Poloxamer 188-Coated Ammonium Methacrylate Copolymer Nanocarriers Enhance Loperamide Permeability across Pgp-Expressing Epithelia.

Loperamide is a µ-opioid agonist with poor gastrointestinal absorption, mainly because of its modest aqueous solubility and being a P-glycoprotein (Pgp) efflux substrate. Nevertheless, studies associated with therapeutic effects strongly suggest that loperamide holds potential pharmacological advantages over traditional µ-opioid agonists commonly used for analgesia. Thus, in this Communication, we assessed in MDCK-hMDR1 cell lines the effects over loperamide uptake and efflux ratio, when loaded into Eudragit RS (ERS) nanocarriers coated with poloxamer 188 (P188). ERS was chosen for enhancing loperamide aqueous dispersibility and P188 as a potential negative Pgp modulator. In uptake assays, it was observed that Pgp limited the accumulation of loperamide into cells and that preincubation with P188, but not coincubation, led to increasing loperamide uptake at a similar extent of Pgp pharmacological inhibition. On the other hand, the efflux ratio displayed no alterations when Pgp was pharmacologically inhibited, whereas ERS/P188 nanocarriers effectively enhanced loperamide uptake and absorptive transepithelial transport. The latter suggests that loperamide transport across cells is significantly influenced by the presence of the unstirred water layer (UWL), which could hinder the visualization of Pgp-efflux effects during transport assays. Thus, results in this work highlight that formulating loperamide into this nanocarrier enhances its uptake and transport permeability.

In Silico, Ex Vivo and In Vivo Studies of Roflumilast as a Potential Antidiarrheal and Antispasmodic agent: Inhibition of the PDE-4 Enzyme and Voltage-gated Ca++ ion Channels.

The aim of the present study was to evaluate the possible gut inhibitory role of the phosphodiesterase (PDE) inhibitor roflumilast. Increasing doses of roflumilast were tested against castor oil-induced diarrhea in mice, whereas the pharmacodynamics of the same effect was determined in isolated rabbit jejunum tissues. For in silico analysis, the identified PDE protein was docked with roflumilast and papaverine using the Autodock vina program from the PyRx virtual screening tool. Roflumilast protected against diarrhea significantly at 0.5 and 1.5 mg/kg doses, with 40% and 80% protection. Ex vivo findings from jejunum tissues show that roflumilast possesses an antispasmodic effect by inhibiting spontaneous contractions in a concentration-dependent manner. Roflumilast reversed carbachol (CCh, 1 µM)-mediated and potassium (K+, 80 mM)-mediated contractile responses with comparable efficacies but different potencies. The observed potency against K+ was significantly higher in comparison to CCh, similar to verapamil. Experiments were extended to further confirm the inhibitory effect on Ca++ channels. Interestingly, roflumilast deflected Ca++ concentration-response curves (CRCs) to the right with suppression of the maximum peak at both tested doses (0.001-0.003 mg/mL), similar to verapamil. The PDE-inhibitory effect was authenticated when pre-incubation of jejunum tissues with roflumilast (0.03-0.1 mg/mL) produced a leftward deflection of isoprenaline-mediated inhibitory CRCs and increased the tissue level of cAMP, similar to papaverine. This idea was further strengthened by molecular docking studies, where roflumilast exhibited a better binding affinity (-9.4 kcal/mol) with the PDE protein than the standard papaverine (-8.3 kcal/mol). In conclusion, inhibition of Ca++ channels and the PDE-4 enzyme explains the pharmacodynamics of the gut inhibitory effect of roflumilast.

Colon-Targeted Delivery of IgY Against Clostridium difficile Toxin A and B by Encapsulation in Chitosan-Ca Pectinate Microbeads.

This study investigated the use of a newly developed chitosan-Ca pectinate microbead formulation for the colon-targeted delivery of anti-A/B toxin immunoglobulin of egg yolk (IgY) to inhibit toxin binding to colon mucosa cells. The effect of the three components (pectinate, calcium chloride, and chitosan) used for the microbead production was examined with the aim of identifying the optimal levels to improve drug encapsulation efficiency, swelling ratio, and cumulative IgY release rate. The optimized IgY-loaded bead component was pectin 5% (w/v), CaCl2 3% (w/v), and chitosan 0.5% (w/v). Formulated beads were spherical with 1.2-mm diameter, and the drug loading was 45%. An in vitro release study revealed that chitosan-Ca pectinate microbeads inhibited IgY release in the upper gastrointestinal tract and significantly improved the site-specific release of IgY in the colon. An in vivo rat study demonstrated that 72.6% of biologically active IgY was released specifically in the colon. These results demonstrated that anti-A/B toxin IgY-loaded chitosan-Ca pectinate oral microbeads improved IgY release behavior in vivo, which could be used as an effective oral delivery platform for the biological treatment of Clostridium difficile infection (CDI).

