Physostigmine antagonizes morphine-induced respiratory depression in human subjects

The involvement of the cholinergic system in Alzheimer disease

This chapter recounts how memory mechanisms were related to the CNS cholinergic system. It also examines how memory loss in aging individuals was later linked to cholinergic deficiencies and how extensive pharmacologic studies in primates led to the "Cholinergic Hypothesis" of geriatric memory loss. Building upon this, a series of influential publications revealed a loss of cholinergic markers in the cerebral cortex of postmortem Alzheimer disease brain samples. These studies were reinforced by histologic evidence of the degeneration of "magnocellular" neurons in the nucleus basalis of Meynert, the region where neurons that project cortical cholinergic synaptic terminals originate. Together, these discoveries gave rise to the so-called Cholinergic hypothesis of Alzheimer disease. This chapter further describes how these insights prompted the development of potential cholinergic therapies, initially involving acetylcholine precursors, followed by the introduction of anticholinesterase inhibitors. This progression began with Tacrine and eventually led to the development of more reliable and better-tolerated anticholinesterases, such as donepezil, rivastigmine, and galantamine-compounds still in use today. The narrative includes a discussion of the benefits and limitations of these drugs, as well as the potential of newly developed muscarinic and nicotinic agonists. The chapter concludes with a brief overview of the synaptic nature of cholinergic transmission, in contrast to the proposed "cloud" neurotransmission. It also emphasizes that the efficacy of anticholinesterase treatment in Alzheimer disease depends on the preservation of a minimal number of remaining cholinergic synapses. Finally, a comparison is made between the symptomatic cognitive outcomes of conventional anticholinesterase therapy and the more recent use of anti-amyloid monoclonal antibodies.

Effects of cholinesterase inhibitors and serotonin-1A receptor agonists on morphine-induced ventilatory depression and antinociception in rats

Ventilatory depression is a serious side-effect of opioid analgesics. Naloxone, an antagonist of opioid receptors, eliminates not only ventilatory depression but also analgesic effect of opioids. Pharmacological dissociation of adverse reactions from the main action is important clinically and basically. Cholinergic and serotonergic mechanisms are suggested to counteract the opioid-induced ventilatory disturbances, but their influence on analgesia is still controversial. The present study evaluated the effects of cholinesterase inhibitors and serotonin-1A (5-HT1A) receptor agonists on morphine (1.0mg/kg, i.v.)-induced ventilatory depression and analgesia in rats. In anesthetized animals, spontaneous ventilation and hind leg withdrawal reflexes against nociceptive thermal stimuli were measured simultaneously. Physostigmine (0.1 and 0.2mg/kg, i.v.) and donepezil (0.5 and 1.0mg/kg, i.v.) relieved the morphine-induced ventilatory depression and enhanced its antinociception. On the other hand, (±)-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 0.03 and 0.1mg/kg, i.v.) and buspirone (0.1 and 0.3mg/kg, i.v.) did not influence antinociception of morphine while they restored the decreased ventilation. In unanesthetized animals, hypercapnic ventilatory response was measured by using whole-body plethysmography. Physostigmine (0.3mg/kg, i.p.), donepezil (1.0mg/kg, i.p.), 8-OH-DPAT (0.3mg/kg, i.p.) and buspirone (3.0mg/kg, i.p.) all recovered the morphine (10mg/kg, i.p.)-induced depression of hypercapnic ventilatory response. The present study suggests that activation of cholinergic or serotonergic (5-HT1A) mechanisms may be a useful therapeutic approach for morphine-induced ventilatory depression without loss of its analgesic action.

