Effects of pharmaceutical excipients on membrane permeability in rat small intestine

Geriatric Drug Delivery - Barriers, Current Technologies and the Road Ahead

The geriatric population encompasses the largest part of the health care system worldwide. Chronic medical conditions are highly prevalent in the elderly, consequently, due to their complex health needs, there is a significant rate of multi-drug therapy. Despite the high numbers of medications prescribed, geriatric patients face several barriers when it comes to successful drug delivery including alterations in cognitive and physical function. The current review highlights the impact of chronic diseases on the aging population along with how changes in drug pharmacokinetics could impact drug efficacy and safety. Also discussed are applications of administration routes in the geriatric population and complications that could arise. A focus is placed on the traditional and upcoming drug delivery advancements being employed in seniors with a focus addressing obstacles faced by this patient category. Nanomedicines, three-dimensional printing, long-acting formulations, transdermal systems, orally disintegrating tablets, and shape/taste modification technologies are discussed. Several barriers to drug delivery in the elderly have been identified in literature and directions for future studies should focus on addressing these gaps for geriatric drug formulation development including personalized medicine, insights into novel drug delivery systems like nanomedicines, methods for decreasing pill burden and shape/size modifications.

Intestinal Absorption Study: Challenges and Absorption Enhancement Strategies in Improving Oral Drug Delivery

The oral route is the most common and practical means of drug administration, particularly from a patient’s perspective. However, the pharmacokinetic profile of oral drugs depends on the rate of drug absorption through the intestinal wall before entering the systemic circulation. However, the enteric epithelium represents one of the major limiting steps for drug absorption, due to the presence of efflux transporters on the intestinal membrane, mucous layer, enzymatic degradation, and the existence of tight junctions along the intestinal linings. These challenges are more noticeable for hydrophilic drugs, high molecular weight drugs, and drugs that are substrates of the efflux transporters. Another challenge faced by oral drug delivery is the presence of first-pass hepatic metabolism that can result in reduced drug bioavailability. Over the years, a wide range of compounds have been investigated for their permeation-enhancing effect in order to circumvent these challenges. There is also a growing interest in developing nanocarrier-based formulation strategies to enhance the drug absorption. Therefore, this review aims to provide an overview of the challenges faced by oral drug delivery and selected strategies to enhance the oral drug absorption, including the application of absorption enhancers and nanocarrier-based formulations based on in vitro, in vivo, and in situ studies.

Oral supramolecular nanovectors for dual natural medicine codelivery to prevent gastric mucosal lesion

The oral administration of a single formulation loaded with more than one natural medicine to treat chronic diseases has advantages such as convenience, effectiveness, and economy. Here, using biomaterials approved by the drug administration, we fabricated supramolecular nanovectors containing dual natural medicines to prevent gastric mucosal lesions. Nanovectors exhibited superior intestinal absorption and bioavailability, which might be due to their high dispersion, good muco-adhesiveness, blood-lymph circulation transport, lipid sensing, and protective effects. Molecular docking results clarified the possible mechanisms in aspects of efflux pump (p-glycoprotein and multidrug resistance protein 1) inhibition effects, metabolic enzyme (cytochrome P450 3A4/1A2) blocking effects, serum albumin deposit effects, and dual drug interaction effects. Nanovectors decreased ethanol-induced gastric mucosal lesions by lowering the gastric ulcer index, preventing oxidative damage, decreasing interleukin-6, tumor necrosis factor-α and malondialdehyde, increasing glutathione, superoxide dismutase, and prostaglandin E2 levels. The interactions of inhibitor of nuclear factor-κB or κB kinase-related proteins and dual drugs or nanovector components were simulated computationally to provide an understanding of the gastro-protective action mechanism. In all, industrializable supramolecular nanovectors could effectively co-deliver dual natural medicines via the oral route by improving the pharmacokinetic behavior and exerting protective efficacy of the gastric mucosa by decreasing the oxidative stress and inflammatory level.

