Dose requirements of ICI 35,868 (propofol, 'Diprivan') in a new formulation for induction of anaesthesia

In order to avoid Cremophor-related reactions and reduce the incidence of pain on injection, diisopropylphenol (ICI 35,868; propofol) has been reformulated as an emulsion. One hundred and fifteen patients received an induction dose of propofol in the new formulation. The dose required to induce anaesthesia in 95% of healthy, unpremedicated patients was 2.5 mg/kg. Induction was associated with a degree of cardiovascular and respiratory depression. There were no adverse reactions although there were a number of minor side-effects. The incidence of pain on injection was low (3%) and the overall quality of induction was assessed as good or adequate in 92% of patients.

The cardiorespiratory effects of ICI 35 868 in patients with valvular heart disease

The haemodynamic effects at induction of anaesthesia with ICI 35 868 (1.5 mg/kg) are reported in ten patients with severe aortic or mitral valve disease. The average decrease of mean arterial pressure was 19.1% (p less than 0.01), heart rate decreased by 10% (p less than 0.01). Cardiac index and stroke volume index were both little changed but there were significant reductions in rate pressure product and left ventricular stroke work index (p less than 0.01).

Effects of ketamine and three other anaesthetics on spinal reflexes and inhibitions in the cat

The effects of ketamine, alphaxalone/alphadolone, methohexitone and di-isopropylphenol have been compared on synaptic excitations and inhibitions in the spinal cord of decerebrate or pentobarbitone-anaesthetized cats. Ketamine selectively and reversibly decreased polysynaptic reflexes over a wide dose range. With the other three anaesthetic drugs decreases in reflex activity were accompanied by increases in the prolonged inhibition of reflexes, and in the amplitude and time course of dorsal root potentials. It was concluded that ketamine decreases synaptic transmission at terminals of excitatory interneurones, whereas the other three anaesthetics enhance synaptic inhibitions mediated by gamma-aminobutyric acid. Such specific effects of anaesthetics on particular synaptic processes do not support a unitary hypotheses of anaesthesia.

Pharmacology of an emulsion formulation of ICI 35 868

Studies with an emulsion formulation of ICI 35 868 (2,6- diisopropylphenol ) indicate that this new formulation has anaesthetic properties in rats and mice, and haemodynamic effects in the mini-pig which are similar to those of the previously available Cremophor formulation. Administration of the emulsion formulation to dogs produced no untoward effect, whereas the Cremophor formulation produced a marked increase in plasma histamine concentration. In the mini-pig, no adverse response was produced by the repeated administration of the emulsion formulation of ICI 35 868, whereas the Cremophor formulation produced anaphylactoid responses when a second injection was given 1 week after an uneventful first exposure to this formulation. Behavioural responses in the rat suggest that the emulsion formulation may produce less discomfort on i.v. injection.

Infusion rates for anaesthesia with propofol

The infusion rate of propofol which would produce anaesthesia, when combined with nitrous oxide in oxygen, was studied in 75 fit unpremedicated patients undergoing body surface operations. The infusion rates were based on multiples of the median dose required to produce anaesthesia by intermittent injection in an additional 20 patients. The scatter of doses showed a right skew, for both intermittent and continuous use. This was corrected by loge transformation and derived data presented graphically.

Brain noradrenaline and anaesthesia: behavioural and electrophysiological evidence

Neonatal administration of 6-hydroxydopamine to rat pups was used to deplete brain noradrenaline in the locus coeruleus projection system to less than 5% of normal and the response to barbiturate and non-barbiturate anaesthetics examined. The sleeping time in response to administration of thiopentone, pentobarbitone, methohexitone or hexobarbitone was markedly increased in 6-hydroxydopamine-treated rats, as it was for the non-barbiturates chloral hydrate and diisopropylphenol. The sleeping time for other non-barbiturates such as althesin, ketamine and ethyl carbamate (urethane) was not affected in noradrenaline-depleted rats. Similarly, an index of the evoked potential, recorded in the primary somatosensory cortex to supramaximal electrical stimulation of the forepaw, decreased more markedly with increasing doses of thiopentone in 6-hydroxydopamine-treated rats than in controls. Potentiation of the effect of diisopropylphenol on the evoked cortical response was also seen in noradrenaline-depleted rats while the effect of althesin did not differ. It is suggested that brain noradrenaline pathways originating from the locus coeruleus may play an important role in the duration and depth of anaesthesia resulting from barbiturate and some related agents.

