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A range of fluorescent polystyrene microparticles (0.15, 0.5, 1.0, 3.0 and 10.0 μm) were administered intraduodenally to Wistar rats to provide an assessment of the levels of absorption of microparticles. Coupling a surgical procedure for the cannulation of the superior mesenteric lymph duct and the removal of Peyer's patches and mesenteric lymph nodes, with a sensitive flow cytometric assay it was possible to quantify microparticle absorption across the intestine. Absorption occurred after 5 min and was temporally variable, for all sizes of microparticles, over the time period studied. The 0.5-μm microparticles were found to be absorbed in significantly greater numbers to the Peyer's patches (P < 0.01) and the mesenteric lymph (P < 0.05) than other sizes and the 3.0-μm microparticles were found to be retained in the mesenteric lymph nodes in greater numbers than particles of other sizes. The 10.0-μn microparticles were retained in the mesenteric lymph nodes in low numbers. The levels of absorption, retention and extravasation of some sizes of microparticles suggests that the delivery of microencapsulated vaccines may allow the controlled delivery of antigens to the gut-associated lymphoid tissue (GALT) and their subsequent systemic dissemination.

The absorption of polystyrene microparticles across the intestine of rats was examined as a preliminary assessment of the efficacy of particles as vaccine delivery systems. The superior mesenteric lymph ducts of groups (n = 5) of Wistar rats were cannulated and the lymph analysed by flow cytometry. This allowed direct quantification of the numbers of particles absorbed. The 0.15 and 1.0 μm particles were absorbed rapidly (after 5 min) in a temporally complex manner, with maximal absorption occurring 65 min after delivery, for both sizes of particles. Microparticles were absorbed in approximately equal numbers over 90 min (5.0 × 104 0.15 μm and 4.9 × 104 1.0 μm particles, respectively). The levels of particle absorption in the current study indicate that microparticulate delivery of vaccines may be a realistic possibility.

The intranasal absorption enhancing and histological effects of a range of lysophospholipids has been investigated in the rat. Blood glucose levels fell rapidly following the administration of insulin (8 IU/kg) in combination with lysophosphatidylcholines (LPC; 0.625% w/v) which had ten or more carbon groups in their fatty acid chain. The effect of the LPC-caproyl (C6) was comparable to that of an unenhanced insulin formulation; the enhancing effect of LPC-decanoyl (C10) was similar to that of an LPC-palmitoyl/stearoyl (C16/C18) for similar concentrations. The effect of LPC-decanoyl was reduced with concentration but was still significant at 0.2% w/v (5mM). Lysophosphatidylglycerol (LPG) had a marked insulin absorption enhancing effect even at 0.0625% w/v. The histological effects of LPC-caproyl were similar to those of an unenhanced insulin formulation, while co-administration of LPC-decanoyl resulted in evidence of epithelial interaction. LPG (0.5% w/v) resulted in similar histological changes as LPC (0.625% w/v) (1), but at 0.0625% w/v no significant changes in epithelial integrity were observed. The length of the fatty acid residue of lysophospholipids was identified as an important factor for intranasal absorption enhancing activity. The nature of the polar head group may also have an influence. Increased insulin absorption was not necessarily accompanied by severe disruption of the nasal epithelium. Careful selection of lysophospholipid type and concentration may enable therapeutic drug levels to be achieved via the nasal route without prohibitive toxic effects.

The absorption of insulin across the vaginal mucosa into the systemic circulation was studied in ovariectomized rats given subsequent estrogen treatment. Blood glucose levels were determined as an indirect measure of insulin absorption, and the effect of various enhancers on the hypoglycemic response was investigated. In the absence of any enhancer, no decrease in blood glucose levels was observed after vaginal administration of insulin. However, the coadministration of sodium taurodihydrofusidate, polyoxyethylene-9-lauryl ether, lysophosphatidylcholine, palmitoylcarnitine chloride, and lysophosphatidylglycerol significantly increased hypoglycemia, whereas citric acid had little effect. The histological changes in the vaginal epithelium after treatment with the enhancer systems were variable and often severe. While the efficacy of these compounds in promoting the vaginal absorption of insulin is encouraging, their mechanisms of action and long-term histological effects are yet to be defined.