Influence of ABCB1 Genotype in Collies on the Pharmacokinetics and Pharmacodynamics of Loperamide in a Dose-Escalation Study.

Thirty-three Collies (14 male and 19 female) were used in a dose-escalation study to determine the impact of ABCB1 genotype on loperamide pharmacokinetics (PK) and pharmacodynamics (PD). Loperamide was orally administered in four ascending doses (0.01, 0.05, 0.1, or 0.2 mg/kg) over a 4-wk period to fasted Collies. Comparisons were made within each dose to genotype, phenotype, and whether Collies received three (3D) or four (4D) loperamide doses. The 3D and 4D groupings had statistically significant differences in systemic drug exposure (defined by the area under the concentration-versus-time profile estimated from time zero to the last quantifiable drug concentration, AUC0-last). In contrast, statistical differences in AUC0-last only occurred in the comparison between wild-type (WT) Collies versus homozygous mutant (Mut) Collies administered 0.1 mg/kg. Statistical differences in the proportionality relationship were observed when comparing 3D to 4D Collies, and the WT to Mut Collies. Intersubject variability in drug exposure tended to be twice as high between Mut and WT Collies. Associations were observed between systemic drug exposure and ataxia or depression but not between systemic drug exposure and mydriasis or salivation. Thus, Collies expressing the greatest sensitivity to CNS-associated effects of loperamide (Mut) tended to have higher drug exposure compared with those less sensitive to the adverse effects of loperamide. Genotype and phenotype only partially explained differences in loperamide PK and PD, suggesting this relationship may not be straightforward and that other factors need to be considered. Accordingly, the PD and PK of one P-glycoprotein substrate only partially predicted the likelihood of adverse responses to unrelated substrates.

Liposomes Coloaded with Elacridar and Tariquidar To Modulate the P-Glycoprotein at the Blood-Brain Barrier.

This study prepared three liposomal formulations coloaded with elacridar and tariquidar to overcome the P-glycoprotein-mediated efflux at the blood-brain barrier. Their pharmacokinetics, brain distribution, and impact on the model P-glycoprotein substrate, loperamide, were compared to those for the coadministration of free elacridar plus free tariquidar. After intravenous administration in rats, elacridar and tariquidar in conventional liposomes were rapidly cleared from the bloodstream. Their low levels in the brain did not improve the loperamide brain distribution. Although elacridar and tariquidar in PEGylated liposomes exhibited 2.6 and 1.9 longer half-lives than free elacridar and free tariquidar, respectively, neither their Kp for the brain nor the loperamide brain distribution was improved. However, the conjugation of OX26 F(ab')2 fragments to PEGylated liposomes increased the Kps for the brain of elacridar and tariquidar by 1.4- and 2.1-fold, respectively, in comparison to both free P-gp modulators. Consequently, the Kp for the brain of loperamide increased by 2.7-fold. Moreover, the plasma pharmacokinetic parameters and liver distribution of loperamide were not modified by the PEGylated OX26 F(ab')2 immunoliposomes. Thus, this formulation represents a promising tool for modulating the P-glycoprotein-mediated efflux at the blood-brain barrier and could improve the brain uptake of any P-glycoprotein substrate that is intended to treat central nervous system diseases.

Effects of HM30181, a P-glycoprotein inhibitor, on the pharmacokinetics and pharmacodynamics of loperamide in healthy volunteers.

