Propofol phosphate, a water-soluble propofol prodrug: in vivo evaluation

Synthesis and Characterization of a Series of Temozolomide Esters and Its Anti-glioma Study

Temozolomide is a first-line therapeutic drug for glioblastoma (GBM), and it has a low solubility, short biological half-life, and resistance to drug limits in clinical applications. Therefore, it is necessary to find more effective anti-tumor drugs to overcome drug resistance and enhance its anti-glioma activity. We therefore used n-butanol, n-hexanol, n-octanol, 1-dodecanol and 1-hexadecanol to synthesize a series of temozolomide ester compounds (TMZEs) and then investigated their physicochemical properties and anti-glioma efficacy. Our results showed that TMZEs had a higher lipophilicity compared to TMZ and could stably exist in plasma and brain homogenates. TMZEs had significantly increased cytotoxicity and cellular uptake in C6 glioma cells as chain lengths increased. Additionally, the IC₅₀ of TMZ-16E towards TMZ-resistant cells (T98G) was 85.9-fold lower than that of TMZ (p < 0.001), and Western blot results demonstrated that TMZ-16E could significantly reduce the expression of O⁶-methylguanine-DNA-methyltransferase (MGMT). The in vivo anti-glioma efficacy of TMZ-16E were then investigated in orthotopic and subcutaneous GBM models. TMZ-16E prolonged the survival time to 35 days in orthotopic glioma bearing rats, which was 1.94-fold longer than the survival time of rats treated with TMZ, and TMZ-16E increased tumor cell apoptosis based on TUNEL staining. Moreover, TMZ-16E (50 mg/kg) noticeably slowed the growth of T98G subcutaneous tumors by down-modulating MGMT expression in subcutaneous GBM-bearing mice, indicating that TMZ-16E could effectively reverse drug resistance. In conclusion, TMZEs improved the lipophilicity and stability of these drugs. Especially, TMZ-16E could reverse drug resistance and improve therapeutic effects of TMZ, which has clinical application potential for GBM treatment.

Design, Synthesis, and Activity Study of Water-Soluble, Rapid-Release Propofol Prodrugs

In this work, a series of water-soluble propofol prodrugs were synthesized, and their propofol release rate and pharmacodynamic characteristics were measured. We found that inserting glycolic acid as a linker between propofol and the cyclic amino acid accelerated the release of propofol from prodrugs into the plasma while preserving its safety. In animal experiments, prodrugs (3e, 3g, and 3j) were significantly better than fospropofol (the only water-soluble propofol prodrug that has been used clinically) in terms of safety, onset, and duration time of anesthesia. Their molar dose, onset time, and anesthesia duration time were comparable to those of propofol, helping to maintain the clinical benefits of propofol. The experimental results showed the potential of such compounds as water-soluble prodrugs of propofol.

An improved water-soluble prodrug of propofol with high molecular utilization and rapid onset of action

Water-soluble prodrugs of propofol often carry an excess of propofol at the effective dose and have a slower onset of action. Sustained release of the original drug can result in propofol accumulation in the body after administration, causing delays in wakefulness. This situation causes the prodrug to lose the benefits of rapid onset and recovery from the effects of propofol. In the present study, HX0921 (sodium 2-(2-(2,6-diisopropylphenoxy)-2-oxoethoxy)acetate), an improved prodrug of propofol with high utilization of propofol and fast onset of action, was studied. The rate of propofol release from HX0921 was much faster than that from fospropofol (a marketed propofol prodrug) in rat plasma. The 50% effective dose (ED₅₀) of propofol, HX0921 and fospropofol to induce anesthesia in rats was 5.78, 22.19 and 42.44 mg/kg, respectively. After administration at 2 × ED₅₀, the onset time of anesthesia in the HX0921 group was significantly shorter than that in the fospropofol group (0.26 ± 0.15 min vs. 2.24 ± 0.35 min, P < 0.01) and the duration of anesthesia in the HX0921 group was also significantly shorter than that in the fospropofol group (22.35 ± 4.05 min vs. 29.15 ± 5.25 min, P < 0.01). These results suggest that the rapid onset and short action time of HX0921 was due to the rapid release and high molecular utilization of propofol carried by HX0921.