Some effects of diisopropyl phenol (ICI 35 868) on the pharmacodynamics of atracurium and vecuronium in anaesthetized man

The effects of a bolus injection of diisopropyl phenol 2 mg kg-1 i.v. and an infusion (150 micrograms kg-1 min-1 for 30 min and 75 micrograms kg-1 min-1 thereafter) on the pharmacodynamics and dose-response curves of atracurium and vecuronium were studied in 52 healthy (ASA I or II) patients. Under anaesthesia with diisopropyl phenol, the cumulative dose-response curves of both myoneural blocking drugs were shifted to the left when compared with previously reported results. However, there was no clinically significant change in the pharmacodynamics of either drug after the bolus injection of the blocking drug. Diisopropyl phenol 2 mg kg-1 i.v. administered during steady-state infusions of vecuronium and atracurium increased the depth of the constant neuromuscular blockade. When diisopropyl phenol alone was given to four patients there was no change in the twitch height. These results show that diisopropyl phenol, given according to the regimen in this study, potentiates both of the neuromuscular blockers studied but does not prolong the duration of action of either drug. During the infusion of diisopropyl phenol, vecuronium was found to be five times more potent, to have a more rapid onset time, and to be shorter acting than an equipotent dose of atracurium.

General kinetic and dynamic principles and their application to continuous infusion anaesthesia

The use of intravenous anaesthetic agents by continuous infusion requires knowledge of their pharmacokinetic properties. In this article, the general pharmacokinetic principles behind the use of infusions of intravenous agents are presented and the literature with regard to the individual drugs used in this way is reviewed.

Hepatic function after anaesthesia for major vascular reconstructive surgery

Three groups of patients received Althesin, minaxolone or di-isopropyl phenol to supplement 67% nitrous oxide in oxygen. A fourth group receiving halothane to supplement nitrous oxide in oxygen acted as a control. Hepatic function tests were measured before operation and on days 1, 3, 5 and 7 after major vascular reconstructive surgery. There were significant increases to a mean value above the upper limit of normal in aspartate amino-transferase activity by day 3 in all groups. Total lactic dehydrogenase activity increased in the patients receiving Althesin, minaxolone and halothane. No change was seen in the alkaline phosphatase in any of the study groups. Gamma glutamyl transpeptidase increased in all groups, but the mean value at day 7 was not greater than the upper limit of normal. The mean activity of ornithine carbamoyl transpeptidase showed no change in any group throughout the study period. Two of the patients receiving minaxolone suffered cholestatic jaundice during the first month. These results suggest that anaesthesia with Althesin or di-isopropyl phenol results in enzyme changes similar to those seen in a comparable group of patients receiving halothane to supplement nitrous oxide in oxygen anaesthesia.

Interactions of diisopropyl phenol (ICI 35868) with suxamethonium, vecuronium and pancuronium in vitro

In vitro studies were performed using the rat phrenic nerve-hemidiaphragm preparation to investigate possible interactions between diisopropyl phenol and its solvent, cremophor, with three neuromuscular blocking drugs. Cumulative concentration curves were constructed for the neuromuscular blockers and linear regression analyses performed. Differences in the calculated effective concentration to produce a 50% decrease in twitch height (EC50) and slope showed that diisopropyl phenol potentiated the action of suxamethonium, vecuronium (Org NC 45) and pancuronium. Cremophor potentiated the action of suxamethonium but antagonized the action of the non-depolarizing neuromuscular blockers. The possible mechanisms of action are discussed.

