Effect of propofol on perception of pain in mice: mechanisms of action

An Overview of Analytical Methods for the Estimation of Propofol in Pharmaceutical Formulations, Biological Matrices, and Hair Marker

Propofol (PFL) owing to its excellent inhibitory property of neurotransmitters in CNS by positive modulation of ligand gated ion channels to an integrated chloride channeled GABA_A thereby acts as a general anesthetic. It differs from other general anesthetics chemically and pharmacologically as it has lesser side effects compared to other general anesthetics and is most commonly used. The present review focuses on two aspects (a) various analytical methods used in quantification of Propofol in pharmaceutical formulations and (b) various analytical methods used to determine Propofol in biological matrices and some biological markers like hair and end tidal nasal air for forensic purpose to estimate drug concentration in suspected cases. Here the various analytical methods are developed using different parameters and validation of employed methods are discussed. Estimated parameters like the linearity, LOQ (Limit of quantification), % recovery, slope, intercept, validation are discussed for the individual method. The critical quality attributes like the wavelength of detection, columns, flow rate, gas flow, and the sample preparation methods for the determination of PFL by bioanalytical methods are also discussed. Type of electrode, mechanism involved and the potential voltage applied for a particular electrochemical method are also discussed.

Effects of intraoperative propofol-based total intravenous anesthesia on postoperative pain in spine surgery: Comparison with desflurane anesthesia - a randomised trial

BACKGROUND

As reported, patients experience less postoperative pain after propofol-based total intravenous anesthesia (TIVA). In the present study, we investigated the postoperative analgesic effects between propofol-based TIVA and desflurane anesthesia after spine surgery.

METHODS

Sixty patients were included who received (surgical time >180 minutes) lumbar spine surgery. Patients were randomly assigned to receive either TIVA (with target-controlled infusion) with propofol/fentanyl-based anesthesia (TIVA group) or desflurane/fentanyl-based anesthesia (DES group), titrated to maintain Bispectral Index values between 45 and 55. All patients received patient-controlled analgesia (PCA) with fentanyl for postoperative pain relief. Numeric pain rating scale (NRS) pain scores, postoperative fentanyl consumption, postoperative rescue tramadol use, and fentanyl-related side effects were recorded.

RESULTS

The TIVA group patients reported lower NRS pain scores during coughing on postoperative day 1 but not day 2 and 3 (P = .002, P = .133, P = .161, respectively). Less fentanyl consumption was observed on postoperative days 1 and 2, but not on day 3 (375 μg vs 485 μg, P = .032, 414 μg vs 572 μg, P = .033, and 421 μg vs 479 μg, P = .209, respectively), less cumulative fentanyl consumption at postoperative 48 hours (790 μg vs 1057 μg, P = .004) and 72 hours (1210 μg vs 1536 μg, P = .004), and total fentanyl consumption (1393 μg vs 1704 μg, P = .007) when compared with the DES group. No difference was found in rescue tramadol use and fentanyl-related side effects.

CONCLUSION

Patients anesthetized with propofol-based TIVA reported less pain during coughing and consumed less daily and total PCA fentanyl after lumbar spine surgery.

Propofol enhances BCR-ABL TKIs' inhibitory effects in chronic myeloid leukemia through Akt/mTOR suppression

Background

The anti-cancer activities of intravenous anesthetic drug propofol have been demonstrated in various types of cancers but not in chronic myeloid leukemia (CML).

Methods

We systematically examined the effect of propofol and its combination with BCR-ABL tyrosine kinase inhibitors (TKIs) in CML cell lines, patient progenitor cells and mouse xenograft model. We analyzed propofol’s underlying mechanism focusing on survival pathway in CML cells.

Results

We show that propofol alone is active in inhibiting proliferation and inducing apoptosis in KBM-7, KU812 and K562 cells, and acts synergistically with imatinib or dasatinib, in in vitro cell culture system and in vivo xenograft model. In addition, propofol is more effective in inducing apoptosis and inhibiting colony formation in CML CD34 progenitor cells than normal bone marrow (NBM) counterparts. Combination of propofol and dasatinib significantly eliminates CML CD34 without affecting NBM CD34 cells. We further demonstrate that propofol suppresses phosphorylation of Akt, mTOR, S6 and 4EBP1 in K562. Overexpression of constitutively active Akt significantly reverses the inhibitory effects of propofol in K562, confirm that propofol acts on CML cells via inhibition of Akt/mTOR. Interestingly, the levels of p-Akt, p-mTOR and p-S6 are lower in cells treated with combination of propofol and imatinib than cells treated with propofol or imatinib alone, suggesting that propofol augments BCR-ABL TKI’s inhibitory effect via suppressing Akt/mTOR pathway.