Recent progress in prodrug design strategies based on generally applicable modifications

The development of prodrugs has progressed with the aim of improving drug bioavailability by overcoming various barriers that reduce drug benefits in clinical use, such as stability, duration, water solubility, side effect profile, and taste. Many conventional drugs act as the precursors of an active agent in vivo; for example, the anti-HIV agent azidothymidine (AZT) is converted into its corresponding active triphosphate ester in the body, meaning that AZT is a prodrug in the broadest sense. However prodrug design is generally difficult owing to the lack of general versatility. Thus, these prodrugs, broadly defined, are often discovered by chance or trial-and-error. Recently, many prodrugs that could release the corresponding parent drugs with or without enzymatic action under physiological conditions have been reported. These prodrugs can be easily designed and synthesized because of their generally applicable modifications. This digest paper provides an overview of recent development in prodrug strategies for drugs with a carboxylic acid or hydroxyl/amino group on the basis of a generally applicable modification strategy, such as esterification, amidation, or benzylation.

The anticancer drug metabolites endoxifen and 4-hydroxy-tamoxifen induce toxic effects on Daphnia pulex in a two-generation study

Although pharmaceutical metabolites are found in the aquatic environment, their toxicity on living organisms is poorly studied in general. Endoxifen and 4-hydroxy-tamoxifen (4OHTam) are two metabolites of the widely used anticancer drug tamoxifen for the prevention and treatment of breast cancers. Both metabolites have a high pharmacological potency in vertebrates, attributing prodrug characteristics to tamoxifen. Tamoxifen and its metabolites are body-excreted by patients, and the parent compound is found in sewage treatment plan effluents and natural waters. The toxicity of these potent metabolites on non-target aquatic species is unknown, which forces environmental risk assessors to predict their toxicity on aquatic species using knowledge on the parent compounds. Therefore, the aim of this study was to assess the sensitivity of two generations of the freshwater microcrustacean Daphnia pulex towards 4OHTam and endoxifen. Two chronic tests of 4OHTam and endoxifen were run in parallel and several endpoints were assessed. The results show that the metabolites 4OHTam and endoxifen induced reproductive and survival effects. For both metabolites, the sensitivity of D. pulex increased in the second generation. The intrinsic rate of natural increase (r) decreased with increasing 4OHTam and endoxifen concentrations. The No-Observed Effect Concentrations (NOECs) calculated for the reproduction of the second generation exposed to 4OHTam and endoxifen were <1.8 and 4.3 μg/L, respectively, whereas the NOECs that were calculated for the intrinsic rate of natural increase were <1.8 and 0.4 μg/L, respectively. Our study raises questions about prodrug and active metabolites in environmental toxicology assessments of pharmaceuticals. Our findings also emphasize the importance of performing long-term experiments and considering multi-endpoints instead of the standard reproduction outcome.

Efficacy comparison of the novel water-soluble propofol prodrug HX0969w and fospropofol in mice and rats

BACKGROUND

HX0969w is a novel water-soluble prodrug designed to release propofol and gamma-hydroxybutyrate (GHB) and has a sedative-hypnotic effect. This study was performed to compare the efficacy of HX0969w with fospropofol in mice and rats.

METHODS

We performed hydrolysis studies in the plasma from mice and rats. The half-maximal effective doses (ED50) and half-maximal lethal doses (LD50) of fospropofol and HX0969w were determined. A pharmacodynamics comparison of these two compounds was also performed. Time to loss of righting reflex, time to return of righting reflex, recovery time, and adverse effects were recorded.

RESULTS

The hydrolysis studies demonstrated that HX0969w released propofol as expected. HX0969w ED50 values in mice and rats were 133.03 and 53.79 mg kg(-1), respectively, and LD50 values were 607.11 and 283.79 mg kg(-1), respectively. The calculated therapeutic index (TI), safety index (SI), and certain safety factor (CSF) of HX0969w were 4.56, 3.33, and 2.92 for mice, and 5.28, 3.94, and 3.49 for rats, respectively. The pharmacodynamic comparison studies suggest that HX0969w has a longer onset time and shorter duration than fospropofol.

