There has been a growing interest in opioid-induced hyperalgesia (OIH), which is an increased sensitivity to pain caused by opioid exposure. Multiple underlying pathways may contribute to the development of OIH, and the mechanism may vary with the duration of opioid exposure, dose, type and route of administration. In addition, the distinction between OIH, tolerance and withdrawal should be made in both the basic and clinical science literature so as to help translate findings to the clinical phenomenon and to help determine the best strategies to prevent or treat OIH.
Analgesics, Opioid ; adverse effects ; Drug Tolerance ; Humans ; Hyperalgesia ; chemically induced ; prevention & control ; Pain Measurement

The use of opioids for the treatment of chronic non-cancer pain has become more widespread recently. Available data support the short-term use of opioids in clearly defined nociceptive and neuropathic pain states. Their use in 'pathological' pain states without a clear diagnosis, such as chronic low back pain, is more contentious. A decision to initiate opioid treatment in these conditions requires careful consideration of benefits and risks; the latter include not only commonly considered adverse effects such as constipation, but also opioid-induced hyperalgesia, abuse, addiction and diversion. Ideally, treatment goals should not only be relief of pain, but also improvement of function. Opioid treatment of chronic non-cancer pain requires informed consent by, and preferably a treatment contract with, the patient. Treatment should be initiated by a trial period with defined endpoints using slow-release or transdermal opioids. Ongoing management of the patient requires ideally a multi-disciplinary setting. Treatment should not be regarded as life-long and can be discontinued by tapering the dose.
Analgesics, Opioid ; adverse effects ; therapeutic use ; Humans ; Hyperalgesia ; chemically induced ; Low Back Pain ; drug therapy ; Pain, Intractable ; drug therapy ; Substance-Related Disorders ; prevention & control

We examined whether pretreatment with a small dose of thiopental was effective in reducing pain induced by the intravenous injection of rocuronium. Withdrawal movement was used to assess pain reduction. Ninety patients were randomly assigned to one of two groups: patients in the control group were pretreated with 2 mL saline, and those in the thiopental group were pretreated with 2 mL (50 mg) thiopental. Thiopental 5 mg/kg was injected intravenously. After a loss of consciousness, the upper arm was compressed with a rubber tourniquet, and the pretreatment drugs were administered. Thirty seconds later the tourniquet was removed and 0.6 mg/kg rocuronium was administered. Withdrawal movement was assessed using a four-grade scale: no movement, movement limited to the wrist, to the elbow or to the shoulder. The frequency of withdrawal movement in the group pretreated with thiopental was lower than in the control group (34 vs. 13, p 0.05). We concluded that pretreatment with 2 mL (50 mg) thiopental is effective in reducing pain caused by the intravenous injection of rocuronium.
Thiopental/*therapeutic use ; Pain Measurement ; Pain/chemically induced/*prevention & control ; Neuromuscular Nondepolarizing Agents/*adverse effects ; Middle Aged ; Male ; Injections, Intravenous ; Humans ; Female ; *Anesthetics, Intravenous ; Androstanols/*adverse effects ; Adult

OBJECTIVETo evaluate the safety of recombinant human interferon alpha-2b for nasal spray for the prevention of SARS and other upper respiratory viral infections.

METHODSField epidemiologic evaluation was conducted, the design was randomized and had a synchronously parallel control group. In the study, the drugs were given for five days and all subjects were followed up for ten days.

RESULTSDuring the period of using interferon, body temperature of the experimental group was normal compared to the control group. Experimental group had more influenza-like symptoms than the control group (P < 0.05), such as headache (4.83%-7.09%), dizziness (7.17%-11.63%), lassitude (8.55%-15.06%), muscular soreness (4.43%-7.09%), pharynx dryness (12.10%-17.85%), angina (6.25%-8.72%), abdominal pain (2.30%-5.50%) and diarrhea (2.45%-5.66%). Most of side effects reached their peak with in the first 3 days. Except for pharynx dryness, the incidences of all other side effects declined after completion of the use of the trial drug, and incidences of some symptoms in experimental group were lower than those of the control group. There were no significant differences in the symptoms of cough and expectoration between the experimental group and the control group. The incidence of exanthem in the control group was significantly higher than that in the experimental group. The side effect of bloody nasal mucus was not observed in experimental group, which had been reported by other authors in several volunteer studies.

