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Naltrexone is a μ-opioid receptor antagonist that has been extensively studied for its ability to block the rewarding effects of ethanol. Opioid receptors are widely distributed within the gastrointestinal tract (GIT). Typically, naltrexone is administered by parenteral routes in nonclinical studies. We initially tested if opioid receptors within the GIT would influence the ability of oral naltrexone to inhibit ethanol oral self-administration in rats using the co-administration of oral loperamide, a peripherally restricted opioid agonist. As expected, oral naltrexone only had modest effects on ethanol intake, and the response was not dose-dependent. However in rats, treatment with loperamide prior to the administration of naltrexone resulted in a suppression of ethanol intake which approached that observed with naltrexone given by the subcutaneous (SC) route. Importantly, administration of loperamide prior to administration of naltrexone did not alter blood concentrations of naltrexone. We then evaluated if oral loperamide would enhance effects of baclofen (a GABA(B) receptor agonist) and AM-251 (a CB-1 receptor antagonist) and found that pre-treatment with loperamide did potentiate the action of both drugs to reduce ethanol self-administration. Finally, the specific opioid receptor type involved was investigated using selective μ- and κ-receptor antagonists to determine if these would affect the ability of the AM-251 and loperamide combination to block ethanol drinking behavior. The effect of loperamide was blocked by ALKS 37, a peripherally restricted μ-receptor antagonist. These data suggest an important role for opioid receptors within the GIT in modulating central reward pathways and may provide new insights into strategies for treating reward disorders, including drug dependency., (Copyright © 2011 Elsevier Inc. All rights reserved.)

In a randomized, double-blind, placebo-controlled trial, 227 US adults with acute diarrhea in Mexico received a single dose of sulfamethoxazole and trimethoprim (1600/320 mg) or 3 days of therapy with loperamide hydrochloride (4-mg loading dose, then 2 mg orally after each loose stool), sulfamethoxazole-trimethoprim (800/160 mg orally twice daily), or the combination of both. Subjects treated with the combination had the shortest average duration of diarrhea compared with the placebo group (1 hour vs 59 hours), took the least amount of loperamide after the loading dose (3.8 mg), and had the shortest duration of diarrhea associated with fecal leukocytes or blood-tinged stools (4.5 hours). A single dose of sulfamethoxazole-trimethoprim was also efficacious (28 vs 59 hours), but loperamide alone was significantly effective only when treatment failures were treated with antibiotics (33 vs 58 hours). The combination of sulfamethoxazole-trimethoprim plus loperamide can be highly recommended for the treatment of most patients with traveler's diarrhea.

In anesthetized dogs, intravenous administration or intrajejunal infusion of Loperamide produced the excitatory effect of gastric, small and large bowel motilities accompanied with elevation of the muscle tone. The excitatory response was slightly suppressed by administration of atropine. Such effects were similar to those of morphine and methadone. In non-anesthetized spinal guinea pigs, Loperamide increased colonic motility accompanied with the augmentation of the colonic muscle tone, but the conduction of the contraction waves was prevented. In anesthetized guinea pigs, intravenous administration of Loperamide reduced the rate of the rhythmic contraction waves of the small intestine, but its effect on the muscle tone was not evident. The activity of Loperamide as an antidiarrheal agent was discussed.

Effects of the currently marketed form of loperamide (Imodium capsules) that might relate to abuse potential were examined. Study I was a double-blind "dose run-up" in adult male subjects with a history of illicit drug use but no history of opioid addiction. Subjective responses to doses of loperamide ranging from 12 to 60 mg were compared with responses to 120 mg codeine sulfate (96 mg base) and to placebo. Based on study I, loperamide (60 mg) was used in study II and its effects were compared with those of codeine (96 mg base) and placebo in an exaddict subject group. Study II subjects had had extensive opioid experience but were not actively addicted at the time of this double-blind, inpatient study. In study II, as in study I, unlike loperamide and placebo, codeine induced pupillary constriction. Loperamide (60 mg) induced a detectable subjective effect in somewhat over half the subjects, was "liked" little or not at all, and was identified as "dope" at a frequency less than that for a threshold dose of oral codeine. It was concluded that in its present form, i.e., capsules containing loperamide mixed with magnesium stearate, loperamide poses little threat of potential abuse.