CONCLUSIONS

Similar to fospropofol, HX0969w is an effective, water-soluble prodrug that is capable of inducing a sedative-hypnotic effect in mice and rats. Unlike fospropofol, HX0969w releases GHB instead of formaldehyde. Further studies regarding the efficacy and safety of HX0969w are necessary.

Synthesis and characterization of novel quick-release propofol prodrug via lactonization

The water-soluble derivatives of propofol have gained attention as a method to increase solubility of propofol. According to the principle of lactonization, the lead compound HX0969 was synthesized first and then the pharmacological features of HX0969 were evaluated in a comparison with those of propofol in the SD rats. Then, HX0969 disodium phosphate monoester (HX0969W) and glycine ester trifluoroacetic acid salt (HX101230) were synthesized, and their pharmacological features were compared with those of Lusedra®, which has been recognized and marketed as a water-soluble prodrug of propofol since 2008. The results showed that HX0969 could produce an anesthetic effect within a few seconds (3.6±3.0s) and its therapeutic index was 4.66 in the SD rat. The pharmacodynamic characteristics of HX0969W were similar to those of the Lusedra®. HX101230 could still produce an anesthetic effect within 60s in the rats though its therapeutic index was not so high (TI=2.96). Therefore, our study has indicated that HX0969 is a potentially useful lead compound of propofol derivative. Its rapid anesthetic effect is probably associated with lactonization.

Minimum infusion rates and recovery times from different durations of continuous infusion of fospropofol, a prodrug of propofol, in rabbits: a comparison with propofol emulsion

OBJECTIVE

To explore, in rabbits, the minimum infusion rates (MIR) required and recovery time from long duration (≤ 8 hours) continuous infusion of fospropofol disodium, a novel water-soluble prodrug of propofol, and compare it with propofol.

STUDY DESIGN

Prospective, randomized, blinded experimental trial.

ANIMALS

Ninety-six adult laboratory rabbits, mean ± SD weight 2.20 ± 0.15 kg.

METHODS

Stage 1. 16 rabbits were assigned to receive fospropofol disodium or propofol to measure MIR, using an up-and-down method with response to tail-clamping stimulus (TCS). Stage 2. Eighty rabbits were allocated to group F (fospropofol disodium) or group P (propofol), and further subdivided (n = 10 in each subgroup) according to infusion time (2, 4, 6 or 8 hours), to groups F(2h), F(4h), F(6h), F(8h) and P(2h), P(4h), P(6h), P(8h). Fospropofol or propofol were infused, and tail clamping applied to maintain the same depth of anaesthesia until infusion was completed. Times to recover righting reflex (RR), to respond to TCS, and total recovery to different durations of continuous infusion of two anaesthetic drugs were noted. Respiratory and pulse rates and oxygen saturation were analyzed. The plasma concentrations of fospropofol disodium, the active metabolite propofol (propofol(F) ) and propofol emulsion were measured with respect to loss and recovery of RR and TCS.

RESULTS

MIR of fospropofol disodium was 2.0 mg kg(-1) minute(-1) , and MIR of propofol was 0.9 mg kg(-1) minute(-1) . Times in minutes to total recovery from anaesthesia in groups F and P were as follows, F(2h) 15 ± 3; F(4h) 26 ± 4; F(6h) 52 ± 6; F(8h) 84 ± 10; and P(2h) 10 ± 1; P(4h) 19 ± 7; P(6h) 36 ± 7; P(8h) 48 ± 5.

CONCLUSIONS AND CLINICAL RELEVANCE

After continuous intravenous infusion in rabbits (≤ 8 hours), fospropofol disodium and propofol both show an extension of recovery time with increasing infusion time, fospropofol disodium showing a significantly greater prolongation compared to propofol emulsion when infusion time increases to 6 and 8 hours.