Lactose hydrate can increase the transcellular permeability of β-naphthol in rat jejunum and ileum

BACKGROUND

The unstirred water layer (UWL) is an integral part of the apical surface of mucosal epithelia and comprises mucins (MUC), for which there are many molecular species. Galectins, a family of β-galactoside-binding lectins, form a lattice barrier on surface epithelial cells by interacting with MUC. Lactose inhibits the galectin-MUC interaction. Therefore, the present study investigated the galectin-MUC interaction in the mucosa of the gastrointestinal tract and its role in intestinal barrier functions.

MATERIALS AND RESULTS

The effects of lactose hydrate (LH) on the membrane permeability of the rat small intestine and Caco-2 cells were examined. LH enhanced the membrane permeability of the rat small intestine, which contains the UWL, via a transcellular route, for which the UWL is the rate limiting factor. The membrane permeability of Caco-2 cells, in which the UWL is insufficient, was not affected by LH. The apparent permeability coefficient (P_app) of a paracellular marker was not significantly altered in the rat small intestine or Caco-2 cells treated with LH at any concentration. Furthermore, the P_app of β-naphthol which is a transcellular marker was not significantly altered in Caco-2 cells treated with LH, but was significantly increased in the rat small intestine in a LH concentration-dependent manner.

CONCLUSIONS

The present results demonstrate that the physical barrier has an important function in gastrointestinal membrane permeability, and LH-induced changes increase the transcellular permeability of β-naphthol in rat small intestine.

Assessing CYP2C8-Mediated Pharmaceutical Excipient-Drug Interaction Potential: A Case Study of Tween 80 and Cremophor EL-35

Pharmaceutical excipients (PEs) are substances included in drug formulations. Recent studies have revealed that some PEs can affect the activity of metabolic enzymes and drug transporters; however, the effects of PEs on CYP2C8 and its interaction potential with drugs remain unclear. In this study, we evaluated the effects of Tween 80 and EL−35 on CYP2C8 in vitro and further investigated their impacts on the PK of paclitaxel (PTX) in rats after single or multiple doses. The in vitro study indicated that Tween 80 and EL−35 inhibited CYP2C8 activity in human and rat liver microsomes. EL−35 also decreased the expression of CYP2C8 in HepG2 cells. In the in vivo study, Tween 80 did not alter the PK of PTX after single or multiple doses, whereas EL−35 administered for 14 days significantly increased the AUC and MRT of PTX. Further analysis indicated that multiple-dose EL−35 reduced the expression of Cyp2c22 and production of 6-OH-PTX in the rat liver. Our study suggested that short-term exposure to both PEs did not affect the PK of PTX in rats, but multiple doses of EL−35 increased the AUC and MRT of PTX by downregulating the hepatic expression of Cyp2c22. Such effects should be taken into consideration during drug formulation and administration.

Interaction of Commonly Used Oral Molecular Excipients with P-glycoprotein

P-glycoprotein (P-gp) plays a critical role in drug oral bioavailability, and modulation of this transporter can alter the safety and/or efficacy profile of substrate drugs. Individual oral molecular excipients that inhibit P-gp function have been considered a mechanism for improving drug absorption, but a systematic evaluation of the interaction of excipients with P-gp is critical for informed selection of optimal formulations of proprietary and generic drug products. A library of 123 oral molecular excipients was screened for their ability to inhibit P-gp in two orthogonal cell-based assays. β-Cyclodextrin and light green SF yellowish were identified as modest inhibitors of P-gp with IC₅₀ values of 168 μM (95% CI, 118-251 μM) and 204 μM (95% CI, 5.9-1745 μM), respectively. The lack of effect of most of the tested excipients on P-gp transport provides a wide selection of excipients for inclusion in oral formulations with minimal risk of influencing the oral bioavailability of P-gp substrates.

Effect of excipients on oral absorption process according to the different gastrointestinal segments

INTRODUCTION

Excipients are necessary to develop oral dosage forms of any Active Pharmaceutical Ingredient (API). Traditionally, excipients have been considered inactive and inert substances, but, over the years, numerous studies have contradicted this belief. This review focuses on the effect of excipients on the physiological variables affecting oral absorption along the different segments of the gastrointestinal tract. The effect of excipients on the segmental absorption variables are illustrated with examples to help understand the complexity of predicting their in vivo effects.