3D QSAR studies of AChE inhibitors based on molecular docking scores and CoMFA

Three-dimensional quantitative structure-activity relationship (3D QSAR) studies were performed on acetylcholinesterase (AChE) inhibitors, based on molecular docking scores obtained by using FlexX and FlexiDock and comparative molecular field analysis (CoMFA). The docking scores were used as molecular descriptors along with the steric and electrostatic field values of CoMFA, for partial least square (PLS) analysis. The high leave one out (LOO) cross-validated correlation coefficient (q(2)=0.714) reveals that the model is a useful tool for the prediction of test set as well as newly designed structures against AChE activity. The superimposed CoMFA models on the receptor site of AChE are guiding the design of potential inhibitory structures directed against AChE activity.

Continuous physostigmine combined with morphine-based patient-controlled analgesia in the postoperative period

BACKGROUND

Recently, new drugs and techniques for the treatment of postoperative pain were introduced, with the goal of enhancing opiates' analgesia while minimizing their side-effects. Cholinergic agents play an antinociceptive role, but their clinical use is quite limited, due to side-effects. Physostigmine is a cholinesterase inhibitor, which crosses the blood-brain barrier and elevates brain acetylcholine level. Physostigmine can produce analgesia by itself, and enhance opiate analgesia; but these effects are of short duration following bolus administration.

METHODS

We compared pain intensity and morphine consumption in two postoperative treatment groups: One group received continuous physostigmine infusion combined with morphine-based patient-controlled analgesia (PCA), and the other received PCA alone. Cholinergic anti-inflammatory pathways have recently been described. We therefore also compared changes in proinflammatory cytokine production in the two pain management groups.

RESULTS

Continuous infusion of physostigmine combined with morphine-based PCA in the postoperative period significantly reduced opiate consumption, and enhanced the analgesic response. Patients in the physostigmine group also exhibited reduced ex-vivo production of the proinflammatory cytokine, IL-1beta. At the same time, physostigmine increased nausea and vomiting, mostly in the first 2 h of the postoperative period.

CONCLUSIONS

Physostigmine combined with morphine in the postoperative period reduced morphine consumption, enhanced analgesia, and attenuated production of the proinflammatory cytokine, IL-1beta. This latter finding may account for the decreased pain observed in this group; this cytokine is known to mediate basal pain sensitivity and induce hyperalgesia in inflammatory conditions. Taking into account the other potential beneficial effects of physostigmine, we suggest that a continuous infusion of physostigmine should be considered as a useful component in multimodal postoperative analgesia.

Anticholinergic Syndrome After Anesthesia: A Case Report and Review

Anticholinergic syndrome may present with a wide variety of signs and symptoms. Central manifestations range from excitatory symptoms including delirium and agitation to central nervous system depression, stupor and coma. Anticholinergic syndrome was once a common phenomenon after general anesthesia because of the frequent administration of the anticholinergic agents atropine and scopolamine. Now that these agents are rarely administered, anesthesia-related anticholinergic syndrome is currently infrequently reported. Still, many prescription and over the counter medications as well as many anesthetic agents possess anticholinergic activity, and this diagnosis should be considered in patients with altered mental status following general anesthesia. We report a case of prolonged somnolence following general anesthesia for an MRI. A rapid improvement of mental status with physostigmine confirmed the diagnosis of anticholinergic syndrome. This case is unique in that anticholinergic syndrome-related respiratory depression was promptly reversed with physostigmine.

Management of opioid side effects in cancer-related and chronic noncancer pain: a systematic review

Side effects can limit opioid dosage and reduce quality of life. The purpose of this systematic review was to assess the management of opioid side effects in the context of cancer pain management or, in the event that no evidence was available for cancer pain, for chronic noncancer pain. The side effects studied were constipation, pruritus, nausea and vomiting, myoclonus, sedation, respiratory depression, and delirium. Opioid rotation to manage side effects was also studied. For each side effect, we searched MEDLINE and the Cochrane Controlled Trials Register and identified 657 possible titles for inclusion. Of these, 67 studies met inclusion criteria for analysis. The lack of well-designed, randomized controlled trials and the heterogeneity of populations and study designs made the drawing of firm conclusions difficult and precluded performance of meta-analysis. The type, strength, and consistency of evidence for available interventions to manage opioid side effects vary from strong (eg, on the use of naloxone to reverse respiratory depression or constipation) to weak (eg, changing from the oral to epidural route of morphine administration to manage sedation). Well-designed trials in the specified populations are required to furnish clinicians with secure evidence on managing opioid side effects successfully.

