Inclusion of lignocaine base into a polar lipid formulation--in vitro release, duration of peripheral nerve block and arterial blood concentrations in the rat

Liposomal-based lidocaine formulation for the improvement of infiltrative buccal anaesthesia

This study describes the encapsulation of the local anaesthetic lidocaine (LDC) in large unilamellar liposomes (LUV) prepared in a scalable procedure, with hydrogenated soybean phosphatidylcholine, cholesterol and mannitol. Structural properties of the liposomes were assessed by dynamic light scattering, nanoparticle tracking analysis and transmission electron microscopy. A modified, two-compartment Franz-cell system was used to evaluate the release kinetics of LDC from the liposomes. The in vivo anaesthetic effect of liposomal LDC 2% (LUV_LDC) was compared to LDC 2% solution without (LDC_PLAIN) or with the vasoconstrictor epinephrine (1:100 000) (LDC_VASO), in rat infraorbital nerve blockade model. The structural characterization revealed liposomes with spherical shape, average size distribution of 250 nm and low polydispersity even after LDC incorporation. Zeta potential laid around -30 mV and the number of suspended liposomal particles was in the range of 10¹² vesicles/mL. Also the addition of cryoprotectant (mannitol) did not provoke structural changes in liposomes properties. In vitro release profile of LDC from LUV fits well with a biexponential model, in which the LDC encapsulated (EE% = 24%) was responsible for an increase of 67% in the release time in relation to LDC_PLAIN (p < 0.05). Also, the liposomal formulation prolonged the sensorial nervous blockade duration (∼70 min), in comparison with LDC_PLAIN (45 min), but less than LDC_VASO (130 min). In this context, this study showed that the liposomal formulations prepared by scalable procedure were suitable to promote longer and safer buccal anaesthesia, avoiding side effects of the use of vasoconstrictors.

The "inverted cup" -- a novel in vitro release technique for drugs in lipid formulations

The aim of this study was to develop a membrane-free in vitro release method for drugs in lipid formulations. It was intended to be applicable to as wide a range as possible of preparations, independently of their polarity and viscosity. The principle of the novel technique is to keep the sample suspended in the release medium in an inverted glass cup, allowing a possible phase transition or swelling. Thirteen formulations containing bupivacaine, lidocaine and/or prilocaine in lipid vehicles with different physical properties were prepared and examined. When possible, in vitro release profiles obtained by the new method were compared to profiles obtained by earlier techniques. For three formulations of either bupivacaine or lidocaine in polar lipid formulations, in vitro release profiles were evaluated in relation to in vivo data, from nerve block and pharmacokinetic studies in rats. Preparations that could be investigated both by the "inverted cup" and by the earlier published "single drop" technique generally showed good agreement between the two release profiles. In the case of the polar lipid formulations, arterial blood concentration curves in rats could reasonably be predicted from the in vitro release profiles. In conclusion, the "inverted cup" technique should potentially be applicable to a wide range of lipid formulations of drugs, both for physico-chemical characterisation and for obtaining in vitro -- in vivo correlations.

Intrathecal fentanyl added to intrathecal bupivacaine for day case surgery: a randomized study

BACKGROUND AND OBJECTIVE

The implication of intrathecal lidocaine in neurological toxicity has made intrathecal bupivacaine the commonly used drug for local anaesthesia in ambulatory surgery. However, in high doses intrathecal bupivacaine may produce a high level of sensory and motor block, and arterial hypotension; discharge from hospital may be delayed. Intrathecal opioids added to low-dose local anaesthetics produce a synergistic effect without increasing the sympathetic block or delaying discharge. The aim of our study was to identify the minimum effective dose of intrathecal fentanyl that in combination with low-dose intrathecal bupivacaine would provide adequate surgical conditions without prolonging recovery.

METHODS

A prospective, single, blind, randomized study was conducted in 45 adult males scheduled for minor urological procedures using intrathecal anaesthesia on a day care basis. Patients were randomly assigned to one of three groups (n = 15 each). They received bupivacaine 0.17% 5 mg--with either fentanyl 7.5 microg (fenta-7.5), 10 microg (fenta-10) or 12.5 microg (fenta-12.5) intrathecally in a total volume of 3 mL. The quality of anaesthesia, haemodynamic stability, time to two-segment and S2 regression, time to micturition, and time to discharge were assessed.