Conclusion

Our work shows that propofol can be repurposed to for CML treatment. Our findings highlight the therapeutic value of Akt/mTOR in overcoming resistance to BCR-ABL TKI treatment in CML.

Electronic supplementary material

The online version of this article (10.1186/s12871-017-0423-2) contains supplementary material, which is available to authorized users.

Effect of Lipid Composition in Propofol Formulations: Decisive Component in Reducing the Free Propofol Content and Improving Pharmacodynamic Profiles

Current endeavor was aimed towards studying significance of lipid composition on free propofol concentration in aqueous phase and associated pain on injection. Three different nanoformulations, namely long-chain triglyceride (LCT)/medium-chain glyceride (MCG)-based nanoemulsion (ProNano), MCG-based self-nanoemulsifying formulation (PSNE), and lipid-free nanoformulation (PNS) were accessed for the same. In vitro and in vivo performances of developed formulations were compared with Diprivan®. ProNano showed minimum free propofol concentration (0.13%) and hence lower pain on injection (rat paw-lick test, 6 ± 2 s) compared to Diprivan®, PSNE, and PNS (0.21%, 0.23%, and 0.51% free propofol, respectively, and rat paw-lick test; 12 ± 3, 14 ± 2, and 22 ± 3 s, respectively). These results conjecture the role of MCG in effective encapsulation of propofol. Anesthetic action assessed by measuring duration of loss of righting reflex (LORR), which was found similar in case of ProNano and PSNE (14 ± 3 and 15 ± 3 min, respectively) compared to Diprivan® (13 ± 3 min). In case of lipid-free formulation, PNS, extended anesthetic action (21 ± 2 min) was observed which may be due to sustained release of propofol from nanosponges. Studies on effect of lipoproteins on propofol release highlighted significance of HDL (100% release with maximum concentration of about 1.2 μg/ml of HDL) from all three formulations.

Synergistic antinociceptive interactions between fospropofol and alfentanil in mice

BACKGROUND

Combination therapy, which provides the opportunity to achieve optimal analgesia with reduced side effects at lower drug doses, is a valid approach for the treatment of pain. The analgesic interaction between fospropofol and alfentanil has not been investigated till date. We sought to determine the nature of the interaction between fospropofol and alfentanil in mice models of the formalin test, hot-plate test and the tail-flick test.

METHODS

The effects of fospropofol, alfentanil and their combinations were examined in the formalin-induced paw inflammatory hyperalgesia, the hot-plate test and the tail-flick test in mice. In the three models, dose-response curves were established and their respective ED50 (50% effective dose) values were determined separately for each agent. Fixed-ratio combinations of fospropofol and alfentanil were tested for their combined antinociceptive effects, and the type of interaction was determined by the isobolographic analysis.

RESULTS

Fospropofol, alfentanil and their combination produced a dose-dependent decrease in the number of flinches during phase 1 of the formalin test. In the hot-plate test and in the tail-flick test, fospropofol, alfentanil and their combination significantly and dose dependently prolonged the latency of withdrawal. In the three models, isobolographic analysis revealed a significant synergistic interaction between fospropofol and alfentanil. The ED50 value for the drug combination was significantly lower than the theoretical additive value (p<0.05).

CONCLUSIONS

The results demonstrate that fospropofol and alfentanil provide synergistic antinociceptive interactions in the formalin, hot-plate, and tail-flick tests. The observed synergistic interaction between fospropofol and alfentanil are indicative of the effectiveness of the combination treatment in pain management and should be explored further in patients undergoing minor surgical procedures.

Inhibition of acid-sensing ion channel currents by propofol in rat dorsal root ganglion neurons

Acid-sensing ion channels (ASICs), part of the epithelial sodium channel/degenerin family, are activated by extracellular protons. The ASICs play a significant role in the acidosis-mediated perception of pain. The anaesthetic agent propofol also exerts antinociceptive effects, but the underlying mechanisms for this effect are not clear. We used whole-cell patch clamping to investigate the effect of propofol on proton-gated currents in: (i) rat dorsal root ganglion (DRG) neurons; and (ii) HEK293 cells transfected with either ASIC1a or ASIC3. Propofol inhibited the amplitude of proton-gated currents in DRG neurons, but did not change the sensitivity of ASICs to H(+). Notably, propofol altered acid-evoked excitability of rat DRG neurons and decreased the number of action potentials induced by acid stimuli. In addition, we demonstrated that propofol inhibited ASICs by directly binding with these channels in HEK293 cells. These results suggest that propofol inhibits proton-gated currents in DRG neurons and that inhibition of proton-gated currents explains, in part, the antinociceptive effects of propofol in primary afferent neurons.