Influence of sample site on blood concentrations of ICI 35868

Simultaneous blood samples from an artery, a peripheral vein and a central vein were analysed for ICI 35868 concentrations following an induction dose of 2.0 mg kg-1 administered i.v. over 60 s, to five patients before cardiac surgery. Up to 60 s after the end of the administration of the drug there were wide differences in drug concentration between the sampling sites. Thus, any attempt to correlate effect with blood concentration over this early period would be problematic. From 60 s there were no significant differences in drug concentration between the three sites. Thus, as long as the mixing period is allowed for, peripheral venous sampling provides an acceptable alternative to arterial puncture in studies to correlate drug effect and concentration and for pharmacokinetic investigations.

Disoprofol (ICI 35868) for total intravenous anaesthesia

The purpose of this study was to evaluate disoprofol as the hypnotic for total intravenous anaesthesia. Sixty women undergoing minor gynaecological surgery participated and were randomly assigned to four groups (N = 15 in each group). Disoprofol, 2 mg/kg was given i.v. to induce anaesthesia after a bolus injection of either fentanyl 1.875 micrograms/kg or alfentanil 18.75 micrograms/kg. Vecuronium, 0.06 mg/kg, was given for muscle relaxation when indicated. One-half of the patients received acute premedication with midazolam, 5 mg i.v. Anaesthesia was maintained with a continuous infusion of disoprofol 150 micrograms/kg/min and either fentanyl 0.125 micrograms/kg/min or alfentanil 1.25 micrograms/kg/min. These drug combinations were compatible and produced good operating conditions. Awakening time was significantly shorter for women who received no premedication and was not affected by the narcotic used. Respiration returned more quickly when fentanyl was the narcotic given and was not affected by premedication. Both hypotension and bradycardia were seen in some patients, but other side effects were infrequent. This total intravenous anaesthesia technique was very well accepted by the patients and the nurses who cared for them in the postoperative period.

New drugs--boon or bane? Premedication and intravenous induction agents

Research on the benzodiazepines has shown that they have certain advantages over the opiates as premedicants. Diazepam, which produces good tranquilization, is well absorbed when given orally though absorption is influenced by other drugs given at the same time. Oral lorazepam leads to more prolonged sedation and amnesia but the final elimination is more rapid. Several new intravenous anaesthetics have been introduced during the last five years but none seems likely to replace thiopental. The theoretical disadvantages of thiopental are offset by its water-solubility, and the use of Cremophor EL in preparations of propanidid, alphaxalone, di-isopropyl phenol and one preparation of diazepam has led to many hypersensitivity reactions. Ketamine is gradually finding its rightful place in anaesthesia but its use is becoming limited to anaesthesia in difficult circumstances. The future concomitant use of other drugs and separation of isomers of ketamine may again broaden its applications. The new water-soluble steroid minaxolone has its own disadvantages, and the water-soluble benzodiazepine midazolam is as unpredictable for induction of anaesthesia as diazepam.

Haemodynamic effects of infusions of diisopropyl phenol (ICI 35 868) during nitrous oxide anaesthesia in man

The haemodynamic effects of diisopropyl phenol in cremophor EL at infusion rates of 50-55 and 100 micrograms kg-1 min-1 in combination with inhalation of 67% nitrous oxide have been studied during spontaneous and controlled ventilation in patients premedicated with morphine and atropine. Under all the conditions studied diisopropyl phenol supplementation of nitrous oxide anaesthesia was associated with a decreased arterial pressure (-20% to -31%) compared with the awake patient, related to a decrease in cardiac output (-27% to 29%) and an increase in systemic vascular resistance (+8% to +30%) during surgery, but to a decrease in cardiac output (-19%) and a decrease in systemic vascular resistance (-17%) during anaesthesia without surgery. Doubling the infusion rate of diisopropyl phenol caused no significant haemodynamic changes during either spontaneous or controlled ventilation. The haemodynamic manifestations of sympathetic nerve activity in response to laryngoscopy and intubation were poorly suppressed by diisopropyl phenol.