AREAS COVERED

The effects of excipients on disintegration, solubility and dissolution, transit time, and absorption are analyzed in the context of the different gastrointestinal segments and the physiological factors affecting release and membrane permeation. The experimental techniques used to study excipient effects and their human predictive ability are reviewed.

EXPERT OPINION

The observed effects of excipient in oral absorption process have been characterized in the past, mainly in vitro (i.e. in dissolution studies, in vitro cell culture methods or in situ animal studies). Unfortunately, a clear link with their effects in vivo, i.e. their impact on Cmax or AUC, which need a mechanistic approach is still missing. The information compiled in this review leads to the conclusion that the effect of excipients in API oral absorption and bioavailability is undeniable and shows the need of implementing standardized and reproducible preclinical tools coupled with mechanistic and predictive physiological-based models to improve the current empirical retrospective approach.

Pharmacological Interactions in the Elderly

Pharmacological therapy in the elderly is particularly complicated and challenging. Due to coexistence of three main predisposing factors (advanced age, multiple morbidity and polypharmacotherapy), this group of patients is prone to occurrence of drug interactions and adverse effects of incorrect drug combinations. Since many years patient safety during the treatment process has been one of key elements for proper functioning of healthcare systems around the world, thus different preventive measures have been undertaken in order to counteract factors adversely affecting the therapeutic effect. One of the avoidable medical errors is pharmacological interactions. According to estimates, one in six elderly patients may be at risk of a significant drug interaction. Hence the knowledge about mechanisms and causes of drug interactions in the elderly, as well as consequences of their occurrence are crucial for planning the process of pharmacotherapy. For the purpose of pharmacovigilance, a review of available methods and tools gives an insight into possible ways of preventing drug interactions. Additionally, recognizing the actual scale of this phenomenon in geriatric population around the world emphasizes the importance of a joint effort among medical community to improve quality of pharmacotherapy.

Influene of Pharmaceutical Excipients on the Membrane Transport of a P-glycoprotein Substrate in the Rat Small Intestine

BACKGROUND AND OBJECTIVES

Generic drugs are generally used worldwide because of affordability compared to brand-name drugs. One of the main differences between brand-name and generic drugs is pharmaceutical excipients. We previously reported the effects of pharmaceutical excipients on the membrane permeation of drugs via the paracellular and transcellular routes, which are passive transport routes. P-glycoprotein (P-gp) is a typical ATP-binding cassette transporter and is mostly responsible for drug-drug interactions involving transporters. In the present study, rhodamine 123 (Rho123) was selected as the P-gp substrate, and the effects of pharmaceutical excipients on its membrane transport in the rat jejunum and ileum were examined.

METHODS

Twenty major pharmaceutical excipients widely used in the pharmaceutical industry were selected. The in vitro diffusion chamber method using the rat jejunum and ileum was employed to investigate the effects of pharmaceutical excipients on the membrane permeation of Rho123.

RESULTS

The results obtained showed that the membrane permeability of Rho123 significantly (P < 0.05) changed under certain dosage conditions of pharmaceutical excipients such as sodium carboxymethyl starch, pullulan, glyceryl monostearate and so on. Furthermore, the effects of pharmaceutical excipients were site specific in the small intestine.

CONCLUSION

The present results demonstrated that some pharmaceutical excipients altered the membrane permeability of Rho123 in the rat small intestine.

Investigation to Explain Bioequivalence Failure in Pravastatin Immediate-Release Products

The purpose of this work is to explore the predictive ability of the biopharmaceutics classification system (BCS) biowaiver based on the dissolution methods for two pravastatin test products, where one of them showed bioequivalence (BE) while the other test failed (non-bioequivalence, or NBE), and to explore the reasons for the BE failure. Experimental solubility and permeability data confirmed that pravastatin is a BCS class III compound. The permeability experiments confirmed that the NBE formulation significantly increased pravastatin permeability, and could explain its higher absorption rate and higher C_max. This finding highlights the relevance of requiring similar excipients for BCS class III drugs. The BCS-based biowaiver dissolution tests at pH 1.2, 4.5, and 6.8, with the paddle apparatus at 50 rpm in 900 mL media, were not able to detect differences in pravastatin products, although the NBE formulation exhibited a more rapid dissolution at earlier sampling times. Dissolution tests conducted in 500 mL did not achieve complete dissolution, and both formulations were dissimilar because the amount dissolved at 15 min was less than 85%. The difference was less than 10% at pH 1.2 and 4.5, while at pH 6.8 f₂, results reflected the C_max rank order.