Anesthetic profile of a non-lipid propofol nanoemulsion

BACKGROUND AND OBJECTIVES

The clinical use of a lipid propofol formulation causes pain during injection, allergic reactions, and bacterial growth. Propofol has been reformulated in different non-lipid presentations to reduce the incidence of adverse effects, but those changes can modify its pharmacokinetics and pharmacodynamics. In the present study, we investigate the pharmacology and toxicology of lipid propofol (CLP) and the non-lipid nanoemulsion (NLP).

METHODS

Conventional lipid formulation of propofol and NLP were infused in the jugular veins of rats and blood pressure (BP), heart rate (HR), and respiratory rate (RR) were measured. Both formulations (1%) were infused (40 μL.min⁻¹) over 1 hour. Hypnotic and anesthetic doses as well as recoveries were determined. The pain induced by the CLP and NLP vehicles was compared by counting the number of abdominal contortions ("writhing test") after the intraperitoneal (i.p.) injection in mice. Acetic acid (0.6%) was used as positive control.

RESULTS

Hypnotic and anesthetic doses of 1% CLP (6.0 ± 1.3 and 17.8 ± 2.6 mg.kg⁻¹, respectively) and 1% NLP (5.4 ± 1.0 and 16.0 ± 1.4 mg.kg⁻¹, respectively) were not significantly different. Recovery from hypnosis and anesthesia was faster with NLP than with CLP. Changes in HR, BP, and RR caused by NLP were not significantly different from those caused by CLP. Acetic acid and the vehicle of CLP caused 46.0 ± 2.0 and 12.5 ± 0.6 abdominal contortions 20 min after i.p. injection, respectively. The absence of abdominal contractions was observed with the vehicle of NLP. Abdominal inflammatory response was not observed after the i.p. injection of both propofol vehicles.

CONCLUSIONS

Non-lipid formulation of propofol can be a better alternative to CPL for intravenous anesthesia with fewer adverse effects.

Monitored anesthesia care (MAC) sedation: clinical utility of fospropofol

Fospropofol, a phosphorylated prodrug version of the popular induction agent propofol, is hydrolyzed in vivo to release active propofol, formaldehyde, and phosphate. Pharmacodynamic studies show fospropofol provides clinically useful sedation and EEG/bispectral index suppression while causing significantly less respiratory depression than propofol. Pain at the injection site, a common complaint with propofol, was not reported with fospropofol; the major patient complaint was transitory perianal itching during the drug's administration. Although many clinicians believe fospropofol can safely be given by a registered nurse, the FDA mandated that fospropofol, like propofol, must be used only in the presence of a trained anesthesia provider.

Fospropofol disodium, a water-soluble prodrug of the intravenous anesthetic propofol (2,6-diisopropylphenol)

BACKGROUND

Today, propofol or 2,6-diisopropylphenol is the anesthetic mainly used for monitored anesthetic care sedation and during intravenous anesthesia. The formulation, a lipid macroemulsion, shows several disadvantages. Therefore, during the past years considerable scientific effort has been undertaken to find either a better formulation or a prodrug of propofol. Fospropofol is the first propofol prodrug that has been intensively studied in man. It has been licensed in 2008 by the FDA for monitored anesthetic care sedation.

OBJECTIVES AND METHODS

This review describes first published study results of fospropofol with regard to its pharmacokinetics/pharmacodynamics, drug safety, tolerability and drug side effects. Using a Medline search all published articles and abstracts containing the words fospropofol or GPI 15715 were included.

RESULTS AND CONCLUSION

As the impact of an errorness drug assay for propofol liberated from fospropofol is not exactly defined, no clear conclusions can be drawn from the first published pharmacokinetic/pharmacodynamic studies. Fospropofol was well tolerated in the first two clinical studies and no serious side effects were reported. After characterization of the true pharmacokinetic/pharmacodynamics profile, fospropofol, an aqueous solution, has the potential to favorably compare with benzodiazepines for procedural sedation and also may be used for long-term sedation and intravenous anesthesia.

