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.

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.

Inclusion Criteria:

1. Presence of radicular pain for at least 3 months;
2. Average pain level during the last week prior to enrollment > 40 (0-100);
3. No use of a new analgesic drug within 30 days prior to entry to the study and
4. Adults who were capable of understanding the purpose and instructions of the study and signing an informed consent.

Exclusion Criteria:

1. Pregnancy or breastfeeding;
2. Presence of Parkinson's disease or any other extra-pyramidal diseases;
3. History of allergy to the investigational drugs: Apomorphine or Domperidone;
4. History of polyneuropathy and
5. Respiratory depression, dementia, psychotic diseases or hepatic insufficiency

Individual participant data will not be shared.