Semi-mechanistic modelling of the analgesic effect of gabapentin in the formalin-induced rat model of experimental pain

PURPOSE

The formalin-induced rat model of nociception involves moderate continuous pain. Formalin-induced pain results in a typical repetitive flinching behaviour, which displays a biphasic pattern characterised by peaks of pain. Here we described the time course of pain response and the analgesic effect of gabapentin using a semi-mechanistic modelling approach.

METHODS

Male Sprague-Dawley rats received gabapentin (10-100 mg/kg) or placebo 1 h prior to the formalin injection, as per standard protocol. A reduction in the frequency of the second peak of flinching was used as a behavioural measure of gabapentin-mediated anti-nociception. The flinching response was modelled using a mono-exponential function to characterise the first peak and an indirect response model with a time variant synthesis rate for the second. PKPD modelling was performed using a population approach in NONMEM v.7.1.2.

RESULTS

The time course of the biphasic response was adequately described by the proposed model, which included separate expressions for each phase. Gabapentin was found to reversibly decrease, but not suppress the flinching frequency of the second response peak only. The mean IC50 estimate was 7,510 ng/ml, with relative standard error (RSE%) of 40%.

CONCLUSIONS

A compartmental, semi-mechanistic model provides the basis for further understanding of the formalin-induced flinching response and consequently to better characterisation of the properties of gabapentin, such as the potency in individual animals. Moreover, despite high exposure levels, model predictions show that gabapentin does not completely suppress behavioural response in the formalin-induced pain model.

Optimised protocol design for the screening of analgesic compounds in neuropathic pain

We have previously shown how screening experiments for neuropathic pain can be optimised taking into account parameter and model uncertainty. Here we demonstrate how optimised protocols can be used to screen and rank candidate molecules. The concept is illustrated by pregabalin as a new chemical entity and gabapentin as a reference compound. ED-optimality was applied to a logistic regression model describing the relationship between drug exposure and response to evoked pain in the complete Freund's adjuvant (CFA) model in rats. Design variables for optimisation of the experimental protocol included dose levels and sampling times. Prior information from the reference compound was used in conjunction with relative in vitro potency as priors. Results from simulated scenarios were then combined with fitting of experimental data to estimate precision and bias of model parameters for the empirical and optimised designs. The pharmacokinetics of pregabalin was described by a two-compartment model. The expected value of EC(50) of pregabalin was 637.5 ng ml(-1). Model-based analysis of the data yielded median (range) of EC(50) values of 1,125 (898-2412) ng ml(-1) for the empirical protocol and 755 (189-756) ng ml(-1) for the optimised design. In contrast to current practice, optimal design entails different sampling schedule across dose levels. ED-optimised designs should become standard practice in the screening of candidate molecules. It ensures lower bias when estimating the drug potency, facilitating accurate ranking and selection of compounds for further development.

Application of ED-optimality to screening experiments for analgesic compounds in an experimental model of neuropathic pain

In spite of the evidence regarding high variability in the response to evoked pain, little attention has been paid to its impact on the screening of drugs for inflammatory and neuropathic pain. In this study, we explore the feasibility of introducing optimality concepts to experimental protocols, enabling estimation of parameter and model uncertainty. Pharmacokinetic (PK) and pharmacodynamic data from different experiments in rats were pooled and modelled using nonlinear mixed effects modelling. Pain data on gabapentin and placebo-treated animals were generated in the complete Freund's adjuvant model of neuropathic pain. A logistic regression model was applied to optimise sampling times and dose levels to be used in an experimental protocol. Drug potency (EC(50)) and interindividual variability (IIV) were considered the parameters of interest. Different experimental designs were tested and validated by SSE (stochastic simulation and estimation) taking into account relevant exposure ranges. The pharmacokinetics of gabapentin was described by a two-compartment PK model with first order absorption (CL = 0.159 l h(-1), V(2) = 0.118 l, V(3) = 0.253 l, Ka = 0.26 h(-1), Q = 1.22 l h(-1)). Drug potency (EC(50)) for the anti-allodynic effects was estimated to be 1400 ng ml(-1). Protocol optimisation improved bias and precision of the EC50 by 6 and 11.9. %, respectively, whilst IIV estimates showed improvement of 31.89 and 14.91 %, respectively. Our results show that variability in behavioural models of evoked pain response leads to uncertainty in drug potency estimates, with potential impact on the ranking of compounds during screening. As illustrated for gabapentin, ED-optimality concepts enable analysis of discrete data taking into account experimental constraints.

Stability of an underactuated bipedal gait

A self-excited biped walking mechanism consisting of two legs that are connected in series at the hip joint through a servomotor is studied as a cyclic system with collisions. A torque proportional to angle between the shank of the swinging leg and the vertical is seen to sustain a gait. Each leg has a thigh and a shank connected at a passive knee joint that has a knee stopper restricting hyperextension similar to the human knee. A mathematical model for the dynamics of the system including the impact equations is used to analyse the stability of the system through examination of phase plane plots. Attractor lines along which the system approaches stability have been identified. A leg length for optimal stability has been identified. The biological basis for the proposed system has been identified by comparison with human gait.

