Prediction of CNS occupancy of dopamine D2 receptor based on systemic exposure and in vitro experiments

Transitory restless arms syndrome in a patient with antipsychotics and antidepressants: a case report

BACKGROUND

Restless arms syndrome (RAS) is characterized by uncomfortable aching or burning sensations in the arms. RAS is regarded as an upper limb variant of restless legs syndrome (RLS). The lack of specific diagnostic criteria makes it difficult to recognize the RAS. Therefore, RAS is usually neglected in clinical practice. Moreover, when a patient was diagnosed with RAS, the adjustment of medications was the first choice for doctors, which may make the patient's condition unstable.

CASE PRESENTATION

A 33-year-old woman was diagnosed with schizophrenia and major depressive disorder. Starting with 0.6 g/d amisulpride, 0.1 g/d quetiapine, 75 mg/d venlafaxine sustained-release tablets, the patient reported symptoms of RAS (itching arms) on the fourth day since the latest hospitalization. After ruling out other factors, her RAS was suspected to be induced by antidepressants or antipsychotics. Without medication adjustment, RAS spontaneously remitted.

CONCLUSIONS

This case suggests that psychiatrists should pay attention to RAS when using antipsychotics and/or antidepressants. Moreover, RAS may be transitory. When a patient manifests RAS, observation may be one choice instead of an immediate medication adjustment.

Impact of P-Glycoprotein-Mediated Active Efflux on Drug Distribution into Lumbar Cerebrospinal Fluid in Nonhuman Primates

Estimation of unbound drug concentration in the brain (C_u,brain) is an essential part of central nervous system (CNS) drug development. As a surrogate for C_u,brain in humans and nonhuman primates, drug concentration in cerebrospinal fluid (C_CSF) collected by lumbar puncture is often used; however, the predictability of C_u,brain by lumbar C_CSF is unclear, particularly for substrates of the active efflux transporter P-glycoprotein (P-gp). Here, we measured lumbar C_CSF in cynomolgus monkey after single intravenous administration of 10 test compounds with varying P-gp transport activities. The in vivo lumbar cerebrospinal fluid (CSF)-to-plasma unbound drug concentration ratios (K_{p,uu,lumbar CSF}) of nonsubstrates or weak substrates of P-gp were in the range 0.885-1.34, whereas those of good substrates of P-gp were in the range 0.195-0.458 and were strongly negatively correlated with in vitro P-gp transport activity. Moreover, concomitant treatment with a P-gp inhibitor, zosuquidar, increased the K_{p,uu,lumbar CSF} values of the good P-gp substrates, indicating that P-gp-mediated active efflux contributed to the low K_{p,uu,lumbar CSF} values of these compounds. Compared with the drug concentrations in the cisternal CSF and interstitial fluid (ISF) that we previously determined in cynomolgus monkeys, the lumbar C_CSF were more than triple for two and all of the good P-gp substrates examined, respectively. Although lumbar C_CSF may overestimate cisternal CSF and ISF concentrations of good P-gp substrates, lumbar C_CSF allowed discrimination of good P-gp substrates from the weak and nonsubstrates and can be used to estimate the impact of P-gp-mediated active efflux on drug CNS penetration. SIGNIFICANCE STATEMENT: This is the first study to systematically evaluate the penetration of various P-glycoprotein (P-gp) substrates into lumbar cerebrospinal fluid (CSF) in nonhuman primates. Lumbar CSF may contain >3-fold higher concentrations of good P-gp substrates than interstitial fluid (ISF) and cisternal CSF but was able to discriminate the good substrates from the weak or nonsubstrates. Because lumbar CSF is more accessible than ISF and cisternal CSF in nonhuman primates, these findings will help increase our understanding of drug central nervous system penetration at the nonclinical stage.

Possibility of Predicting Serotonin Transporter Occupancy From the In Vitro Inhibition Constant for Serotonin Transporter, the Clinically Relevant Plasma Concentration of Unbound Drugs, and Their Profiles for Substrates of Transporters

Accurate prediction of target occupancy facilitates central nervous system drug development. In this review, we discuss the predictability of serotonin transporter (SERT) occupancy in human brain estimated from in vitro K_i values for human SERT and plasma concentrations of unbound drug (C_u,plasma), as well as the impact of drug transporters in the blood-brain barrier. First, the geometric means of in vitro K_i values were compared with the means of in vivo K_i values (K_i,u,plasma) which were calculated as C_u,plasma values at 50% occupancy of SERT obtained from previous clinical positron emission tomography/single photon emission computed tomography imaging studies for 6 selective serotonin transporter reuptake inhibitors and 3 serotonin norepinephrine reuptake inhibitors. The in vitro K_i values for 7 drugs were comparable to their in vivo K_i,u,plasma values within 3-fold difference. SERT occupancy was overestimated for 5 drugs (P-glycoprotein substrates) and underestimated for 2 drugs (presumably uptake transporter substrates, although no evidence exists as yet). In conclusion, prediction of human SERT occupancy from in vitro K_i values and C_u,plasma was successful for drugs that are not transporter substrates and will become possible in future even for transporter substrates, once the transporter activities will be accurately estimated from in vitro experiments.

Quantitative prediction of histamine H1 receptor occupancy by the sedative and non-sedative antagonists in the human central nervous system based on systemic exposure and preclinical data

Significant histamine H1 receptor occupation in the central nervous system (CNS) is associated with sedation. Here we examined the time profiles of the H1 receptor occupancy (RO) in the CNS using sedative (diphenhydramine and ketotifen) and non-sedative (bepotastine and olopatadine) antagonists at their therapeutic doses by integrating in vitro and animal data. A pharmacokinetic model was constructed to associate plasma concentrations and receptor binding in the brain. Dissociation and association rate constants with the H1 receptor and plasma and brain unbound fractions were determined in vitro. Passive and active clearances across the blood-brain barrier (BBB) were estimated based on physicochemical properties and microdialysis studies in mice and monkeys. The estimated RO values were comparable with the reported values determined at time to maximum concentration (T_max) of plasma by positron-emission tomography in humans. The simulation suggested that the predicted maximum ROs by bepotastine and olopatadine were greater than the reported values. Sensitivity analysis showed that active transport across BBB had a significant impact on the RO duration of the H1 antagonists examined. The present study demonstrated that modeling and simulation permits a reasonable RO estimation in the human CNS. Our findings will facilitate the development of CNS-acting drugs.