Enhancement of the intestinal absorption of low molecular weight heparin (LMWH) in rats and pigs using Carbopol 934P

Development, in vitro and in vivo evaluation of a self-emulsifying drug delivery system (SEDDS) for oral enoxaparin administration

AIM

The aim of this study was to develop SEDDS for oral enoxaparin administration and evaluate it in vitro and in vivo.

METHODS

The emulsifying properties of SEDDS composed of long chain lipids (LC-SEDDS), medium chain lipids (MC-SEDDS), short chain lipids (SC-SEDDS) and no lipids (NL-SEDDS) were evaluated. Thereafter, enoxaparin was incorporated via hydrophobic ion pairing in the chosen SEDDS, which were evaluated regarding their mucus permeating properties, stability towards pancreatic lipase, drug release profile and cytotoxicity. Finally, in vivo performance of SEDDS was evaluated.

RESULTS

The average droplet size of chosen LC-SEDDS, MC-SEDDS and NL-SEDDS ranged between 30 and 40nm. MC-SEEDS containing 30% Captex 8000, 30% Capmul MCM, 30% Cremophor EL and 10% propylene glycol and NL-SEDDS containing 31.5% Labrafil 1944, 22.5% Capmul PG-8, 9% propylene glycol, 27% Cremophor EL and 10% DMSO exhibited 2-fold higher mucus diffusion than LC-SEDDS and were therefore chosen for further studies. The enoxaparin-dodecylamine complex (ENOX/DOA) was incorporated in a payload of 2% (w/w) into MC-SEDDS and NL-SEDDS. After 90min 97% of MC-SEDDS and 5% of NL-SEDDS were degraded by pancreatic lipase. Both MC-SEDDS and NL-SEDDS showed sustained in vitro enoxaparin release. Furthermore, orally administrated MC-SEDDS and NL-SEDDS yielded an absolute enoxaparin bioavailability of 2.02% and 2.25%, respectively.

CONCLUSION

According to the abovementioned findings, SEDDS could be considered as a potential oral LMWH delivery system.

Strategies to Overcome Heparins' Low Oral Bioavailability

Even after a century, heparin is still the most effective anticoagulant available with few side effects. The poor oral absorption of heparins triggered the search for strategies to achieve oral bioavailability since this route has evident advantages over parenteral administration. Several approaches emerged, such as conjugation of heparins with bile acids and lipids, formulation with penetration enhancers, and encapsulation of heparins in micro and nanoparticles. Some of these strategies appear to have potential as good delivery systems to overcome heparin’s low oral bioavailability. Nevertheless, none have reached the market yet. Overall, this review aims to provide insights regarding the oral bioavailability of heparin.

Trends in the development of oral anticoagulants

Anticoagulation remains the therapy of choice for the prevention and treatment of venous and arterial thromboembolic disorders which can cause major organ damage or death. Heparins represent the antithrombotic drugs of choice in short and medium-term prophylaxis and therapy of thromboembolic diseases. Fondaparinux, a synthetic and structural analog of the antithrombin-binding pentasaccharide domain of heparin, has selective anti-Xa activity and longer half-life. However, anticoagulants are poorly absorbed by oral route because of their high molecular weight, hydrophilicity and negative charges. Long-term anticoagulation therapy is problematic because of side effects and frequent monitoring. Formulation approaches are particularly promising.

Heparin-derived supersulfated disaccharide inhibits allergic airway responses in sheep

The tetrasaccharide sequence of heparin oligosaccharides is the minimum chain length possessing anti-allergic activity, as the disaccharide fraction is inactive. Since sulfation pattern can modify the biological actions of heparin, we hypothesized that "supersulfation" of the inactive heparin disaccharide could confer anti-allergic activity to this molecule. To test this, we produced a supersulfated heparin disaccharide (Hep-SSD) and evaluated its anti-allergic activity in sheep with documented antigen-induced early and late airway responses (EAR and LAR) and airway hyperresponsiveness (AHR). Porcine intestinal heparin was depolymerized with nitrous acid, the disaccharide fraction separated by size exclusion chromatography, and then treated with pyridine-sulfur trioxide complex to yield Hep-SSD. Its chemical structure [IdoU2',3',4'S (1→4) AMan1,3,6S] was confirmed by HPLC, Mass Spectrometry and NMR analysis. Inhaled doses of 5 mg, 10 mg and 20 mg Hep-SSD produced inhibition of EAR (8%, 35% and 35%), LAR (50%, 80%, and 77%) and AHR (67%, 100% and 75%), respectively. A single oral dose of 2 mg/kg Hep-SSD given 90 min before challenge significantly inhibited EAR, LAR and AHR, but 1 mg/kg was ineffective. Multi dose oral treatment with Hep-SSD had a cumulative effect, as a once daily dose of 2 mg/kg for 3 days (last dose, 16 h before antigen) inhibited EAR, LAR and AHR by 30%, 75% and 74%, respectively. Finally, the oral activity of Hep-SSD could be enhanced 4 fold by formulating it with Carbopol(®)934P, in an enteric coated capsule. These data demonstrate that "supersulfation" can confer biological activity to the inactive heparin disaccharide. Both inhaled and oral Hep-SSD demonstrate significant anti-allergic activity and, therefore, may have therapeutic potential.