Admission ECG predicts long-term outcome in acute coronary syndromes without ST elevation

BACKGROUND

Acute coronary syndromes (ACS) without ST elevation are a frequent cause of hospital admission, myocardial infarction and death.

AIM

To explore the role of the ECG in stratifying ACS patients.

DESIGN

Prospective, centrally-coordinated multicentre registry involving 56 centres throughout the UK.

METHODS

Consecutive patients admitted with ACS without ST elevation on the presenting ECG (n = 1046) were followed for 6 months. A subgroup (n = 653) were flagged with the UK Office for National Statistics and followed-up for death over 4 years.

RESULTS

Mean follow-up for the group as a whole was 2.4 years. In the first 6 months, the death rate was 7.3%. Survival at 1 year was 90.8% (95%CI 88.2%-92.8%); at 45 months it was 77.8% (95%CI 74.1%-81.1%). We compared data in those with ST depression or bundle branch block on the admission ECG (n = 304, 29%) with those with T wave inversion, Q waves and minor ST segment changes (n = 576, 55%) and those with a normal ECG (n = 166, 16%). Their respective incidences of death were 15%, 5% and 2% (p < 0.01) at 6 months, and 38%, 22% and 7% (p < 0.01) at 4 years.

DISCUSSION

Rates of adverse events are high in patients admitted to UK hospitals with ACS without ST elevation. The ECG remains a very important and simple discriminator of both short- and long-term risk, enabling more aggressive, proven therapies to be targeted towards those at highest risk.

Indoor/outdoor relationships of carbon monoxide and oxides of nitrogen in domestic homes with roadside, urban and rural locations in a central Indian region

Indoor air quality (IAQ) has been a matter of public concern these days whereas air pollution is normally monitored outdoors as part of obligations under the National air quality strategies. Much little is known about levels of air pollution indoors. Simultaneous measurements of indoor and outdoor carbon monoxide (CO) and oxides of nitrogen (NO and NO2) concentrations were conducted at three different environments, i.e. rural, urban and roadside in Agra, India, using YES - 205 multigas monitor during the winter season, i.e. October 2002-February 2003. A statistical correlation analysis of indoor concentration levels with outdoor concentrations was carried out. CO was maximum at roadside locations with indoor concentrations 2072.5 +/- 372 p.p.b. and outdoor concentrations 1220 +/- 281 p.p.b. (R2 = 0.005). Oxides of nitrogen were found maximum at urban site; NO concentration was 385 +/- 211 and 637 +/- 269 p.p.b. for indoors and outdoors respectively (R2 = 0.90792), where as NO2 concentration was 255 +/- 146 p.p.b. for indoors and 460 +/- 225 p.p.b. for outdoors (R2 = 0939464). Although indoor concentration at all the houses of the three sites have a positive correlation with outdoor concentration, CO variation indoors was very less due to outdoor sources. An activity schedule of inside and outside these homes were also prepared to see its influence and concentrations of pollutants. As standards for indoor air were not available for the Indian conditions these were compared with the known standards of other countries, where as outdoor concentrations were compared with the standards given by the Central Pollution Control board, which shows that indoor concentrations of both NO(x) and CO lie below permissible limits but outdoor concentrations of NO(x) cross the standard limits.

PRACTICAL IMPLICATIONS

''India currently bears the largest number of indoor air pollution (IAP) related health problems in world. An estimated 500,000 women & children die in India each year due to IAP-related cause--this is 25% of estimated IAP-related deaths worldwide. This study will be useful for policy makers, health related officials, academicians and Scientists who have interest in countries of developing world''.

A clinical trial of the efficacy and safety of montelukast as monotherapy in patients with chronic stable bronchial asthma

This study is aimed to evaluate the efficacy and safety of montelukast, as monotherapy, in the treatment of chronic stable bronchial asthma in adults. This was a multicentre, open label, non-comparative, prospective, 4-week study. Eligible patients discontinued all anti-inflammatory medication (steroids, chromoglycate sodium) 2 weeks prior to starting therapy with montelukast (10 mg daily). The primary efficacy criteria were improvements in forced expiratory volume in one second (FEV1), peak exploratory flow rate (PEFR) after 4 weeks of therapy. Secondary efficacy criteria were improvement in the patients' symptoms (assessed on an ordinal scale), decrease in discomfort levels (scored on a scale of 0-100), change in peripheral eosinophil counts, decrease in total daily dose of inhaled beta2 agonist (salbutamol). A total of 148 patients, mean age (+/- SD) 40.21 +/- 13.70 years, were enrolled into the study. At the end of the study there were significant improvements in FEV1 and PEFR (29% and 28% increase respectively from baseline values, p<0.000001). The mean total daily dose of inhaled salbutamol decreased significantly from prestudy values of 461 +/- 332 microg/day to 161 +/- 207 microg/day (p<0.000001). The mean eosinophil counts fell from 5.80 +/- 4.90% (+/- SD) to 4.84 +/- 4.42% (+/- SD) (p=0.02). Symptom scores improved significantly as did subjective assessment of discomfort. A total of 29 (19.6%) adverse events were reported, all of which were of mild to moderate intensity. Monotherapy with montelukast significantly improved parameters of asthma control. It was well tolerated with no reports of serious or severe adverse events.