Casein nanoparticles in combination with 2-hydroxypropyl-β-cyclodextrin improves the oral bioavailability of quercetin

The aim of this work was to optimize the preparative process of quercetin loaded casein nanoparticles as well as to evaluate the pharmacokinetics of this flavonoid when administered orally in Wistar rats. Nanoparticles were obtained by coacervation after the incubation of casein, 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and quercetin in an aqueous environment. Then, nanoparticles were purified and dried. The resulting nanoparticles displayed a size of 200 nm with a negative zeta potential and a payload of about 32 μg/mg. Release studies showed a zero-order kinetic, suggesting a mechanism based on erosion of the nanoparticle matrix. For the pharmacokinetic study, quercetin was orally administered to rats as a single dose of 25 mg/kg. Animals treated with quercetin-loaded casein nanoparticles displayed higher plasma levels than those observed in animals receiving the solution of the flavonoid (control). Thus, the relative oral bioavailability of quercetin when administered as casein nanoparticles (close to 37%) was found to be about 9-times higher than the oral solution of the flavonoid in a mixture of PEG 400 and water. In summary, the combination of casein and 2-hydroxypropyl-β-cyclodextrin produces nanoparticles that may be a good option to load quercetin for both nutraceutical and pharmaceutical purposes.

Ion-pair approach coupled with nanoparticle formation to increase bioavailability of a low permeability charged drug

Atenolol is a drug widely used for the treatment of hypertension. However, the great drawback it presents is a low bioavailability after oral administration. To obtain formulations that allow to improve the bioavailability of this drug is a challenge for the pharmaceutical technology. The objective of this work was to increase the rate and extent of intestinal absorption of atenolol as model of a low permeability drug, developing a double technology strategy. To increase atenolol permeability an ion pair with brilliant blue was designed and the sustained release achieved through encapsulation in polymeric nanoparticles (NPs). The in vitro release studies showed a pH-dependent release from NPs, (particle size 437.30 ± 8.92) with a suitable release profile of drug (atenolol) and counter ion (brilliant blue) under intestinal conditions. Moreover, with the in vivo assays, a significant increase (2-fold) of atenolol bioavailability after administering the ion-pair NPs by oral route was observed. In conclusion, the combination of ion-pair plus polymeric NPs have proved to be a simple and very useful approach to achieve a controlled release and to increase the bioavailability of a low permeability charged drugs.

Excipient-drug pharmacokinetic interactions: Effect of disintegrants on efflux across excised pig intestinal tissues

Pharmaceutical excipients were designed originally to be pharmacologically inert. However, certain excipients were found to have altering effects on drug pharmacodynamics and/or pharmacokinetics. Pharmacokinetic interactions may be caused by modulation of efflux transporter proteins, intercellular tight junctions and/or metabolic enzyme amongst others. In this study, five disintegrants from different chemical classes were evaluated for P-glycoprotein (P-gp) related inhibition and tight junction modulation effects. Bidirectional transport studies of the model compound, Rhodamine 123 (R123) were conducted in the absence (control group) and presence (experimental groups) of four concentrations of each selected disintegrant across excised pig jejunum tissue. The results showed that some of the selected disintegrants (e.g. Ac-di-sol^® and Kollidon^® CL-M) increased R123 absorptive transport due to inhibition of P-gp related efflux, while another disintegrant (e.g. sodium alginate) changed R123 transport due to inhibition of P-gp in conjunction with a transient opening of the tight junctions in a concentration dependent way. It may be concluded that the co-application of some disintegrants to the intestinal epithelium may lead to pharmacokinetic interactions with drugs that are susceptible to P-gp related efflux. However, the clinical significance of these in vitro permeation findings should be confirmed by means of in vivo studies.

