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Dissociation between opiate-like and antidiarrheal activities of antidiarrheal drugs.

Three synthetic antidiarrheals, diphenoxylate, loperamide and SC 27166, and two narcotics, morphine and codeine, were evaluated in rats by the intravenous and oral route for specificity and duration of their antidiarrheal, opiate-like and acute toxic effects. The activity in the castor oil test, the tail withdrawal test and the acute toxicity test was used to determine the relative antidiarrheal specificity and relative safety margins. An analysis of animal and clinical data indicate these tests to be excellent indicators of clinical usefulness and specificity. Intravenously, all five agents induced opiate-like central effects, loperamide and SC 27166 at near toxic doses only. When administered orally loperamide and SC 27166 were devoid of opiate-like central nervous system activity. Analysis of the plasma levels after oral loperamide indicated that this drug does not attain a concentration high enough to induce opiate-like central effects. All agents were effective antidiarrheals by the oral route with loperamide being the most potent (ED50 = 0.15 mg/kg), longest acting (ED50 8 hr = 1.81 mg/kg) and most specific (relative antidiarrheal specificity, 8 hr greater than or equal to 88) and having the greatest relative safety margin (8 hr = 102).

Administration, Oral

Antidiarrheal and central nervous system activities of SC-27166 (2-[3 - 5 - methyl - 1, 3, 4 - oxadiazol - 2 - yl) - 3, 3 - diphenylpropyl] - 2 - azabicyclo [2.2.2]octane), a new antidiarrheal agent, resulting from binding to opiate receptor sites of brain and myenteric plexus.

Pharmacological studies were performed to investigate the interaction of SC-27166 (2-[3-(5-methyl-1,3,4--oxadiazol-2-yl)-3,3-diphenylpropyl]-2-azabicyclo[2.2.2]octane), a new antidiarrheal agent, with opiate receptor sites in vitro and in vivo. Morphine, loperamide and SC-27166 inhibited the binding of [3H]naloxone to homogenates of guinea-pig brain and myenteric plexus and the inhibition was diminished in the presence of 100 mM Na+. Unlike that of morphine and [3H]naloxone itself, the binding of loperamide and SC-27166 was complex and Scatchard plots indicated the presence of low and high affinity sites for both compounds. Morphine, loperamide and SC-27166 inhibited the contractions of electrically driven longitudinal muscle from guinea-pig ileum and naloxone antagonized these effects. In the anesthetized dog, i.v. administration of morphine and SC-27166 enhanced the contractile activity of circular muscle in proximal and distal duodenum and distal ileum but duodenal longitudinal muscle was relaxed; these effects were completely reversed by subsequent administration of naloxone. In the rat, p.o. administration of loperamide and SC-27166 inhibited intestinal propulsion at doses considerably lower than were necessary to produce activity in the hot plate test; this specificity of action was not seen with morphine. In the rat, p.o. administration of loperamide and SC-27166 inhibited diarrhea at doses considerably lower than were necessary to produce withdrawal symptoms. The authors concluded that both loperamide and SC-27166 are specific antidiarrheal agents that produce both their central and antidiarrheal effects by binding to opiate receptor sites.

Animals

In vivo antimotility and antidiarrheal activity of lidamidine hydrochloride (WHR-1142A), a novel antidiarrheal agent. Comparison with diphenoxylate and loperamide.

1-(2,6-Dimethylphenyl)-3-methyl-amidinourea hydrochloride (WHR-1142A, lidamidine hydrochloride) was shown to have potent antimotility, antidiarrheal and intestinal antisecretory activity in mice, rats and dogs. Antimotility activity was demonstrated in charcoal intestinal motility, gastric emptying and gastric and intestinal intraluminal pressure studies. Antidiarrheal activity was evaluated in castor oil-, prostaglandin E2-, carbachol-, and serotonin-induced diarrhea. Intestinal secretion induced by cholera toxin was inhibited by WHR-1142A. In general, WHR-1142A was more potent than diphenoxylate and loperamide although species differences were noted. The ED50 for inhibition of castor oil-induced diarrhea was 1.8 mg/kg p.o. and the duration of action at 16 mg/kg p.o. was at least 6 h. Unlike diphenoxylate, WHR-1142A showed no tolerance.

Amidines

Over-the-counter antidiarrheal medications used for the self-treatment of acute nonspecific diarrhea.

