Pharmacological Aspects of Over-the-Counter Opioid Drugs Misuse.

Several over-the-counter (OTC) drugs are known to be misused. Among them are opioids such as codeine, dihydrocodeine, and loperamide. This work elucidates their pharmacology, interactions, safety profiles, and how pharmacology is being manipulated to misuse these common medications, with the aim to expand on the subject outlined by the authors focusing on abuse prevention and prevalence rates. The reviewed literature was identified in several online databases through searches conducted with phrases created by combining the international non-proprietary names of the drugs with terms related to drug misuse. The results show that OTC opioids are misused as an alternative for illicit narcotics, or prescription-only opioids. The potency of codeine and loperamide is strongly dependent on the individual enzymatic activity of CYP2D6 and CYP3A4, as well as P-glycoprotein function. Codeine can also be utilized as a substrate for clandestine syntheses of more potent drugs of abuse, namely desomorphine ("Krokodil"), and morphine. The dangerous methods used to prepare these substances can result in poisoning from toxic chemicals and impurities originating from the synthesis procedure. OTC opioids are generally safe when consumed in accordance with medical guidelines. However, the intake of supratherapeutic amounts of these substances may reveal surprising traits of common medications.

Molecular determinants of loperamide and N-desmethyl loperamide binding in the hERG cardiac K+ channel.

Abuse of the common anti-diarrheal loperamide is associated with QT interval prolongation as well as development of the potentially fatal arrhythmia torsades de pointes. The mechanism underlying this cardiotoxicity is high affinity inhibition of the human ether-a-go-go-related gene (hERG) cardiac K+ channel. N-Desmethyl loperamide is the major metabolite of loperamide and is a close structural relative of the parent molecule. To date no information is available regarding the affinity of N-desmethyl loperamide for human cardiac ion channels. The effects of N-desmethyl loperamide on various cloned human cardiac ion channels including hERG, KvLQT1/mink and Nav1.5 were studied and compared to that of the parent. N-Desmethyl loperamide was a much weaker (7.5-fold) inhibitor of hERG compared to loperamide. However, given the higher plasma levels of the metabolite relative to the parent, it is likely that N-desmethyl loperamide can contribute, at least secondarily, to the cardiotoxicity observed with loperamide abuse. We used the recently solved cryo-EM structure of the hERG channel together with previously published inhibitors, to understand the basis of the interactions as well as the difference that a single methyl plays in the hERG channel blocking affinities of these two compounds.

Identification of novel small-molecule inhibitors targeting menin-MLL interaction, repurposing the antidiarrheal loperamide.

Leukemia with a mixed lineage leukemia (MLL) rearrangement, which harbors a variety of MLL fusion proteins, has a poor prognosis despite the latest improved treatment options. Menin has been reported to be a required cofactor for the leukemogenic activity of MLL fusion proteins. Thus, the disruption of the protein-protein interactions between menin and MLL represents a very promising strategy for curing MLL leukemia. Making use of menin-MLL inhibitors with a shape-based scaffold hopping approach, we have discovered that the antidiarrheal loperamide displays previously unreported mild inhibition for the menin-MLL interaction (IC50 = 69 ± 3 µM). In an effort to repurpose this drug, a series of chemical modification analyses was performed, and three of the loperamide-based analogues, DC_YM21, DC_YM25 and DC_YM26 displayed better activities with IC50 values of 0.83 ± 0.13 µM, 0.69 ± 0.07 µM and 0.66 ± 0.05 µM, respectively. Further treatment with DC_YM21 demonstrated potent and selective blockage of proliferation and induction of both cell cycle arrest and differentiation of leukemia cells harboring MLL translocations, which confirmed the specific mechanism of action. In conclusion, molecules of a novel scaffold targeting menin-MLL interactions were reported and they may serve as new potential therapeutic agents for MLL leukemia.

Preparation and Evaluation of Stomatitis Film Using Xyloglucan Containing Loperamide.