Donepezil in the treatment of opioid-induced sedation: report of six cases

Donepezil, an oral acetylcholinesterase inhibitor approved for the treatment of Alzheimer's disease, was given to 6 cancer pain patients having sedation related to the analgesic use of opioids. Each patient was taking more than 200 mg of oral morphine equivalents per day, and several were receiving complex analgesic regimens consisting of multiple adjuvant medications. Sedation improved at least moderately in 5 of the patients and mildly in 1 after they began taking donepezil. Patients reported a decrease in episodes of spontaneous sleeping during the day, fewer myoclonic twitches, improved daily function and greater social interaction. Several also reported improved sleep at night. Analgesia was not compromised by the use of donepezil, and in some cases it appeared improved. Donepezil may be a valuable alternative to psychostimulants in the treatment of opioid-induced sedation. A prospective controlled trial comparing the treatment effects of psychostimulants and donepezil on patients having opioid-induced sedation is underway.

Analgesic and adverse effects of a low dose of intrathecally administered hyperbaric neostigmine alone or combined with morphine in patients submitted to spinal anaesthesia: pilot studies

We report the analgesic and adverse effects of intrathecally administered hyperbaric neostigmine, alone or combined with morphine, in two patients suffering from severe lower limb ischaemic pain (group 1), five patients undergoing Caesarean section (group 2) and 19 patients scheduled for orthopaedic surgery (group 3) under spinal anaesthesia. These patients were enrolled in three pilot studies undertaken before the initiation of the planned controlled studies. Hyperbaric neostigmine (50 micrograms in glucose 8%) produced analgesia lasting more than 6 h in patients of group 1, but the effect was accompanied by episodes of vomiting. A lower dose of hyperbaric neostigmine (25 micrograms), alone (two patients) or combined with morphine (50 micrograms) (one patient) produced no discernible analgesic effect but was followed by severe nausea and vomiting within 15 min of intrathecal injection in patients of group 2. Two patients who received hyperbaric morphine (100 micrograms) had analgesia for more than 24 h and exhibited mild pruritus. In patients of group 3, hyperbaric neostigmine alone (25 micrograms) produced analgesia of shorter duration than neostigmine (25 micrograms) plus morphine (50 micrograms) or morphine (100 micrograms). Neostigmine alone or combined with morphine was associated with adverse events, mainly nausea and vomiting that lasted up to 9-12 in some patients. Other adverse events observed included anxiety, somnolence and involuntary defaecation. Most patients who received the combination of neostigmine and morphine exhibited more severe nausea, vomiting and somnolence. The low clinical efficacy of intrathecally administered neostigmine alone or in combination with morphine impairs the design of a double-blind protocol and might restrict the clinical usefulness of the drug combination.

The respiratory effects of the cytokine regulating agent HP 228 alone and in combination with morphine in human volunteers

HP 228 is a synthetic heptapeptide analog of alpha-MSH that attenuates the production and release of inflammatory cytokines. The purpose of this study was to define HP 228's effects, alone and in combination with morphine, on resting ventilation and the ventilatory response to hypoxia and hypercarbia. Six healthy nonsmoking young adult males completed the four-session experiment. Subjects first underwent an initial training session. During subsequent sessions, each subject was tested for the respiratory effects of intravenous HP 228 (30 microg/kg), morphine (0.15 mg/kg), or HP 228 (30 microg/kg) plus morphine (0.15 mg/kg) in a double-blind placebo-controlled randomized balanced within-subjects experimental design. Sessions began with baseline measurement of resting ventilation, oxygen consumption, the isocapnic hypoxic ventilatory response (HVR), and normoxic hypercapnic ventilatory response (HCVR). A second set of respiratory measurements were obtained 10 min after completion of HP 228 or placebo infusion. Morphine or placebo was then administered and ventilatory responses were determined 15 and 40 min postinfusion. HP 228 produced cutaneous flushing, but had no significant effect on respiration or hemodynamics. Morphine significantly decreased metabolism, resting ventilation, and hypoxic and hypercarbic ventilatory responsiveness, independent of prior HP 228 administration. A seventh subject experienced a significant cardiac arrhythmia upon exposure to hypoxia after receiving both HP 228 and morphine and was withdrawn from further study. In conclusion, in this early Phase I clinical trial, HP 228 was found to neither depress ventilation nor augment morphine-induced respiratory depression in healthy young males.

