The effect of Leptospermum petersonii essential oil on Candida albicans and Aspergillus fumigatus.

A variety of assays were utilized to determine the effects of Leptospermum petersonii essential oil on both Candida albicans and Aspergillus fumigatus. Hyphal morphology, susceptibility of spheroplasts and uptake of propidium iodide following exposure to the oil suggest that the mode of action of L. petersonii essential oil is through direct disturbance of the fungal cell membrane. Data also confirms that the volatile component of the oil is highly antifungal, independent of direct contact between the liquid oil and the fungal membrane. The degree of inhibition was greater when fungi were directly exposed to oil volatiles compared to pre-inoculation exposure of oil volatiles into the agar. It is likely that the essential oil volatiles are acting both directly and indirectly on the fungi to produce growth inhibition.

Antifungal activity of Leptospermum petersonii oil volatiles against Aspergillus spp. in vitro and in vivo.

OBJECTIVES: This study investigates the volatile (vapour) component of an essential oil derived from the Australian native Leptospermum petersonii as a potential treatment for aspergillosis. METHODS: The in vitro antifungal effects of the volatiles were assayed by a variety of methods. In vitro mammalian cell toxicity of the oil and the oil volatiles was also determined prior to animal testing. Efficacy of the volatiles in vivo was assessed using a murine model. RESULTS: L. petersonii oil volatiles were found to be potent inhibitors of fungal growth in vitro, with fungicidal activity displayed following short exposure times (< or =1 h). No significant mammalian cell toxicity was found to be associated with the volatiles. In the absence of treatment, Aspergillus fumigatus infection of animals resulted in an increase in inflammatory cell counts and high fungal burden within the lung tissue. Chitin levels in treated animals were significantly reduced compared with control animals. No viable fungi could be recovered from animals that had completed the treatment regimen. CONCLUSIONS: The significant reduction in fungal burden in the lungs of infected animals by the volatiles of L. petersonii oil was larger than that reported for conventional antifungal drugs of choice.

Effect of essential oil concentration on the pH of nutrient and Iso-sensitest broth.

The role of pH on the antimicrobial activity of essential oils has not been well studied. The effect of four essential oils: Backhousia citriodora, Melaleuca alternifolia, Lavandula angustifolia and Santalum spicatum (0.1% to 10%) on the pH of two commonly used media, nutrient broth and Iso-sensitest broth, was therefore undertaken. Small (less than 0.5 pH units) but statistically significant differences between the pH of the two media followed the addition of M. alternifolia, L. angustifolia and S. spicatum essential oil. In general the effect on pH was greatest at higher concentrations and the fall in pH was greatest in the nutrient broth. The addition of B. citriodora essential oil to nutrient broth resulted in a fall in pH from 7.29 +/- 0.02 (no oil) to 5.2 +/- 0.03 (10% oil). This effect was not observed in the Iso-sensitest broth.

No effect of circulating drug upon isolated forearm block.

Controversy exists as to whether the recovery of isolated arm blockade is primarily determined by resultant plasma drug concentrations, or by the affinity of the drug for the biophase. We have investigated the effect of the circulating drug produced by the isolated forearm experiment upon its recovery profile. Paralysis from retrograde spread of drug after the intravenous injection of 20 ml saline containing vecuronium 0.3 mg into a forearm isolated from the circulation was achieved in three groups of five experiments. Group 1 were used as controls, the tourniquet being released after 3-4 min and the recovery of block observed. In group 2 the tourniquet was similarly released but a repeat dose of vecuronium 0.3 mg was administered into the systemic circulation at 10% recovery. In group 3 the tourniquet was released at 50% twitch depression and the repeat dose of vecuronium 0.3 mg given when the twitch height had recovered to that level. The mean (SD) 25% to 75% recovery indices of groups 1, 2 and 3 were: 9.2 (2.4), 8.7 (1.2) and 9.9 (1.9) min. There was no noticeable effect on the recovery slope of any of the traces when the second dose of myoneural blocker was given systemically in groups 2 and 3. The findings indicate that the main determinant of recovery of the isolated forearm experiment is not its plasma drug concentration but a mechanism which maintains the drug in the effect compartment.

Mivacurium in the myasthenic patient.

