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.

A Novel Ileocolonic Release Peppermint Oil Capsule for Treatment of Irritable Bowel Syndrome: A Phase I Study in Healthy Volunteers.

INTRODUCTION: Peppermint oil (PO) has been shown to reduce abdominal pain in patients with irritable bowel syndrome (IBS). PO is assumed to induce intestinal smooth muscle relaxation and desensitization of nociceptive nerve afferents. To increase colonic PO concentration, an ileocolonic release peppermint oil (IC-PO) capsule has been developed. The aim of this study was to compare pharmacokinetic parameters of the currently available small intestinal release PO (SI-PO) and the novel IC-PO. METHODS: In this randomized, double-blind, crossover study, subjects received 182 mg of either SI-PO or IC-PO in a crossover design with a washout period of more than 14 days. Blood samples were collected to determine menthol glucuronide concentrations. RESULTS: Eight healthy volunteers (50% female, median age 22) were included. The time to reach the maximum concentration (Tmax) of IC-PO was significantly longer compared to SI-PO with a median (IQR) of 360 (360-405) versus 180 (120-180) min. The lag time (Tlag) was significantly longer with a median (IQR) of 225 (204-284) for IC-PO compared to 37 (6-65) min for SI-PO. The areas under the menthol glucuronide plasma concentration-time curves were significantly smaller with a median (IQR) of 2331 µg h/L (2006-2510) for IC-PO compared to 2623 µg h/L (2471-2920) for SI-PO. No significant differences were found in peak concentrations and elimination half-lives. CONCLUSION: IC-PO has a significantly delayed peak menthol glucuronide concentration and Tlag, both pointing to the release of PO in the more distal part of the intestine. This may enhance therapeutic efficacy as it results in increased exposure of colonic mucosal afferents to the PO. A randomized controlled trial investigating the efficacy of SI and IC-PO in IBS is currently ongoing. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT02291445, EudraCT database 2014-004195-32.

Efecto espasmolítico de Jasonia glutinosa en intestino de roedores / Spasmolytic effect of Jasonia glutinosa on rodent intestine

Antecedentes: Jasonia glutinosa es una planta utilizada en la Península Ibérica y en el sur de Francia por su efecto espasmolítico, pero sin evidencia científica sobre ello. Objetivo: examinar el efecto espasmolítico de un extracto de té de roca. Métodos: estudiamos el efecto de dicho extracto sobre las contracciones espontáneas en duodeno de rata in vitro y sobre el tránsito gastrointestinal en el ratón in vivo. Resultados: el extracto de té de roca redujo las contracciones espontáneas en el músculo liso longitudinal del duodeno de rata, inhibió las contracciones inducidas por KCl, bloqueó la contracción causada por la entrada de Ca2+ extracelular y la contracción inducida por el Bay K8644, agonista de los canales de Ca2+ tipo L. El efecto inhibitorio del extracto de té de roca fue similar al del verapamilo, inhibidor de los canales de Ca2+ tipo L. El té de roca no modificó el tránsito gastrointestinal total en ratones sanos. Sin embargo, tras el tratamiento con dextrano sulfato de sodio, un inductor de colitis, el extracto de té de roca revirtió el aumento del tránsito gastrointestinal asociado a dicho tratamiento. Conclusión: el extracto de té de roca relajó el músculo liso duodenal a través de canales de Ca2+ tipo L y normalizó el tránsito gastrointestinal en un modelo de colitis. Estos resultados validan el uso tradicional de Jasonia glutinosa en alteraciones digestivas. Así, el té de roca podría ser utilizado como espasmolítico en el tratamiento de diversas patologías gastrointestinales (AU)

Introduction: Jasonia glutinosa is an endemic plant species of the Iberian Peninsula and Southern France traditionally used in infusions as a spasmolytic; this plant is also known as "té de roca" (rock tea) but there is no scientific evidence about the effects of this plant. Aim: To evaluate the spasmolytic effect of rock tea. Methods: We have studied the in vitro effect of a rock tea extract on rat duodenum spontaneous contractions and the in vivo effect on mice gastrointestinal transit. Results: Rock tea extract reduced the spontaneous contractions of rat duodenal smooth muscle, inhibited KCl-induced contractions and blocked the contractions invoked by both extracellular Ca2+ and the agonist of L-type calcium channels Bay K8644. This inhibitory effect was similar to the one observed after the addition of the antagonist of L-type calcium channels verapamil. Rock tea did not modify gastrointestinal transit in healthy mice. However, after the treatment with dextran sulfate sodium, an inducer of colitis, rock tea extract reverted the increase in the gastrointestinal transit associated with this treatment. Conclusion: Rock tea extract relaxed duodenal smooth muscle via L-type calcium channels and normalized gastrointestinal transit in a model of colitis. These results may validate the traditional use of Jasonia glutinosa in patients with gastrointestinal alterations. Thus, rock tea may be used as a spasmolytic agent to treat gastrointestinal disorders (AU)