Physostigmine increases the dose of propofol required to induce anaesthesia

PURPOSE

This prospective, randomized, double-blind study was performed to determine the effect of administration of physostigmine on the dose of propofol required to produce loss of consciousness.

METHODS

Forty female unpremedicated patients were assigned in a random blind design to receive either 2 mg physostigmine or equal volume of normal saline i.v. five minutes before induction of anaesthesia with propofol. All patients received general anaesthesia for breast surgery. Propofol was infused at a constant rate of 200 ml.hr-1 while patients were breathing oxygen 100% via a face mask. In each patient the dose of propofol required to produce loss of the ability to grasp a 20 ml syringe was recorded as the end-point of loss of consciousness. At this point the protocol was terminated and, after intubation of the trachea, anaesthesia was maintained with a nitrous oxide-isoflurane or sevoflurane mixture in oxygen, increments of an opioid and a muscle relaxant. Doses of anaesthetic drugs and duration of anaesthesia varied and depended on the type of breast surgery, determined by frozen section.

RESULTS

The mean +/- SD dose of propofol required to produce loss of consciousness was 2.4 +/- 0.6 mg.kg-1 and 2.0 +/- 0.4 mg.kg-1 in the physostigmine and in the normal saline groups respectively (P = 0.014).

CONCLUSION

Physostigmine pretreatment increases the dose of propofol required to produce loss of consciousness.

Analgesic effect of subarachnoid neostigmine in two patients with cancer pain

Two patients suffering with severe pain due to metastatic abdominal neoplasm were selected to examine whether subarachnoid neostigmine provided effective pain relief. Neostigmine was injected through a catheter introduced into the subarachnoid space at L4-L5. Patients were monitored for changes in arterial blood pressure, cardiac and respiratory rates, body temperature, level of consciousness and neurologic change. Pain was classified by the patients on a verbal four-grade scale, and analgesia was classified on a verbal three-grade scale. Complete pain relief was obtained 2 h after neostigmine (0.2 mg) in one patient and 4 h after neostigmine (0.1 mg) in the second patient. Pain of mild intensity returned 20 and 22 h after drug administration, respectively. Gastrointestinal discomfort was observed in both cases, but nausea and vomiting occurred only in the patient treated with the highest dose of neostigmine. No significant change in the monitored parameters was observed, except for a 6-h period of decreased blood pressure in the patient treated with the lower dose of neostigmine which required no specific treatment. The results obtained in these anecdotal cases indicate that subarachnoid neostigmine may provide analgesia in patients with pain arising from neoplasia, but further studies using controlled trials are needed before the drug is brought into clinical use.

Effects of cholinomimetics on cocaine-induced hypotension and apneusis at a ventral brainstem cardiorespiratory control site