We have used mivacurium in four myasthenic patients presenting for thymectomy. Supramaximal single twitch stimulation was applied to the ulnar nerve at the wrist and the force of contraction of the adductor pollicis was measured. After an initial bolus dose of 30 micrograms kg-1 (approximately one-fifth of the normal intubating dose), we observed a mean 37.5 (SEM 5.6)% reduction in evoked twitch tension. Neuromuscular block was increased with incremental doses and maintained with repeat bolus doses of 15 micrograms kg-1 at 25% recovery. The interval between maintenance bolus doses remained constant (mean 5.9 (0.7) min). Spontaneous offset was rapid with a mean recovery index (T25-T75) of 11.9 (2.1) min. Provided anticholinesterase therapy is withheld in the immediate preoperative period, mivacurium would appear to be a safe and appropriate neuromuscular blocker in this variably sensitive group of patients. The cumulative dose required to establish full neuromuscular block varied between 60 and 90 micrograms kg-1. A maintenance infusion, commencing at 3 micrograms kg-1 min-1, is recommended, guided by neuromuscular monitoring.

Sensitivity to second dose of mivacurium.

The sensitivity of patients to a second dose of mivacurium has been studied following complete recovery of the twitch response after > 95% neuromuscular block produced by a systemic bolus of the drug. In further experiments we have excluded one arm from the effect of a systemic bolus ED95 dose of mivacurium for 100 s so as to obtain two different levels of neuromuscular block in the two arms of the same patient. Upon recovery from the block in the paralysed arm the dose response of both arms to a second dose of mivacurium was studied in order to investigate the effect of the amount and duration of block upon second dose sensitivity. An approximately 50% diminution in the ED95 dose requirement of mivacurium was found following complete recovery from an ED95 dose in spite of the rapid plasma clearance of this drug. A similar increase in sensitivity was observed in the arm that had been excluded for 100 s from the peak effect of the drug. It was concluded that the second dose sensitivity was not due to a receptor effect or to residual drug in plasma.

Curare modification of suxamethonium blockade.

Tubocurare (0.125 mg.kg-1 or 0.25 mg.kg-1) was injected 10 s before 1 mg.kg-1 suxamethonium in patients anaesthetised with enflurane 1-1.5%. Measurement of electromyographic response was recorded using a 0.2 Hz train-of-four every 20 s. The modified blocks were slower in onset, of lesser intensity, and of shorter duration than that of suxamethonium alone, but were much closer to those of suxamethonium than of tubocurare. However, the train-of-four fade observed during onset of the modified blocks were similar to that of their tubocurare controls and significantly different from the suxamethonium group. We conclude that effective amounts of tubocurare are present in the neuromuscular junction within the 30 s following intravenous injection of the drugs, and this affects the onset of action of the suxamethonium block. The presence of train-of-four fade during a predominantly agonist block is difficult to explain on the basis of diminished acetylcholine release and a postsynaptic site of action of suxamethonium.

Recovery of mivacurium and doxacurium versus vecuronium in the isolated forearm.

To assess rate of biophase recovery, the recovery from neuromuscular block with mivacurium in the isolated forearm was compared with that from vecuronium simultaneously administered into the other isolated forearm of six volunteers. In a second series of similar experiments, recovery from doxacurium was compared with that from vecuronium. Neuromuscular block was monitored using the adductor pollicis mechanomyographic response to ulnar nerve stimulation at 0.2 Hz. Comparable degrees of maximum twitch tension depression were obtained in each series. In the first series, mean (SD) 25-75% recovery index for mivacurium was 8.4 (1.5) min and 10.5 (1.9) min for vecuronium. In the second series, mean (SD) recovery index for doxacurium was 18.3 (4.2) min and 12.2 (5.0) min for vecuronium. The recovery index of doxacurium in the isolated forearm was significantly greater, and the recovery index of mivacurium significantly less, than the recovery index of simultaneously administered vecuronium. Mivacurium block in the isolated forearm recovers rapidly, although not faster than after systemic injection; this is consistent with a drug that is retained in the biophase despite rapid plasma metabolism. Doxacurium block in the isolated forearm is slow to recover, compared with vecuronium; this suggests that high affinity for the biophase may contribute to its long duration of action.

Effect of voluntary tetanus on recovery of vecuronium block in the isolated forearm.

This study was conducted to investigate the effect of voluntary tetanus on the recovery from neuromuscular block produced by a nondepolarising drug, vecuronium, in the isolated forearm. We have studied the recovery indices and train of four fade at different levels of recovery following vecuronium in both isolated forearms simultaneously, in six sets of experiments. In one hand the volunteer performed a maximum contraction of his thumb repeatedly at fixed intervals. We found that following voluntary tetanus there is an increased rate of recovery from nondepolarising neuromuscular block; mean Recovery Index (7.4, SD 0.97) compared to control Recovery Index (10.55, SD 2.58), p < 0.05. The train-of-four fade also showed a sustained reduction in the isolated forearm which underwent voluntary tetanus. During the later phase of recovery the train-of-four fade showed significant difference statistically (p < 0.01). The findings of this study supports the hypothesis that more rapid recovery associated with voluntary tetanus is due to a reduction in the presynaptic block thus resulting in an increased rate of transmitter release.

