An animal model for assessing pain-on-injection of antibiotics

Assessment of Pain Associated with the Injection of Sodium Pentobarbital in Laboratory Mice (Mus musculus)

The AVMA Guidelines for the Euthanasia of Animals considers injection of barbiturates to be an acceptable method of euthanasia in rodents but states there is a potential for pain when administered intraperitoneally. This study examined the potential for pain in mice by assessing visceral pain after intraperitoneal administration and acute pain by using a paw-lick test. Male and female mice (n = 160) intraperitoneally received a euthanizing dose of sodium pentobarbital at a concentration of 5, 50, or 390 mg/mL and were observed for writhing, peritoneum-directed behaviors (PDB), loss of righting reflex, and time to death. Writhing was not observed in any animal. There was no significant difference in the number of mice exhibiting PDB or in the rate of PDB for responders receiving either saline or the 390-mg/mL solution. There was a significant treatment effect on time, with greater concentration and dose resulting in more rapid loss of righting reflex and death. In the second set of experiments, the same solutions were injected subcutaneously into the plantar hindpaw of male and female mice (n = 84). The number of responders, latency until the first lick, and the number of licks per responder were recorded. The number of responders was increased in the 50-mg/mL group; however, there was no difference in latency or the number of licks per responder. These results show that intraperitoneal injection of sodium pentobarbital for euthanasia in mice did not result in increased behavioral signs of pain, and animals lose consciousness more rapidly than the onset of pain seen in the pawlick test. Therefore, although sodium pentobarbital is capable of inducing inflammation, euthanasia through intraperitoneal administration is rapid and does not result in overt signs of pain when compared with injection of saline.

Biocompatible riboflavin laurate long-acting injectable nanosuspensions allowing sterile filtration

The aim of this research was to prepare biocompatible riboflavin laurate (RFL) long-acting injectable nanosuspensions for intramuscular injection with a small particle size allowing sterile filtration. RFL nanosuspensions were manufactured by a precipitation-combined high-pressure homogenization method. Three kinds of mixed stabilizers-d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) as a primary stabilizer, and egg lecithin (PL-100M), Kollidon VA64, Kollidon S-630 as a secondary stabilizer, were separately applied to avoid further aggregation. In the three optimized formulations, the mean particle size of the RFL nanosuspensions was about 170 nm allowing sterilization by filtration. Results from transmission electron microscopy, differential scanning calorimeter, powder X-ray diffraction and Fourier transform infrared reflectance spectroscopy revealed that RFL existed as rod-like crystals. However, a few nano-spheres under 100 nm were found only when PL-100 was used as a secondary stabilizer, possibly due to TPGS and PL-100, which inserted into RFL during the process of crystallization and homogenization. In irritation testing, RFL long-acting injection (LAI) stabilized by TPGS and PL-100 led to mild paw-licking responses and a slight inflammatory reaction, which returned to normal by 14 d after administration. The endogenous PL-100 and nano-spheres with a small size may have contributed to the excellent biocompatibility. As a result, TPGS and PL-100 were selected as blended stabilizers to prepare the irritation-free RFL-LAI that could be sterilized by passage through a 0.22 μm millipore membrane filter.

Characteristics and evaluation of an injectable clarithromycin lipid-based complex in vitro and in vivo

The purpose of this paper is to prepare a less-irritating and lipid-based clarithromycin complex (LCC) by the route of intravenous administration qualified with high drug-loading and fine particle size. The LCC was prepared by the injection of organic solvent phase (containing clarithromycin, sodium cholesterol sulfate and phospholipid at a molar ratio of 1:1:1.5) into the Tris buffer solution (0.05 M, pH 7.2) at 40 °C, and then was concentrated by ultrafiltration to remove the organic solvent. The technique of lyophilization was applied to obtain the LCC lyophilized products. Evaluation of the injectable LCC was performed by particle sizes analysis, transmission electron microscope, entrapment efficiency, stability and irritation tests. The LCC possessed a log-normal size distribution with an average size of 75.4 nm. The drug entrapment efficiency was above 97.0%, which was influenced by the amount of phospholipid, pH value of the media and ionic strength of aqueous suspension. The results of stability and irritation tests proved that LCC had more stability and less irritation. This unique LCC formulation may be applied to the human by the route of injection with less or no irritation. LCC could be an appropriate candidate for intravenous preparation and has a great potential for clinical and industrial-scale production.