The current study was undertaken to evaluate the effects of cholinomimetic drugs on cocaine-induced central cardiorespiratory depression. Cats anesthetized by urethane (2.0 g/kg) were subjected to topical application at the caudal ventrolateral medullary surface (cVMS) of cocaine and two cholinomimetic pretreatment drugs. The following drug regimens were tested: 37 mM cocaine 1) given alone; 2) given 5 min after 2.7 mM carbachol pretreatment; and 3) given 5 min after 3.6 mM physostigmine pretreatment. In 7 of 11 cats, pretreatment with physostigmine decreased the incidence of cocaine-induced apneusis and hypoventilation significantly (p < 0.05); these animals showed no significant change in the mean arterial blood pressure during the 5-min pretreatment before administration of cocaine. In 4 of 11 cats, the physostigmine pretreatment produced a significant decrease in mean arterial blood pressure followed by lethal cardiorespiratory arrest when cocaine was administered. Pretreatment with carbachol resulted in cardiorespiratory responses which were not significantly different from those produced by cocaine alone. In anesthetized cats not exhibiting hypotensive responses to physostigmine, pretreatment may ameliorate cocaine-induced respiratory failure by ventral brainstem control mechanisms.

Effects of eseroline on the ventilatory response to CO2

The effect of eseroline on the normoxic hypercapnic ventilatory response was assessed in nine alpha-chloralose-urethane-anaesthetized cats. The ventilatory responses to step changes in end-tidal PCO2 were determined before (control), during i.v. infusion of eseroline (bolus of 1.2 mg.kg-1 followed by 0.65 mg.kg-1 x h-1) and 1 h after the end of the infusion. Each response was separated into central and peripheral chemoreflexes, characterized by CO2 sensitivity, time constant, time delay and apnoeic threshold. We found that eseroline depressed ventilation by affecting both tidal volume and breathing frequency. The ventilatory response to CO2 was depressed due to a decrease in the CO2 sensitivity of peripheral chemoreceptors from 0.20 to 0.12 l.min-1 x kPa-1 and in the CO2 sensitivity of central chemoreceptors from 1.04 to 0.50 l.min-1 x kPa-1 (P < 0.01). However, the ratio of these sensitivities was not changed, like the apnoeic threshold. The depressant effect was reversed by naloxone. We conclude that the depressant effect of eseroline on ventilatory response to CO2 is mainly due to an action on the respiratory integrating centres in the brainstem rather than on the CO2 sensitivity of peripheral and central chemoreceptors.

Antagonism of morphine-induced respiratory depression by novel anticholinesterase agents

This study compared the effects of 3 novel antiAChE agents (derivatives of dimethylaminoethyl-phenyl carbamate) with that of physostigmine on the respiratory depression induced by morphine in rabbits. Each drug, RA6, (1 mg i.v., 2 mg s.c.) RA7 (1 or 2 mg i.v.); RA15 (0.25 or 0.5 mg i.v.), physostigmine (0.05 or 0.1 mg i.v.) or saline (1 ml), was injected simultaneously with morphine (8 mg i.v.) to groups of 6-10 rabbits. Respiration rate, blood gases and pH were monitored for 3 hr. Plasma ChE was measured before and at 15 min intervals after injection. The 4 antiAChE's were given to 40 other rabbits, which were sacrificed at the time of maximal antagonism of the respiratory depressant effect of morphine, in order to measure the activity of AChE in the medulla, cortex and hippocampus. Physostigmine (0.1 mg) only antagonized the increase in paCO2 induced by morphine at 15 and 30 min. The drugs RA15 (0.5 mg), RA6 (2.5 mg) and RA7 (2 mg) almost completely prevented the respiratory depression, without obvious signs of peripheral cholinergic hyperactivity, for at least 3 hr. There was no relationship between the degree of antagonism of the effects of morphine with any drug and that of inhibition of ChE in plasma. In contrast, a highly significant correlation (P less than 0.01) was found between the former and the amount of inhibition of AChE in the medulla. It is suggested that the novel carbamates may have potential therapeutic application in reducing the respiratory depression of opiates, without impairing analgesia.