RESULTS

The time to two-segment regression and S2 regression with fenta-12.5 was significantly longer than with fenta-7.5 and fenta-10 (P < 0.01). Fenta-7.5 had a significantly higher number of failed blocks (four patients) compared with fenta-12.5 (P < 0.05). The time out of bed, time to micturition and time to discharge were significantly longer with fenta-10 and fenta-12.5 compared with fenta-7.5, and also with fenta-12.5 compared with fenta-10 (P < 0.01). Haemodynamic stability did not differ for all the drug combinations.

CONCLUSIONS

Fentanyl 12.5 microg added to low-dose bupivacaine (5 mg) intrathecally provides better surgical anaesthesia and increased reliability of block than intrathecal fentanyl 7.5 or 10 microg. Haemodynamic stability was the same for all dose combinations used.

Important physical principles in anaesthesiology

The aim of this Review is to introduce anaesthesiologists to the basic physical principles that are important for their work. A better understanding of the underlying processes during anaesthesia is required for greater safety and efficiency. Relevant physical quantities are presented along with the area of anaesthesiology where they are used. This approach provides better targeting to the needs of practising anaesthesiologists. This text has been a part of a specialist course in anaesthesiology at the University of Ljubljana for some years. Current results show that both the students and the specialist anaesthesiologists now show a better understanding of the underlying physical principles required for their work and are more successful in fulfilling the needs of their practical work.

High-dose midazolam and the attenuation of the contractile response to vasoconstrictors in coronary artery segments

BACKGROUND AND OBJECTIVE

Benzodiazepines may cause hypotension and are reported to interfere with smooth vascular muscle activity. The aim was to elucidate the influence of three different benzodiazepines on the vascular reactivity of coronary arteries.

METHODS

Using the model of isolated vessels, we studied the impact of midazolam (0.15, 1.5, 15 microg mL(-1)), diazepam (0.1, 1.0, 10 microg mL(-1)) and flunitrazepam (0.01, 0.1, 1.0 microg mL(-1)) on the contractile responses to histamine (2 x 10(-5) mol L(-1)) and serotonin (3 x 10(-5) mol L(-1)) in isolated intact and denuded coronary arteries.

RESULTS

Midazolam significantly attenuated the contractile response when administered in high concentrations (15 microg mL(-1)). This effect was more pronounced in intact than in denuded preparations (histamine: -22.7 versus -7.3%, P = 0.0079; serotonin: -47.1 versus -15.9%, P < 0.0001). Diazepam and flunitrazepam exerted no significant effects on the vascular tone of coronary arteries.

CONCLUSIONS

Midazolam, but not diazepam or flunitrazepam, attenuates the contractile responses to vasoconstrictors in concentrations beyond those used in clinical practice. This effect is in part mediated by endothelial factors.

Anaesthesia for day case surgery: a survey of adult clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of consultant day case anaesthetists in the UK to explore the range and variation in the practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). The survey was carried out as part of a larger study that comprised a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery). We report the findings of this national survey of adult urology and orthopaedic day case anaesthetic practice in the UK.

METHODS

The survey used a structured postal questionnaire and collected data on the duration of the surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flows used for anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74% (63% for urology, 67% for orthopaedics). The survey indicated the following practice in adult urology and adult orthopaedic day case surgery: 6 and 12% used premedication; propofol was the preferred induction agent (96 and 97%) and isoflurane the preferred maintenance agent (56 and 58%); 32 and 41% used prophylactic antiemetics; 86 and 93% used a laryngeal mask.

CONCLUSIONS

This survey identifies the variation in current clinical practice in adult day surgery anaesthesia in the UK and discusses this variation in the context of current published evidence.

Effect of dexamethasone on motor brachial plexus block with bupivacaine and with bupivacaine-loaded microspheres in a sheep model

BACKGROUND AND OBJECTIVE

It has been suggested that dexamethasone potentiates the sensory block produced by bupivacaine when both drugs are loaded in microspheres. The aim of the study was to evaluate the effect of dexamethasone on the brachial plexus block obtained with plain bupivacaine and bupivacaine-loaded microspheres.