Oral drug delivery systems using chemical conjugates or physical complexes

Oral delivery of therapeutics is extremely challenging. The digestive system is designed in a way that naturally allows the degradation of proteins or peptides into small molecules prior to absorption. For systemic absorption, the intact drug molecules must traverse the impending harsh gastrointestinal environment. Technologies, such as enteric coating, with oral dosage formulation strategies have successfully provided the protection of non-peptide based therapeutics against the harsh, acidic condition of the stomach. However, these technologies showed limited success on the protection of therapeutic proteins and peptides. Importantly, inherent permeability coefficient of the therapeutics is still a major problem that has remained unresolved for decades. Addressing this issue in the context, we summarize the strategies that are developed in enhancing the intestinal permeability of a drug molecule either by modifying the intestinal epithelium or by modifying the drug itself. These modifications have been pursued by using a group of molecules that can be conjugated to the drug molecule to alter the cell permeability of the drug or mixed with the drug molecule to alter the epithelial barrier function, in order to achieve the effective drug permeation. This article will address the current trends and future perspectives of the oral delivery strategies.

Sustained-release self-dissolving micropiles for percutaneous absorption of insulin in mice

Microparticles-adsorbed insulin and zinc insulin (PenfilN) were molded to self-dissolving micropiles (SDMPs) with chondroitin sulfate as the base for the percutaneous administration of insulin. Porous silicon dioxide (Sylysia 320, 440 and 730) and porous calcium silicate (FloriteRE) were used as microparticles. As a reference, insulin loaded SDMPs were prepared. SDMPs were percutaneously administered to mice at the insulin dose level of 2.5 IU/kg. After the insertion of SDMPs to mouse skin, blood samples were collected for 8 h and plasma glucose levels were measured. There were not significant differences on minimum plasma glucose levels between the test preparations. However, T(mins), the time when the minimum glucose level appeared were 1.5 +/- 0.2 h (Sylysia 320), 1.3 +/- 0.2 h (Sylysia 440), 1.6 +/- 0.4 h (Sylysia 730), 2.1 +/- 0.3 h (Florite) and 1.7 +/- 0.3 h (zinc insulin) which were greater than insulin SDMP, 0.8 +/- 0.1 h. In addition, greater hypoglycemic effects were observed with SDMPs containing adsorbent-insulin and/or zinc insulin than insulin SDMP. The mean AACs (area above the plasma glucose level vs. time curve) of SDMPs containing adsorbent-insulin and zinc insulin were 357.8% h for FloriteRE, 333.1% h for Sylysia 320, 308.1% h for Sylysia 440, 328.1% h for Sylysia 730, and 374.7% h for zinc insulin, respectively, which were about two folds higher than that of insulin SDMN, 161.2% h. Those results suggest the usefulness of SDMPs composed of adsorbent-insulin as a long-acting percutaneous insulin preparation.

N-sulfonato-N,O-carboxymethylchitosan: A novel polymeric absorption enhancer for the oral delivery of macromolecules