CONCLUSIONUsing recombinant human interferon alpha-2b for nasal spray could lead to some influenza-like symptoms, however, all those symptoms were mild , reversible, and relieved after completion of the use of the trial drug. No serious side effects were found during the period of following up. The authors conclude that the drug is safe.

Abdominal Pain ; chemically induced ; Adolescent ; Adult ; Antiviral Agents ; administration & dosage ; adverse effects ; therapeutic use ; Dizziness ; chemically induced ; Female ; Follow-Up Studies ; Headache ; chemically induced ; Humans ; Interferon-alpha ; administration & dosage ; adverse effects ; therapeutic use ; Male ; Recombinant Proteins ; SARS Virus ; drug effects ; Severe Acute Respiratory Syndrome ; prevention & control ; virology ; Treatment Outcome ; Young Adult

Investigation of pain requires measurements of nociceptive sensitivity and other pain-related behaviors. Recent studies have indicated the superiority of gait analysis over traditional evaluations (e.g., skin sensitivity and sciatic function index [SFI]) in detecting subtle improvements and deteriorations in animal models. Here, pain-related gait parameters, whose criteria include (1) alteration in pain models, (2) correlation with nociceptive threshold, and (3) normalization by analgesics, were identified in representative models of neuropathic pain (spared nerve injury: coordination data) and inflammatory pain (intraplantar complete Freund's adjuvant: both coordination and intensity data) in the DigiGait™ and CatWalk™ systems. DigiGait™ had advantages in fixed speed (controlled by treadmill) and dynamic SFI, while CatWalk™ excelled in intrinsic velocity, intensity data, and high-quality 3D images. Insights into the applicability of each system may provide guidance for selecting the appropriate gait imaging system for different animal models and optimization for future pain research.
Analgesics ; administration & dosage ; Animals ; Freund's Adjuvant ; administration & dosage ; Gait ; drug effects ; Gait Analysis ; methods ; Image Processing, Computer-Assisted ; Inflammation ; chemically induced ; Male ; Neuralgia ; physiopathology ; prevention & control ; Pain ; etiology ; physiopathology ; prevention & control ; Rats, Sprague-Dawley

OBJECTIVETo study the analgesic, antipyretic and anti-inflammatory effect of Bailian Caogen granule.

METHODThe antipyretic effects of Bailian Caogen granule was evaluated in rabbit fever model induced by peptone. The analgesic effect of the drug was studied with pain model of mice induced by acetic acid and hot plate, The severity of oedema in inflamed animal was observed to study the anti-inflammatory effects of Bailian Caogen granule.

RESULTBailian Caogen granule could obviously inhibit the fever of rabbits. The number of writhing induced by acetic acid was reduced and the pain threshold of mice was increased by Bailian Caogen granule. Bailian Caogen granule also had anti-inflammatory activity against xylene-induced mouse ear swelling and carrageenin-induced rat paw edema.

CONCLUSIONBailian Caogen granule has significant analgesic, antipyretic and anti-inflammatory activities.

Acetic Acid ; Analgesics, Non-Narcotic ; pharmacology ; Animals ; Body Temperature ; drug effects ; Coptis ; chemistry ; Drug Combinations ; Drugs, Chinese Herbal ; pharmacology ; Edema ; pathology ; prevention & control ; Female ; Fever ; physiopathology ; prevention & control ; Glycyrrhiza uralensis ; chemistry ; Hot Temperature ; Hyperalgesia ; etiology ; physiopathology ; prevention & control ; Male ; Mice ; Pain ; chemically induced ; physiopathology ; prevention & control ; Pain Threshold ; drug effects ; Phellodendron ; chemistry ; Plants, Medicinal ; chemistry ; Pueraria ; chemistry ; Rabbits ; Random Allocation ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo optimize the extraction process of Tuirezhitongsan and extract the pharmacodynamically active fractions.