Pharmacokinetic evaluation of ICI 35 868 in man. Single induction doses with different rates of injection

Blood concentrations of ICI 35 868 have been measured in patients following a single bolus dose of 2 mg kg-1. Three different rates of injection of the anaesthetic agent (3-5s, 20s and 40 or 50s) were examined. Pharmacokinetic indices, derived from blood concentrations of ICI 35 868, were independent of the speed of injection. The blood profiles could be described by a two-compartment open model with a mean alpha-phase half-life of 2.5 min and a mean beta-phase half-life of 54.5 min. The mean total body clearance was 3454 ml min-1. Similar data were obtained from a 4-mg kg-1 dose. The mean recovery time (4.4 min) and concentration of ICI 35 868 at awakening (1.05 micrograms ml-1) were also independent of the rate of injection. Using the derived pharmacokinetic model, predictions of drug concentrations have been made for repeated bolus doses, or infusions, of ICI 35 868.

Recovery from intravenous anaesthesia. Comparison of disoprofol with thiopentone and methohexitone

Using the endpoints of spontaneous opening of eyes, giving date of birth, sitting up unaided and normal pegboard time, recovery from 2 and 3 mg/kg disoprofol was compared with that from 4 and 6 mg/kg thiopentone and 1.5 mg/kg methohexitone in groups each of 10 unpremedicated patients. The study method differentiated between recovery from the two doses of disoprofol and thiopentone at the first two endpoints only. A between-drug comparison showed early recovery was slightly faster with thiopentone than with equivalent doses of the new drug while no differences were detected between the recovery from equivalent doses of methohexitone and thiopentone. The differences found in this study are felt to be of no clinical significance and recovery from anaesthesia with disoprofol would not be expected to be any slower than that from equivalent doses of thiopentone.

Recovery from day-case anaesthesia: comparison of a further four techniques including use of the new induction agent diprivan

Eighty unpremedicated patients received thiopentone and halothane, propanidid and fentanyl, diprivan (ICI 35 868) alone, or diprivan and fentanyl, each supplementing 66% nitrous oxide in oxygen. Diprivan alone, or in combination with fentanyl, resulted in a more rapid awakening than thiopentone and halothane, and significantly shorter recovery times than both thiopentone and halothane and propranidid and fentanyl. Administration of fentanyl with diprivan significantly reduced the total dose of the latter and all indices of recovery. Propanidid and fentanyl did not produce shorter overall recovery times than thiopentone and halothane but nausea and vomiting after operation were significantly increased when compared with the other techniques.

Blood disoprofol levels in anesthetised patients. Correlation of concentrations after single or repeated doses with hypnotic activity

The blood concentrations of disoprofol (Diprivan) after single intravenous doses of 1, 2 or 3 mg/kg have been examined in a subpopulation from previously reported clinical studies. The linear relationship between sleep time and dose could be explained by the linearity of the pharmacokinetics at these doses. After a single injection the awakening concentration was independent of dose, with a mean value of 1.04 micrograms/ml. No acute tolerance occurred with disoprofol. On repeated 1 mg/kg bolus injections the sleeping time rose initially but stabilised after four doses. The waking concentration was independent of the number of doses administered. The clinical findings fitted an agent with a very rapid distribution phase and a short elimination half-life.

Disoprofol and fentanyl for total intravenous anaesthesia

Ninety patients undergoing a variety of surgical procedures were anaesthetised with a disoprofol infusion and increments of fentanyl. The first 40 patients constituted a preliminary dose finding study and the subsequent 50 patients a dose comparison study. The second 50 patients were alternately allocated to receive a maintenance infusion of disoprofol 150 or 200 micrograms/kg/minute. Fentanyl (1 microgram/kg) at induction was followed by further small increments when indicated. Maintenance dosage of 200 micrograms/kg/minute provided good operating conditions and rapid uncomplicated recovery in spontaneously breathing patients, while 150 micrograms/kg/minute proved inadequate to prevent patient movement.

Effect of preanaesthetic medication on anaesthesia with ICI 35, 868

The effect of three commonly used premedicants and a control on anaesthesia with ICI 35, 868 is described. Two randomized studies were performed--one a group study of induction characteristics at 2 mg kg-1 and the other a detailed study in patients undergoing minor gynaecological surgery with an induction dose of 1.5 mg kg-1 and maintenance with incremental doses plus 66% nitrous oxide in oxygen. Premedication had little effect on the already good induction characteristics. Only heavy opiate premedication produced reliable induction at 1.5 mg kg-1, but with an increase in side-effects. Diazepam appears to be the premedicant of choice, although the overall frequency of pain on injection has not been affected by premedication.