Chitosan has been shown to act on the mucosal epithelial barriers mainly when protonated at acidic pH values in which it is soluble. Soluble chitosan is able to improve the permeation and absorption of neutral to cationic macromolecules only, as it forms polyelectrolyte complexes with anionic macromolecules. LMWH (Low Molecular Weight Heparin) is an anionic polysaccharide finding clinical application as an improved antithrombotic agent compared to Unfractionated Heparin (UFH). In this study we have employed N-sulfonato-N,O-carboxymethylchitosan (SNOCC) as a potential intestinal absorption enhancer of LMWH, Reviparin. SNOCC was prepared at 3 different viscosity grades 20, 40 and 60 cps and identified as SNOCC-20, SNOCC-40 and SNOCC-60, respectively. SNOCC materials were tested in vitro for their ability to decrease the Trans Epithelial Electrical Resistance (TEER) of Caco-2 cell monolayers. They were further tested as transport enhancers of hydrophilic compounds such as (14)C-mannitol, FITC-Dextran (MW 4400 Da) and Reviparin (LMWH). Solutions of Reviparin, with or without SNOCC, were administered intraduodenally in vivo in rats and the absorption of the drug was assessed by measuring the Anti-Xa levels in rat plasma. In vitro studies showed that SNOCC materials were able to induce a concentration dependent decrease in the TEER of the Caco-2 monolayers. SNOCC-40 and -60 were shown to decrease resistance more readily compared to the low viscosity SNOCC-20. (14)C-mannitol permeation data across intestinal epithelia were in agreement with the observed decrease in TEER; the higher viscosity SNOCC-60 was the most effective demonstrating a 51-fold enhancement of the permeation of the radiolabeled marker. Studies with both FITC-Dextran and Reviparin demonstrated significantly increased permeation across Caco-2 cell monolayers when they were co-incubated at the apical side of the monolayer. Intestinal absorption of Reviparin in rats was increased when it was co-administered with SNOCC-40 and -60, in agreement with in vitro data. Anti-Xa levels were elevated to and above the antithrombotic levels and were sustained for at least 6 h, giving an 18.5-fold increase in the AUC of LMWH in rats. In conclusion, SNOCC-40 and -60 have been shown to enhance both permeation and absorption of Reviparin across intestinal epithelia proving their potential as polymeric absorption enhancers.

Modulation of gastrointestinal permeability of low-molecular-weight heparin by L-arginine: in-vivo and in-vitro evaluation

L-Arginine is the principal physiological precursor of nitric oxide (NO, a key neurotransmitter) that plays a versatile role in the physiology of the gastrointestinal tract. In this study, the efficacy of L-arginine in enhancing intestinal absorption of ardeparin, a low-molecular-weight heparin (LMWH) was investigated in Caco-2 cell monolayers and a rat model. Regional permeability studies using rat intestine were performed using a modified Ussing chamber. Cell viability in the presence of various concentrations of enhancer was determined by MTT assay. Furthermore, the eventual mucosal epithelial damage was histologically evaluated. LMWH formulated with L-arginine was administered orally to male Sprague-Dawley rats and the absorption of LMWH was determined by measuring plasma anti-factor Xa activity. Higher ardeparin in-vitro permeability (approximately 3 fold) compared with control was observed in the presence of 2% L-arginine. Regional permeability studies indicated predominant absorption in the colon region. Cell viability studies showed no significant cytotoxicity below 0.8% L-arginine. The oral bioavailability of ardeparin formulated with L-arginine (250 mg kg(-1)) was increased by approximately 2 fold compared with control. The formulation was well tolerated by the rats and no abnormal histopathological findings were observed in intestinal tissues of rats exposed to L-arginine. These results suggest that L-arginine may be useful in enhancing the intestinal absorption of LMWHs.

Zonula occludens toxin synthetic peptide derivative AT1002 enhances in vitro and in vivo intestinal absorption of low molecular weight heparin

Zonula occludens toxin (Zot) is an enterotoxin obtained from the bacterium vibrio cholerae that has been shown to reversibly and safely open the tight junctions and enhance paracellular transport. AT1002 is a novel synthetic hexapeptide derived from Zot. The hypothesis to be tested in this study is that AT1002 enhances the oral absorption of ardeparin, a low molecular weight heparin (LMWH). To test this hypothesis, drug transport through Caco-2 cell monolayers was monitored in the presence and absence of AT1002. Regional permeability studies using rat intestine were performed. Cell viability in the presence of various concentrations of enhancer was determined. The absorption of ardeparin after oral administration in rats was measured by anti-factor Xa assay. Furthermore, the eventual mucosal and epithelial damage was histologically evaluated. Higher ardeparin permeability (approximately 2-fold) compared to control was observed in the presence of 0.025% of AT1002. Regional permeability studies revealed that the permeability of ardeparin across the duodenal membrane was improved by the AT1002. Cell viability studies showed no significant cytotoxicity below 0.0028% of AT1002. In the presence of 100 microg/kg of AT1002, ardeparin oral bioavailability was significantly increased (F(relative/s.c) approximately 20.5%). Furthermore, AT1002 at a dose of 100 microg/kg did not induce any observable morphological damage on gastrointestinal (GI) tissues in vivo. These in vivo and in vitro results suggest that the co-administration of LMWH with AT1002 may be a useful delivery strategy to increase its permeability and hence oral absorption.