Stomatitis induced by radiation therapy or cancer chemotherapy is a factor in sleep disorders and/or eating disorders, markedly decreasing patient quality of life. In recent years, disintegrating oral films that are easy to handle have been developed; therefore, we focused on the formulation of these films. We prepared an adhesive film for the oral cavity using xyloglucan (Xylo), which is a water-soluble macromolecule. We used loperamide, which has been reported to relieve pain caused by stomatitis effectively, as a model drug in this study. Films were prepared from Xylo solutions (3% (w/w)) and hypromellose (HPMC) solutions (1% (w/w)). Xylo and HPMC solutions were mixed at ratios of 1 : 1, 2 : 1, or 3 : 1 for each film, and films 2×2 cm weighing 3 g were prepared and dried at 37°C for 24 h. Physicochemical properties such as strength, adhesiveness, disintegration behavior, and dissolution of loperamide from films were evaluated. Films prepared from Xylo solution alone had sufficient strength and mucosal adhesion. On the other hand, films prepared from a mixture of Xylo and HPMC were inferior to those made from Xylo, but showed sufficient strength and mucosal adhesion and were flexible and easy to handle. The films prepared in this study are useful as adhesion films in the oral cavity.

Synthesis and characterization of [N-methyl-3H]loperamide.

Loperamide is a piperidine butyramide mu-opiate receptor agonist and currently employed to treat diarrhea. Because a single past report of tritiating loperamide was limited to only a very low specific activity product without technical details or extensive analysis, the synthesis of [N-methyl-(3)H]loperamide at high specific activity is now described in detail. An imine precursor was alkylated with [(3)H]methyl iodide to obtain a quaternary intermediate, which was then reacted with 4-(4-chlorophenyl)-4-hydroxypiperidine to afford the desired product [N-methyl-(3)H]loperamide, characterized by thin layer chromatography (TLC), HPLC, MS, UV, and proton-decoupled tritium NMR.

A high-yield route to synthesize the P-glycoprotein radioligand [11C]N-desmethyl-loperamide and its parent radioligand [11C]loperamide.

N-Desmethyl-loperamide and loperamide were synthesized from α,α-diphenyl-γ-butyrolactone and 4-(4-chlorophenyl)-4-hydroxypiperidine in five and four steps with 8% and 16% overall yield, respectively. The amide precursor was synthesized from 4-bromo-2,2-diphenylbutyronitrile and 4-(4-chlorophenyl)-4-hydroxypiperidine in 2 steps with 21-57% overall yield. [(11)C]N-Desmethyl-loperamide and [(11)C]loperamide were prepared from their corresponding amide precursor and N-desmethyl-loperamide with [(11)C]CH3OTf through N-[(11)C]methylation and isolated by HPLC combined with solid-phase extraction (SPE) in 20-30% and 10-15% radiochemical yields, respectively, based on [(11)C]CO2 and decay corrected to end of bombardment (EOB), with 370-740 GBq/µmol specific activity at EOB.

P-glycoprotein-based loperamide-cyclosporine drug interaction at the rat blood-brain barrier: prediction from in vitro studies and extrapolation to humans.

We have shown that the rat can quantitatively predict the verapamil-cyclopsorine A (CsA) drug-drug interaction (DDI) at the human blood-brain barrier (BBB). In addition, the potency (EC(50)) of CsA to inhibit rat BBB P-gp can be predicted from in vitro studies in MDRI-transfected cells. To assess if these excellent agreements extend to other substrates, we determined the magnitude of P-gp-based DDI at the rat BBB between loperamide (Lop) or its metabolite, N-desmethyl Lop (dLop), and escalating CsA blood concentrations. The percent increase in the brain:blood Lop concentration ratio was described by the Hill equation, E(max) = 2000%, EC(50) = 7.1 µM and γ = 3.7. The potency (EC(50)) of CsA to inhibit P-gp at the rat BBB was independent of the substrate used (verapamil, Lop, or dLop). Like the verapamil-CsA DDI, the potency (EC(50)) of CsA to inhibit rat BBB P-gp could be predicted from studies in MDRI-transfected cells. When (11)C-Lop was coadministered with a 10 mg/kg iv infusion of CsA (1) yielding ~5.6 uM CsA blood concentration to healthy volunteers, the brain distribution of (11)C-radioactivity was increased by 110%. (1) When corrected for diffusible Lop metabolite(s), this translates into an increase in (11)C-Lop brain distribution of 457%. Based on our rat data, we estimated a similar value at 5.6 µM blood CsA concentration, 588% increase in Lop brain distribution. These data support our conclusion that the rat is a promising model to predict P-gp based DDI at the human BBB.

Discovery of loperamide as an antagonist of angiopoietin1 and angiopoietin2 by virtual screening.