Comparison of the effect of diisopropyl phenol (ICI 35, 868) and thiopentone on response to somatic pain

The response to somatic pain with sub-hypnotic doses of ICI 35, 868 (diisopropyl phenol in cremophor) and thiopentone was compared using tibial pressure algesimetry. Studies were also carried out following recovery from larger doses of both drugs. The patients underwent gynaecological procedures using only one of the two i.v. agents and nitrous oxide in oxygen. The studies confirmed the known antanalgesic action of thiopentone and demonstrated that diisopropyl phenol has an analgesic action which is an attractive feature in an i.v. anaesthetic agent.

Continuous intravenous infusion of disoprofol (ICI 35868, Diprivan). Comparison with Althesin to cover surgery under local analgesia

Disoprofol has been used to induce and, by continuous infusion, to maintain a light level of general anaesthesia in 100 patients undergoing surgery with the aid of a regional block. Its effects have been compared with 100 patients anaesthetised in a similar manner with Althesin. Disoprofol proved to be a very satisfactory agent for use by this method and apart from an appreciable incidence of pain on injection the number of complications was small and comparable to those found with Althesin, which caused more involuntary movements. Recovery was particularly rapid and clear-headed following disoprofol, and occurred highly significantly more quickly than after Althesin. Disoprofol, however, will not be marketed in the present formulation which has Cremophor EL as the solubilising agent.

Use of di-isopropyl phenol as main agent for short procedures

The use of di-isopropyl phenol (Diprivan) for induction of anaesthesia was assessed in doses ranging from 1 to 3 mg kg-1. With less than 1.75mg kg-1 not all patients were anaesthetized; 2.0 mg kg-1 appeared to be a satisfactory induction dose. Involuntary muscle movement, cough and hiccup at induction were rare with any dose studied. However, the frequency of hypotension and respiratory depression were related to the dose given. Pain on injection was uncommon when the drug was given into an antecubital vein, but occurred in 39% of patients when injected to the back of the hand or wrist. Recovery was rapid, and characterized by lack of emetic sequelae. Di-isopropyl phenol 1.5 - 2.0 mg kg-1 given rapidly during reactive hyperaemia can produce anaesthesia in one arm-brain circulation time. A reaction involving flush, hypotension, cough, laryngospasm and bronchospasm occurred in one patient receiving 2.5 mg kg-1 given over 20 s.

Dose-response relationship for disoprofol (ICI 35868; Diprivan). Comparison with methohexitone

The duration of sleep following intravenous administration of three doses of disoprofol (1.2 and 3 mg/kg) was compared with that following methohexione 1 or 2 mg/kg. Disoprofol and methohexitone were shown to be approximately equipotent. Side-effects were dose-related for both drugs, but the incidence was significantly less following disoprofol than methohexitone 2 mg/kg. The most frequent side-effects were pain on injection, myoclonia and hiccup. Studies of blood concentrations of disoprofol show that the profile is dose-independent and conforms to a two-compartment model with a very short distribution phase (about 2 minutes) and short elimination phase (about 70 minutes). Waking blood levels gave no indication of acute tolerance. Disoprofol would appear to be particularly useful for induction of a short period of sleep using a small dose given quickly, or for maintenance of sleep by continuous infusion.

Comparison of the respiratory effects of ICI 35 868 and thiopentone in the rabbit

The effects of thiopentone and ICI 35 868 on minute volume, respiratory frequency, tidal volume and arterialized venous PCO2, pH and standard bicarbonate have been compared in the rabbit. ICI 35 868 has two to three times the potency of thiopentone, but equivalent anaesthetic doses cause similar decreases in minute volume. ICI 35 868 decreased tidal volume to a greater extent than thiopentone. Whilst the time courses of the two drugs were similar in most respects, thiopentone produced a more prolonged increase in PCO2. This was accompanied by an increase in standard bicarbonate which was not seen in rabbits treated with ICI 35 868.