Symptom scores, stool data, and the transit of a standard, solid meal were measured in 28 patients with irritable bowel syndrome (IBS) during baseline conditions and after five weeks of treatment with placebo and loperamide, given as a flexible dosage regime in the form of a double-blind, cross-over trial. All patients had undergone a comprehensive series of diagnostic investigations and had failed to respond to dietary supplementation with coarse wheat bran (10-30 g daily). Loperamide treatment accelerated gastric emptying, compared with placebo (1.2 +/- 0.1 vs 1.5 +/- 0.1 hr; P less than 0.001) and delayed both small bowel (6.2 +/- 0.3 vs 4.3 +/- 0.3 hr; P less than 0.001) and whole gut transit (56 +/- 5 vs 42 +/- 4 hr; P less than 0.01). Eighteen patients said they felt better taking loperamide compared with placebo and, at follow up, 15 of these patients remained satisfied with the effects of the drug. Most symptoms improved significantly on placebo compared with the baseline period, but three of these [diarrhea (P less than 0.01), urgency (P less than 0.01) and borborygmi (P less than 0.05)] showed a further significant improvement on loperamide. Improvement in diarrhea was not associated with any change in stool weight but was associated with reductions in stool frequency (P less than 0.001), passage of unformed stools (P less than 0.01), and incidence of urgency (P less than 0.001). Urgency was the only symptom that was significantly more common in the success group, compared with the group who did not feel better on loperamide.

A pharmacokinetic study of the antidiarrheal agent loperamide hydrochloride (Imodium) was conducted in six male subjects. The study utilized a random crossover design and employed a 2-mg capsule and a 0.2-mg/ml syrup formulation. Each treatment consisted of a single oral dose of 8 mg loperamide HCl followed by a two-week interval before the next treatment. Serum and urine samples obtained at various times after drug administration were assayed for loperamide using a radioimmunoassay specific for the drug. The mean biologic half-life, calculated from the elimination phase of the log serum concentration-versus-time data, was 10.8 +/- 0.6 hours for the overall study, 10.2 +/- 0.6 hours for the syrup formulation, and 11.2 +/- 0.8 hours for the capsules. The loperamide from the syrup was absorbed more rapidly than from the capsule formulation, with the peak serum levels observed at a mean time of 2.4 +/- 0.7 hours for the syrup and 5.2 +/- 0.3 hours for the capsule formulation. The relative areas under the serum loperamide concentration-versus-time curves suggested that the two formulations have comparable physiologic availability. The maximum observed serum concentrations were also similar, indicating the safety of the syrup formulation. Excretion of approximately 1 per cent of the dose in the urine as unchanged loperamide after seven days was observed independent of the particular dosage form that was administered.

A total of 315 young children with acute diarrhoea were included in a double blind, hospital based multicentre trial of loperamide at two dose levels (0.8 mg and 0.4 mg/kg/24 h), given with standard oral rehydration therapy versus placebo plus oral rehydration therapy. The overall recovery rate was slowest in the placebo group and fastest in the group given loperamide 0.8 mg. Comparisons between weights on admission and weights by day 3 showed that a larger proportion of children in the loperamide groups gained weight than in the placebo group. No serious side effects of loperamide were observed, but the drug was withdrawn in one infant because of mild abdominal distention. The results indicate that loperamide, in the doses employed, is safe and may in selected cases be a useful adjunct to oral rehydration in the management of acute diarrhoea in well nourished children.

Loperamide is an effective and safe antidiarrheal agent which served as a very useful adjunct in the treatment in 79% of 47 patients with chronic diarrhea. One of the major advantages of loperamide to the patient with chronic diarrhea is its convenience. Usually, a single dose in the morning effectively controlled diarrhea during the day. Patients with nocturnal or early morning diarrhea obtained good control with a second bedtime dose of the drug.

Effects of loperamide on peristalsis in the guinea pig intestines were investigated in comparison with those of morphine and atropine. The following results were obtained. The ejection of intraluminal fluid produced by the peristaltic contraction of the isolated ileum was suppressed by loperamide at a concentration of 10(-8) or 2 X 10(-8) g/ml. Peristalsis in the intestinal loop of anesthetized guinea pigs was inhibited by i.v. administration of loperamide at a dose of 0.03 mg/kg. Morphine (0.03 mg/kg i.v.) and atropine (0.05 mg/kg i.v.) also inhibited the peristaltic contraction. The effect of loperamide continued longer than that of morphine. Peristalsis in the colonic loop of anesthetized guinea pigs was inhibited by i.v. administration of loperamide at a dose of 0.01 or 0.03 mg/kg. Morphine (0.1 mg/kg i.v.) and atropine (0.03 mg/kg i.v.) also inhibited the peristaltic contraction of the colonic loop. Loperamide (0.01 or 0.03 mg/kg i.v.) and morphine (0.1 mg/kg i.v.) caused a slight and temporary increase of resting level of intraluminal pressure with inhibition of peristalsis in the colonic loop. These results suggest that loperamide suppresses the peristaltic contraction caused by distension of the intestinal lumen.