The angiopoietin-Tie2 binding and related signal transduction pathways are crucial for vascular angiogenesis, blood vessel integrity and maturation. In this study, we preformed a virtual screening of small molecules targeting to Tie2. The binding site was selected at the extracellular ligand binding region of Tie2, rather than its conventional endocellular ATP binding region. It was found that loperamide, a widely-used antidiarrhea drug, was among the top hits. The binding between loperamide and Tie2 was confirmed by surface plasmon resonance (SPR) assay. Loperamide competitively inhibited the binding of both angiopoietin1 and angiopoietin2. These results indicate that loperamide is an antagonist of angiopoietin1 and angiopoietin2.

A facile synthesis for novel loperamide analogs as potential μ opioid receptor agonists.

A facile synthesis for novel loperamide analogs as potential μ opioid receptors is described. The synthetic procedure for compound 5, which contains two 4-phenyl piperidine scaffolds, was optimized, and this compound was synthesized in excellent yield. We also describe a mild and highly efficient protocol for the synthesis of compounds 6 and 7.

Antidiarrhetic loperamide hydrochloride.

Single crystals of the anhydrous form of the title compound {systematic name: 1-[3-(dimethylcarbamoyl)-3,3-diphenylpropyl]-4-hydroxy-4-(4-chlorophenyl)piperidin-1-ium chloride}, C(29)H(34)ClN(2)O(2)(+)·Cl(-), were obtained by diffusion of acetone into a solution in 2-propanol. In the structure, N-H...Cl(-) and O-H...Cl(-) hydrogen bonds connect neighbouring molecules and chloride anions to form chains along the c-axis direction. Neighbouring chains along the b-axis direction are connected by intermolecular C-H...Cl(-) contacts, defining layers parallel to the (100) planes. The layers are connected by weak intermolecular C-H...Cl interactions only, which may account for the plate-like shape of the crystals.

N-desmethyl-loperamide is selective for P-glycoprotein among three ATP-binding cassette transporters at the blood-brain barrier.

[(11)C]N-desmethyl-Loperamide ([(11)C]dLop) is used in positron emission tomography (PET) to measure the in vivo activity of efflux transporters that block the passage of drugs across the blood-brain barrier. The three most prevalent ATP-binding cassette efflux transporters at the blood-brain barrier are P-glycoprotein (P-gp), multidrug resistance protein 1 (Mrp1), and breast cancer resistance protein (BCRP). We sought to measure the selectivity of dLop among these three transporters. The selectivity of dLop at low concentrations (< or =1 nM) was measured both as the accumulation of [(3)H]dLop in human cells that overexpress each transporter and as the uptake of [(11)C]dLop in brains of mice that lack genes encoding P-gp, Mrp1, or BCRP. The selectivity of dLop at high concentrations (> or =20 microM) was measured as the inhibition of uptake of a fluorescent substrate and the change in cytotoxicity of drugs effluxed at each transporter. Accumulation of [(3)H]dLop was lowest in cells overexpressing P-gp, and the uptake of [(11)C]dLop was highest in brains of mice lacking P-gp. At high concentrations, dLop selectively inhibited P-gp function and also decreased the resistance of only the P-gp-expressing cells to cytotoxic agents. dLop is selective for P-gp among these three transporters, but its activity is dependent on concentration. At low concentrations (< or =1 nM), dLop acts only as a substrate; at high concentrations (> or =20 microM), it acts as both a substrate and an inhibitor (i.e., a competitive substrate). Because low concentrations of radiotracer are used for PET imaging, [(11)C]dLop acts selectively and only as a substrate for P-gp.

Future Oncotargets: Targeting Overexpressed Conserved Protein Targets in Androgen Independent Prostate Cancer Cell Lines.

BACKGROUND: Targeting evolutionarily conserved proteins in malignant cells and the adapter proteins involved in signalling that generates from such proteins may play a cardinal role in the selection of anti-cancer drugs. Drugs targeting these proteins could be of importance in developing anti-cancer drugs. OBJECTIVES: We inferred that drugs like loperamide and promethazine that act as antagonists of proteins conserved in cancer cells like voltage-gated Calcium channels (Cav), Calmodulin (CaM) and drug efflux (ABCB1) pump may have the potential to be re-purposed as an anti-cancer agent in Prostate Cancer (PCa). METHODS: Growth and cytotoxic assays were performed by selecting loperamide and promethazine to target Cav, CaM and drug efflux (ABCB1) pumps to elucidate their effects on androgen-independent PC3 and DU145 PCa cell lines. RESULT: We show that loperamide and promethazine in doses of 80-100µg/ml exert oncocidal effects when tested in DU145 and PC3 cell lines. Diphenhydramine, which shares its targets with promethazine, except the CaM, failed to exhibit oncocidal effects. CONCLUSION: Anti-cancer effects can be of significance if structural analogues of loperamide and promethazine that specifically target Cav, CaM and ABCB1 drug efflux pumps can be synthesized, or these two drugs could be re-purposed after human trials in PCa.