METHODS

Dexamethasone alone (Group 5) or added to plain bupivacaine (75 mg) with (Groups 3 and 4) and without pH correction (Group 2) was compared with plain bupivacaine (75 mg; Group 1). The effect of a small dose of dexamethasone (0.42 mg) was then evaluated on the brachial plexus block obtained with bupivacaine (750 mg) as bupivacaine-loaded microspheres (Group 6). Dexamethasone was added either in the suspending medium (Group 7) or incorporated with bupivacaine into microspheres (Group 8). The motor block was evaluated in a plexus brachial sheep model.

RESULTS

Dexamethasone alone did not produce any motor block. When added to plain bupivacaine without pH correction, complete motor block could not be obtained. When the pH was corrected, addition of dexamethasone to plain bupivacaine seemed to delay the onset of motor block and did not prolong its duration, and it had no effect on the pharmacokinetics of bupivacaine. With bupivacaine-loaded microspheres, the duration of complete motor block was reduced when a small dose of dexamethasone was added in the suspending medium. However, the duration of motor block was significantly prolonged when dexamethasone was incorporated with bupivacaine into microspheres.

CONCLUSIONS

Despite the delayed onset of motor block, the incorporation of dexamethasone in bupivacaine-loaded microspheres dramatically increases the duration of action (700 +/- 485-5160 +/- 2136 min), which could be clinically relevant when such a drug-delivery system will be available.

Haemodynamic response to a small intravenous bolus injection of epinephrine in cardiac surgical patients

BACKGROUND AND OBJECTIVE

The aim was to study the rapid changes in cardiac output and systemic vascular resistance produced by intravenous epinephrine (5 microg) on a beat-by-beat basis.

METHODS

Ten patients were studied during cardiac surgery. Radial or brachial arterial pressure was recorded continuously during intravenous administration of epinephrine (5 microg). Cardiac output and systemic vascular resistance were derived for each beat using arterial pulse contour analysis calibrated by lithium indicator dilution. In each patient a further dose of epinephrine (5 microg) was administered during cardiopulmonary bypass with the blood flow kept constant so that changes in arterial pressure corresponded to changes in systemic vascular resistance.

RESULTS

When the patients were not on cardiopulmonary bypass, the epinephrine produced an initial increase in systemic vascular resistance to 129 +/- 15% (mean +/- SD) of control, followed by a more prolonged reduction to 57 +/- 13% of control. Cardiac output showed a small initial reduction coincident with the increase in systemic vascular resistance, followed by an increase to 152 +/- 24% of control. During cardiopulmonary bypass, the changes produced by epinephrine on systemic vascular resistance were qualitatively similar but smaller in amplitude, probably because of a greater volume of dilution in the bypass circuit.

CONCLUSIONS

Small bolus doses of epinephrine produce an initial increase in systemic vascular resistance followed by a much greater reduction that may cause hypotension.

Anaesthesia for day case surgery: a survey of paediatric clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of day case consultant anaesthetists in the UK to explore the range and variation in practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). This paper reports the findings of this national survey of paediatric day case anaesthetic practice carried out as part of a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery).

METHODS

The survey used a structured postal questionnaire and collected data on the duration of surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flow rates used for general anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74 and 63% for the paediatric section of the survey. Respondents indicated that 19% used premedication, 63% used propofol for induction, 54% used isoflurane for maintenance, 24% used prophylactic antiemetics and 85%, used a laryngeal mask. The findings of this national survey are discussed and compared with published evidence.

CONCLUSIONS

This survey identifies the variation in clinical practice in paediatric day surgery anaesthesia in the UK.

Recollection of dreams after short general anaesthesia: influence on patient anxiety and satisfaction

BACKGROUND AND OBJECTIVE

We ascertained whether dreams during short general anaesthesia influence subsequent patient satisfaction and anxiety.

METHODS

Fifty female patients were randomized into two groups to test for a difference between intravenous and inhalational anaesthesias. In Group Propo, anaesthesia was induced and maintained with propofol; in Group Metho-Iso, anaesthesia was induced with methohexital and maintained with isoflurane. Satisfaction and anxiety with anaesthesia were evaluated using a visual analogue scale from 0 to 100. Dream incidence rate, satisfaction and anxiety were assessed from immediately after waking until 3 months later.

