Bupivacaine salts of diflunisal and other aromatic hydroxycarboxylic acids: aqueous solubility and release characteristics from solutions and suspensions using a rotating dialysis cell model

A prodrug approach involving in situ depot formation to achieve localized and sustained action of diclofenac after joint injection

Long-acting nonsteroidal anti-inflammatory drug formulations for intra-articular injection might be effective in the management of joint pain and inflammation associated sports injuries and osteoarthritis. In this study, a prodrug-based delivery system was evaluated. The synthesized diclofenac ester prodrug, a weak base (pKa 7.52), has relatively high solubility at low pH (6.5 mg mL(-1) at pH 4) and much lower solubility at physiological pH (4.5 μg mL(-1) at pH 7.4) at 37°C. In biological media including 80% (v/v) human synovial fluid (SF), the prodrug was cleaved to diclofenac mediated by esterases. In situ precipitation of the prodrug was observed upon addition of a concentrated slightly acidic prodrug solution to phosphate buffer or SF at pH 7.4. The degree of supersaturation accompanying the precipitation process was more pronounced in SF than in phosphate buffer. In the rotating dialysis cell model, a slightly acidic prodrug solution was added to the donor cell containing 80% SF resulting in a continuous appearance of diclofenac in the acceptor phase for more than 43 h after an initial lag period of 8 h. Detectable amounts of prodrug were found in the rat joint up to 8 days after knee injection of the acidic prodrug solution.

Incorporation of proteinase inhibitors into silk-based delivery devices for enhanced control of degradation and drug release

Controlling the rate of silk degradation is critical to its potential use in biomedical applications, including drug delivery and tissue engineering. The effect of protease concentration on accelerating degradation, and the use of ethylenediamine tetraacetic acid (EDTA) on reducing rates of degradation and on drug release from silk-based drug carriers was studied. Increased rates of proteolysis resulted in increased dye release from silk carriers, while EDTA release from the silk carriers inhibited proteolysis. The sustained release of EDTA from silk carriers in combination with the release of the small molecule anti-convulsant adenosine was investigated in vitro. This combination of factors resulted in delayed release of adenosine by inhibiting proteolytic activity. These results introduce a promising strategy to control drug delivery through the regulation of silk degradation rate, achieved via manipulation of local proteolytic activity. This ability to modulate enzyme function could be applicable to a range of silk biomaterial formats as well as other biodegradable polymers where enzymatic functions control biomaterial degradation and drug release rates.

Physicochemical characteristics and in vitro release from oil-based vehicles of peptidomimetics: parenteral depots for intra-articular administration

RESULTS

Basic physicochemical properties including their apparent solubility in aqueous buffer and vegetable oils of a series of 11 peptidomimetics varying with respect to chain length and degree of N-methylation were estimated. It was observed that the compounds in contact with water transformed into sticky, slowly dissolving semisolid materials. Based on these observations, the in vitro release behavior of selected peptide derivatives from oil solutions and in situ formed precipitates was investigated using a validated in vitro release model.

CONCLUSION

The results of this investigation suggest that both types of oil-based drug delivery systems might constitute alternative sustained release formulation principles of such amorphous peptide derivatives for the intra-articular route of administration.

Intra-articular depot formulation principles: role in the management of postoperative pain and arthritic disorders

The joint cavity constitutes a discrete anatomical compartment that allows for local drug action after intra-articular injection. Drug delivery systems providing local prolonged drug action are warranted in the management of postoperative pain and not least arthritic disorders such as osteoarthritis. The present review surveys various themes related to the accomplishment of the correct timing of the events leading to optimal drug action in the joint space over a desired time period. This includes a brief account on (patho)physiological conditions and novel potential drug targets (and their location within the synovial space). Particular emphasis is paid to (i) the potential feasibility of various depot formulation principles for the intra-articular route of administration including their manufacture, drug release characteristics and in vivo fate, and (ii) how release, mass transfer and equilibrium processes may affect the intra-articular residence time and concentration of the active species at the ultimate receptor site.

Diflunisal salts of bupivacaine, lidocaine and morphine

The present work describes the characterization of diflunisal salts of the analgesic agents bupivacaine, lidocaine, and morphine including their solubility behaviour and release characteristics from solutions and selected salt suspensions in vitro using the rotating dialysis cell model. The solubility of the 1:1 salts at pH 7.4 differed by a factor of 9 with the bupivacaine and lidocaine salts representing the poorest and most soluble salt (0.73 and 6.6mM, respectively). Common ion effects were observed for the diflunisal salts of bupivacaine and morphine when various concentrations of the lidocaine-diflunisal salt were present in aqueous buffer (pH 7.4). The most pronounced salting-out effect was observed for the poorest soluble salt. From Setschenow type plots apparent salting-out constants of 265 M(-1) (bupivacaine) and 54.7 M(-1) (morphine) were calculated. After instillation of mixed salt suspensions comprising the diflunisal salts of bupivacaine and lidocaine into the donor cell of the release model, lidocaine appeared rapidly in the acceptor phase. After clearance of lidocaine from the donor cell, equal and constant fluxes of bupivacaine and diflunisal were observed. The residence times of bupivacaine within the donor compartment was prolonged with increasing lidocaine-diflunisal salt load in the mixed suspensions whereas the slopes of the linear part of the bupivacaine release profiles were affected to a minor extent only. The obtained data indicate that local multimodal analgesia, characterized by rapid onset and extended duration of action, can be achieved upon injection of mixed suspensions of salts differing with respect to aqueous solubility comprising a common ion into a small body compartment (such as the joint cavity).

In vitro assessment of drug release rates from oil depot formulations intended for intra-articular administration

In vitro drug release rates from oil depot formulations intended for intra-articular injection have been investigated by using the rotating dialysis cell. The rate of drug appearance in the acceptor phase after instillation of sesame oil solutions of naproxen and lidocaine into the small aqueous donor compartment applied to first-order kinetics. In the present three-compartment model oil-aqueous phase distribution equilibrium was maintained at all times in the donor phase and thus drug efflux from the donor compartment was dictated by the distribution coefficient. A mathematical description of the rate of drug release into the acceptor phase and the interdependence of the observed apparent first-order rate constants and the drug oil-water distribution coefficients is provided. The in vitro model may constitute a valuable tool in formulation design and development allowing comparison of drug release rates originating from alteration of the oil vehicle composition, the drug compound or the composition of the release media to be performed.