AIMS: HM30181 is a third generation P-glycoprotein (P-gp) inhibitor currently under development. The objectives of this study were to evaluate the effects of a single dose of HM30181 on the pharmacodynamics and pharmacokinetics of loperamide, a P-gp substrate, and to compare them with those of quinidine. METHODS: Eighteen healthy male subjects were administered loperamide alone (period 1) or with loperamide plus quinidine or HM30181 in period 2 or 3, respectively. In period 3, subjects randomly received one of three HM30181 doses: 15, 60 or 180 mg. Changes in pupil size, alertness, oxygen saturation and the oral bioavailability of loperamide were assessed in each period. In addition, the pharmacokinetics of HM30181 were determined. RESULTS: Pupil size, alertness and oxygen saturation did not change over time when loperamide alone or loperamide plus HM30181 was administered while HM30181 significantly increased the systemic exposure to loperamide, i.e. the geometric mean ratio (90% confidence interval) of AUC(0,tlast ) for loperamide with and without HM30181 was 1.48 (1.08, 2.02). Co-administered quinidine significantly increased the systemic exposure to loperamide 2.2-fold (1.53, 3.18), which also markedly reduced pupil size, resulting in a decrease of 24.7 mm h in the area under the effect curve of pupil size change from baseline compared with loperamide alone. CONCLUSIONS: HM30181 inhibits P-gp mainly in the intestinal endothelium, which can be beneficial because pan-inhibition of P-gp, particularly in the brain, could lead to detrimental adverse events. Further studies are warranted to investigate adequately the dose-exposure relationship of HM30181, along with its duration of effect.

Impact of loperamide on the pharmacokinetics and tissue disposition of ritonavir-boosted oral docetaxel therapy; a preclinical assessment.

PURPOSE: An oral docetaxel formulation boosted by the Cytochrome P450 (CYP) 3 A inhibitor ritonavir, ModraDoc006/r, is currently under clinical investigation. Based on clinical data, the incidence of grade 1-2 diarrhea is increased with this oral docetaxel formulation compared to the conventional intravenous administration. Loperamide, a frequently used diarrhea inhibitor, could be added to the regimen as symptomatic treatment. However, loperamide is also a substrate of the CYP3A enzyme, which could result in competition between ritonavir and loperamide for this protein. Therefore, we were interested in the impact of coadministered loperamide on the pharmacokinetics of ritonavir-boosted oral docetaxel. METHODS: We administered loperamide simultaneously or with an 8-hour delay to humanized CYP3A4 mice (with expression in liver and intestine) receiving oral ritonavir and docetaxel. Concentrations of docetaxel, ritonavir, loperamide and two of its active metabolites were measured. RESULTS: The plasma exposure (AUC and Cmax) of docetaxel was not altered during loperamide treatment, nor were the ritonavir plasma pharmacokinetics. However, the hepatic and intestinal dispositions of ritonavir were somewhat changed in the simultaneous, but not 8-hour loperamide treatment groups, possibly due to loperamide-induced delayed drug absorption. The pharmacokinetics of loperamide itself did not seem to be influenced by ritonavir. CONCLUSION: These results suggest that delayed loperamide administration can be added to ritonavir-boosted oral docetaxel treatment, without affecting the overall systemic exposure of docetaxel.

Effects of Hange-shashin-to (TJ-14) and Keishi-ka-shakuyaku-to (TJ-60) on contractile activity of circular smooth muscle of the rat distal colon.

The Japanese Kampo medicines Hange-shashin-to (TJ-14) and Keishi-ka-shakuyaku-to (TJ-60) have been used to treat symptoms of human diarrhea on an empirical basis as Japanese traditional medicines. However, it remains unclear how these drugs affect smooth muscle tissues in the distal colon. The aim of the present study was to investigate the effects of TJ-14 and TJ-60 on the contractile activity of circular smooth muscle from the rat distal colon. TJ-14 and TJ-60 (both 1 mg/ml) inhibited spontaneous contractions of circumferentially cut preparations with the mucosa intact. Blockade of nitric oxide (NO) synthase or soluble guanylate cyclase activity abolished the inhibitory effects of TJ-60 but only attenuated the inhibitory effects of TJ-14. Apamin (1 µM), a blocker of small-conductance Ca(2+)-activated K(+) channels (SK channels), attenuated the inhibitory effects of 5 mg/ml TJ-60 but not those of 5 mg/ml TJ-14. TJ-14 suppressed contractile responses (phasic contractions and off-contractions) evoked by transmural nerve stimulation and increased basal tone, whereas TJ-60 had little effect on these parameters. These results suggest that 1 mg/ml TJ-14 or TJ-60 likely inhibits spontaneous contractions of the rat distal colon through the production of NO. Activation of SK channels seems to be involved in the inhibitory effects of 5 mg/ml TJ-60. Since TJ-14 has potent inhibitory effects on myogenic and neurogenic contractile activity, TJ-14 may be useful in suppressing gastrointestinal motility.

Cardiovascular effects, pharmacokinetics and cross-reactivity in digitalis glycoside immunoassays of an antidiarrheal uzara root extract.