Loperamide was compared double-blind with diphenoxylate and a placebo in 59 women with diarrhoea due to prostaglandin administration for mid-trimester abortion. Treatment was started with the intake of two capsules two hours before the first intramuscular injection of 15(S-)15 methyl prostaglandin F2alpha and was then adapted individually, i.e. one capsule after each unformed stool, with a maximum of ten per 24 hours. Both antidiarrhoeals were significantly more effective than the placebo in preventing diarrhoea, and loperamide was found to be more active than diphenoxylate. The course of abortion, BP and vital signs, or prostaglandin side-effects other than diarrhoea were not affected by either antidiarrhoeal, nor could any adverse experience be specifically attributed to them.

The effects of metoclopramide, bethanechol, and loperamide on the gastric residence time (GRT), gastric emptying (GE), and mouth-to-cecum transit time (MCTT) of a solution were investigated in three separate studies of five healthy male volunteers each. Metoclopramide in doses of 5, 10, and 15 mg prolonged GRT by 33, 88, and 162%, respectively, almost reaching statistical significance (p 0.058). A relationship was observed between GRT prolongation, and metoclopramide area under the plasma-time curve (p 0.01) and metoclopramide observed time to maximum concentration (p 0.01). Metoclopramide had an inconsistent effect on MCTT. Bethanechol 50 mg prolonged GRT by 64% (p 0.031) and had no effect on MCTT. Loperamide at doses of 2 and 8 mg prolonged GRT by 18 and 115% (p 0.043) and MCTT by 30 and 130% (p 0.0001), respectively. None of these motility-altering agents affected GE.

As no adequate comparison of these widely used drugs has been made, we have performed a double-blind cross-over trial in 30 individuals with chronic diarrhea. Each underwent three randomized treatment periods of 4 wk duration. Patients were instructed to increase the daily dose gradually until control was achieved or side effects became intolerable. Stool frequency, consistency, urgency, and incontinence were then compared when a stable dose was reached. Though 2.3 capsules (4.6 mg) of loperamide, 2.3 capsules (103.5 mg) of codeine and 2.5 capsulses (12.5 mg) of diphenoxylate all reduced stool frequency to the same extent, diphenoxylate was significantly less effective in producing a solid stool. Before treatment 95% of patients experienced urgency, sometimes associated with fecal incontinence, often as their major diability. Loperamide and codeine were more effective in relieving this than was diphenoxylate. Side effects, particularly central nervous effects, were greatest with diphenoxylate and least with loperamide. Approximately equal numbers discontinued each preparation; poor control and central-nervous-system side effects were the usual reasons for stopping diphenoxylate and codeine, and abdominal pain and constipation for stopping loperamide. We conclude that both loperamide and codeine phosphate are superior to diphenoxylate in the symptomatic treatment of chronic diarrhea.

Fifteen patients (20-66 years) with persistent diarrhoea of varying aetiology were selected for an open trial of loperamide 2 mg capsules. The optimal daily dose for substantial reduction of the diarrhoea ranged from two to seven capsules. Eleven patients showed a significant improvement in stool consistency, a highly significant decrease in stool frequency and a decrease of abdominal cramps. One ileostomy patient with abundant ileostomy output and intermittent leaking of the ileosotmy appliance at night experienced a substantial reduction of the stoma output with virtual disappearance of soiling accidents as night. Loperamide appeared to be ineffective in two patients with cholerrhoeic diarrhoea; in one patient with laxative-induced diarrhoea and in one patient with probable nervous diarrhoea. The eleven successfully treated patients then entered a doubleblind placebo-controlled trial for ten days or util relaps, the daily dose being indentical to the optimal one previously determined in the open phase of the study. The investigator was able to guess the code correctly in ten out of eleven cases. The drug was well tolerated. Because of its considerable efficacy and low side-effect liability, loperamide has to be considered a promising drug in the treatment of chronic diarrhoea.

Loperamide, a butyramide derivative is a new agent for use in symptomatic control of acute non-specific diarrhoea and chronic diarrhoea. Unlike diphenoxylate or codeine, loperamide does not appear to exert opiate activity in man at normal therapeutic doses. In acute diarrhoea, loperamide provides more rapid control of symptoms than diphenoxylate when given in a flexible dosage according to unformed bowel movements, and in single dose studies 4mg loperamide has a much longer duration of effect than 5mg diphenoxylate. Loperamide is probably superior to diphenoxylate in providing symptomatic control of chronic diarrhoea such as that associated with chronic inflammatory bowel disease or following gastrointestinal surgery. It has been used for up to 3 years in such conditions without evidence of tolerance. The possibility of once daily dosage of loperamide in chronic diarrhoea is an advantage. Side-effects have not proved a problem.

Loperamide, a novel antidiarrheal agent, was compared with diphenoxylate in a double blind crossover study of 23 patients with chronic diarrhea of various etiologies. Both agents were found to be capable of controlling or greatly reducing chronic diarrhea. Loperamide was superior to diphenoxylate in its abiltiy to decrease the frequency and improve the consistency of the stools, even at a 2.5-fold lower dose level.