METHODSOrthogonal test methods and supercritical-CO(2) fluid extraction (SFE-CO(2)) were used for the extraction, and the the pharmacodynamically active fractions were screened with analgesic experiments.

RESULTSThe optimal extraction of the active fractions was achieved with the extraction pressure at 25 MPa, extraction temperature at 45 degrees celsius, resolution pressure at 6.7 MPa, and resolution temperature at 50 degrees celsius.

CONCLUSIONSFE- CO(2) is rapid, efficient, and energy-saving in the extraction of the active fractions in Tuirezhotongsan, and provides a mew method for extraction of traditional Chinese medicine.

Acetic Acid ; Animals ; Anti-Inflammatory Agents, Non-Steroidal ; chemistry ; isolation & purification ; pharmacology ; Chromatography, Supercritical Fluid ; methods ; Drugs, Chinese Herbal ; chemistry ; isolation & purification ; pharmacology ; Female ; Male ; Mice ; Pain ; chemically induced ; prevention & control

BACKGROUND/AIMS: Acidic saline injections produce mechanical hyperresponsiveness in male Sprague-Dawley rats. We investigated the effect of milnacipran in conjunction with tramadol on the pain threshold in an acidic saline animal model of pain. METHODS: The left gastrocnemius muscle of 20 male rats was injected with 100 microL of saline at pH 4.0 under brief isoflurane anesthesia on days 0 and 5. Rats administered acidic saline injections were separated into four study subgroups. After determining the pre-drug pain threshold, rats were injected intraperitoneally with one of the following regimens; saline, milnacipran alone (60 mg/kg), milnacipran (40 mg/kg) plus tramadol (20 mg/kg), or milnacipran (40 mg/kg) plus tramadol (40 mg/kg). Paw withdrawal in response to pressure was measured at 30 min, 120 min, and 5 days after injection. Nociceptive thresholds, expressed in grams, were measured with a Dynamic Plantar Aesthesiometer (Ugo Basile, Italy) by applying increasing pressure to the right or left hind paw until the rat withdrew the paw. RESULTS: A potent antihyperalgesic effect was observed when tramadol and milnacipran were used in combination (injected paw, p=0.001; contralateral paw, p=0.012). This finding was observed only at 30 min after the combination treatment. CONCLUSIONS: We observed potentiation of the antihyperalgesic effect when milnacipran and tramadol were administered in combination in an animal model of fibromyalgia. Further research is required to determine the efficacy of various combination treatments in fibromyalgia in humans.
Analgesics, Opioid/administration & dosage/*pharmacology ; Animals ; Antidepressive Agents/administration & dosage/*pharmacology ; Behavior, Animal/drug effects ; Cyclopropanes/administration & dosage/*pharmacology ; Disease Models, Animal ; Drug Synergism ; Drug Therapy, Combination ; Fibromyalgia/chemically induced/complications/*prevention & control ; Hydrogen-Ion Concentration ; Hyperalgesia/etiology/*prevention & control ; Injections, Intraperitoneal ; Male ; Pain/etiology/*prevention & control ; Pain Measurement ; Pain Threshold/*drug effects ; Rats ; Rats, Sprague-Dawley ; Sodium Chloride ; Time Factors ; Tramadol/administration & dosage/*pharmacology

