Pharmacokinetics and pharmacodynamics of the new propofol prodrug GPI 15715 in rats

Structural Modification in Anesthetic Drug Development for Prodrugs and Soft Drugs

Among the advancements in drug structural modifications, the increased focus on drug metabolic and pharmacokinetic properties in the anesthetic drug design process has led to significant developments. Drug metabolism also plays a key role in optimizing the pharmacokinetics, pharmacodynamics, and safety of drug molecules. Thus, in the field of anesthesiology, the applications of pharmacokinetic strategies are discussed in the context of sedatives, analgesics, and muscle relaxants. In this review, we summarize two approaches for structural optimization to develop anesthetic drugs, by designing prodrugs and soft drugs. Drugs that both failed and succeeded during the developmental stage are highlighted to illustrate how drug metabolism and pharmacokinetic optimization strategies may help improve their physical and chemical properties.

Activation and Delivery of Tetrazine-Responsive Bioorthogonal Prodrugs

Prodrugs, which remain inert until they are activated under appropriate conditions at the target site, have emerged as an attractive alternative to drugs that lack selectivity and show off-target effects. Prodrugs have traditionally been activated by enzymes, pH or other trigger factors associated with the disease. In recent years, bioorthogonal chemistry has allowed the creation of prodrugs that can be chemically activated with spatio-temporal precision. In particular, tetrazine-responsive bioorthogonal reactions can rapidly activate prodrugs with excellent biocompatibility. This review summarized the recent development of tetrazine bioorthogonal cleavage reaction and great promise for prodrug systems.

Gastrointestinal delivery of propofol from fospropofol: its bioavailability and activity in rodents and human volunteers

BACKGROUND

Propofol is a safe and widely used intravenous anesthetic agent, for which additional clinical uses including treatment of migraine, nausea, pain and anxiety have been proposed (Vasileiou et al. Eur J Pharmacol 605:1-8, 2009). However, propofol suffers from several disadvantages as a therapeutic outside anesthesia including its limited aqueous solubility and negligible oral bioavailability. The purpose of the studies described here was to evaluate, in both animals and human volunteers, whether fospropofol (a water soluble phosphate ester prodrug of propofol) would provide higher propofol bioavailability through non-intravenous routes.

METHODS

Fospropofol was administered via intravenous, oral and intraduodenal routes to rats. Pharmacokinetic and pharmacodynamic parameters were then evaluated. Based on the promising animal data we subsequently conducted an oral and intraduodenal pharmacokinetic/pharmacodynamic study in human volunteers.

RESULTS

In rats, bioavailability of propofol from fospropofol delivered orally was found to be appreciable, in the order of around 20-70%, depending on dose. Availability was especially marked following fospropofol administration via the intraduodenal route, where bioavailability approximated 100%. Fospropofol itself was not appreciably bioavailable when administered by any route except for intravenous. Pharmacologic effect following oral fospropofol was confirmed by observation of sedation and alleviation of thermal hyperalgesia in the rat chronic constrictive injury model of neuropathic pain. The human data also showed systemic availability of propofol from fospropofol administration via oral routes, a hereto novel finding. Assessment of sedation in human volunteers was correlated with pharmacokinetic measurements.

CONCLUSIONS

These data suggest potential utility of oral administration of fospropofol for various therapeutic indications previously considered for propofol.

Selective water-soluble gelatinase inhibitor prodrugs

SB-3CT (1), a selective and potent thiirane-based gelatinase inhibitor, is effective in animal models of cancer metastasis and stroke; however, it is limited by poor aqueous solubility and extensive metabolism. We addressed these issues by blocking the primary site of metabolism and capitalizing on a prodrug strategy to achieve >5000-fold increased solubility. The amide prodrugs were quantitatively hydrolyzed in human blood to a potent gelatinase inhibitor, ND-322 (3). The arginyl amide prodrug (ND-478, 5d) was metabolically stable in mouse, rat, and human liver microsomes. Both 5d and 3 were nonmutagenic in the Ames II mutagenicity assay. The prodrug 5d showed moderate clearance of 0.0582 L/min/kg, remained mostly in the extracellular fluid compartment (Vd = 0.0978 L/kg), and had a terminal half-life of >4 h. The prodrug 5d had superior pharmacokinetic properties than those of 3, making the thiirane class of selective gelatinase inhibitors suitable for intravenous administration in the treatment of acute gelatinase-dependent diseases.

Perspectives on the role of fospropofol in the monitored anesthesia care setting

Monitored anesthesia care (MAC) is a safe, effective, and appropriate form of anesthesia for many minor surgical procedures. The proliferation of outpatient procedures has heightened interest in MAC sedation agents. Among the most commonly used MAC sedation agents today are benzodiazepines, including midazolam, and propofol. Recently approved in the United States is fospropofol, a prodrug of propofol which hydrolyzes in the body by alkaline phosphatase to liberate propofol. Propofol liberated from fospropofol has unique pharmacological properties, but recently retracted pharmacokinetic (PK) and pharmacodynamic (PD) evaluations make it difficult to formulate clear conclusions with respect to fospropofol's PK/PD properties. In safety and efficacy clinical studies, fospropofol demonstrated dose-dependent sedation with good rates of success at doses of 6.5 mg/kg along with good levels of patient and physician acceptance. Fospropofol has been associated with less pain at injection site than propofol. The most commonly reported side effects with fospropofol are paresthesia and pruritus. Fospropofol is a promising new sedation agent that appears to be well suited for MAC sedation, but further studies are needed to better understand its PK/PD properties as well its appropriate clinical role in outpatient procedures.

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 injection for the sedation of patients undergoing colonoscopy

Sedation plays a central role in making colonoscopy tolerable for patients and feasible for the endoscopist to perform. The array of agents used for endoscopic sedation continues to evolve. Fospropofol (FP), a prodrug of propofol with a slower pharmacokinetic profile, is currently under evaluation for use during endoscopic procedures. Preliminary data suggests that FP dosed at 6.5 mg/kg is well tolerated by most patients with perineal paresthesias being the most commonly experienced adverse effect. This article will examine the current literature on the use of FP for the sedation of patients undergoing colonoscopy, highlighting the pharmacokinetics, pharmacodynamics, risks, and common adverse events associated with the novel sedative/hypnotic.

A novel, lipid-free nanodispersion formulation of propofol and its characterization

PURPOSE

Propofol is a widely used anesthetic agent with highly desirable fast "on" and "off" effects. It is currently formulated as lipid emulsions, which are known to support microbial growth. In this study, a novel, lipid-free nanodispersion formulation of propofol was characterized.

METHODS

The formulation was evaluated for its physical and chemical stability, in vitro compatibility with red blood cells, and its antimicrobial effectiveness. In vivo pharmacokinetic and pharmacodynamic properties of the formulation were evaluated in rats.

RESULTS

Our data suggest that this lipid-free formulation is physically and chemically stable. Compared to the commercial emulsion formulation Diprivan, it causes less hemolysis with red blood cells and has improved antimicrobial activity. In addition, the lipid-free formulation demonstrates similar pharmacological effects to Diprivan in rats.

CONCLUSIONS

This novel, lipid-free formulation exhibits improved in vitro properties without compromising in vivo effects, therefore representing a promising new alternative for propofol.