Because there are approximately 100 over-the-counter (OTC) products available for self-treatment of acute diarrhea, it is difficult for consumers or even pharmacists and physicians to be sure which products are both safe and effective. Until Congress expanded the authority of the Food and Drug Administration in 1962, manufacturers only had to prove that their products were safe. Unfortunately, a majority of OTC products that are now available were on the market before 1962. To eliminate all noneffective products, the Food and Drug Administration established a three-phase OTC drug review process. The ultimate goal of this process is to ensure that all OTC medications are safe and effective and carry full and informative labeling. In 1975, the Advisory Review Panel on OTC Laxative, Antidiarrheal, Emetic, and Antiemetic Drug Products published its recommendations on which OTC antidiarrheal ingredients were both safe and effective [Antidiarrheal drug products for over-the-counter human use: proposed monograph. Federal Register 1975; 40: 12902-12944]. After consideration of these recommendations, public comment, and presented new evidence, the Food and Drug Administration published its preliminary safe and effective ingredient listing [Antidiarrheal drug products for over-the-counter human use: tentative final monograph. Federal Register 1986; 51 (83): 16138-16149]. At this time, only three ingredients fulfill both requirements: attapulgite, polycarbophil, and loperamide. The Food and Drug Administration's final decision (to be reported in a monograph) is still forthcoming. Upon publication of this monograph, only antidiarrheal products that contain ingredients in this listing will be allowed to be marketed.

Acute Disease

Studies of the antidiarrheal action of clonidine. Effects on motility and intestinal absorption.

Clonidine, an alpha 2-adrenergic agonist, has been reported to stimulate the rate of electrolyte absorption in vitro, to alter intestinal motility in vivo, and to have antidiarrheal effects in animals. Experiments were performed in 8 healthy volunteers in order to evaluate the antidiarrheal effect of clonidine in humans. When diarrhea was induced by intragastric infusion of 2700 ml of balanced electrolyte solution over 90 min, oral administration of 0.3 mg of clonidine reduced the volume of rectal effluent by 48% (from 1233 +/- 62 to 640 +/- 77 ml, p less than 0.001), a clear-cut antidiarrheal effect. Clonidine increased total gut volume significantly (from 987 +/- 91 to 1830 +/- 142 ml, p less than 0.001), suggesting that clonidine exerted its antidiarrheal effect by altering gut motility, i.e., increasing the capacity of the gut and slowing the transit of fluid through the intestine. In other experiments, the net absorption rate of the whole gut during steady state total gut perfusion was measured. The rate of absorption of fluid was transiently stimulated by clonidine by 15% (from 696 +/- 77 to 799 +/- 55 ml/h, p less than 0.02), indicating an additional effect on mucosal cell function. These studies indicate that in this experimental diarrhea model, clonidine has antidiarrheal properties that are due largely to effects on motility of the gut but that clonidine also modestly stimulates the net rate of absorption by intestinal mucosa.

Adult

Is in vivo dissociation between the antipropulsive and antidiarrheal properties of opioids in rats related to gut selectivity?

The antipropulsive activity of a series of opioids in the charcoal test was compared with their antidiarrheal activity in the castor oil test and their analgesic activity in the tail withdrawal test. The obtained antipropulsive/antidiarrheal potency ratios varied from 0.71 to greater than 552 [pethidine (oral ED50's in mg/kg: 21.5/30.2), fentanyl (0.77/0.49), dextromoramide (5.39/2.90), methadone (14.2/6.38), codeine (98.4/10.8), morphine (56.6/5.21), diphenoxylate (8.15/0.54), nufenoxole (74.7/1.72), difenoxin (7.10/0.16), loperamide oxide (greater than 160/0.34) and loperamide (greater than 160/0.29)]. The above ratios correlated with the gut selectivity of the compounds as defined by their analgesic/antidiarrheal potency ratios (r = 0.92, P less than 0.001). Furthermore, inhibition of propulsion was found to correlate with central analgesic activity (r = 0.93, P less than 0.001) but not with protection from diarrhea (r = 0.023, P greater than 0.05). Indeed, gut-selective opioids such as loperamide and loperamide oxide failed to affect propulsion up to doses more than 450 times their antidiarrheal doses. In contrast, alpha 2-adrenoceptor agonists delayed propulsion at doses comparable to their antidiarrheal doses [clonidine (0.085 vs 0.021), lidamidine (2.35 vs 1.66)] and anticholinergics inhibited propulsion even at doses many times below their antidiarrheal doses [atropine (0.26 vs 9.30), dexetimide (0.13 vs 5.03) and isopropamide (0.78 vs 74.6)]. The present results indicate that the in vivo inhibition of gastrointestinal propulsion by opioids in rats is mediated by a central action. Effects on intestinal fluid transport or, alternatively, on motility events distal to the ileocecal junction rather than effects on propulsion through the small intestine, seem to be the primary mechanism of antidiarrheal action of gut-selective opioids such as loperamide and loperamide oxide.

Adrenergic alpha-Agonists

The pharmacology of SC-27166: a novel antidiarrheal agent.