Total intravenous anaesthesia with high-dose remifentanil does not aggravate postoperative nausea and vomiting and pain, compared with low-dose remifentanil: a double-blind and randomized trial

The study was designed to investigate postoperative nausea and vomiting (PONV) in low- and high-dose remifentanil regimens for total intravenous anaesthesia (TIVA) in adult female patients with American Society of Anaesthesiologists physical status classification I undergoing local breast excision. Propofol and remifentanil 5 ng·mL⁻¹ (L group) or 10 ng·mL⁻¹ (H group) were administered for anaesthesia induction and maintenance. Propofol was titrated within range of 0.1 μg·mL⁻¹ to maintain bispectral index (BIS) values between 40 and 60. Haemodynamic parameters during the intra- and postoperative periods and 24 h postoperative visual analogue scale (VAS) and PONV were evaluated. Each group with 63 patients was analyzed. The H group showed higher use of remifentanil and lower use of propofol, with similar recovery time. Mean systemic arterial blood pressure (MBP), heart rate, and BIS did not differ significantly before and after endotracheal intubation in the H group. However, significant increases in MBP and BIS were apparent in the L group. Postoperative VAS, PONV incidence and scale, and Rhodes index did not differ significantly between the two groups. In conclusion, TIVA with high-dose remifentanil did not aggravate PONV with similar postoperative pain, compared with low-dose remifentanil. Furthermore, high-dose remifentanil showed more haemodynamic stability after endotracheal intubation. This trial is registered with KCT0000185.

The antinociceptive and antihyperalgesic effects of topical propofol on dorsal horn neurons in the rat

BACKGROUND

Propofol (2,6-diisopropylphenol) is an IV anesthetic used for general anesthesia. Recent evidence suggests that propofol-anesthetized patients experience less postoperative pain, and that propofol has analgesic properties when applied topically. We presently investigated the antinociceptive effects of topical propofol using behavioral and single-unit electrophysiological methods in rats.

METHODS

In behavioral experiments with rats, we assessed the effect of topical hindpaw application of propofol (1%-25%) on heat and mechanically evoked paw withdrawals. In electrophysiological experiments, we recorded from lumbar dorsal horn wide dynamic range (WDR)-type neurons in pentobarbital-anesthetized rats. We assessed the effect of topical application of propofol to the ipsilateral hindpaw on neuronal responses elicited by noxious heat, cold, and mechanical stimuli. We additionally tested whether propofol blocks heat sensitization of paw withdrawals and WDR neuronal responses induced by topical application of allyl isothiocyanate (AITC; mustard oil).

RESULTS

Topical application of propofol (1%-25%) significantly increased the mean latency of the thermally evoked hindpaw withdrawal reflex on the treated (but not opposite) side in a concentration-dependent manner, with no effect on mechanically evoked hindpaw withdrawal thresholds. Propofol also prevented shortening of paw withdrawal latency induced by AITC. In electrophysiological experiments, topical application of 10% and 25% propofol, but not 1% propofol or vehicle (10% intralipid), to the ipsilateral hindpaw significantly attenuated the magnitude of responses of WDR neurons to noxious heating of glabrous hindpaw skin with no significant change in thermal thresholds. Maximal suppression of noxious heat-evoked responses was achieved 15 minutes after application followed by recovery to the pre-propofol baseline by 30 minutes. Responses to skin cooling or graded mechanical stimuli were not significantly affected by any concentration of propofol. Topical application of AITC enhanced the noxious heat-evoked response of dorsal horn neurons. This enhancement of heat-evoked responses was attenuated when 10% propofol was applied topically after application of AITC.

CONCLUSIONS

The results indicate that topical propofol inhibits responses of WDR neurons to noxious heat consistent with analgesia, and reduced AITC sensitization of WDR neurons consistent with an antihyperalgesic effect. These results are consistent with clinical studies demonstrating reduced postoperative pain in surgical patients anesthetized with propofol. The mechanism of analgesic action of topical propofol is not clear, but may involve desensitization of TRPV1 or TRPA1 receptors expressed in peripheral nociceptive nerve endings, engagement of endocannabinoids, or activation of peripheral γ-aminobutyric acid A receptors.