Formulation and evaluation of nimodipine-loaded lipid microspheres

The purpose of this study was to develop an alternative, improved and better tolerated formulation and investigate the pharmacokinetic profile of the new formulation of nimodipine (NM) compared with nimodipine ethanol solutions. Lipid microspheres (LMs) prepared using lecithin and vegetable oils have attracted a lot of interest owing to their versatile properties, such as non-immunogenicity, being easily biodegradable and exhibiting high entrapment efficiency. NM incorporated in LMs could reduce irritation by avoiding the use of ethanol as a solubilizer. The solubility of NM was also increased by dissolving it in the oil phase. The particle size distribution, zeta potential, entrapment efficacy and assay of the NM-loaded LMs were found to be 188.2 ± 5.4 nm, −31.6 mV, 94.2% and 1.04 mg mL−1, respectively. The preparation was stable for 1 year at 4–10°C. The formulation and some physicochemical properties of NM-loaded LMs were investigated. The pharmacokinetic and biodistribution studies were performed in rats at a dose of 1.2 mg kg−1. From the observed data, there is no obvious retention of NM-loaded LMs in plasma. Moreover, incorporation of NM in LMs did not alter the tissue distribution significantly except for the relatively greater drug accumulation in the liver and spleen. The stimulation studies demonstrate that LMs of NM reduce irritation markedly compared with NM solutions. These results suggest that the LM system is a promising option to replace NM ethanol solutions as an intravenous treatment.

A less irritant norcantharidin lipid microspheres: formulation and drug distribution

Lipid microspheres (LM) have recently been used as intravenous (i.v.) carriers for drugs, which are sufficiently soluble in oil. However, in the case of norcantharidin (NCTD), which is poorly soluble in both the water and oil phases, this approach is not feasible. In this study, NCTD-loaded LM was prepared by transferring the drug to the interfacial surface of the oil and aqueous phases to produce a less irritating i.v. formulation of NCTD. A probe type sonicator was used to disperse NCTD into the oil phase together with lecithin and Tween 80. A high-pressure homogenization process was used to prepare the lipid microspheres and localize the drug at the surfactant layer. The LM loaded with NCTD consisted of 0.02% drug. Characterization of LMs and short-term stability was performed by photon correlation spectroscopy (PCS) and a centrifugation test was also carried out. The results showed that NCTD-loaded LM (2 mg/ml) with over 80% NCTD loaded in the interfacial surface were stable for a period of 2 months, and were suitable for i.v. injection in terms of size and stability, whether be diluted or not. Such formulations produced less pain and irritation in animal studies.

Microemulsion formulation of clonixic acid: solubility enhancement and pain reduction

Clonixic acid is currently marketed as a salt form because of its poor water-solubility. However, the commercial dosage form causes severe pain after intramuscular or intravenous injection. To improve the solubility of clonixic acid and to reduce pain on injection, clonixic acid was incorporated into oil-in-water microemulsions prepared from pre-microemulsion concentrate composed of varying ratios of oil and surfactant mixture. As an oil phase for drug incorporation, up to 14% castor oil could be included in the pre-microemulsion concentrate without a significant increase in droplet size. Both drug contents and droplet size increased as the weight ratio of Tween 20 to Tween 85 decreased. Taken together, when microemulsions were prepared from pre-microemulsion concentrate composed of 5:12:18 weight ratio of castor oil:Tween 20:Tween 85, clonixic acid could be incorporated at 3.2 mg mL(-1) in the microemulsion with a droplet size of less than 120 nm. The osmotic pressure of this microemulsion was remarkably lower than the commercial formulation, irrespective of the dilution ratios. The rat paw-lick test was used to compare pain responses among formulations. The microemulsion formulation significantly reduced the number of rats licking their paws as well as the total licking time, suggesting less pain induction by the microemulsion formulation. The pharmacokinetic parameters of clonixic acid after intravenous administration of the clonixic acid microemulsion to rats were not significantly different from those of the commercial formulation, lysine clonixinate. The present study suggests that microemulsion is an alternative formulation for clonixic acid with improved characteristics.

Patient tolerance study of topical chlorhexidine diphosphanilate: a new topical agent for burns

Effective topical antimicrobial agents decrease infection and mortality in burn patients. Chlorhexidine phosphanilate (CHP), a new broad-spectrum antimicrobial agent, has been evaluated as a topical burn wound dressing in cream form, but preliminary clinical trials reported that it was painful upon application. This study compared various concentrations of CHP to determine if a tolerable concentration could be identified with retention of antimicrobial efficacy. Twenty-nine burn patients, each with two similar burns which could be separately treated, were given pairs of treatments at successive 12-h intervals over a 3-day period. One burn site was treated with each of four different CHP concentrations, from 0.25 per cent to 2 per cent, their vehicle, and 1 per cent silver sulphadiazine (AgSD) cream, an antimicrobial agent frequently used for topical treatment of burn wounds. The other site was always treated with AgSD cream. There was a direct relationship between CHP concentration and patients' ratings of pain on an analogue scale. The 0.25 per cent CHP cream was closest to AgSD in pain tolerance; however, none of the treatments differed statistically from AgSD or from each other. In addition, ease of application of CHP creams was less satisfactory than that of AgSD. It was concluded that formulations at or below 0.5 per cent CHP may prove acceptable for wound care, but the vehicle system needs pharmaceutical improvement to render it more tolerable and easier to use.