Pharmacokinetics of Compound D, the Major Bioactive Component of Zingiber cassumunar, in Rats.

Rhizomes of Zingiber cassumunar have been used for many years in traditional Thai medicine as an anti-inflammatory agent. The major bioactive component of this plant is Compound D [E-4-(3', 4'-dimethoxyphenyl)but-3-en-1-ol], which is a strong smooth muscle relaxant, and has antihistamine and anti-inflammatory actions. There is, however, incomplete information available for the pharmacokinetics of Compound D in mammals. In this study, we examined the pharmacokinetic profiles of Compound D in male Wistar rats. A standardized extract of Z. cassumunar containing 4 % w/w Compound D was administered intravenously at 25 mg/kg or by oral gavage at 25, 75, or 250 mg/kg to Wistar rats. Blood, tissues, urine, and feces were collected from 0 to 48 h after dosing and the level of Compound D was determined by liquid chromatography-tandem mass spectrometry. The concentration of Compound D ranged from 10-100 µg/L, reached a maximum approximately 0.15 h after oral dosing. Compound D exhibited an excellent tissue to plasma ratio, ranging from 1- to 1000 in several organs at 1-4 h after oral dosing. Less than 1 % of unchanged Compound D was excreted in the urine and feces. Further studies on tissue uptake and metabolite identification are required to obtain complete pharmacokinetic information and to develop appropriate dosing strategies of Compound D and the standardized extract of Z. cassumunar.

Characterization of in vitro ADME properties of diosgenin and dioscin from Dioscorea villosa.

Dioscorea villosa (wild yam) is native to North America and has been widely used as a natural alternative for estrogen replacement therapy to improve women's health as well as to treat inflammation, muscle spasm, and asthma. Diosgenin and dioscin (glycoside form of diosgenin) are reported to be the pharmacologically active compounds. Despite the reports of significant pharmacological properties of dioscin and diosgenin in conditions related to inflammation, cancer, diabetes, and gastrointestinal ailments, no reports are available on ADME properties of these compounds. This study was carried out to determine ADME properties of diosgenin and dioscin and their effects on major drug metabolizing enzymes (CYP 3A4, 2D6, 2C9, and 1A2). The stability was determined in simulated gastric and intestinal fluids (SGF, pH 1.2 and SIF, pH 6.8), and intestinal transport was evaluated in Caco-2 model. Phase I and phase II metabolic stability was determined in human liver microsomes and S9 fractions, respectively. Quantitative analysis of dioscin and diosgenin was performed by UPLC-MS system. Dioscin degraded up to 28.3 % in SGF and 12.4 % in SIF, which could be accounted for by its conversion to diosgenin (24.2 %. in SGF and 2.4 % in SIF). The depletion of diosgenin in SGF and SIF was < 10 %. Diosgenin was stable in HLM but disappeared in S9 fraction with a half-life of 11.3 min. In contrast, dioscin was stable in both HLM and S9 fractions. Dioscin showed higher permeability across Caco-2 monolayer with no significant efflux, while diosgenin was subjected to efflux mediated by P-glycoprotein. Diosgenin and dioscin inhibited CYP3A4 with IC50 values of 17 and 33 µM, respectively, while other CYP enzymes were not affected. In conclusion, dioscin showed better intestinal permeability. Conversion of dioscin to diosgenin was observed in both gastric and intestinal fluids. No phase I metabolism was detected for both compounds. The disappearance of diosgenin in S9 fraction indicated phase II metabolism.

Pharmacokinetic comparisons of two different combinations of Shaoyao-Gancao Decoction in rats: competing mechanisms between paeoniflorin and glycyrrhetinic acid.