Treatment of vitiligo

Vitiligo, particularly in darker skinned individuals, is a psychosocial disaster. With patient education, proper therapeutic selection and persistence, favorable repigmentation can be achieved in the majority of individuals with vitiligo. Attention to the activity state of the disease, the type, location and extent of the vitiligo must be carefully balanced against the patient's expectations, time commitment and assumption of risks. In this review, Dr Taneja succinctly summarizes the wide range of therapeutic options available today for the vitiligo patient.

Evaluation of immunogenicity and tolerance of single dose haemophilus influenzae type B (PRP-T) vaccine

OBJECTIVE

Evaluation of immunogenicity and acceptability of PRP-T vaccine among the Indian children.

DESIGN

Multicentric, open, parallel group, comparative study of Haemophilus influenzae type B vaccine, given as single (Group I) or associated (Group II) with DPT vaccine.

SETTING

Five different vaccination clinics.

SUBJECTS

125 children between the age group of 18-24 months.

PARAMETERS

Measurement of (i) pre and post vaccination antibody titres of Haemophilus influenze type B specific antibody; (ii) Adverse events; and (iii) Tolerance as graded by the physician.

RESULTS

Prevaccination antibody levels were > 0.15 mcg/ml in 56.3% in Group I and 35.7% in Group II. Post-seroconversion was seen in 97% in Group II receiving single and all in Group II (P > 0.05). The vaccine was well tolerated.

CONCLUSIONS

The probability of subclinical infection or cross immunity is high in India. ACTHIB vaccine has a good immunogenicity and tolerance and association with DPT does not modify the immunogenicity of ACTHIB vaccine.

Fibronectin levels in Indian neonates in health & disease

Cord blood samples were estimated for serum fibronectin (Fn) by immunoelectrophoresis (IE) and enzyme linked immuno sorbent assay (ELISA) in 250 newborn healthy and sick infants classified into 6 categories: i.e., term appropriate for date (TAFD), preterm appropriate for date (PTAFD), term small for date (TSFD), preterm small for date (PTSFD), birth asphyxia (BA) and septicemia (SEP). TAFD infants were assayed for plasma Fn in addition. Comparison of Fn levels in the different groups by the Wilcoxan rank sum test indicated no significant difference between term and preterm infants, between PTAFD and PTSFD, TAFD and TSFD and in infants with and without birth asphyxia. Babies with septicemia had a significantly (P < 0.01) lower Fn level (29.97 +/- 29.03 mg/l) than those with no septicemia (42.77 +/- 30.20 mg/l). TAFD infants had Fn levels (serum 41.44 +/- 31.08 mg/l, plasma 85.20 +/- 33.38 mg/l) that are less than half the levels reported in the Western literature for newborn term infants. A possible cause could be the associated medical problems in mothers as 41 per cent of mothers of TAFD infants had conditions such as pregnancy induced hypertension, gestational diabetes, rheumatic heart disease, infection etc.

Variable-transformed collocation method for field propagation through waveguiding structures

We show that an appropriate variable transformation can redistribute the sample points for the field in the collocation method such that the numerical accuracy of the field-propagation algorithm improves significantly. We also present results for some specific transformations that improve the accuracy by more than 2 orders of magnitude.

Alloimmunisation to platelet transfusions in the Indian patients

Twenty nine patients of acute and chronic leukemia undergoing chemotherapy and receiving blood transfusions (BT) and platelet transfusions (PT) from random donors (3-20 PT from 4-56 donors) were followed up for alloimmunisation using the platelet immunofluorescence test. Two women patients aged 65 and 28 yr reacted positive. Both patients had received multiple BT but no PT at the time of testing. Both were parous women. Our results point to the need to test for alloimmunisation prior to starting PT in parous women who have received multiple BT, although a study on larger number of patients is necessary for confirmation.

Simple numerical technique for the analysis of cylindrically symmetric refractive-index profile optical fibers

We extend an earlier proposed matrix method for the analysis of cylindrically symmetric arbitrary refractive-index profile optical fibers to calculate the propagation constant and leakage/absorption loss of modes. This method involves only straightforward multiplications of 2 x 2 matrices and is highly attractive, since no complex plane iterations are performed even to obtain leakage or absorption losses. Thus the method is ideally suited for implementation on desktop computers. The applicability of the method has been shown through calculations of propagation constants and leakage loss of the LP(01) mode in depressed inner clad fibers.

Unconditionally stable procedure to propagate beams through optical waveguides using the collocation method

The collocation method developed earlier for propagating beams through optical waveguides is unstable for moderately large values of the extrapolation interval. A new procedure is presented to solve the matrix propagation equation in a method that is unconditionally stable for arbitrarily large extrapolation intervals. The new method uses the Fresnel approximation. The numerical performance of the new formulation is compared with that of the original method and with the propagating-beam method.