Distribution pattern of mirtazapine and normirtazapine in blood and CSF

Therapeutic advances in neuroinfectious diseases

There have been several major advances in therapeutic options for the treatment of neurological infections over the past two decades. These advances encompass both the development of new antimicrobial therapies and the repurposing of existing agents for new indications. In addition, advances in our understanding of the host immune response have allowed for the development of new immunomodulatory strategies in the treatment of neurological infections. This review focuses on the key advances in the treatment of neurological infections, including viral, bacterial, fungal, and prion diseases, with a particular focus on immunomodulatory treatment options. This review also highlights the process by which clinicians can request access to therapeutic agents on a compassionate or emergency basis when they may not be commercially available. While many therapeutic advances have been achieved in the past several years, there remains a pressing need for the continued development of additional therapeutic agents in the treatment of neurological infections.

Differences in P-glycoprotein activity in human and rodent blood-brain barrier assessed by mechanistic modelling

Variation in the efficacy and safety of central nervous system drugs between humans and rodents can be explained by physiological differences between species. An important factor could be P-glycoprotein (Pgp) activity in the blood–brain barrier (BBB), as BBB expression of this drug efflux transporter is reportedly lower in humans compared to mouse and rat and subject to an age-dependent increase. This might complicate animal to human extrapolation of brain drug disposition and toxicity, especially in children. In this study, the potential species-specific effect of BBB Pgp activity on brain drug exposure was investigated. An age-dependent brain PBPK model was used to predict cerebrospinal fluid and brain mass concentrations of Pgp substrate drugs. For digoxin, verapamil and quinidine, in vitro kinetic data on their transport by Pgp were derived from literature and used to scale to in vivo parameters. In addition, age-specific digoxin transport was simulated for children with a postnatal age between 25 and 81 days. BBB Pgp activity in the model was optimized using measured CSF data for the Pgp substrates ivermectin, indinavir, vincristine, docetaxel, paclitaxel, olanzapine and citalopram, as no useful in vitro data were available. Inclusion of Pgp activity in the model resulted in optimized predictions of their brain concentration. Total brain-to-plasma AUC values (Kp,brain) in the simulations without Pgp were divided by the Kp,brain values with Pgp. Kp ratios ranged from 1 to 45 for the substrates investigated. Comparison of human with rodent Kp,brain ratios indicated ≥ twofold lower values in human for digoxin, verapamil, indinavir, paclitaxel and citalopram and ≥ twofold higher values for vincristine. In conclusion, BBB Pgp activity appears species-specific. An age-dependent PBPK model-based approach could be useful to extrapolate animal data to human adult and paediatric predictions by taking into account species-specific and developmental BBB Pgp expression.

Antivirals against human polyomaviruses: Leaving no stone unturned

Human polyomaviruses (HPyVs) encompass more than 10 species infecting 30%-90% of the human population without significant illness. Proven HPyV diseases with documented histopathology affect primarily immunocompromised hosts with manifestations in brain, skin and renourinary tract such as polyomavirus-associated nephropathy (PyVAN), polyomavirus-associated haemorrhagic cystitis (PyVHC), polyomavirus-associated urothelial cancer (PyVUC), progressive multifocal leukoencephalopathy (PML), Merkel cell carcinoma (MCC), Trichodysplasia spinulosa (TS) and pruritic hyperproliferative keratinopathy. Although virus-specific immune control is the eventual goal of therapy and lasting cure, antiviral treatments are urgently needed in order to reduce or prevent HPyV diseases and thereby bridging the time needed to establish virus-specific immunity. However, the small dsDNA genome of only 5 kb of the non-enveloped HPyVs only encodes 5-7 viral proteins. Thus, HPyV replication relies heavily on host cell factors, thereby limiting both, number and type of specific virus-encoded antiviral targets. Lack of cost-effective high-throughput screening systems and relevant small animal models complicates the preclinical development. Current clinical studies are limited by small case numbers, poorly efficacious compounds and absence of proper randomized trial design. Here, we review preclinical and clinical studies that evaluated small molecules with presumed antiviral activity against HPyVs and provide an outlook regarding potential new antiviral strategies.

Neural cell adhesion molecule peptide mimetics modulate emotionality: pharmacokinetic and behavioral studies in rats and non-human primates

Recent evidence highlights the fibroblast growth factor (FGF) family in emotion modulation. Although ligands that activate FGF receptors have antidepressant and anxiolytic effects in animal models, FGF ligands have a broad range of actions both in the brain and the periphery. Therefore, identifying molecular partners that may function as allosteric modulators could offer new avenues for drug development. Since neural cell adhesion molecule (NCAM) activates FGF receptors, we asked whether peripherally administered NCAM peptide mimetics penetrate the brain and alter the behavior of standardized tests that have predictive validity for drug treatments of anxiety or depression. The NCAM peptide mimetic, plannexin, acutely increased and chronically decreased anxiety, but did not have antidepressant effects in rats. Another NCAM peptide mimetic, FGL_L, had acute anxiogenic effects and chronic antidepressant effects in rats. A related NCAM peptide mimetic, FGL_S, had antidepressant effects without modulating anxiety-like behavior, and these antidepressant effects were blocked by an AMPA receptor antagonist. Cisternal cerebrospinal fluid (CSF) levels of FGLs correlated with blood plasma levels in rats and non-human primates, and CSF-to-blood ratios of FGL_S were comparable in both species. Results indicate that NCAM peptide mimetics penetrate the brain and support the suggestion that FGL_S may be a candidate for further development as a novel treatment for major depressive disorder in humans.

Pregnancy exposure to citalopram - Therapeutic drug monitoring in maternal blood, amniotic fluid and cord blood

RATIONALE

Aim of the study was to measure and correlate citalopram concentrations in maternal blood, amniotic fluid and umbilical cord blood to account for the distribution of the drug between these three compartments.