ETHNOPHARMACOLOGICAL RELEVANCE: Shaoyao-Gancao Decoction (SGD), a well-known traditional Chinese medicine prescription, is a combination of Radix Paeoniae Alba (Paeonia lactiflora Pall, root) and Glycyrrhizae uralensis (Glycyrrhiza uralensis Fisch., root and rhizome, honeyed) for spasmolysis and emergency pain relief. Paeoniflorin (PF) and glycyrrhetinic acid (GA) are two typical active components of SGD for pain relief. AIM OF THE STUDY: To study comparative pharmacokinetics of ten bioactive compounds in SGDs with two different combinations of RP and GU, and therefore to investigate the herb-herb interaction mechanisms of Shaoyao-Gancao Decoction for better spasmolysis and emergency pain relief in rats. MATERIALS AND METHODS: Herbal IR macro-fingerprinting was implemented to provide the full chemical fingerprints of RP, GU and SGD decoctions and to investigate the variation rule of the full chemical profile of SGDs with various combinations of RP and GU. A specifically developed HPLC-MS/MS assay coupled with protein precipitation method was employed to determine the plasma concentrations of the ten analytes. Male Wistar rats were orally administered with SGD1 (RP:GU, 1:1 (w/w)) and SGD2 ((RP:GU, 4:1 (w/w)) equivalent to 9.5 g/kg body weight of GU. RESULTS: Full chemical fingerprints of RP, GU and SGDs with various combinations of RP and GU were provided in the form of IR macro-fingerprints. Except for liquiritin, there were statistically significant differences (p<0.05 or p<0.01) of these analytes between SGD1 and SGD2 in in vivo pharmacokinetic study. Compared with the results when oral administrated with SGD1, six glycosides (PF, albiflorin, oxypaeoniflorin, isoliquiritin, ononin, and glycyrrhizin) exhibited higher systematic exposure levels (AUC0-t) and slower elimination rates (CL) whereas two glycones (GA and isoliquiritigenin) were the reverse when administrated with SGD2. CONCLUSIONS: Increasing the amount of RP attenuated the inhibitory effect of GA via competing being consumed by intestinal bacteria (or ß-glucosidase) to reduce the conversion amount of glycyrrhizin to GA and subsequently to afford significantly higher bioavailability and longer efficacy of PF, glycyrrhizin, albiflorin, oxypaeoniflorin, isoliquiritin, and ononin, leading to better spasmolysis and emergency pain relief.

Metabolic and toxicological considerations for the latest drugs used to treat irritable bowel syndrome.

INTRODUCTION: The high prevalence of irritable bowel syndrome (IBS), a chronic gastrointestinal (GI) disorder, its lack of satisfactory effective drugs and its complicated pathophysiology lead to the demand of new therapeutic agents. During a new drug development process, the pharmacokinetic profiling is of a great considerable importance comparable to drug's efficacy. This involves the drug's absorption, distribution, metabolism and excretion, all of which are crucial to its usefulness. In addition, the toxicological profile and possible adverse reactions of the drug should be identified. Also its interactions should be identified at different phases of trials. Several pharmacokinetic studies are carried out to achieve drugs with the best absorption and bioavailability and the least adverse effects and lowest toxicity. AREAS COVERED: To make an update on new clinically introduced drugs for IBS and their dynamics and kinetics data, the present systematic review was accomplished. All relevant bibliographic databases were searched from the year 2003 up to May 2012 to identify all clinical trials that evaluated the potential efficacy of a novel agent in IBS. EXPERT OPINION: Some evaluated drugs, such as ramosetron (5-HT3 antagonist) and pexacerfont (CRF1 receptor antagonist), have shown some benefits in diarrhea-predominant IBS (D-IBS), while, prucalopride and mosapride (5-HT4 agonist) with prokinetic effect were found useful in constipation-predominant IBS (C-IBS). Besides, dexloxiglumide, lubiprostone and linaclotide have shown beneficial effects in C-IBS patients. Melatonin regulates GI tract motility and, asimadoline, gabapentin and pregabalin show reduction of pain threshold and visceral hypersensitivity. Glucagon-like peptide analog, calcium-channel blockers and neurokinin receptor antagonists have shown benefits in pain attacks. More time is required to indicate both efficacy and safety in long-term treatment due to multifactorial pathophysiology, variations in individual responses and insufficient assessment methods, which limit the right decision-making process about the efficacy and tolerability of these new drugs.