Uzara glycosides (UG) extracted from Xysmalobium undulatum are used for treating non-specific diarrhea.Cross-reactivity has been described for UG in digitalis glycoside assays but digitalis-like cardiac effects are controversially discussed. Therefore, we performed a randomized, singleblind cross-over study in 18 healthy volunteers receiving a commercially available Uzara product (Uzara® Lösung N, Stada AG, Bad Vilbel, Germany (ULN)), digoxin (1 mg, i.v., positive control) and placebo in double-dummy technique. Pharmacodynamic effects were quantified by means of ECG and impedance cardiography (ICG). After oral administration of ULN, main metabolites were determined using HPLC-MS/MS and digitalis-like serum levels (DLSL) were measured in two digitoxin and digoxin assays, respectively. In comparison to placebo, ULN did not change significantly any PD parameters whereas digoxin altered significantly area under the effect curve of several ECG and ICG parameters, respectively. Since some serum levels of three ULN ingredients (uzarin, uzarigenin and xysmalorin) were below LLQ, PK analyses could only be performed for allouzarigenin and revealed a marked inter-individual variability. Therefore, median values (min; max) were calculated as follows: Cmax = 0.39 (0.15; 1.81) ng/ml, tmax = 7.0 (3.0; 36.0) h, T1/2 = 5.2 (0.8; 23.6) h, AUC0-36h = 4.2 (0.8; 11.1) ng/ml×h, AUC0-∞ = 5.8 (1.8; 13.1) ng/ml×h. DLSL reached Cmax of 28 ng/ml and 1,980 ng/ml for digoxin and digitoxin, respectively. We could not observe significant cardiovascular pharmacodynamic effects after oral administration of the recommended single dose of Uzara extract to healthy volunteers. However, considerable DLSL could be detected, proving cross-reactivity of uzara components with the conventional digitalis assays used. However, none of the metabolites we had suspected to be the cause for the crossreactivity could be identified in reasonable quantities.

Oral absorption and drug interaction kinetics of moxifloxacin in an animal model of weightlessness.

To investigate the effect of simulated weightlessness on the pharmacokinetics of orally administered moxifloxacin and the antacid Maalox or the antidiarrheal Pepto-Bismol using a tail-suspended (TS) rat model of microgravity. Fasted control and TS, jugular-vein-cannulated, male Sprague-Dawley rats received either a single 5 mg/kg intravenous dose or a single 10 mg/kg oral dose of moxifloxacin alone or with a 0.625 mL/kg oral dose of Maalox or a 1.43 mL/kg oral dose of Pepto-Bismol. Plasma concentrations of moxifloxacin were measured by HPLC. Pharmacokinetic data were analyzed using WinNonlin. Simulated weightlessness had no effect on moxifloxacin disposition after intravenous administration but significantly decreased the extent of moxifloxacin oral absorption. The coadministration of moxifloxacin with Maalox to either control or TS rats caused significant reductions in the rate and extent of moxifloxacin absorption. In contrast, the coadministration of moxifloxacin with Pepto-Bismol to TS rats had no significant effect on either the rate or the extent of moxifloxacin absorption. These interactions showed dose staggering when oral administrations of Pepto-Bismol and moxifloxacin were separated by 60 min in control rats but not in TS rats. Dose staggering was more apparent after the coadministration of Maalox and moxifloxacin in TS rats.

Oral bioavailability of P-glycoprotein substrate drugs do not differ between ABCB1-1Δ and ABCB1 wild type dogs.

Previous studies have indicated that intestinal P-glycoprotein (P-gp) limits the oral bioavailability of substrate drugs and alters systemic pharmacokinetics. In this study, dogs lacking functional P-gp were used to determine the contribution of P-gp to the oral bioavailability and systemic pharmacokinetics of several P-gp substrate drugs. The P-gp substrates quinidine, loperamide, nelfinavir, cyclosporin and the control (non P-gp substrate) drug diazepam were individually administered intravenously and per os to ABCB1-1Δ dogs, which have a P-gp null phenotype and ABCB1 wildtype dogs. ABCB1-1Δ dogs have been shown to have greater brain penetration of P-gp substrates, but limited information is available regarding oral bioavailability of P-gp substrate drugs in this animal model. Plasma drug concentration vs. time curves were generated and pharmacokinetic parameters were calculated for each drug. There were no differences in oral bioavailability between ABCB1-1Δ dogs and ABCB1 wildtype dogs for any of the drugs studied, suggesting that intestinal P-gp does not significantly affect intestinal absorption of these particular substrate drugs in ABCB1-1Δ dogs. However, small sample sizes and individual variability in CYP enzyme activity may have affected the power of the study to detect the impact of P-gp on oral bioavailability.