Using Physiologically Based Pharmacokinetic (PBPK) Modeling to Evaluate the Impact of Pharmaceutical Excipients on Oral Drug Absorption: Sensitivity Analyses

Drug solubility, effective permeability, and intestinal metabolism and transport are parameters that govern intestinal bioavailability and oral absorption. However, excipients may affect the systemic bioavailability of a drug by altering these parameters. Thus, parameter sensitivity analyses using physiologically based pharmacokinetic (PBPK) models were performed to examine the potential impact of excipients on oral drug absorption of different Biopharmaceutics Classification System (BCS) class drugs. The simulation results showed that changes in solubility had minimal impact on C_max and AUC_0-t of investigated BCS class 1 and 3 drugs. Changes in passive permeability altered C_max more than AUC_0-t for BCS class 1 drugs but were variable and drug-specific across different BCS class 2 and 3 drugs. Depending on the drug compounds for BCS class 1 and 2 drugs, changes in intestinal metabolic activity altered C_max and AUC_0-t. Reducing or increasing influx and efflux transporter activity might likely affect C_max and AUC_0-t of BCS class 2 and 3 drugs, but the magnitude may be drug dependent. Changes in passive permeability and/or transporter activity for BCS class 2 and 3 drugs might also have a significant impact on fraction absorbed and systemic bioavailability while changes in intestinal metabolic activity may have an impact on gut and systemic bioavailability. Overall, we demonstrate that PBPK modeling can be used routinely to examine sensitivity of bioavailability based on physiochemical and physiological factors and subsequently assess whether biowaiver requirements need consideration of excipient effects for immediate release oral solid dosage forms.

Absorption-Enhancing Effect of Nitric Oxide on the Absorption of Hydrophobic Drugs in Rat Duodenum

Nitric oxide (NO), an endogenous gas that plays a versatile role in the physiological system, has the ability to increase the intestinal absorption of water-soluble compounds through the paracellular route. However, it remains unclear whether NO can enhance the absorption of hydrophobic drugs through the transcellular route. In this study, we examined the absorption-enhancing effect of NO on intestinal permeability of hydrophobic drugs in rat intestine. The pretreatment of rat gastrointestinal sacs with NOC7, a NO-releasing reagent, significantly increased the permeation of griseofulvin from mucosa to serosa in the sacs prepared from the duodenum, but not in those prepared from the other regions such as jejunum, ileum, and colon. The absorption-enhancing effect of NOC7 on the duodenal permeation varied depending on the hydrophobicity of the drugs used. Furthermore, NOC7 treatment was found to be apparently ineffective on the griseofulvin permeation in the duodenum pretreated with dithiothreitol (DTT) that was used as a mucus remover, even though the permeation was increased by pretreatment with DTT alone. These results suggest that NO increases the absorption of hydrophobic drugs through the transcellular route in the duodenum by modulating the mucus layer function.

Cyclodextrins, blood-brain barrier, and treatment of neurological diseases

Biological barriers are the main defense systems of the homeostasis of the organism and protected organs. The blood-brain barrier (BBB), formed by the endothelial cells of brain capillaries, not only provides nutrients and protection to the central nervous system but also restricts the entry of drugs, emphasizing its importance in the treatment of neurological diseases. Cyclodextrins are increasingly used in human pharmacotherapy. Due to their favorable profile to form hydrophilic inclusion complexes with poorly soluble active pharmaceutical ingredients, they are present as excipients in many marketed drugs. Application of cyclodextrins is widespread in formulations for oral, parenteral, nasal, pulmonary, and skin delivery of drugs. Experimental and clinical data suggest that cyclodextrins can be used not only as excipients for centrally acting marketed drugs like antiepileptics, but also as active pharmaceutical ingredients to treat neurological diseases. Hydroxypropyl-β-cyclodextrin received orphan drug designation for the treatment of Niemann-Pick type C disease. In addition to this rare lysosomal storage disease with neurological symptoms, experimental research revealed the potential therapeutic use of cyclodextrins and cyclodextrin nanoparticles in neurodegenerative diseases, stroke, neuroinfections and brain tumors. In this context, the biological effects of cyclodextrins, their interaction with plasma membranes and extraction of different lipids are highly relevant at the level of the BBB.