Prodrugs: design and clinical applications

Prodrugs are bioreversible derivatives of drug molecules that undergo an enzymatic and/or chemical transformation in vivo to release the active parent drug, which can then exert the desired pharmacological effect. In both drug discovery and development, prodrugs have become an established tool for improving physicochemical, biopharmaceutical or pharmacokinetic properties of pharmacologically active agents. About 5-7% of drugs approved worldwide can be classified as prodrugs, and the implementation of a prodrug approach in the early stages of drug discovery is a growing trend. To illustrate the applicability of the prodrug strategy, this article describes the most common functional groups that are amenable to prodrug design, and highlights examples of prodrugs that are either launched or are undergoing human trials.

Synthesis, in vitro and in vivo characterization of novel ethyl dioxy phosphate prodrug of propofol

A novel ethyl dioxy phosphate prodrug of propofol (3) was synthesized and characterized in vitro and in vivo as safer alternative for phosphonooxymethyl prodrugs. The synthesis of 3 was achieved via vinyl and 1-chloroethyl ether intermediates, followed by addition of phosphate group. Aqueous solubility and chemical stability of 3 was determined in buffer solutions and the bioconversion of 3 to propofol was determined in vitro and in vivo. The results show that 3 greatly enhanced the aqueous solubility of propofol (solubility over 10 mg/mL) and the stability in buffer solution (t1/2=5.2+/-0.2 days at pH 7.4, r.t.) was sufficient for i.v. administration. The enzymatic hydrolysis of 3 to propofol was extremely rapid in vitro (t1/2=21+/-3s) and 3 was readily converted to propofol in vivo in rats. During bioconversion, 3 releases acetaldehyde, a less toxic compound than the formaldehyde released from the phosphonooxymethyl prodrug of propofol (Aquavan), currently undergoing clinical trials. The maximum plasma concentration of propofol, 3.0+/-0.2 microg/mL, was reached within 2.1+/-0.8 min after the i.v. administration of 3. The present study indicates that ethyl dioxy phosphate represents a potentially useful water-soluble prodrug structure suitable for i.v. administration.

Design and evaluation of microemulsions for improved parenteral delivery of propofol

The objective of this investigation was to evaluate the potential of the microemulsions to improve the parenteral delivery of propofol. Pseudo-ternary phase diagrams were plotted to identify microemulsification region of propofol. The propofol microemulsions were evaluated for globule size, physical and chemical stability, osmolarity, in vitro hemolysis, pain caused by injection using rat paw-lick test and in vivo anesthetic activity. The microemulsions exhibited globule size less than 25 nm and demonstrated good physical and chemical stability. Propofol microemulsions were slightly hypertonic and resulted in less than 1% hemolysis after 2 h of storage with human blood at 37 degrees C. Rat paw-lick test indicated that propofol microemulsions were significantly less painful as compared to the marketed propofol formulation. The anesthetic activity of the microemulsions was similar to the marketed propofol formulation indicating that they do not compromise the pharmacological action of propofol. The stability studies indicated that the microemulsions were stable for 3 months when stored at 5 +/- 3 degrees C. Thus, microemulsions appeared to be an interesting alternative to the current propofol formulations.

Development of a new generation of propofol

PURPOSE OF REVIEW

The current advance in development of a new generation of propofol and its clinical implications are reviewed.

RECENT FINDINGS

All currently available formulations of propofol have side effects related to propofol itself, as well as to the emulsion delivery systems. A search for better and safer propofol continues. Improvement of the emulsion delivery systems is one of approaches, which can be achieved by identifying better inactive components, enhancing stability, and applying new technologies such as nanotechnology. Modification of chemical structure is another approach, particularly with the development of propofol prodrugs.

SUMMARY

There is a continuous need to develop a better and safer propofol. The development of a new propofol should be focused on minimizing the unwanted side effects, while preserving the beneficial profiles. Hopefully, just such a new propofol will be available in the near future for clinical use.