Potential Implications of Gut Microbiota in Drug Pharmacokinetics and Bioavailability.

Gut microbial communities are capable of enzymatically transforming pharmaceutical compounds into active, inactive, and toxic metabolites, thus potentially affecting the pharmacokinetics and bioavailability of orally administered medications. Our understanding of the impact and clinical relevance of how gut microbial communities can directly and indirectly affect drug metabolism and, ultimately, clinical outcomes, is limited. Interindividual variability of gut microbial composition may partially explain differences observed in drug efficacy and toxicity in certain patient populations. This review provides an overview of how gut microbial communities can potentially contribute to individual drug response. This review focuses on the current landscape of clinical and preclinical research that defines the microbiome contribution on medication response with the goal of improving medication efficacy and decreasing medication toxicity.

[Loperamide abuse - constipation or heart attack?]

Loperamide is a µ-opioid receptor agonist with antidiarrhoeal effects. It is considered to have a low abuse potential because of substantial first-pass metabolism and P-glycoprotein-mediated efflux at the level of the blood-brain barrier. Previous case reports have described that high dosage of loperamide can induce an opioid-like effect on the central nervous system. The most common presentation of loperamide intoxication is syncope which is caused by serious cardiac dysrhythmia and can lead to death. Therefore, it was decided to analyze whether drug prescriptions in the prescription drug database from The Directorate of Health would indicate loperamide misuse in Iceland from 2006-2017. In total 94 individuals used more than one DDD (10 mg) and 17 individuals used more than two DDD (20 mg), if taken daily over one year. These results indicate that loperamide is being used excessively but the reason for each prescription and the total amount sold over the counter is unknown. Increased surveillance and decreased availability of prescription opioids might possibly boost the usage of drugs with similar function such as loperamide. Loperamide overdose can result in serious adverse effects and thus, it is important to inform healthcare employees about such severe consequences.

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.

Loperamide metabolite-induced cardiomyopathy and QTc prolongation.

Loperamide is an over-the-counter, peripherally acting, µ-opioid receptor agonist used for the treatment of diarrhea. In recent times users have found that at higher doses, loperamide crosses the blood-brain barrier and reaches central µ-receptors in the brain, leading to central opiate effects including euphoria and respiratory depression. We report a case of a 37-year-old female who attempted suicide with over 200 loperamide tablets. During her overdose, her QTc was significantly prolonged at >600 ms. Our case aims to add to the growing body of literature describing life-threatening ventricular arrhythmias associated with loperamide toxicity and further suggests that a metabolite of loperamide, desmethylloperamide, may play a role in the pathogenesis.

Extended-release but not immediate-release and subcutaneous methylnaltrexone antagonizes the loperamide-induced delay of whole-gut transit time in healthy subjects.

Methylnaltrexone (MNTX) is approved for subcutaneous treatment (MNTX-SC) of opioid induced constipation. MNTX in oral immediate-release (MNTX-IR) and extended-release (MNTX-ER) dosage forms may antagonize the opioid induced delay in oro-cecal transit time (OCT) as measured by using radiolabeled lactulose. Because lactulose acts laxative by its own and efficacy of MNTX on colon transit time (CTT) was unknown, the opioid antagonistic effects MNTX-IR and MNTX-ER (both 500 mg) relative to MNTX-SC (12 mg) were evaluated in 15 healthy subjects with loperamide (LOP, 3 × 4 mg, 12 hourly) induced experimental constipation using the sulfasalazine/sulfapyridine method and radio-opaque markers to measure OCT and whole gut transit time (WGT). MNTX-ER significantly antagonized the LOP effects in 12 of our 15 subjects who responded to LOP with prolongation of WGT by 20.6-74.1 h (OCT by 0.50-10.5 h, CTT by 18.3-73.6 h). MNTX-SC and MNTX-IR were without significant influence. Compared to MNTX-SC, bioavailability of MNTX-IR and MNTX-ER was 1.53-5.49% and 0.11-1.24%, respectively. MNTX-SC and MNTX-IR achieved active serum levels only for ∼ 3-5 h. MNTX-ER antagonized the opioid-induced delay of CTT most likely by local effects on µ-opioid receptors in the colon.

Validation of a liquid chromatographic-tandem mass spectrometric method for the determination of loperamide in human plasma.