Design flaws in randomized, placebo controlled, double blind clinical trials

The hypothesis in drug clinical trials is that the drug is better than a placebo in patients suffering from a disease. The unstated assumption is that the drug cures the disease or is a powerful treatment for the disease. This is an incorrect assumption. Drugs do not cure or treat diseases. The body heals itself; drugs promote this ability of the body to heal itself. Placebos are assumed to be inactive; however, placebos can also promote the ability of the body to heal itself. Placebos are actually treatments that can stimulate endogenous healing mechanisms. The possible place of placebos in health management is controversial. Clinical trial design should be altered. The hypothesis of clinical trials should be that the drug speeds up or improves the healing of the patient, putting patient healing as the first objective. Placebos should not be used as controls but could be tested as drugs in their own right. The control in clinical trials should be no treatment. Alternatively, new drugs could be compared to existing drugs in clinical trials.

[Biological rhythms for anaesthesia and intensive care]

Knowledge of biological rhythms has led to better understanding of the time-of-day dependent effects of anaesthetic drugs. These chronopharmacological effects are currently explained by the biological rhythms modulating the pharmacokinetic, toxic and pharmacodynamic parameters of these substances. Such effect has been described for general anesthetics, local anaesthetics, analgesics as well as for antibiotics. But recent data also highlight that general anaesthetics, probably part of their brain effects, also alter the regulation of biological rhythms, including the sleep-wake or the endogenous circadian temperature rhythms. This desynchronization of biological rhythms can led to disturbance of the circadian secretion of many substances, including hormones. Finally, biological rhythms have been also described with regard to physiology of pain and cardiovascular physiopathology. The concept of biological rhythm should be present in mind not only for the clinical management of patients but also for setting studies in the field of anaesthesia, pain and intensive care.

The experimental and clinical pharmacology of propofol, an anesthetic agent with neuroprotective properties

Propofol (2,6-diisopropylphenol) is a versatile, short-acting, intravenous (i.v.) sedative-hypnotic agent initially marketed as an anesthetic, and now also widely used for the sedation of patients in the intensive care unit (ICU). At the room temperature propofol is an oil and is insoluble in water. It has a remarkable safety profile. Its most common side effects are dose-dependent hypotension and cardiorespiratory depression. Propofol is a global central nervous system (CNS) depressant. It activates gamma-aminobutyric acid (GABA A) receptors directly, inhibits the N-methyl-d-aspartate (NMDA) receptor and modulates calcium influx through slow calcium-ion channels. Furthermore, at doses that do not produce sedation, propofol has an anxiolytic effect. It has also immunomodulatory activity, and may, therefore, diminish the systemic inflammatory response believed to be responsible for organ dysfunction. Propofol has been reported to have neuroprotective effects. It reduces cerebral blood flow and intracranial pressure (ICP), is a potent antioxidant, and has anti-inflammatory properties. Laboratory investigations revealed that it might also protect brain from ischemic injury. Propofol formulations contain either disodium edetate (EDTA) or sodium metabisulfite, which have antibacterial and antifungal properties. EDTA is also a chelator of divalent ions such as calcium, magnesium, and zinc. Recently, EDTA has been reported to exert a neuroprotective effect itself by chelating surplus intracerebral zinc in an ischemia model. This article reviews the neuroprotective effects of propofol and its mechanism of action.

Modulation of Remifentanil-Induced Postinfusion Hyperalgesia by Propofol

BACKGROUND

Experimental and clinical studies suggest that brief opioid exposure can enhance pain sensitivity. During anesthesia, however, opioids are commonly administered in combination with either IV or inhaled hypnotic drugs. In this investigation we sought to determine the analgesic and antihyperalgesic properties of propofol in subhypnotic concentrations on remifentanil-induced postinfusion hypersensitivity in an experimental human pain model.

METHODS

Fifteen healthy volunteers were included in this randomized, double-blind, and placebo-controlled study in a cross-over design. Transcutaneous electrical stimulation at high current densities (41.7 +/- 14.3 mA) induced spontaneous acute pain (numerical rating scale = 6 of 10) and stable areas of hyperalgesia. Pain intensities and areas of hyperalgesia were assessed before, during and after a 30 min target-controlled infusion of propofol (1.5 microg/mL) and remifentanil (0.05 microg x kg(-1) x min(-1)), either alone or in combination (propofol 1.5 microg/mL with remifentanil 0.025 or 0.05 microg x kg(-1) x min(-1)).