The recovery of the rat vaginal epithelium from the histological effects of absorption enhancers was assessed 24 h after treatment with laureth-9 and lysophosphatidylglycerol (LPG) solutions. In a control group of rats, the vaginal epithelium had a regular appearance and showed no sign of damage 24 h after administration of buffer solution. The vaginas treated with 0.5% LPG solution were similar to those of the control group although small sites showing reduced epithelial height were occasionally found. In contrast, 24 h after treatment with 1% laureth-9 solution, severe and widespread epithelial cell loss was evident with few signs of cellular regeneration and recovery. As previous studies have demonstrated absorption enhancing activity of both compounds, these results show that absorption enhancement is not necessarily linked with mucosal damage.

A method is described which enables the controlled assessment of the effects of intranasal drug formulations on rat nasal epithelium. Damage to the nasal mucosa caused by the surfactant laureth-9 (1% w/v) was used as an indicator of the distribution of dose volumes (100, 50 and 20 μl) administered to one side of the nasal cavity. Only the 20 μl volume was retained exclusively in the dosed side. Using this dose volume therefore, the epithelium on the undosed side could be used as control tissue and a direct comparison made between experimental and control tissue in the same section. Errors due to inter-animal variablity and tissue sampling are thus minimised, and the total number of animals required for future studies reduced.

Mortality and morbidity data continue to indicate there is a compelling need for the derivation of a new generation of vaccine delivery systems that can be usefully applied via injection and also mucosally. One technology that has potential for design as an effective vaccine delivery system is the formulation of biodegradable microparticles from the polymers and poly lactide co-glycolide (PLGA) in particular. The potential advantages of the delivery of vaccines within such microparticles is discussed. The potential for eliciting and optimising immunity after the mucosal delivery of biodegradable microparticles is also discussed.

Quantitative histology was used to assess the interaction of suppositories of hard fats (Suppocire AP and OS1X; Witepsol H12 and H19) and polyethylene glycol (PEG 1500) with the rectal mucosa of rats. All bases significantly increased epithelial cell loss but only following PEG treatment was the natural capacity of the epithelium to resist disruption exceeded, thereby resulting in areas of complete desquamation with a bare basal lamina. On the basis of these data it was possible to rank the interaction of the suppositories with the rectal lining; Suppocire OS1X < Suppocire AP = Witepsol H12 < H19 < PEG 1500.

The closed gut segment technique was used to investigate the effects of various concentrations of polyoxyethylene (40) stearate (Myrj 52) and Polyethylene glycol 2000 (PEG 2000) solutions on the histology of the intestinal mucosa and on fluid movements across the intestinal barrier. The results show that the higher concentrations of Myrj 52 and PEG 2000 induced cell loss and epithelial damage, and in addition solutions of PEG 2000 caused an unequal loss of enterocytes and goblet cells. Cell loss is likely to be a transient phenomena, with normal cell proliferation in the intestinal crypt being responsible for the restoration of villus architecture. Solutions of Myrj 52 caused little movement of fluid across the intestinal barrier but PEG 2000 at similar concentrations induced a considerable fluid loss from the mucosa to the lumen. The mechanism of this effect appears to be related to the anomalous osmotic behaviour of the PEG 2000 solutions, which dramatically changes the normal osmotic gradient across the intestinal barrier.

Propranolol solution administered vaginally to ovariectomised rats was absorbed rapidly with peak plasma levels attained 2 min after administration. In addition, the acute effects of propranolol and buffer solutions on the morphology of the vaginal epithelium were quantitated. The thickness of the vaginal epithelium was reduced by each treatment and propranolol solution caused significantly more damage than buffer alone.

The dissolution of fenbufen and ethanolamine fenbufen from Polyethylene glycol 1500, Witepsol H12 and Suppocire AP suppository bases was determined. The more soluble ethanolamine salt produced significantly faster dissolution than the parent drug, with the Witepsol H12 base giving the most rapid release. In vivo studies showed that the incorporation of ethanolamine fenbufen into Witepsol H12 increases the morphological change in the rectal tissue l h after insertion but there was no difference with the control tissue after 24 h. The data highlights the importance of parallel in vitro and in vivo studies in the development of rectal formulations.

