The Effects of Apomorphine on Experimental and Clinical Pain in Patients With Chronic Radicular Pain

Study Overview
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Brief Summary
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The study aimed to explore the effect of the dopamine agonist apomorphine on spontaneous pain intensity and evoked cold clinical and experimental pain in patients with lumbar radicular neuropathic pain (NP). Patients received either apomorphine or placebo in a randomized double-blinded manner.

Detailed Description
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Although evidence suggests that dopaminergic systems are involved in pain processing, the efficacy of dopaminergic interventions in reducing pain remains questionable. This randomized, double blinded, placebo-controlled, cross-over study was aimed to explore the effect of the dopamine agonist apomorphine on spontaneous pain intensity and evoked cold clinical and experimental pain in patients with lumbar radicular neuropathic pain (NP). Data was collected from 35 patients (18 men, mean age 56.2±13.1 years). The following five pain measures were tested before (baseline) and 30, 75 and 120 min subsequent to subcutaneous injection of 1.5 mg apomorphine or placebo in two separate sessions: spontaneous pain intensity, threshold and tolerance to cold pain in the most painful site in the affected leg and in a remote healthy site in the dominant hand.

Official Title
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The Effects of the Dopamine Agonist (Apomorphine) on Experimental and Clinical Pain in Patients With Chronic Radicular Pain: a Randomized, Double-blind, Placebo-controlled, Cross-over Study

Conditions
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Chronic Low Back Pain

Intervention / Treatment
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* Drug: Apomorphine
* Drug: Normal Saline


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Presence of radicular pain for at least 3 months; Average pain level during the last week prior to enrollment > 40 (0-100); No use of a new analgesic drug within 30 days prior to entry to the study and Adults who were capable of understanding the purpose and instructions of the study and signing an informed consent. Exclusion Criteria: Pregnancy or breastfeeding; Presence of Parkinson's disease or any other extra-pyramidal diseases; History of allergy to the investigational drugs: Apomorphine or Domperidone; History of polyneuropathy and Respiratory depression, dementia, psychotic diseases or hepatic insufficiency

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Triple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: apomorphine<br>1.5 mg apomorphine, administered subcutaneously | Drug: Apomorphine<br> <br> |
| Placebo Comparator: Normal saline<br>saline, administered subcutaneously | Drug: Normal Saline<br> <br> |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Experimental and clinical cold pain tolerance measured in seconds |  | Up to 120 minutes after drug administration | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Experimental and clinical cold pain threshold measured in seconds |  | Up to 120 minutes after drug administration | 
| Spontaneous clinical pain intensity measured on a numeric pain scale (NPS, 0-100) |  | Up to 120 minutes after drug administration |