Prodrug strategies to overcome poor water solubility

Drug design in recent years has attempted to explore new chemical spaces resulting in more complex, larger molecular weight molecules, often with limited water solubility. To deliver molecules with these properties, pharmaceutical scientists have explored many different techniques. An older but time-tested strategy is the design of bioreversible, more water-soluble derivatives of the problematic molecule, or prodrugs. This review explores the use of prodrugs to effect improved oral and parenteral delivery of poorly water-soluble problematic drugs, using both marketed as well as investigational prodrugs as examples. Prodrug interventions should be considered early in the drug discovery paradigm rather than as a technique of last resort. Their importance is supported by the increasing percentage of approved new drug entities that are, in fact, prodrugs.

AQUAVAN® Injection, a Water-soluble Prodrug of Propofol, as a Bolus Injection: A Phase I Dose-escalation Comparison with DIPRIVAN® (Part 2): Pharmacodynamics and Safety: Retracted

BACKGROUND

AQUAVAN Injection (AQ) (GPI 15715; Guilford Pharmaceuticals Inc., Baltimore, MD) is a water-soluble prodrug of propofol. The authors explored the pharmacodynamics and safety of AQ and compared it with propofol lipid emulsion (PropofolD).

METHODS

After institutional review board approval, 36 volunteers with American Society of Anesthesiologists physical status of I were randomly allocated into six cohorts (male/female: 3/3 per cohort) and given a single bolus of AQ (5, 10, 15, 20, 25, or 30 mg/kg). A Bispectral Index monitor (Aspect Medical Systems Inc., Newton, MA) measured the hypnotic effect. The lowest Bispectral Index level (BISpeak) was recorded. One week later, PropofolD was given to the same subjects at 50 mg/min to reach a similar BISpeak. Heart rate, oxygen saturation measured by pulse oximetry, blood pressure, and side effects were monitored. Incidence and duration of apnea and loss (LOCverbal) and return of response to verbal command were measured. A population compartmental pharmacokinetic-pharmacodynamic model was developed for AQ using NONMEM and evaluated using simulations, leverage, and bootstrap analyses.

RESULTS

In the higher dosages (cohorts 4-6), all subjects achieved LOCverbal. Similar times until LOCverbal were seen for AQ and PropofolD. A dose-related increase in duration of LOCverbal was longer for AQ than for PropofolD. AQ BISpeak occurred later than with PropofolD. Pain on injection was only present with PropofolD (12 of 36). With AQ, transient paresthesias and pruritus were seen. Hemodynamic profiles were similar for both drugs, except for an initial tachycardia after AQ administration. Dose-dependent apnea was more pronounced with PropofolD than with AQ. The AQ combined pharmacokinetic-pharmacodynamic profile was best described by a nonlinear, six-compartment pharmacokinetic model and an effect site compartment. A dependency of the ke0 value on the PropofolGPI plasma concentration was noted.

CONCLUSION

Bolus administration of AQ achieves LOCverbal at a similar time as an equipotent amount of PropofolD but shows a longer time to BISpeak and prolonged pharmacodynamics. For both drugs, excellent drug safety was achieved, although there was a tendency of fewer and shorter duration of apneas for AQ.

Sedation with GPI 15715, a Water-Soluble Prodrug of Propofol, Using Target-Controlled Infusion in Volunteers: Retracted

GPI 15715 is the first water-soluble propofol prodrug that has been studied in humans. Present propofol lipid formulations have well known undesirable properties, for example, pain on injection and increased triglyceride concentrations. We investigated whether GPI 15715 is suitable to achieve and maintain moderate sedation for 2 h. Six male and six female volunteers received a target-controlled infusion of GPI 15715, with an initial propofol target concentration of 1.8 microg/mL and the possibility to adjust the propofol target once after 1 h. Propofol concentrations, the bispectral index, and modified Observer's Assessment of Alertness/Sedation Scale (MOAA/S) scores were monitored. The median MOAA/S score was 4 during the first hour and was 3 during the second hour of infusion. The propofol target had to be changed to 2.4 microg/mL in seven volunteers and to 3.0 microg/mL in two volunteers. A propofol concentration of 1.9 microg/mL had the highest probability to result in an MOAA/S score of 3, which corresponds with moderate sedation. We observed no serious side effects. We conclude that GPI 15715 produces excellent sedation.