Esencia de menta al 1, 6% como espasmolítico intestinalen la colangiopancreatografía retrógrada endoscópica / 1.6% Peppermint oil solution as intestinal spasmolytic in retrograde endoscopic cholangiopancreatography

Objetivos: La aparición de peristaltismo intestinal puede dificultar la realización de exploraciones o intervenciones mediante colangiopancreatografía retrógrada endoscópica(CPRE). Con el fin de disminuirlo es frecuente la utilización de espasmolíticos sistémicos, pese a los efectos adversos anticolinérgicos que presentan. Se propuso formular una preparación de esencia de menta al 1,6% de uso local para evitar estos efectos adversos. Método: Se formuló la preparación de la esencia de menta al 1,6% según la bibliografía encontrada. La efectividad de la fórmula fue valorada de manera semicualitativa según la disminución del peristaltismo. Resultados: Se ensayaron 2 emulgentes siendo polisorbato el más adecuado. El estudio piloto llevado a cabo en 8 pacientes demostró su efectividad y seguridad en la disminución del peristaltismo intestinal. Conclusiones: La esencia de menta al 1,6% constituye una alternativa efectiva y segura a la utilización de espasmolíticos sistémicos. Se requieren posteriores estudios incluyendo un mayor número de pacientes para establecer su utilidad en la práctica clínica habitual (AU)

Objectives: Intestinal peristalsis can impede explorations and interventions using retrograde endoscopic cholangiopancreatography. Systemic spasmolytics are frequently employed to reduce this phenomenon, in spite of the adverse anti-cholinergic effects they are associated with. We proposed a formula using 1.6% peppermint oil solution with local use in order to avoid these adverse side effects. Method: We formulated a preparation of 1.6% peppermint oil solution in accordance with the medical literature. The effectiveness of the formula was evaluated in a semi-qualitative manneraccording to the reduction in peristalsis. Results: We tested two different emulgents, and polysorbate provided the best results. The pilot study carried out with 8 patients demonstrated its effectiveness and safety in reducing intestinal peristalsis. Conclusions: 1.6% peppermint oil solution constitutes an effective and safe alternative to the use of systemic spasmolytics. More studies are needed with a larger sample size in order to establish its usefulness in normal clinical practice (AU)

Shenfushu granule and atropine attenuate microvasculature loss in rat models with 5/6 nephrectomy.

OBJECTIVE: To investigate the effect of Shenfushu granule (SFSG) and atropine treatment on microvessels of the kidney and intestine after chronic renal failure (CRF) induced by 5/6 nephrectomy. METHODS: Sprague Dawley rats were randomly divided into a sham group, a model group, an SFSG group, and an SFSG + atropine group. SFSG was administered daily 1 week after inducing CRF. Rats were sacrificed at the end of the eighth week. Urinary protein and stool and serum urea nitrogen (UN) and creatinine (Cr) levels were assessed. Hematoxylin and eosin and periodic acid-Schiff staining of the kidney and examination of the vascular endothelial growth factor (VEGF) and microvessel density (MVD) levels in kidney and intestine were performed. RESULTS: The Cr and UN levels were significantly increased in blood and stool of the model group. SFSG significantly improved renal function, and the protective effects were further enhanced with the addition of atropine. Glomerular sclerosis, tubulointerstitial fibrosis, and microvessel loss were observed in CRF rats, and these pathological changes were ameliorated in the two treatment groups (p < 0.05), especially in the SFSG + atropine group. The expression of VEGF and MVD was decreased in the CRF rats compared with the sham group. SFSG treatment increased the expression of these proteins and reversed the degree of microvessel loss, glomerular sclerosis, and tubulointerstitial fibrosis (p < 0.05). Co-treatment with atropine enhanced these effects. CONCLUSIONS: SFSG alleviated renal function, upregulated the expression of VEGF and MVD in the kidney and intestine, and attenuated the degree of microvessel loss, glomerular sclerosis, and tubulointerstitial fibrosis in the early stages of CRF in rats, and addition of atropine enhanced these effects.

Absorption pattern of trospium chloride along the human gastrointestinal tract assessed using local enteral administration.