Preparation and evaluation of oral solid heparin using emulsifier and adsorbent for in vitro and in vivo studies

Oral anticoagulant therapy with heparin has been challenged by formulating heparin in oral solid preparation. As heparin, low molecular weight heparin (LMWH) was used. LMWH was dispersed with a surfactant used for the self-microemulsifying drug delivery system (SMEDDS), PEG-8 caprylic/capric glycerides (Labrasol), and the mixture was solidified with three kinds of adsorbents, microporous calcium silicate (Florite RE), magnesium alminometa silicate (Neusilin US(2)) and silicon dioxide (Sylysia 320). The in vitro release study showed that the T50%s were 3.2+/-0.1min for Sylysia 320, 4.6+/-0.2min for Florite RE, 13.7+/-0.1min for Neusilin US(2). The in vivo rat absorption study showed that Florite RE system had the highest C(max), 0.42+/-0.01IU/mL and AUC, 0.59+/-0.06IUh/mL, where plasma LMWH levels were measured as anti-Xa activity. Other preparations had the C(max) and AUC, 0.12+/-0.01IU/mL and 0.15+/-0.02IUh/mL for Neusilin US(2) and 0.25+/-0.02IU/mL and 0.40+/-0.03IUh/mL for Sylysia 320, respectively. The bioavailability (BA) of LMWH from the microporous calcium silicate preparation, Florite RE, was 18.8% in rats by comparing the AUC obtained after i.v. injection of LMWH, 40IU/kg to another group of rats. Florite RE system was evaluated in dogs after oral administration in an enteric capsule made of Eudragit S100 at the LMWH dose of 200IU/kg. High plasma anti-Xa activity levels were obtained, i.e., the C(max) was 0.48+/-0.11IU/mL and AUC was 1.64+/-0.32IUh/mL. These results suggest that adsorbent system is useful as an oral solid delivery system of poorly absorbable drugs such as LMWH.

The quest for non-invasive delivery of bioactive macromolecules: a focus on heparins

The development of a non-invasive drug delivery system for unfractionated heparin (UFH) and low molecular weight heparins (LMWHs) has been the elusive goal of several research groups since the initial discovery of this glycosaminogylcan by McLean in 1916. After a brief update on current parenteral formulations of UFH and LMWHs, this review revisits past and current strategies intended to identify alternative routes of administration (e.g. oral, sublingual, rectal, nasal, pulmonary and transdermal). The following strategies have been used to improve the bioavailability of this bioactive macromolecule by various routes: (i) enhancement in cell-membrane permeabilization, (ii) modification of the tight-junctions, (iii) increase in lipophilicity and (iv) protection against acidic pH of the stomach. Regardless of the route of administration, a simplified unifying principle for successful non-invasive macromolecular drug delivery may be: "to reversibly overcome the biological, biophysical and biochemical barriers and to safely and efficiently improve the in vivo spatial and temporal control of the drug in order to achieve a clinically acceptable therapeutic advantage". Future macromolecular drug delivery research should embrace a more systemic approach taking into account recent advances in genomics/proteomics and nanotechnology.

Evaluation of the Oral Bioavailability of Low Molecular Weight Heparin Formulated With Glycyrrhetinic Acid as Permeation Enhancer

Low molecular weight heparin (LMWH) is the agent of choice for anticoagulant therapy and prophylaxis of thrombosis and coronary syndromes. However, its therapeutic use is limited due to poor oral bioavailability. The aim of this study was to investigate the oral delivery of LMWH, ardeparin formulated with 18-beta glycyrrhetinic acid (GA), as an alternative to currently used subcutaneous (sc) delivery. Drug transport through Caco-2 cell monolayers was monitored in the presence and absence of GA by scintillation counting and transepithelial electrical resistance. Regional permeability studies using rat intestine were performed using a modified Ussing chamber. Cell viability in the presence of various concentrations of enhancer was determined by MTT assay. The absorption of ardeparin after oral administration in rats was measured by an anti-factor Xa assay. Furthermore, the eventual mucosal epithelial damage was histologically evaluated. Higher ardeparin permeability (~7-fold) compared to control was observed in the presence of 0.02 % GA. Regional permeability studies indicated predominant absorption in the duodenal segment. Cell viability studies showed no significant cytotoxicity below 0.01 % GA. Ardeparin oral bioavailability was significantly increased (F(relative)/(S.C). = 13.3%) without causing any damage to the intestinal tissues. GA enhanced the oral absorption of ardeparin both in vitro and in vivo. The oral formulation of ardeparin with GA could be absorbed in the intestine. These results suggest that GA may be used as an absorption enhancer for the oral delivery of LMWH.