Recent advances in intravenous anaesthesia

Efforts to develop new hypnotic compounds continue, although several have recently failed in development. Propofol has been reformulated in various presentations with and without preservatives. Pharmacokinetic and pharmacodynamic differences exist between some of these preparations, and it is currently unclear whether any have substantial advantages over the original presentation. The use of target-controlled infusion (TCI) has been extended to include paediatric anaesthesia and sedation. Application of TCI to remifentanil is now licensed. Linking of electroencephalogram (EEG) monitoring to TCI for closed-loop anaesthesia remains a research tool, although commercial development may follow. The availability of stereoisomer ketamine and improved understanding of its pharmacology have increased non-anaesthetic use of ketamine as an adjunct analgesic. It may be useful in subhypnotic doses for postsurgical patients with pain refractory to morphine administration.

Evaluation of new propofol aqueous solutions for intravenous anesthesia

The aim of this study was to evaluate the potential of using three new aqueous formulations of propofol for intravenous (i.v.) anesthesia. The first formulation can be prepared by using hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) as a solubilizer. Phase-solubility analysis showed a linear increase in the solubility of propofol to a maximum of 16.6 mg/ml in 30% (w/v) HP-gamma-CD. Moreover, phase-solubility studies demonstrated that 18% (w/v) HP-beta-CD or SBE-beta-CD and 24% HP-gamma-CD solutions, respectively, are required to dissolve 10mg of propofol in 1 ml of the vehicle; the corresponding solutions, however, are slightly hypertonic. Autoclaving the 10 mg/ml CD-based formulations for 15 min at 121 degrees C caused a change in pH which was more evident for the HP-beta-CD-based formulation while, in any case, no detectable fall in propofol concentration was observed. The second formulation herein evaluated is a co-solvent mixture (i.e., propylene glycol:water (1:1), v/v) which is able to dissolve 10 mg/ml of the anesthetic agent. However, although it is simple to prepare, the stability of this formulation is limited. The third aqueous formulation can be prepared by using the prolinate ester of propofol and its water-soluble derivative dissolved in water at equimolar concentration. The efficacy of all these formulations as i.v. anesthetic agents was assessed using a pharmacodynamic measure (onset and duration of loss of the righting reflex, LORR), and compared with that of the commercial propofol formulation (Diprivan, 10 mg/ml) in rats. It was found that minimizing the amount of cyclodextrin in all CD-based formulations, anesthetic effects comparable to those of propofol in Diprivan were still observed. Moreover, the prolinate ester constituted an effective i.v. anesthetic formulation with the same duration of action but with a longer induction time than Diprivan.

Highly water-soluble derivatives of the anesthetic agent propofol: in vitro and in vivo evaluation of cyclic amino acid esters

Cyclic amino acid esters of propofol were synthesized in an attempt to develop new water-soluble anesthetic agents. Their solubility and stability in aqueous solution, and their ability to release propofol in vitro under physiological conditions were determined. L-Proline (6a) and racemic nipecotic acid (6c) esters were found to be highly soluble in water. Sufficiently stable at physiological pH (half-lives >6 h), the alpha-amino acid esters, 6a and 6b, were found to be quantitatively hydrolyzed in plasma and liver esterase solutions within a few minutes, showing prodrug behavior. The in vitro activity of the esters, determined either by the [(35)S]tert-butylbicyclophosphorothionate ([(35)S]TBPS) binding assay or electrophysiological measurements of the action at cloned human receptors, proved to be a mechanism involving allosteric modulation of GABA(A) receptors. Indeed, L-proline (6a), and racemic pipecolinate (6b) and nipecotate (6c), like propofol, reduced [(35)S]TBPS binding, whereas isonipecotate (6d) showed bicuculline-like behavior, increasing [(35)S]TBPS binding. A nonlinear relation between GABA(A) receptor binding affinity and lipophilicity, as assessed by reversed-phase high-performance liquid chromatography, emerged as a trend. The in vivo anticonvulsant and anesthetic activities of prolinate 6a, intraperitoneally administered in water solution, showed that is a water-soluble propofol prodrug candidate for developing formulations useful for parenteral administration.