BACKGROUND AND OBJECTIVES: The antimuscarinic drug trospium chloride is hydrophilic and therefore does not enter the CNS when used for the treatment of overactive bladder disturbances. However, the same property is the main reason for low and variable oral bioavailability. The present study was performed to assess the influence of intestinal site on absorption of the drug as the basis for the development of modified release preparations. METHODS: In a change-over pilot study, 8 healthy male volunteers received single 20 mg doses oftrospium chloride orally as a tablet (reference), as Eudragit-coated tablets dissolving at pH 6.0 (local administration into the small intestine), and rectally via a mini enema (corresponding to local administration into the large intestine). Plasma concentrations of trospium chloride were determined up to 36 hours after administration using GC/MS. RESULTS: Extent and rate of trospium chloride absorption declined rapidly upon administration into more distal regions of the gastrointestinal tract. C(max) (median: 6.42 ng/ml) and AUC(0.tlast) (42.28 ng/ml x h) were highest and t(max) (3.5 h) was shortest after administration of the reference tablet. AUC(0-tlast) reached 78% (90% CI 43 - 139%) after small intestine administration and 2% (90% CI 1 - 9%) following rectal administration, respectively, relative to the values for the oral tablet. CONCLUSION: Trospium chloride is absorbed primarily in the upper gastrointestinal tract. Development of modified release preparations must balance prolonged apparent absorption rates of the drug against a decrease in bioavailability.

Pharmacokinetics and bioequivalence of tiropramide in healthy volunteers.

Two formulations of tiropramide ((+/-)alpha-(benzoylamino)-4-[2-(diethylamino) ethoxy]-N,N-dipropyl-benzenepropanamide hydrochloride, CAS 55837-29-1), an antispasmodic agent, were orally administered to 16 healthy volunteers by the Latin cross-over design with the purpose of evaluating bioequivalence and pharmacokinetics of tiropramide. Tiropramide in human plasma was determined by a gas chromatography/nitrogen phosphorus detector. The detection limit of tiropramide was 5 ng/ml. Cmax values of test and reference formulations were 93.9 +/- 54.3 and 96.4 +/- 51.6 ng/ml, respectively. AUC0-->last and AUC0-->inf were 330.7 +/- 193.9 and 349.5 +/- 205.3 ng.h/ml, respectively, for the test formulation, 348.9 +/- 207.7 and 380.8 +/- 239.0 ng.h/ml, respectively, for the reference formulation. The terminal half-life was 2.34-2.61 h. Bioavailability differences for Cmax and AUC0-->last were -2.48% and -5.22%, respectively. Minimum detection differences were less than 20% for both Cmax and AUC0-->last. The 90% confidence limits of geometric mean values for logarithmically transformed Cmax and AUCs were within 0.8-1.25. Based on these results, the two formulations of tiropramide are considered to be bioequivalent.

Quantitative analysis of tiropramide in human blood by gas chromatography with nitrogen-phosphorus detector.

The analytical method of antispasmodic agent tiropramide ((+/-)alpha-(benzoylamino)-4-[2-(diethylamino)ethoxy]-N,N-dipropylbenzenepropanamide hydrochloride) was developed by gas chromatography/nitrogen-phosphorus detector (GC/NPD) in human plasma. Two kinds of tiropramide tablets were orally administered to volunteers by Latin square crossover design, and blood was withdrawn as designed schedule. The plasma of 1 mL was loaded on Sep-pak C18 cartridge and eluted with methanol after washing with 30% methanol. The residue dissolved in 100 microL of methanol after evaporation was analyzed by GC/NPD. Precision (CV%) of intra-day was located within 2.6% and accuracy was less than 9.7%. Inter-day precision was below 8.7% and accuracy was relatively good as less than 14%. Plasma samples obtained from human volunteers were analyzed for the determination of tiropramide concentration by using this method. The method was sensitive, rapid and suitable enough to be applied for pharmacokinetic and bioequivalence studies of tiropramide in human volunteers.

Bioavailabilities of quercetin-3-glucoside and quercetin-4'-glucoside do not differ in humans.