A sensitive and selective method based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for the quantitative determination of loperamide in human plasma. Automated solid-phase extraction (SPE) on disposable extraction cartridges (DEC) is used to isolate the compounds from the biological matrix and to prepare a cleaner sample before injection and analysis in the LC-MS/MS system. After conditioning, the plasma sample is loaded on the DEC filled with endcapped ethyl silica (C2(EC)) and washed twice with water. The analytes are therefore eluted by dispensing methanol. The eluate is then collected and added with ammonium acetate solution in order to inject an aliquot of this final extract in the LC-MS/MS system. On-line LC-MS/MS system using atmospheric pressure chemical ionization (APCI) has been developed for the determination of loperamide. The separation is obtained on a octadecylsilica based stationary phase using a mobile phase consisting in a mixture of methanol and 5mM ammonium acetate solution (25:75, v/v). Clonazepam is used as internal standard (IS). The MS/MS ion transitions monitored are m/z 477--> 266 and 316--> 270 for loperamide and clonazepam, respectively. The most appropriate regression model of the response function as well as the limit of quantitation were first selected during the pre-validation step. These latter criteria were then assessed during the formal validation step. The limit of quantitation (LOQ) was around 50 pg/ml for loperamide. The method was also validated with respect to recovery, precision, trueness, accuracy and linearity.

In vivo pharmacology and antidiarrheal efficacy of a thiazolidinone CFTR inhibitor in rodents.

A small-molecule inhibitor of the cystic fibrosis transmembrane conductance regulator (CFTR), 3-[(3-trifluoromethyl)phenyl]-5-[(4-carboxyphenyl)methylene]-2-thioxo-4-thiazolidinone (CFTR(inh)-172), reduces enterotoxin-induced intestinal fluid secretion in rodents. Here, we study CFTR(inh)-172 pharmacology and antidiarrheal efficacy in rodents using (14)C-labeled CFTR(inh)-172, liquid chromatography/mass spectrometry, and a closed intestinal loop model of fluid secretion. CFTR(inh)-172 was cleared primarily by renal glomerular filtration without chemical modification. CFTR(inh)-172 accumulated in liver within 5 min after intravenous infusion in mice, and was concentrated fivefold in bile over blood. At 30-240 min, CFTR(inh)-172 was found mainly in liver, intestine, and kidney, with little detectable in the brain, heart, skeletal muscle, or lung. Pharmacokinetic analysis in rats following intravenous bolus infusion showed a distribution volume of 770 mL with redistribution and elimination half-times of 0.14 h and 10.3 h, respectively. CFTR(inh)-172 was stable in hepatic microsomes. Closed-loop studies in mice indicated that a single intraperitoneal injection of 20 microg CFTR(inh)-172 inhibited fluid accumulation at 6 h after cholera toxin by >90% in duodenum and jejunum, approximately 60% in ileum and <10% in colon. No toxicity was seen after high-dose CFTR(inh)-172 administration (3 mg/kg/day in two daily doses) in mice over the first 6 weeks of life. The metabolic stability, enterohepatic recirculation, slow renal elimination, and intestinal accumulation of CFTR(inh)-172 account for its efficacy as an antidiarrheal.

Tissue distribution of loperamide and N-desmethylloperamide following a fatal overdose.

We report a case involving a fatal intoxication with loperamide (Imodium). Loperamide is a synthetic opioid of the phenyl piperidine class used as an over-the-counter antidiarrheal. It exerts its effects through interaction with micro-opiate receptors in the intestine to reduce peristalsis. Loperamide lacks the typical euphoric opiate effects when administered at recommended doses. Both loperamide and its major metabolite, N-desmethylloperamide, were isolated by liquid-liquid extraction into n-butyl chloride from alkalinized samples. Extracts were analyzed by liquid chromatography-electrospray-mass spectrometry in selected-ion-monitoring mode. Rapid separation of the drug, metabolite, and internal standard (diphenoxylate) was achieved using a high-resolution C18 column with 1.8-microm particle diameter. The mobile phase consisted of 0.1% formic acid in deionized water (60%) and acetonitrile (40%) at a flow rate of 0.5 mL/min. Heart blood concentrations for loperamide and its metabolite were 1.2 mg/L and 3.3 mg/L, respectively. In contrast, reported peak plasma concentrations of loperamide after administration of recommended daily doses of 16 mg did not exceed 0.012 mg/L in controlled trials. Because the heart blood ethanol concentration was 0.08 g/dL, the medical examiner ruled that the cause of death was loperamide and ethanol intoxication, and the manner of death as undetermined.