A new laser pain threshold model detects a faster onset of action from a liquid formulation of 1 g paracetamol than an equivalent tablet formulation

Activation of C-fiber nociceptors by low-power diode laser

ABSTRACT Objective The evaluation of selective activation of C-fibers to record evoked potentials using the association of low-power diode laser (810 nm), tiny-area stimulation and skin-blackening. Method Laser-evoked potentials (LEPs) were obtained from 20 healthy young subjects. An aluminum plate with one thin hole was attached to the laser probe to provide tiny-area stimulation of the hand dorsum and the stimulated area was covered with black ink. Results The mean intensity used for eliciting the ultra-late laser-evoked potential (ULEP) was 70 ± 32 mW. All subjects showed a clear biphasic potential that comprised a negative peak (806 ± 61 ms) and a positive deflection (1033 ± 60 ms), corresponding to the ULEP related to C-fiber activation. Conclusion C-fiber-evoked responses can be obtained using a very low-power diode laser when stimulation is applied to tiny areas of darkened skin. This strategy offers a non-invasive and easy methodology that minimizes damage to the tissue.

Decreased Pain Threshold in Juvenile Idiopathic Arthritis: A Cross-sectional Study

Objective.

To examine the pain threshold in children with juvenile idiopathic arthritis (JIA) compared with healthy children by using a digital pressure algometer.

Methods.

Fifty-eight children with JIA born between 1995 and 2000 and 91 age-related healthy children participated in the study. We used a digital pressure algometer to measure the pain threshold on 17 symmetric, anatomically predefined joint-related or bone-related areas. All children were asked to rate their current pain on a Faces Pain Scale, and parents of children with JIA were asked to complete a parental revised version of the Child Health Assessment Questionnaire (CHAQ-R). Clinical data were registered on children with JIA.

Results.

The pain threshold was significantly lower among children with JIA (total mean PT = 1.33 ± 0.69 kg/cm2) when compared with the healthy control group (total mean PT = 1.77 ± 0.67 kg/cm2). The same pattern was found in all areas measured, including negative control areas that are normally unaffected in JIA (p = 0.0001 to 0.005). Overall, the pain threshold was 34% lower in females than in males in both groups (p < 0.0001). We found no correlation between pain threshold and age, current pain experience, disease duration, or disease activity.

Conclusion.

Children with JIA had a substantially lower pain threshold even in areas usually unaffected by arthritis. Our findings suggest that JIA alters the pain perception and causes decreased pain threshold.

Development of a simple radiant heat induced experimental pain model for evaluation of analgesics in normal healthy human volunteers

Objective:

Human experimental pain models help to understand the mechanism of the painful conditions and can also be adopted to test analgesic efficacy of drugs. In early phases, the clinical development of new analgesics is hindered due to the lack of reliable tests for the experimental pain models. In the present study, we have developed and validated a simple radiant heat pain model which can be used for future screening of various analgesic agents.

Materials and Methods:

We have standardized the thermal pain model by recording pain threshold and pain tolerance time in seconds at three different intensities and levels in 24 healthy subjects. Reproducibility of the test procedure was evaluated by recording the pain parameters by two observers on three consecutive days. Validity of model was further tested by evaluating the analgesic effect of tramadol.

Results and Conclusions:

Use of radiant heat pain model with high intensity and short level was found to produce low variability with coefficient of variation less than 5%. Interobserver and interperiod reproducibility was very good as shown by Bland - Altman plot; with most of the values within ± 2SD. Tramadol produced statistically significant increase in pain threshold time. The newly developed pain model produces a type of experimental pain which is responsive to analgesic effects of tramadol at clinically relevant doses.

A simple contact heat experimental pain model for evaluation of analgesic agents in healthy volunteers

BACKGROUND

Human experimental pain models help to understand the mechanism of the underlying clinical pain conditions and can be adopted to test analgesic efficacy of drugs used in the management of pain. In early phases, the clinical development of new analgesic agents is severely hindered due to lack of reliable sensitive tests for the experimental pain models.

OBJECTIVE

The aim of the present study was to standardize and validate a simple contact heat pain model that can be used for future screening of various analgesic agents.

METHODS

The method was standardized by recording heat detection and heat pain detection threshold in degrees centigrade in 24 healthy volunteers. Reproducibility of the test procedure was evaluated by recording the thermal threshold parameters by a single observer on 2 sessions (inter-day reproducibility) and a second observer on 1 session (inter-observer reproducibility) separately. Validity of model was further tested by evaluating the analgesic effect of tramadol on 12 healthy volunteers.

RESULTS

Thermal pain model using contact heat method was found to produce low variability with coefficient of variation <5%. Inter-observer and inter-day reproducibility was very good, as shown by Bland-Altman Plot; with most of the values within 2 SD. There was a significant difference in both heat detection threshold and heat pain detection threshold produced by tramadol, as compared with placebo (P < 0.05).

CONCLUSIONS

The newly developed pain model produces a type of experimental pain that is responsive to analgesic effects of tramadol at clinically relevant doses. The model might be useful in early screening of new therapeutic agents before proceeding to expensive clinical trials in acute and chronic pain sufferers.