Tetradecylmaltoside (TDM) enhances in vitro and in vivo intestinal absorption of enoxaparin, a low molecular weight heparin

Tetradecylmaltoside (TDM) was evaluated as a potential gastrointestinal absorption enhancer for low molecular weight heparin (LMWH), enoxaparin. The in vitro efficacy of TDM (0.0625, 0.125 and 0.25% w/v) in enhancing transport of 3H-enoxaparin or 14C-mannitol was investigated in human colonic epithelial cells (C2BBel). Metabolic stability of the drug was determined in C2BBel cell extracts. Transepithelial electrical resistance (TEER) was measured before and after exposure of the cells to TDM. Enoxaparin was further administered to anesthetized Sprague-Dawley rats in oral formulations in the absence or presence of increasing concentrations of TDM and drug absorption was monitored by measuring anti-factor Xa activity in rat blood. In vitro permeability study shows that apparent permeability (Papp) of 3H-enoxaparin across C2BBe1 cells was increased by 8-fold in the presence of 0.0625% TDM compared to untreated cells. The movement of 14C-mannitol across the cell monolayer followed a similar pattern in the presence of increasing concentrations of TDM. No degradation or depolymerization of enoxaparin was observed when the drug was incubated in C2BBel cell extract. TEER was reversible after 60 min exposure of the cells to 0.0625% (w/v) TDM. Oral formulations of enoxaparin containing TDM administered to anesthetized rats significantly and rapidly increased gastrointestinal absorption as compared to those animals which received enoxaparin plus saline (p < 0.05). In the presence of 0.125% TDM in the formulation, enoxaparin oral bioavailability was increased by 2.5-fold compared to the saline control group. Overall, the data on the effect of TDM on the in vitro and in vivo intestinal permeation of enoxaparin suggest that TDM may represent a promising excipient for use in oral LMWH formulations.

Tricaprylin microemulsion for oral delivery of low molecular weight heparin conjugates

Heparin is available to patients only by parenteral administrations due to its low oral bioavailability. For the oral delivery of low molecular weight heparin (LMWH), LMWH-DOCA was synthesized by chemical conjugation of LMWH and deoxycholic acid (DOCA) and this conjugate was formulated in a microemulsion system. The coupling ratios of DOCA to LMWH for LD1 and LD2 were 1.33 and 2.37, respectively. The microemulsion was composed of tricaprylin, surfactant mixture (Tween 80 and Span 20) and LMWH-DOCA in water, and their volume ratio was 5:3:1:1. Pharmacokinetic parameters of LMWH were not significantly changed by conjugation with DOCA; however, when LMWH-DOCA in tricaprylin microemulsion was orally administered in mice, its bioavailability was increased up to 1.5%. Furthermore, the enhancing effect of the conjugated DOCA in the tricaprylin microemulsion on the absorption of LMWH in the intestine was more significantly increased in monkey than in mice. Since the tricaprylin microemulsion could dissolve LMWH-DOCA, this formulation could maximize the enhancing effect of the conjugated DOCA on the absorption of LMWH in the intestine. Finally, it was expected that 20 mg/kg of LMWH-DOCA in the tricaprylin microemulsion was enough to prevent deep vein thrombosis (DVT) and pulmonary embolism (PE).

Enhanced ileal absorption of a hydrophilic macromolecule, pentosan polysulfate sodium (PPS)

An in situ gelling, bioadhesive liquid formulation was developed to enhance the bioavailbility (BA) of a polysaccharide, pentosan polysulfate sodium (PPS). The formulation was tested to determine its bioavailability enhancement in a non-flush/non-ligated rat ileal model. A potent synergistic effect was found with a gelling agent Cremophor and a permeation enhancer sodium salicylate. The absolute bioavailabilities were 1.9%, 4.6%, 6.3% and 46.4%, respectively, for the PPS solution in saline, sodium salicylate/PPS, Cremophor/PPS and Cremophor/sodium salicylate/PPS. Therefore, we successfully demonstrated the approach of utilizing an in situ gelling/bioadhesive liquid carrier to enhancing the bioavailability of a hydrophilic macromolecule at the distal small intestine.