METHODS

Concentrations of citalopram were measured in twelve mother infant pairs at the time of delivery. Data are provided as median values, first (Q1) and third (Q3) quartiles as well as ranges. To account for the penetration ratio into amniotic fluid and cord blood, the concentration of citalopram in was divided by the concentration in maternal serum. Correlations between daily dosage, maternal serum concentrations and umbilical cord blood concentrations were computed for twelve patients. As amniotic fluid was only available for nine mother infant pairs, appropriate calculations are provided for these mother-infant pairs.

RESULTS

The median daily dosage of citalopram was 20mg (Q1: 10mg, Q3: 20mg; range 10-40mg). The relation between the daily dosage of citalopram and its concentrations in maternal serum was highly significant (r=0.667, p=0.018). Maternal serum concentrations and cord blood concentrations were positively correlated (r=0.790, p=0.002) with a median penetration ratio into the fetal circulation of 0.78 (Q1: 0.52, Q3: 1.16, range 0.46-1.66). The median penetration ratio into amniotic fluid was 1.8 (Q1: 1.07, Q3: 2.64; range 0.52-6.97).

CONCLUSIONS

Citalopram concentrations in amniotic fluid and cord blood give evidence that maternally administered citalopram is constantly accessible to the fetus via amniotic fluid. A high correlation between maternal serum concentrations of citalopram and umbilical cord blood concentrations highlights a predictive role of quantifying drug concentrations in maternal serum for assessing drug concentrations in the fetal circulation. Findings support the important role of therapeutic drug monitoring in maintaining the safety of pregnant women and exposed infants.

Measuring citalopram in blood and cerebrospinal fluid: revealing a distribution pattern that differs from other antidepressants

The aim of this study was to measure blood and cerebrospinal fluid concentrations of citalopram and its weakly active N-demethylated metabolite desmethylcitalopram to account for the distribution between the two compartments. The findings are discussed in the context with own preceding studies on the distribution pattern of different antidepressants. Concentrations of citalopram were measured in blood serum and cerebrospinal fluid of 18 patients treated with daily doses of 10-40 mg. Daily doses were correlated with serum and cerebrospinal fluid concentrations, and serum concentrations were correlated with concentrations in cerebrospinal fluid. Serum concentrations of citalopram and desmethylcitalopram showed no significant correlation to the daily dose, r=0.164, P=0.515, and r=0.174, P=0.505, respectively, whereas citalopram concentrations in serum and cerebrospinal fluid were highly correlated (r=0.763, P<0.001). The cerebrospinal fluid/serum ratio for citalopram (total=bound+unbound concentration) varied between 0.14 and 0.86 (mean 0.35, SD 0.16). By correcting the mean cerebrospinal fluid/serum ratio for 80% plasma protein binding, cerebrospinal fluid concentrations of citalopram were on average 77% higher than the calculated unbound serum concentration with a ratio of 1.77 (SD 0.81, range 0.68-4.29). Findings indicate a very good ability of citalopram to cross the blood-brain and cerebrospinal fluid barrier. High concentrations of citalopram in the cerebrospinal fluid are indicative of active transport of citalopram into or missing active transport out of the cerebrospinal fluid. The results suggest a high ability of citalopram to enter the brain with sufficiently high drug concentrations at the target sites within the brain, contributing toward clinical efficacy.

Duloxetine enters the brain - But why is it not found in the cerebrospinal fluid

BACKGROUND

Antidepressants enter the brain to reach their site of action in a different extent. However, there has been no study to date about duloxetine's ability to enter the brain and cerebrospinal fluid. Aim of this study was to measure blood and cerebrospinal fluid concentrations of duloxetine and to account for the distribution between the two compartments.

METHODS

Concentrations of duloxetine were measured in blood serum and cerebrospinal fluid of 19 patients treated with daily doses of 30-120mg. Daily doses were correlated with serum and cerebrospinal fluid concentrations and serum concentrations were correlated with concentrations in cerebrospinal fluid.

RESULTS

Serum concentrations of duloxetine showed a moderate but significant correlation with the applied daily dose, r=+0.473, p=0.04. Duloxetine concentrations in the cerebrospinal fluid above the designated limit of quantification of 2.0ng/mL were only found in three of the 19 patients.

CONCLUSIONS AND LIMITATIONS

Contrasting to own preceding studies on venlafaxine, mirtazapine and citalopram with comparably high concentrations in cerebrospinal fluid, the here presented findings indicate that duloxetine shows a very different distribution pattern. Very low concentrations in the cerebrospinal fluid may be due to the fact that the drug crosses the blood-cerebrospinal fluid barrier much worse than other antidepressants do, suggesting a low ability of duloxetine to enter the brain. Alternatively, low drug concentrations may be interpreted in a sense of a missing residence time in cerebrospinal fluid due to active transport mechanisms out of this environment either back into the bloodstream or into the brain.

Current advances in biosampling for therapeutic drug monitoring of psychiatric CNS drugs

Many CNS drugs are effective for the treatment of psychiatric disorders. Psychotropic drugs work differently, thus clinical outcomes for many patients may be insufficient. For this reason it could be useful the measurement of drug levels for clinical decision-making. Analytical goals in therapeutic drug monitoring (TDM) should be established by selecting the appropriate biological matrix. The aim of this review is to highlight the usefulness of TDM for antiepileptics, antidepressants and antipsychotics, with a focus on current advances in biosampling. The literature on TDM was reviewed up to March 2015. An overview on the use of alternative biological matrices is provided to address the current issues and advances in the field of biosampling for psychiatric CNS drug TDM.