RESULTS

During infusion, propofol significantly reduced the electrically evoked pain to 72% +/- 21% of control. Subhypnotic concentrations of propofol did not lead to any hyperalgesic effects. Coadministration of remifentanil led to synergistic analgesic effects (to 62% +/- 26% and 58% +/- 25% of control, for 0.025 or 0.05 microg x kg(-1) x min(-1), respectively), but upon withdrawal, pain and hyperalgesia increased above control level.

CONCLUSIONS

The results suggest clinically relevant interactions of propofol and remifentanil in humans, since propofol led to a delay and a weakening of remifentanil-induced postinfusion anti-analgesia in humans. Nevertheless, pronociceptive effects were not completely antagonized by propofol, which may account for the increased demand for analgesics after remifentanil-based anesthesia in clinical practice.

The Antinociceptive Effects of Local Injections of Propofol in Rats Are Mediated in Part by Cannabinoid CB1 and CB2 Receptors

BACKGROUND

Propofol can inhibit fatty acid amidohydrolase, the enzyme responsible for the metabolism of anandamide (an endocannabinoid). To study the potential antinociceptive effect of propofol, we administered different doses (0.005, 0.05, 0.5, 5, and 500 microg) of the anesthetic in the hind paw of animals to determine an ED50. To further investigate the mechanisms by which propofol produced its antinociceptive effect, we used specific antagonists for the cannabinoid CB1 (AM251) and CB2 (AM630) receptors and measured fatty-acid amide/endocannabinoid (anandamide, 2-arachidonylglycerol, and palmitoylethanolamide) concentrations in skin paw tissues.

METHODS

Formalin tests were performed on 65 Wistar rats allocated to six different groups: 1) control (Intralipidtrade mark 10%); 2) propofol (ED50 dose); 3) AM251; 4) AM251 + propofol; 5) AM630; 6) AM630 + propofol. Drugs were injected subcutaneously in the dorsal surface of the hind paw (50 microL) 15 min before 2.5% formalin injection into the same paw. Fatty-acid amide/endocannabinoid levels were measured by high performance liquid chromatography/mass spectrometry analysis.

RESULTS

Propofol produced a dose-dependent antinociceptive effect for the early and late phases of the formalin test with an ED50 of 0.08 +/- 0.061 microg for the latter phase. This effect was antagonized by AM251 and AM630. It was locally mediated, since a higher dose of propofol given in the contralateral paw was not antinociceptive. Finally, only paw concentrations of palmitoylethanolamide were significantly increased.

CONCLUSION

In a test of inflammatory pain, locally injected propofol decreased pain behavior in a dose-dependent manner. This antinociceptive effect was mediated, in part, by CB1 and CB2 receptors.

Effects of intracerebroventricular NMDA and non-NMDA receptor agonists or antagonists on general anesthesia of propofol in mice

The effects of intracerebroventricular (icv) agonists and antagonists of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptors on the general anesthesia of propofol were studied. A total of 144 Kunming mice, male and female with body mass of (22±3) g, were used. Part One of the Experiment: a total of 104 Kunming mice, male and female, were randomly divided into 13 groups. Intracerebroventricular artificial cerebral fluid (aCSF) or different doses of NMDA, AMPA, MK-801 or NBQX was injected immediately after intravenously administered propofol 25 mg/kg and the recovery time following the loss of righting reflex (LORR) was recorded. Part Two of the Experiment: a total of 40 Kunming female mice were divided randomly into 5 groups and injected with icv aCSF or NMDA, AMPA, MK-801 or NBQX after intraperitoneally administered propofol 50 mg/kg. The pain threshold of the mice was then investigated by hot-plate test (HPPT). NMDA (0.05 or 0.075μg, icv) or AMPA (0.05 μg, icv) exhibited no effects on the LORR, but NMDA (0.1 μg, icv) or AMPA (0.075 or 0.1 μg, icv) prolonged the LORR significantly compared with the aCSF group (P<0.05, P<0.01). The LORR of the 2 μg MK-801 group had no changes, while those of the 4 or 8 μg MK-801 groups were prolonged significantly. The LORR of the 0.5, 2 or 4 μg NBQX groups were all prolonged significantly. NMDA 0.05 μg or AMPA 0.05 μg decreased the pain threshold slightly but did not differ in effect compared with the aCSF group; 2 μg MK-801 or 0.5 μg NBQX both increased the pain threshold significantly. Our results indicate that propofol produces general anesthesia partly through an interaction with brain NMDA and AMPA receptors in mice.