A study of three doses of ici 35 868 for induction and maintenance of anaesthesia

Three doses (1.5, 2.0 and 2.5 mg kg-1) of diisopropyl phenol (ICI 35 868) were compared for induction and maintenance of anaesthesia in healthy females undergoing short gynaecological procedures. Induction of anaesthesia was smooth and rapid. Cardiovascular changes (which were dose-dependent) included a decrease in arterial pressure and an increase in heart rate. These changes were magnitudes comparable to those reported for other induction agents. Recovery from the effects of the drug was rapid and uneventful.

ICI 35868 (Diprivan): a new intravenous anaesthetic. A comparison with Althesin

ICI 35868 (Diprivan), 1-2 mg/kg was used to induce anaesthesia in 20 patients, and the results compared with induction of anaesthesia by Althesin 0.5 ml/kg given to a similar group of 20 patients. ICI 35868 was effective in inducing anaesthesia, but produced more respiratory depression, and cardiovascular effects which were significantly different from those produced by Althesin. ICI 35868 gave a smoother induction. It is concluded that ICI 35868 is a promising new induction agent which may also find application for the maintenance of anaesthesia.

ICI 35868 (Diprivan): a new intravenous induction agent. A comparison with methohexitone

ICI 35868 (Diprivan) has been used as an induction agent in patients undergoing minor gynaecological surgery and as the sole anaesthetic agent during bronchoscopy, and its effects were compared with those of methohexitone. The new agent proved to be satisfactory, although induction of anaesthesia was significantly longer than following methohexitone. complications were similar with both drugs. ICI 35868 deserves full investigation as an intravenous anaesthetic agent.

Animal studies of the anaesthetic activity of ICI 35 868

The activity of a new i.v. anesthetic agent ICI 35 868, a compound unrelated to currently used barbiturate, eugenol or steroid agents, has been examined in a range of animal species. Some of the properties of ICI 35 868 resemble those of thiopentone in that it is a rapidly acting agent which produces anaesthesia of short duration and without excitatory side-effects. Both agents have a similar therapeutic index and produce equivalent cardiovascular and respiratory effects. In the mouse ICI 35 868 is 1.8 times more potent than thiopentone as a hypnotic. However, the anaesthetic profile of ICI 35 868 differs from that of thiopentone in that recovery is rapid following repeated administration, no tissue damage is produced by perivascular or intra-arterial injection and greater reflex depression and more profound e.e.g. changes are produced at equipotent doses. This new agent has been shown to be compatible with a wide range of drugs used for preanaesthetic medication, inhalation anaesthetics, and neuromuscular blocking drugs.

Pharmacokinetics in laboratory animals of ICI 35 868, a new i.v. anaesthetic agent

Blood concentrations of ICI 35 868 have been determined in rat, pig, rabbit and cat after single i.v. injections. In all species the initial distribution volume was greater than blood volume and the overall distribution volume was large. Half-lives of the distribution phase were extremely short (1-6 min) and the terminal half-lives were also short (16-55 min). In all species examined a correlation existed between the systemic blood concentration of ICI 35 868 and duration of sleep, with concentrations in the range 1-4 micrograms ml-1 being effective in producing unconsciousness. No changes in pharmacokinetics or in the effective concentration occurred on repeated administration or after infusion.

Preliminary experience with ICI 35 868 as an i.v. induction agent: comparison with althesin

In a small open dose-finding study the i.v. dose of ICI 35 868 required to induce anaesthesia in healthy adults was 2 mg kg-1. Comparison of this dose with Althesin 0.05 ml kg-1 for i.v. induction, both injected over 30 s suggests that they have similar effects on heart rate, arterial pressure and breathing. The mean times to loss of eyelash reflex were 57 +/- SD 10.1 s (ICI 35 868) and 46 +/- 3.9s (Althesin). The new drug was associated with pain and discomfort on injection in seven of 10 patients, but with less involuntary movement than occurred with Althesin.