Citalopram and paroxetine are selective serotonin reuptake inhibitors and also have antinociceptive effects. We investigated the antiallodynic and antihyperalgesic effects of intrathecally administered morphine, citalopram, paroxetine, and combinations thereof, in a rat model in which peripheral inflammation was induced by complete Freund's adjuvant (CFA). Drugs were intrathecally administered via direct lumbar puncture. Mechanical allodynia was measured using a Dynamic Plantar Aesthesiometer. Thermal hyperalgesia and cold allodynia were determined by measuring latency of paw withdrawal in response to radiant heat and cold water. Behavioral tests were run before and 15, 30, 45, and 60 min after intrathecal injection. Intraplantar injection of CFA produced mechanical allodynia, thermal hyperalgesia, and cold allodynia. Intrathecally administered morphine (0.3 or 1 microg) had antiallodynic or antihyperalgesic effects (24.0%-71.9% elevation). The effects of morphine were significantly increased when a combination of citalopram (100 microg) and paroxetine (100 microg) was added (35.2%-95.1% elevation). This rise was reversed by naloxone and methysergide. The effects of citalopram and paroxetine were also reversed by naloxone and methysergide. We suggest that the mu opioid receptor and serotonin receptors play major roles in production of the antiallodynic and antihyperalgesic effects of morphine, citalopram, paroxetine, and combinations thereof, in animals experiencing inflammatory pain.
Analgesics, Opioid/administration & dosage/*pharmacology ; Animals ; Behavior, Animal/drug effects ; Citalopram/administration & dosage/pharmacology ; Disease Models, Animal ; Hyperalgesia/etiology ; Inflammation/*chemically induced/pathology ; Injections, Spinal ; Male ; Morphine/administration & dosage/*pharmacology ; Pain/*prevention & control ; Pain Measurement ; Pain Threshold/drug effects ; Paroxetine/administration & dosage/pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Serotonin/*chemistry/metabolism ; Serotonin Uptake Inhibitors/administration & dosage/*pharmacology ; Temperature ; Time Factors

Mounting evidence supports an important role of chemokines, produced by spinal cord astrocytes, in promoting central sensitization and chronic pain. In particular, CCL2 (C-C motif chemokine ligand 2) has been shown to enhance N-methyl-D-aspartate (NMDA)-induced currents in spinal outer lamina II (IIo) neurons. However, the exact molecular, synaptic, and cellular mechanisms by which CCL2 modulates central sensitization are still unclear. We found that spinal injection of the CCR2 antagonist RS504393 attenuated CCL2- and inflammation-induced hyperalgesia. Single-cell RT-PCR revealed CCR2 expression in excitatory vesicular glutamate transporter subtype 2-positive (VGLUT2) neurons. CCL2 increased NMDA-induced currents in CCR2/VGLUT2 neurons in lamina IIo; it also enhanced the synaptic NMDA currents evoked by dorsal root stimulation; and furthermore, it increased the total and synaptic NMDA currents in somatostatin-expressing excitatory neurons. Finally, intrathecal RS504393 reversed the long-term potentiation evoked in the spinal cord by C-fiber stimulation. Our findings suggest that CCL2 directly modulates synaptic plasticity in CCR2-expressing excitatory neurons in spinal lamina IIo, and this underlies the generation of central sensitization in pathological pain.
Animals ; Benzoxazines ; pharmacology ; therapeutic use ; Chemokine CCL2 ; antagonists & inhibitors ; genetics ; metabolism ; pharmacology ; Excitatory Amino Acid Agents ; pharmacology ; Excitatory Amino Acid Agonists ; pharmacology ; Female ; Freund's Adjuvant ; toxicity ; Hyperalgesia ; chemically induced ; metabolism ; prevention & control ; Long-Term Potentiation ; drug effects ; physiology ; Luminescent Proteins ; genetics ; metabolism ; Male ; Mice ; Mice, Inbred C57BL ; Mice, Transgenic ; Myelitis ; chemically induced ; drug therapy ; metabolism ; Neurons ; drug effects ; Pain Management ; Somatostatin ; genetics ; metabolism ; Spinal Cord ; cytology ; Spiro Compounds ; pharmacology ; therapeutic use ; Vesicular Glutamate Transport Protein 2 ; genetics ; metabolism ; Vesicular Inhibitory Amino Acid Transport Proteins ; genetics ; metabolism