In situ intestinal absorption studies on low molecular weight heparin in rats using Labrasol as absorption enhancer

Oral absorption of low molecular weight heparin (LMWH) is limited by its molecular size and negative charge. Development of its oral formulations would allow outpatient treatment with LMWH and decrease the hospital expenses. Studies were aimed at evaluating Labrasol for improving intestinal absorption of LMWH. Formulations containing LMWH and Labrasol were administered to duodenum, jejunum, and ileum of the fasted rats. The doses of LMWH and Labrasol were 200 IU/kg and 50 mg/kg, respectively. Reversibility of absorption enhancing effect of Labrasol was assessed by administering LMWH to jejunum after 0.5 and 1 h of administration of Labrasol. The effect of different doses of Labrasol on LMWH absorption was studied by administering Labrasol at 50, 100, and 200 mg/kg doses. Administration of LMWH formulation tojejunum resulted in the highest plasma anti-Xa activity (0.50+/-0.03 IU/ml) compared to duodenum (0.19+/-0.03 IU/ml), and ileum (0.29 +/-0.06 IU/ml) and the anti-Xa levels were maintained above the therapeutic level for about 160 min. The absorption of LMWH was negligible when LMWH was administered at 0.5 and 1 h post-Labrasol administration. Increasing the dose of Labrasol has decreased the absorption of LMWH from jejunum. Labrasol increased the intestinal absorption of LMWH, and jejunum was found to be the best site of absorption. Intestinal membrane permeability changes induced by Labrasol were transient and reversible. Maintaining high drug concentration gradient across intestinal wall is important to obtain increased intestinal LMWH absorption.

Studies on the Intestinal Absorption of Low Molecular Weight Heparin Using Saturated Fatty Acids and Their Derivatives as an Absorption Enhancer in Rats

Intestinal absorption of low molecular weight heparin (LMWH) as well as unfractionated heparin (UFH) is limited due to its large molecular size and extensive negative charge. Development of its oral formulations would allow outpatient treatment with LMWH and UFH, and contribute a reduction in hospital expenses. The present study was aimed at evaluating the absorption enhancers Labrasol and Gelucire 44/14, which mainly consist of glycerides and fatty acids esters, to improve the intestinal absorption of LMWH. The absorption effects of saturated fatty acids with several carbon chain lengths (C6-C14) were also investigated. LMWH formulated with or without absorption enhancer was administered to the duodenum of fasted rats. The doses of LMWH and absorption enhancer were 20 mg/kg and 30 mg/kg, respectively. Plasma anti-Xa activity was measured as a marker of the LMWH absorption. By administration of the LMWH formulation with Labrasol but not with Gelucire 44/14, the plasma anti-Xa activity was increased to a level above 0.2 IU/ml which is the critical level for elucidation of its anticoagulant activity. Saturated fatty acids also enhanced the intestinal absorption of LMWH, and the order of absorption-enhancing effect was C10=C12>C14>C16>C8> or =C6. These results suggest that the intestinal absorption of LMWH varies with carbon chain lengths of the saturated fatty acids.

Nasal administration of low molecular weight heparin

The main objective of this study was to determine if the systemic absorption of therapeutic amounts of heparin was possible following nasal administration. Sprague-Dawley rats received nosedrops containing a low molecular weight heparin (LMWH) or unfractionated heparin (UFH) formulated with or without tetradecylmaltoside (TDM). TDM is a nonionic surfactant that has been previously shown to be a potent absorption enhancer in studies with peptide drugs. LMWH/UFH absorption was determined by measuring plasma anti-Factor Xa activity. The inclusion of 0.25% TDM in nasal formulations containing LMWH resulted in a significant increase in the C(max) and area under the curve (AUC) of anti-Factor Xa activity when compared to LMWH formulated in saline alone. The addition of TDM to a nasal formulation containing UFH resulted in a much smaller increase in the C(max) and the AUC of anti-Factor Xa activity. The absolute bioavailability of LMWH was increased from 4.0 +/- 0.4% in the absence of TDM to 19 +/- 0.3% in the presence of TDM. The reversibility of the absorption enhancing effect of TDM was studied by applying LMWH nasally 60 or 120 min after the enhancer. The effect of TDM on the nasal epithelia appeared to be rapidly reversible. In conclusion, nasal delivery of LMWH, but not UFH, was successful when an absorption enhancer was included to increase nasal permeability.