The volume of rectal epithelial mucus was quantified histologically following a single suppository treatment. It was: unchanged by suppositories of Witepsol H12; reduced significantly by suppositories of PEG 1540 1, 6 and 24 h post-treatment but increased after 48 h.

The application of an in situ loop technique to the determination of rectal water flux and drug absorption in the rat is described. The procedure requires minimal surgical skill and allows rapid sampling of luminal fluid. The method was assessed by studies on: (a) the effect of sodium salicylate solutions (1% and 5% w/v) and equiosmotic solutions of mannitol (2.5% and 11.8% w/v) on rectal water flux and tissue morphology; and (b) the rectal uptake of [3H]prednisolone from aqueous solution. The 1% sodium salicylate and 2.5% mannitol solutions induced water movement into the lumen but caused no apparent change in the tissue morphology. The more hypertonic 5% salicylate solution and the equiosmotic mannitol solution induced water flux into the lumen and resulted in extensive cell loss. The uptake of [3H]prednisolone from the loop was confirmed by a simultaneous increase in plasma tritium levels.

The vaginal absorption of gentamicin in ovariectomized rats was markedly increased by the coadministration of absorption enhancers. By comparison of the AUCs of the serum concentrations of gentamicin with time profiles, the enhancers investigated could be ranked in terms of efficacy; 1% palmitoylcarnitine 0.5% lysophosphatidylcholine 1% laureth-9 10% citric acid. The acute effects of solutions of gentamicin and enhancers on the morphology of the vaginal epithelium were quantitated. All enhancers significantly reduced epithelial thickness with laureth-9 and lysophosphatidylcholine causing complete desquamation of approximately 50% of the areas assessed. On the basis of these data, it was possible to rank the severity of the interaction of the drug and enhancer solutions with the vaginal lining; 0.5% lysophosphatidylcholine = 1% laureth-9 1% palmitoylcarnitin 10% citric acid.

The distribution of small labeled latex test particles has been studied after intravenous administration to the rabbit using the noninvasive technique of gamma scintigraphy. The reticuloendothelial system was suppressed using polystyrene latex particles and dextran sulfate as blocking agents. Both materials gave rise to significant uptake of particles in the lungs of the order of 60% of the administered dose. The effect seen with suppression with latex particles remained unaltered over an 8-d period, while for suppression with dextran sulfate the effect was transient, and particles that were initially deposited in the lungs were subsequently redistributed to the liver. The results are discussed in terms of previous studies on reticuloendothelial suppression using different agents, test colloids, and animal models.

The blood clearance and organ deposition of polystyrene and cellulose (DEAE) particles have been studied in the rabbit using labelled material and the technique of gamma scintigraphy in order to investigate the importance of particle size, shape and nature. Small (1.27 μm diameter) polystyrene microspheres were taken up by the reticuloendothelial system of the liver, while large polystyrene particles (15.8 μm diameter) were mechanically filtered by capillary beds of the lungs. Cellulose microspheres and fibres were also taken up into lung tissue. Large cellulose fibres, 30 μm diameter, proved to be toxic whereas large cellulose microspheres were well tolerated. The implications for drug targeting are discussed.

A model of ulcerated bowel was produced in the rat rectum by treatment with Brij 35 suppositories. Prednisolone absorption from enemas in normal and damaged bowel was assessed using an in situ rectal loop. In animals 20 h after damage drug absorption was reduced but returned to normal levels after one week. Co-administration of equiosmolar sodium salicylate (1 and 2% w/v) and mannitol (2.5 and 4.1% w/v) solutions in normal bowel induced a significant water flux into the lumen and changed the plasma tritium profile compared to the control. In damaged bowel plasma tritium levels remained low following co-administration of mannitol (2.5% w/v) but were restored to normal control levels by co-administration of salicylate (1% w/v). The altered absorption in normal bowel can be attributed in part to osmotic stress but in damaged bowel the difference between the effect of equiosmotic solutions of salicylate and mannitol suggests that a different mechanism is operating.