Evidence for peripherally antinociceptive action of propofol in rats: Behavioral and spinal neuronal responses to subcutaneous bee venom

In the present study, behavioral and in vivo electrophysiological methods were used to examine the peripheral effects of propofol on tonic ongoing pain-related responses produced by subcutaneous bee venom-induced inflammatory pain state. Local administration of 0.5 microg propofol produced significant suppression of the well-established ongoing pain responses in both conscious rats and dorsal horn nociceptive neurons. The locally antinociceptive action of propofol is not caused by systemic effect, because contralateral administration of the same dose of drug did not produce any effect. This result indicates that besides central actions, propofol has peripherally antinociceptive action as well.

Effects of intrathecal 6-hydroxydopamine, alpha1 and alpha2 adrenergic receptor antagonists on antinociception of propofol in mice

AIM

To investigate the relationship between spinal cord norepinephrine, alpha1 and alpha2 adrenergic receptors and antinociception of propofol in mice.

METHODS

Kunming mice were used. Antinociceptive tests were investigated with the tail-immersion test and the acetic acid-induced writhing test. The effects of subcutaneous (sc), intrathecal (ith) and intracerebroventricular (icv) injection propofol on pain threshold were observed. The influences of pretreatment with ith 6-hydroxydopamine, alpha1R antagonist prazosin, or alpha2R antagonist yohimbine on the antinociception of propofol were studied.

RESULTS

Significant antinociception was produced by propofol (25, 50 mg/kg, sc) and propofol (20, 40 microg, ith) in tail-immersion test and acetic the acid-induced writhing test (P<0.05 or P<0.01). Icv propofol (10, 20, and 40 microg) did not produce any effect on pain threshold in mice (P>0.05). The 6-hydroxydopamine (5 and 10 microg), prazosin (5 and 10 microg), or yohimbine (5 and 10 microg) ith alone did not affect basal tail-flick latency (TFL) in conscious mice, but significantly reduced the TFL as measured by tail-immersion test in propofol (50 mg/kg, sc)-treated mice, compared with basal TFL and vehicle groups (P<0.05 or P<0.01).

CONCLUSION

The spinal cord is a target of propofol antinociception. In mice propofol antinociception is partly mediated by spinal norepinephrine, alpha1R and alpha2R.

Intravenous Subhypnotic Propofol in Central Pain

OBJECTIVE

To validate IV subhypnotic propofol, a gamma-aminobutyric acid A (GABA-A) agonist, as a diagnostic test for central pain.

METHODS

The efficacy of systemic propofol (0.2 mg/kg IV bolus) was evaluated in a double-blind, placebo-controlled and crossover fashion on both spontaneous ongoing pain and allodynia in 44 patients with chronic central pain of both brain and cord origin.

RESULTS

Propofol was significantly superior to the placebo (Intralipid, Kabi Pharmacia) in reducing the intensity of spontaneous ongoing pain for up to 1 hour after the injection: 24 of 44 patients (55%) receiving propofol showed a significant reduction in spontaneous pain, whereas only 6 patients showed this after the placebo. Propofol also significantly reduced the intensity of both mechanical and cold allodynia. In a few cases, only the evoked components were abolished but not the spontaneous pain. In general, the side effects were minimal and consisted mainly of transitory burning upon injection of both propofol and placebo and slight lightheadedness in a few cases.

CONCLUSIONS

Systemic propofol induces analgesic effects on all studied components of central pain and highlights the key role of GABA modulation in central pain.

Intravenous propofol in the treatment of refractory headache

We analyzed the results of treating patients who had chronic daily headaches that were refractory to standard medications with repetitive low-dose boluses of intravenous propofol (2,6-diisopropylphenol). Patients were treated over a 1-year period at Thomas Jefferson University Hospital. A total of 18 patients were treated a total of 21 times. Over 90% of patients had at least some headache relief after treatment. The headache cycle was broken in eight patients. There were no complications. Intravenous propofol is safe and effective when used under monitored conditions and should be considered for patients who have refractory chronic daily headache and have failed other interventions.