[Central anticholinergic syndrome during postoperative period]

The central anticholinergic syndrome (CAS) includes central signs (somnolence, confusion, amnesia, agitation, hallucinations, dysarthria, ataxia, delirium, stupor, coma) and peripheral signs (dry mouth, dry skin, tachycardia, visual disturbances and difficulty in micturition). It occurs when central cholinergic sites are occupied by specific drugs and also as a result of an insufficient release of acetylcholine. The CAS can be caused by atropine sulphate, hyoscine (scopolamine), promethazine, benzodiazepines, opioids, halothane, influrane, ketamine. The incidence of CAS during the postoperative period depends on choice and dose of anaesthetic agents, type of surgery, patient's condition and diagnostic criteria. It is close to 10% following general anaesthesia and 4% following regional anaesthesia with sedation. The differential diagnosis of CAS includes an overdose of anaesthetic drugs or an alteration in pharmacokinetics, altered hydratation, electrolyte or acid-base state, hypoglycaemia, hypoxia, hypercapnia, hypocapnia, hyperthermia, hypothermia, hormonal disorders, neurological damage resulting from surgery, embolism, haemorrhage or trauma. The diagnosis of CAS is often determined by a process of exclusion and not actually made until a positive therapeutic response to physostigmine, a centrally active anticholinesterase agent has taken place.

Reversal of postoperative somnolence using a two-rate infusion of physostigmine

In order to antagonize immediate postoperative somnolence, 24 surgical patients were given a two-rate infusion of physostigmine, aiming at a constant plasma concentration in the range of 1 to 10 ng/ml. Plasma concentrations of physostigmine were determined during infusion and after infusion and the effects of physostigmine on analgesia and postoperative sedation, and its side effects were monitored throughout. On the 1st postoperative day some of the patients (n = 8) were given 5 mg physostigmine orally, after which plasma concentrations as well as effects were measured. Steady-state concentrations were generally lower than predicted. Clearance varied between 10 and 85 ml/min x kg with a mean of 40.8 +/- 21.0 ml/min x kg. Oral bioavailability was 25.3 +/- 11.1%. Physostigmine administered as an intravenous infusion antagonized immediate postoperative somnolence in 21 out of 24 patients. Effects were poorly correlated with the established steady-state concentration of physostigmine. The patients' experience of postoperative pain relief was mostly satisfactory and the side effects of physostigmine infusion were generally limited. The effects of physostigmine in the immediate postoperative period seemed dependent on the dose as well as on the time which had elapsed since administration of anticholinergic drugs. After oral physostigmine administration the following morning, the majority of patients experienced side effects such as nausea and abdominal pain. In conclusion, physostigmine given as infusion antagonizes postoperative somnolence. However, the arousal effect was considered not better than that resulting from a bolus dose of the drug, although the infusion regimen allowed a prolonged clinical effect duration.

Reversal of sedation and respiratory depression after anaesthesia by the combined use of physostigmine and naloxone in neurosurgical patients

A clinical trial of the combination of naloxone in a low dose (1-1.5 micrograms X kg-1 body weight) with physostigmine (0.5-1.0 mg i.v.) was made to elucidate whether this combination could reverse postanaesthetic overdosing in neurosurgical patients without increasing postoperative pain. The investigation was made following previous findings that physostigmine has analgesic properties in addition to its systemic antisedative and anticholinergic effects as well as a stimulatory effect on morphine-depressed ventilation. Altogether 198 neurosurgical patients were investigated. The results showed that postanaesthetic over-sedation can be safely treated by a combination of naloxone and physostigmine in the dosages named above, resulting in the rapid reversal of sedation, where opiates, neuroleptics and benzodiazepines have been used. In contrast, this combination has very little effect on sedation following the administration of agents such as halothane and isoflurane. In the great majority of patients (95%), the treatment resulted in excellent analgesia during the first postoperative hour. The incidence of nausea and vomiting was increased somewhat by this treatment, but these side-effects could be minimized by decreasing the rate of drug administration. Physostigmine is contra-indicated in patients having symptoms and signs similar to those of Parkinson's disease, and the dose of physostigmine should also be reduced to 0.5 mg i.v. in all patients over the age of 65.