The flavonoid quercetin is an antioxidant which occurs in foods mainly as glycosides. The sugar moiety in quercetin glycosides affects their bioavailability in humans. Quercetin-3-rutinoside is an important form of quercetin in foods, but its bioavailability in humans is only 20% of that of quercetin-4'-glucoside. Quercetin-3-rutinoside can be transformed into quercetin-3-glucoside by splitting off a rhamnose molecule. We studied whether this 3-glucoside has the same high bioavailability as the quercetin-4'-glucoside. To that end we fed five healthy men and four healthy women (19-57 y) a single dose of 325 micromol of pure quercetin-3-glucoside and a single dose of 331 micromol of pure quercetin-4'-glucoside and followed the plasma quercetin concentrations. The bioavailability was the same for both quercetin glucosides. The mean peak plasma concentration of quercetin was 5.0+/-1.0 micromol/L (+/-SE) after subjects had ingested quercetin-3-glucoside and 4.5+/-0.7 micromol/L after quercetin-4'-glucoside consumption. Peak concentration was reached 37 +/-12 min after ingestion of quercetin-3-glucoside and 27+/-5 min after quercetin-4'-glucoside. Half-life of elimination of quercetin from blood was 18.5+/-0.8 h after ingestion of quercetin-3-glucoside and 17.7+/-0.9 h after quercetin-4'-glucoside. We conclude that quercetin glucosides are rapidly absorbed in humans, irrespective of the position of the glucose moiety. Conversion of quercetin glycosides into glucosides is a promising strategy to enhance bioavailability of quercetin from foods.

Soft drugs--XVI. Design, evaluation and transdermal penetration of novel soft anticholinergics based on methatropine.

Atropine has been reported to produce unwanted systemic side effects on topical administration into the eye. The same problem could arise when atropine is used topically as a suppressant of eccrine sweating. In this study, the principles of soft drug design were applied to methatropine. A hypothetical carboxylate metabolite of methatropine was reactivated by esterification with cyclic and alicyclic alcohols to yield a series of compounds (3a-g). In vitro evaluation by guinea pig ileum assay indicated that the compounds are potent anticholinergics and the lead carboxylate metabolite is about 60 times less potent than the most active compound of the series. The activity was found to decrease with the increasing side chain length. The n-octanol/water partition coefficients were found to be directly dependent on the chain length for the compounds made with straight chain alcohols. The transdermal permeability coefficients across the hairless mice skin were found to be directly dependent on the partition coefficients. The soft drugs are found to metabolize extensively during the penetration process compared to the unmetabolizable nature of methatropine. The soft drugs reported in this study will probably be able to elicit a local action at the site of application but will probably be metabolized rapidly in the systemic circulation, thereby avoiding the systemic side effects with a consequent increase in the therapeutic index.

Opioid receptor agonists D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin and ethylketocyclazocine in the brain accentuate digoxin-induced arrhythmias.

OBJECTIVE: To examine the potential effects of two opioid receptor agonists in the brain on digoxin-induced cardiac arrhythmias and to explore cholinergic mechanisms in any potential effect on arrhythmias. METHODS AND RESULTS: Digoxin-induced arrhythmias were produced in guinea pigs (weighing between 280 and 350 g) that received digoxin 50 micrograms/kg intravenous bolus plus digoxin 500 micrograms/kg/h intravenously. Animals received D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin (FK 33,824) (50 or 100 micrograms/kg), ethylketocyclazocine (EKC) (50, 10 or 1 micrograms/kg) or saline (control) into the lateral cerebroventricle prior to digoxin. FK 33,824 produced significant (P less than 0.05) dose-dependent reductions in the threshold for digoxin-induced arrhythmias. The mean digoxin dosage at the development of fatal arrhythmias after the 100 micrograms/kg of FK 33,824 was 30% lower than the control group. EKC also produced significant (P less than 0.05) dose-dependent reductions in the threshold for digoxin-induced arrhythmias and the mean dose at development of fatal arrhythmias was 67% lower than the control group after 50 micrograms/kg of EKC. In the absence of digoxin, the highest dosages of each of these opioids did not produce arrhythmias. Changes in blood pressure and heart rate were unlikely explanations for the observed actions of these opioids because D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin accentuated the increase in blood pressure that accompanied digoxin while EKC reduced the blood pressure response to digoxin and neither altered the heart rate response to digoxin. In the control group, fatal digoxin-induced arrhythmias were ventricular tachyarrhythmias in two-thirds of cases and complete heart block in the remainder. These opioids accentuated the development of complete heart block. The role of the cholinergic system was explored for only EKC because both opioids produce similar effects on arrhythmias, using atropine sulphate which crosses the blood brain-barrier and atropine methylnitrate which does not enter the central nervous system. Atropine sulphate, but not atropine methylnitrate, slightly blunted but did not reverse the action of EKC. CONCLUSIONS: These data indicate that: two opioids in the brain--D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin and EKC--alter the threshold for development of digoxin-induced arrhythmias, specifically accentuating development of complete heart block produced by digoxin; and cholinergic mechanisms play only a small role in modulating the action of EKC on digoxin-induced bradyarrhythmias.