Pain after spinal intrathecal clonidine

Determination of pharmacological interactions of uliginosin B, a natural phloroglucinol derivative, with amitriptyline, clonidine and morphine by isobolographic analysis

Uliginosin B is a natural phloroglucinol derivative, obtained from Hypericum species native to South America. Previous studies have shown that uliginosin B presents antidepressant-like and antinociceptive effects. Although its mechanism of action is still not completely elucidated, it is known that it involves the activation of monoaminergic neurotransmission. The aim of the current study was to further investigate the antinociceptive mechanism of action of uliginosin B by combining it with different drugs used for treating pain in clinical practice. The intraperitoneal administration of uliginosin B, morphine, amitriptyline and clonidine, alone or in mixture, produced a dose-dependent antinociceptive effect in the hot-plate assay in mice. The effect of the mixtures of drugs was studied using an adapted isobologram analysis at the effect level of 50% of the maximal effect observed. The analysis showed that the interactions between uliginosin B and morphine was synergistic, while the interactions between uliginosin B and amitriptyline or clonidine were additive. These findings point to uliginosin B as a potential adjuvant for pain pharmacotherapy, especially for opioid analgesia.

Long-term outcomes during treatment of chronic pain with intrathecal clonidine or clonidine/opioid combinations

To evaluate the effectiveness of intrathecal clonidine or clonidine/opioid admixture for the treatment of chronic pain states, a retrospective chart audit of 15 patients seen by the Pain Medicine and Neurosurgical Services was performed. Subjects included 9 men and 6 women aged 26-86 years. Diagnoses included complex regional pain syndrome, neuropathic pain, and cancer pain. All patients received a trial of single-shot and/or short-term infusion of clonidine. Those reporting a significant reduction in pain, or at least 50% reduction in their visual analog scale (VAS), received long-term therapy. Intrathecal clonidine as a single-shot dose, infusion, or as intrathecal polytherapy did not improve VAS scales from pre-treatment values in 5 patients. Ten patients reported significant pain relief or >50% decrease in VAS scores with the initial trial and received long-term therapy. Two received clonidine alone for 7-11 months before the therapy failed; others failed after just a few days. Seven of eight initially responded to clonidine alone (75-950 microg/day) before failing and requiring a second drug. Three received hydromorphone (200-8000 microg/day) and four morphine (0.15-15 mg/day) with clonidine. Four patients then failed 2-drug therapy (duration 6-21 months). Two continue with intrathecal clonidine/hydromorphone (duration 19-29 months) and 1 with clonidine/morphine (duration 21 months). After initiation of intrathecal clonidine, one patient reported good relief with clonidine/morphine until his death 5 months later. In this population, intrathecal clonidine was of limited utility for most patients. It may be of benefit for subset(s) of patients, but in our experience, duration of relief is typically <18 months.

Role of signal transduction in anesthetic action. Alpha 2 adrenergic agonists

The molecular mechanism for general anesthetic action is not known. The alpha 2 adrenergic agonists represent a novel class of "anesthetic-like" agent because of their selectivity for receptor binding sites and because the transmembrane signaling systems mediating their biologic responses in non-CNS systems are known. We have begun to characterize the signal transduction pathway involved in the anesthetic-like action of the alpha 2 adrenergic agonists. The alpha 2 adrenergic agonists potently decrease both central noradrenergic neurotransmission and halothane anesthetic requirements (MAC). Since MAC is only reduced by 30-40% when noradrenergic neurotransmission is totally abolished and since the reduction in MAC with the highly selective alpha 2 adrenergic agonists exceeds 90%, factors in addition to noradrenergic neurotransmission must be contributing to the anesthetic action of the alpha 2 agonists. Studies with the superselective alpha 2 agonist dexmedetomidine confirmed this, as the alpha 2 agonist could still reduce the MAC for halothane in rats depleted of their central norepinephrine stores. The profound reduction in anesthetic requirements with dexmedetomidine raised the possibility that alpha 2 adrenergic agonists may be considered an anesthetic hypnotic agent by itself. This sole anesthetic hypnotic response was established together with the confirmation that a central alpha 2 adrenoceptor mediated this action. Subsequently, data using molecular biologic techniques suggested that the alpha 2 C4 isoreceptor was the probable receptor that mediated the anesthetic response. We further explored the postreceptor effector mechanism for the signal transduction pathway for alpha 2 anesthetic action and identified the participation of two other molecular components, namely, a pertussis-toxin-sensitive G protein and a 4-aminopyridine-sensitive ion channel. Whether the signal transduction pathway for alpha 2 anesthetic action mediates the further response to other non-alpha 2 anesthetic agents needs to be defined.