Resistance to decamethonium neuromuscular block after prior administration of vecuronium.

Prior administration of nondepolarizing neuromuscular blocking drugs reduces the potency of subsequently administered succinylcholine. To assess whether this interaction is also observed with the depolarizing drug, decamethonium, the potency of decamethonium alone and decamethonium after vecuronium (10 micrograms/kg) were assessed using a cumulative dose-response technique in two groups of six healthy patients each. Patients were premedicated with meperidine and promethazine and anesthetized with thiopental, isoflurane, and nitrous oxide in oxygen. Twitch tension was monitored using adductor pollicis mechanomyography in response to ulnar nerve stimulation at 0.1 Hz. The mean (SEM) dose of decamethonium producing 80% twitch tension depression (ED80) when administered alone was 37 (4.0) micrograms/kg. After recovery of twitch tension (but persistence of train-of-four fade) from vecuronium, the mean (SEM) ED80 for decamethonium was increased to 89 (4.4) micrograms/kg (P < 0.01). The shift to the right of the dose-response curve for decamethonium was nonparallel. Antagonism is observed when decamethonium is administered after a small dose of vercuronium; this interaction, which is also seen with succinylcholine, is likely to be a feature of depolarizing block. Nonparallel shift of the dose-response curve to decamethonium indicates that this is not likely to be a simple agonist-antagonist effect at a single site.

The effect of residual receptor occupancy on sensitivity to repeated vecuronium.

Cumulative dose-response curves were obtained for vecuronium in 10 patients anaesthetised with thiopentone, enflurane and nitrous oxide using adductor pollicis mechanomyography. Five patients received vecuronium systemically, which was repeated at 100% twitch recovery to obtain initial and repeat curves. Another five patients received 0.3 mg vecuronium into an isolated forearm and at 100% recovery of this arm received vecuronium systemically to obtain simultaneous dose-response curves in both the previously isolated and nonisolated arms. There was no significant difference between the calculated ED50 obtained after initial systemic administration [16.2 (1.7) micrograms.kg-1], after recovery in the previously isolated arm [14.8 (2.0) micrograms.kg-1] and simultaneously in the nonisolated arm [16.1 (2.9) micrograms.kg-1]. The ED50 obtained after repeated systemic administration was significantly reduced [8.2 (2.9) micrograms.kg-1]. These results suggest that the reduction in ED50 at 100% twitch recovery from systemic vecuronium is not due to residual drug at the biophase/receptor but to drug persisting in the plasma.

Tetanic fade during recovery from vecuronium block: comparison of systemic and isolated forearm administration.

We have compared the degree of tetanic fade relative to twitch depression occurring after isolated forearm block with vecuronium and that after systemic i.v. injection. Fifteen patients received either vecuronium 0.3 mg into an isolated forearm or vecuronium 0.05 mg kg-1 systemically. Adductor pollicis mechanomyography was used to monitor recovery of twitch height at 0.2 Hz. At 25, 50, 75 and 100% recovery of twitch height, a 5-s, 50-Hz tetanus was administered and tetanic fade ratio measured. There was significantly less tetanic fade in the isolated forearm group (P < 0.01; unpaired ttest) at 25, 50 and 75% twitch height. This suggests that twitch depression and tetanic fade are independently mediated effects of vecuronium.

Recovery from pancuronium and vecuronium administered simultaneously in the isolated forearm and the effect on recovery following administration after cross-over of drugs.

If recovery of neuromuscular block in the isolated arm is determined by biophase binding, then a significant amount of drug will still be present in the biophase at 50% recovery of twitch response. To test this hypothesis we administered pancuronium at 50% recovery from vecuronium block and vecuronium at 50% recovery from pancuronium block in the isolated forearms of volunteers. To ensure that any effect of drug released into the plasma did not affect the results, both experiments were performed simultaneously, one in each forearm of each volunteer. Control experiments were performed to determine the effect of subsequent injections of the same drug at 50% recovery and of subsequent injections of the alternative drug (i.e., vecuronium following pancuronium and pancuronium following vecuronium) at 100% recovery of the twitch response. Prior administration of vecuronium significantly shortened the recovery from subsequent pancuronium when administered at 50% recovery, but not 100% recovery, and pancuronium significantly increased the recovery rate of vecuronium when given at 50% recovery but not 100% recovery. These findings support the concept of biophase binding of nondepolarizing neuromuscular blocking drugs.