A double-blind trial of the analgesic properties of physostigmine in postoperative patients

A double-blind clinical trial of the analgesic and antisedative effects of physostigmine was carried out on surgical patients (n = 60) during the first hours postoperatively. Pethidine and placebo were included for comparison in the double-blind study. The degree of pain and sedation was estimated when the patient demanded analgesics and immediately before the administration of the test drug. The dosage administered i.v. was: physostigmine salicylate 2 mg, placebo = saline, or pethidine chloride 50 mg. After this, the same parameters were recorded at regular intervals. In addition, ventilatory rate, pulse rate, systolic blood pressure and side effects, if any, were noted. The results showed that physostigmine caused analgesia that was of the same magnitude as pethidine during the first 15 min, after which it decreased to the level of the placebo at 30 min. An antisedative or arousal effect was recorded over a somewhat longer time period; after this, there was no difference between placebo and physostigmine. In contrast to pethidine, physostigmine caused no decrease in the ventilatory rate. The pulse rate and systolic blood pressure did not change in any of the groups. Although the durations of the analgesic and antisedative effects of physostigmine were short, the use of this drug may well be preferable to the use of e.g. naloxone when immediate alertness of the patient is wanted without causing an increase in postoperative pain.

Pharmacokinetics of physostigmine after intravenous, intramuscular and subcutaneous administration in surgical patients

The pharmacokinetics of physostigmine after intravenous, intramuscular or subcutaneous administration as well as its arousal effect after anaesthesia have been studied in surgical patients in the early postoperative period. After intravenous administration physostigmine had a very rapid plasma elimination with a plasma clearance ranging from 47 to 163 l/h with a mean +/- s.d. of 92.5 +/- 37.7 l/h. The volume of distribution was 46.5 +/- 19.2 l, while distribution and plasma elimination half-lives were 2.3 and 22 min, respectively. A fraction of the dose was probably hydrolyzed in blood since its blood elimination half-life in vitro was approximately 190 min. After both intramuscular and subcutaneous administration the systemic availability was almost complete, the plasma terminal half-lives only being somewhat longer than after intravenous administration. Plasma clearance, volume of distribution and elimination half-life of physostigmine were not correlated to age or body weight of the patients. The rapid plasma clearance of physostigmine resulted in a short duration of antisedative effect. After administration of 1 mg physostigmine salicylate i.v., drug-induced sedation was rapidly reversed with a duration of 30-60 min. The duration of action was similar after intramuscular injection but onset was delayed by 20-30 min. It was concluded that a plasma concentration of 3-5 ng/ml of physostigmine should be exceeded if an adequate analeptic effect is to be achieved, meaning that 2 mg of physostigmine had to be administered subcutaneously in order to achieve a satisfactory reversal of sedation. The short duration of action may hamper the use of physostigmine as an agent for reversal of drug-induced sedation and anticholinergic effects after surgery.

The reversal of epidural morphine induced somnolence with physostigmine

Two case reports are presented of patients with post-thoracotomy pain treated with epidural morphine who developed somnolence several hours after the procedure. Physostigmine, 1 mg IV successfully reversed the somnolence without any effect on analgesia.

Physostigmine versus naloxone in heroin-overdose

Two groups of 10 chronically heroin addicted patients who were admitted to the Emergency Ward because of hypoventilation and coma, were treated random- aselectively with naloxone, 3 micrograms kg-1 BW iv, or with physostigmine salicylate 0,04 mg kg-1 BW iv. Patients in both groups completely regained consciousness and breathed spontaneously, regularly and adequately within 10 minutes. One essential difference in the treatment was that physostigmine caused no signs of acute opiate withdrawal, the patients felt fine and stayed for further control, in contrast with naloxone where the patients felt bad and occasionally escaped prematurely from the ward. Another difference is that the beneficial effect of one dose of physostigmine is shorter lived than that of naloxone. Authors emphasise the fact that treatment of heroin overdose in an addict need not jeopardize the patient's well-being by a withdrawal syndrome.