicated by displacement of radioligand binding (Ki: 1.4 nM), activity in isolated striatal slices (IC50: 0.89 nM), and antagonism of peripherally (ED50: 0.0057 mg/kg in dogs) and centrally acting D2 receptor agonists (ED50: 0.056-0.15 mg/kg in rats). Risperidone shows all effects common to D2 antagonists, including enhancement of prolactin release. However, some central effects such as catalepsy and blockade of motor activity occur at high doses only. Risperidone is 4-10 times less potent than haloperidol as a central D2 antagonist in rats and it differs from haloperidol by the following characteristics: predominant 5-HT2 antagonism; LSD antagonism; effects on sleep; smooth dose-response curves for D2 antagonism; synergism of combined 5-HT2/D2 antagonism; pronounced effects on amphetamine-induced oxygen consumption; increased social interaction; and pronounced effects on dopamine (DA) turnover. Risperidone displays similar activity at pre- and postsynaptic D2 receptors and at D2 receptors from various rat brain regions. The binding affinity for D4 and D3 receptors is 5 and 9 times weaker, respectively, than for D2 receptors; interaction with D1 receptors occurs only at very high concentrations. The pharmacological profile of risperidone includes interaction with histamine H1 and alpha-adrenergic receptors but the compound is devoid of significant interaction with cholinergic and a variety of other types of receptors. Risperidone has excellent oral activity, a rapid onset, and a 24-h duration of action. Its major metabolite, 9-hydroxyrisperidone, closely mimics risperidone in pharmacodynamics. Risperidone can be characterized as a potent D2 antagonist with predominant 5HT2 antagonistic activity and optimal pharmacokinetic properties.