RESULTS

Seventeen patients (34%) dreamed during anaesthesia. There were no significant differences in satisfaction or anxiety after anaesthesia between the dreaming and non-dreaming patients (satisfaction, 92.3 +/- 21.6 versus 92.1 +/- 21.6; anxiety, 21.1 +/- 21.1 versus 30.3 +/- 32.1), or between Group Propo and Group Metho-Iso (satisfaction, 94.4 +/- 19.3 versus 90.0 +/- 23.4; anxiety, 26.0 +/- 27.6 versus 28.4 +/- 30.7). There was no significant difference in the incidence rate of dreaming with the type of anaesthesia used (Group Propo, 11 patients; Group Metho-Iso, 6 patients).

CONCLUSIONS

Dreaming during general anaesthesia is common but does not influence satisfaction or anxiety after anaesthesia.

Determinants of drug onset

PURPOSE OF REVIEW

The timing and magnitude of drug onset can be influenced by factors in the chain of drug delivery from the site of administration to the site of effect. This review examines recent evidence regarding the contribution and significance of these factors.

RECENT FINDINGS

It is apparent that drug formulations and mixtures can play a significant role in drug onset. An extension of this is the effect of coadministration of drugs, which can influence drug effect both by altering the physiology underlying drug delivery and by an effect at the target organ. Of the physiological variables, cardiac output and its distribution are clearly important. Cardiac output is a significant source of variability in drug response, and indeed has been successfully incorporated into pharmacokinetic models. The pattern of cardiac output distribution is also relevant. In particular, the blood flow to target organs will influence both the timing and magnitude of the effect of some anaesthetic drugs. In addition, the role of the lung in affecting drug distribution may be important for some drugs. At the site or organ of effect itself, variability in drug distribution, drug-receptor interactions, and the influence of other drugs, can all impact on the profile of drug onset.

SUMMARY

Factors in the chain of drug delivery have been demonstrated to affect the nature of drug onset, and can account for some of the observed variability in response. The significance to dosing guidelines and strategies, and to predictions of variability in response, remains to be explored.

In-vitro release of bupivacaine from injectable lipid formulations investigated by a single drop technique--relation to duration of action in-vivo

The aim of this study was to develop an in-vitro release method suitable for injectable slow-release lipid formulations of local anaesthetics (or other drugs). We also aimed that the results of the in-vitro measurements should have a clear relationship to duration of action in-vivo. Six formulations of bupivacaine base in medium-chain triglyceride-glyceryl dilaurate mixtures were developed. A new apparatus was constructed for determination of their in-vitro release profiles. A bulbous glass tube was fixed inside a standard glass bottle, which was then filled with release medium. A stirring magnet was enclosed in the perforated polypropylene cylinder holding the glass tube. The stirring created a continuous, rotating downward flow of medium inside the tube, which kept the lipid phase, introduced by means of a syringe, suspended as a single, free drop. Release profiles were obtained by sampling of the release medium for up to 72 h and analysis by gas-liquid chromatography. The duration of action in-vivo of the respective formulations was tested by the hot-plate method in rats. The release profiles of bupivacaine in-vitro were mono-exponential for four formulations and bi-exponential for the other two. There was a positive correlation between the proportion of glyceryl dilaurate in the formulation and the slow half-life of release of bupivacaine. All formulations showed prolonged duration of action in-vivo, median values within the range 4.5-12 h, as compared with a 2-h effect of bupivacaine hydrochloride solution. A comparison of in-vitro release curves and durations of action in-vivo suggested that to maintain nerve blockade in-vivo the formulations must release bupivacaine at a rate of approximately 350 microg h(-1) under the in-vitro conditions. To conclude, we designed and tested a novel apparatus for measuring release of a local anaesthetic (or other drug) from a fluid or semi-solid formulation in-vitro. Release rates obtained in-vitro by means of this technique may be used to guide the development of formulations with suitable durations of action in-vivo. The apparatus is, however, as yet a prototype. Rigorous evaluation of performance should be carried out on devices built to specific standards according to their intended application.