Multi-dose oral abuse deterrent formulation of loperamide using hot melt extrusion.

Loperamide, an over the counter anti-diarrheal drug, also infamously referred to as "poor man's methadone". Due to the ease of availability and low price, people/patients abuse it by consuming more than 30 tablets to achieve euphoric effect and to combat opioid withdrawal. But supratherapeutic doses of loperamide result in severe respiratory depression, cardiac dysrhythmia and mortality. To address this issue, we developed a unique and innovative technology to deter multi-dose oral abuse. The concept is to design a tablet which can immediate release loperamide in diarrheic patients (single tablet) while stops loperamide release in case of intentional multi-dose ingestion. Loperamide was molecularly dispersed into gastric soluble cationic polymers - Eudragit® EPO and Kollicoat® Smartseal 100P using hot melt extrusion to obtain filament. Filaments were milled and compressed into tablets ((Eudragit® EPO (SJU1) and Kollicoat® Smartseal (SJU2)) with optimized amount of L-Arginine. Dissolution in 250 mL of Fasted state simulated gastric fluid (FaSSGF) revealed that single tablet of Imodium® (marketed formulation) and SJU1 showed >85% of release within 15 min. Most importantly, in multi-unit dissolution (15 tablets), Imodium® exhibited >90% release but SJU tablets showed <2% of drug release thus demonstrating its ability to deter multi-dose oral abuse.

In situ dissolution testing using potentiometric sensors.

Potentiometric sensors can be used to determine the amount of API dissolved in the dissolution medium in function of time by measuring directly in the dissolution vessel of a Paddle (USP type 2) and Basket (USP type 1) apparatus. The prototype potentiometric sensor instrumentation showed very promising results for a selection of APIs with different physico-chemical properties. The applicability, benefits and limitations of the prototype were explored. The applicability of the measurement technique strongly depends on the log(P) of the API. Here, it is shown that measurements can easily be performed for APIs with a log(P)>4. Electrode performance however decreases with decreasing logP of the APIs due to decreased drug selectivity in comparison to the excipients and ionic strength of the applied dissolution medium. The potentiometric sensors are shown to be insensitive towards undissolved particles and air bubbles as opposed to UV spectrometric measurement where these can lead to severe light scattering. For the tested APIs, the obtained dissolution profiles are very reproducible and show a low variation compared to the measurements using manual sampling and UV or HPLC analysis. The measurements demonstrate that potentiometric sensors are a very promising technology that can become a standard for in situ dissolution measurements.

Comparison and validation of drug loading parameters of PEGylated nanoparticles purified by a diafiltration centrifugal device and tangential flow filtration.

This article describes drug loading validation of nanoparticles. Ultracentrifugation was avoided because of problems arising from small-sized particles. Ultrafiltration was adopted in two different modes followed by monitoring of polyvinyl alcohol (PVA), dextran sulfate (DS), and loperamide HCl contents. Diafiltration centrifugation removed all PVA at the fourth cycle and provided significantly (p = .000, .017) higher drug loading values compared with tangential flow filtration (TFF). This was due to residual PVA associated with the nanoparticles. TFF enabled satisfactory dry weight recovery (101.66 +/- 4.45%, n = 3) of nanoparticles during extended purification. Indirect drug loading (from the purification curve) was not significantly different (p = .450, .487) to the direct drug loading values. Encapsulation parameters were obtained from the purification curve once quantitative estimation of the all formulation components was established.

A mechanistic approach for the optimization of loperamide loaded nanocarriers characterization: Diafiltration and mathematical modeling advantages.

