Intrathecal administration of doxepin attenuated development of formalin-induced pain in rats

Doxepin for Radiation Therapy-Induced Mucositis Pain in the Treatment of Oral Cancers

Radiotherapy (RT), an integral part of the oncologic treatment for patients with head and neck cancer, can cause adverse side effects such as oral mucositis (OM). Pain from OM can impact a patient’s quality of life and interrupt RT treatment schedules, which decreases the probability for achieving cancer cure. Conventionally, RT-induced OM pain is treated with analgesics and/or mouthwash rinses. Doxepin, a traditional tricyclic antidepressant with analgesic and anesthetic properties when applied topically to the mucosa, has been shown to lower OM pain in multiple single-arm trials (Epstein et al.) and more recently, in a placebo-controlled crossover study (Leenstra and Miller et al.). Currently, a placebo-controlled study (Sio and Miller et al.) using doxepin for esophagitis pain caused by RT to the thorax is underway. Doxepin will also be further compared with magic mouthwash and a placebo solution in a three-arm trial (Miller and Sio et al.) with head and neck cancer patients with OM pain caused by RT. Doxepin may represent a new standard for treating RT-induced OM pain in the future.

Analgesic effects of antidepressants alone and after their local co-administration with morphine in a rat model of neuropathic pain

BACKGROUND

The therapy of neuropathic pain may include the use of co-analgesics, such as antidepressants, however, their desired analgesic effect is associated with significant side effects. An alternative approach to this is their local administration which has been proposed, but there is little data regarding their local co-administration with morphine and the nature of the interaction between morphine and either doxepin or venlafaxine, two antidepressant drugs that have been recently used in neuropathic pain therapies.

METHODS

This study was performed on rats after chronic constriction injury (CCI) to the sciatic nerve. The von Frey and Hargreaves' tests were used to assess mechanical allodynia and thermal hyperalgesia, respectively, after intraplantar (ipl) or subcutaneous (sc) administration of amitriptyline, doxepin, or venlafaxine, or their ipl co-administration with morphine on day 12-16 after injury.

RESULTS

The ipl administration of amitriptyline (3, 15 mg), doxepin (1, 5, 10, 15 mg), or venlafaxine (2, 7 mg) was effective in antagonizing CCI-induced allodynia. Their sc injection at a site distal to the injured side, did not induce alterations in pain thresholds, which supports the local mode of action. Of the three antidepressants used in this study, only ipl co-administration of amitriptyline with morphine significantly enhanced its effect in contrast to doxepin and venlafaxine, both of which weakened the analgesic effect of morphine.

CONCLUSIONS

In summary, the results suggest that when amitriptyline (but not doxepin or venlafaxine) is locally co-administered with morphine the effectiveness under neuropathic pain is enhanced, although additional studies are necessary to explain differential mechanisms of interaction of antidepressant drugs with morphine after local administration.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).