Oral bioavailability of loperamide is restricted by its limited absorption in the gastrointestinal tract due to its poor aqueous solubility and its P-glycoprotein (Pgp) substrate characteristic. In addition, ammonium methacrylate copolymers have shown to have mucoadhesive properties, whereas poloxamer 188, has been suggested as a Pgp inhibitor. Thus, in this work, we evaluate conditions that affect physicochemical parameters of ammonium methacrylate/poloxamer 188-based nanocarriers loaded with loperamide hydrochloride. Nanocarriers were synthesized by nanoprecipitation, enhancing loperamide encapsulation efficiency by modifying the aqueous phase to basic pH. The isolation of the non-encapsulated drug fraction from the nanocarriers-incorporated fraction was conducted by centrifugation, ultrafiltration, vacuum filtration and diafiltration. The last method was effective in providing a deeper understanding of drug-nanocarrier loading and interactions by means of modeling the data obtained by it. Through diafiltration, it was determined an encapsulation efficiency of about 93%, from which a 38% ±6 was shown to be reversibly (thermodynamic interaction) and a 62% ±6 irreversibly (kinetic interaction) bound. Finally, release profiles were assessed through empirical and semi-empirical modeling, showing a biphasic release behavior (burst effect 11.34% and total release at 6 h = 33% ±1). Thus, encapsulation efficiency and release profile were shown to have a strong mathematical modeling-based correlation, providing the mechanistic approach presented in this article a solid support for future translational investigations.

A Conformationally Gated Model of Methadone and Loperamide Transport by P-Glycoprotein.

P-glycoprotein (Pgp) is a multidrug resistance transporter that limits the penetration of a wide range of neurotherapeutics into the brain including opioids. The diphenylpropylamine opioids methadone and loperamide are structurally similar, but loperamide has about a 4-fold higher Pgp-mediated transport rate. In addition to these differences, they showed significant differences in their effects on Pgp-mediated adenosine triphosphate (ATP) hydrolysis. The activation of Pgp-mediated ATP hydrolysis by methadone was monophasic, whereas loperamide activation of ATP hydrolysis was biphasic implying methadone has a single binding site and loperamide has 2 binding sites on Pgp. Quenching of tryptophan fluorescence with these drugs and digoxin showed competition between the opioids and that loperamide does not compete for the digoxin-binding site. Acrylamide quenching of tryptophan fluorescence to probe Pgp conformational changes revealed that methadone- and loperamide-induced conformational changes were distinct. These results were used to develop a model for Pgp-mediated transport of methadone and loperamide where opioid binding and conformational changes are used to explain the differences in the opioid transport rates between methadone and loperamide.

Calculating Kinetic Rates and Membrane Permeability from Biased Simulations.

We present a simple approach to calculate the kinetic properties of lipid membrane crossing processes from biased molecular dynamics simulations. We demonstrate that by using biased simulations, one can obtain highly accurate kinetic information with significantly reduced computational time with respect to unbiased simulations. We describe how to conveniently calculate the transition rates to enter, cross, and exit the membrane in terms of the mean first passage times. To obtain free energy barriers and relaxation times from biased simulations only, we constructed Markov models using the dynamic histogram analysis method (DHAM). The permeability coefficients that are calculated from the relaxation times are found to correlate highly with experimentally evaluated values. We show that more generally, certain calculated kinetic properties linked to the crossing of the membrane layer (e.g., barrier height and barrier crossing rates) are good indicators of ordering drugs by permeability. Extending the analysis to a 2D Markov model provides a physical description of the membrane crossing mechanism.

Loperamide: a pharmacological review.

Loperamide is an antidiarrheal medication approved for the control of diarrhea symptoms and is available without a prescription. Loperamide works by a number of different mechanisms of action that decrease peristalsis and fluid secretion, resulting in longer gastrointestinal transit time and increased absorption of fluids and electrolytes from the gastrointestinal tract. It is a phenylpiperidine derivative with a chemical structure similar to opiate receptor agonists such as diphenoxylate and haloperidol. It was designed to maintain the antidiarrheal activity of these drugs, but minimize the negative aspects associated with their effects on the opiate receptor. Because of loperamides's low oral absorption and inability to cross the blood-brain barrier, it has minimal central nervous system effects. It also has a longer duration of action than diphenoxylate. However, it has no clinically significant analgesic activity and does not decrease the pain associated with some forms of irritable bowel syndrome and diarrhea. Loperamide is metabolized by the cytochrome P450 (CYP) system and is a substrate for the CYP3A4 isoenzyme. Concurrent administration with CYP3A4 inhibitors may elevate loperamide concentrations. Common adverse reactions to loperamide include cramps and nausea. Loperamide is an effective treatment for patients with painless diarrhea and is considered to be free of abuse potential.