SC-27166 is the result of continuing efforts to discover selective and orally active antidiarrheal agents. SC-27166, which is chemically unrelated to opiates or neuroleptics, possesses potent constipating and antidiarrheal activity in several animal models. Tolerance to the constipating actions of SC-27166 did not develop in mice. On the other hand, gut tolerance rapidly developed to morphine sulfate and loperamide. The basic mechanism of the antidiarrheal action of SC-27166 is a consequence of increased intestinal circular muscle contractile activity. Supportive pharmacological studies indicated that SC-27166 has equivocal analgesia in mice which is manifested at near toxic dose levels. SC-27166 was also evaluated for potential dependence liability in morphine abstinence-induced jumping in mice. The abstinence-induced jumping was suppressed to a far lesser extent by SC-27166 than by either loperamide or diphenoxylate at equal doses. SC-27166 was also devoid of anticbholinergic activity. When compared with the reference standards morphine and diphenoxylate, these pharmacological studies indicated that SC-27166 has a high degree of separation of undesirable central nervous system actions from its antidiarrheal properties and may have important therapeutic potential.

Analgesics

Spinally mediated opioid antidiarrheal effects.

To assess the role of opioid receptors in the spinal cord in regulation of functions of the intestinal mucosa in a secretory model, we evaluated the ability of i.t. administered mu (PL017), delta (DPDPE) and kappa (U50,488H) selective opioid agonists to inhibit diarrhea produced in mice by an injection of prostaglandin E2 (PGE2) (200 micrograms/mouse, i.p.). I.t. PL017 and DPDPE inhibited diarrhea in a dose-related fashion. U50,488H had only minimal antidiarrheal effects. The i.t. doses of PL017 and DPDPE required to inhibit diarrhea were higher than the doses required to produce antinociception and inhibit gastrointestinal transit. Spinally administered PL017 and DPDPE were considerably less potent in the diarrhea model than after i.c.v. administration but far more effective than after peripheral (s.c.) dosing. The antidiarrheal effects of spinally administered opioids were antagonized by concurrently administered naloxone. These data indicate that opioid chemosensitive sites in the spinal cord can modulate diarrhea produced by PGE2, and that the receptor specific opioids, PL017 and DPDPE, and to a lesser extent U50,488H, all possess antidiarrheal activity when administered i.t.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh

Pharmacological aspects of therapy in inflammatory bowel diseases: antidiarrheal agents.

We review the use of antidiarrheal medications in inflammatory bowel disease, commenting on potential underlying immunologic mechanisms as a background for discussion of the clinical usage of antidiarrheal medications in this disease spectrum. We comment on new directions for the development of more effective therapeutic approaches and discuss the mechanism of action of antidiarrheal drugs, with emphasis on synthetic opiates.

Antidiarrheals

Decreased tetracycline bioavailability caused by a bismuth subsalicylate antidiarrheal mixture.

Oral coadministration of a single 250-mg tetracycline capsule and 60 ml of a bismuth subsalicylate antidiarrheal mixture reduced tetracycline absorption by 34% without appearing to perturb its absorption or disposition rate. A pronounced increase in intersubject tetracycline absorption variability also was noted. Apparently, the reduction in tetracycline bioavailability previously reported with a kaolin-pectin suspension is not peculiar to kaolin-pectin but can be expected with almost any antidiarrheal whose mechanism of action is adsorptive in nature.

Adult

The antidiarrheal action of bismuth subsalicylate in the mouse and the rat.

The antidiarrheal effectiveness of bismuth subsalicylate was determined in two species of laboratory animals. Doses of castor oil were, at first, found to accelerate significantly the movement of a charcoal test meal along the small intestine of the mouse and rat and also to increase both the fecal output (dry or wet weight) and the frequency of diarrhea in mice. Bismuth subsalicylate significantly prevented the enhancement of charcoal-meal transport induced by castor oil in both mice and rats. Increased fecal outut (dry or wet weight) and increased frequency of diarrhea in mice were also significantly reduced by bismuth subsalicylate in a dose-related fashion. The findings in these experiments lead to the definitive conclusion that bismuth subsalicylate exerts antidiarrheal activity in the mouse and in the rat and support its use in therapy of common clinical diarrheal states.

Animals

Antidiarrheal therapy. Prospects for new agents.

Successful treatment of severe diarrhea has traditionally relied upon opiates or opiate derivatives. Recent advances in our understanding of intestinal fluid and electrolyte absorption have provided the opportunity to develop therapeutic agents specific for various points in the secretory and absorptive process. Present and proposed antidiarrheal agents, in addition to antimotility activity, will be capable of stimulating intestinal fluid absorption, inhibiting intestinal fluid secretion, or both. The mechanism(s) of action and clinical implications for proposed antidiarrheal agents are reviewed.

Antidiarrheals

Normalization of small intestinal propulsion with loperamide-like antidiarrheals in rats.

Gastrointestinal propulsion and the presence of diarrhea were assessed in rats pretreated with various opioids and challenged orally with either castor or paraffin oil, which both contained phenol red as a marker of gastrointestinal propulsion. In solvent-pretreated rats, diarrhea was always observed within 90 min after castor oil, reflecting a state of hyperpropulsive activity of the gut, but never (up to 8 h) after paraffin oil, reflecting normal intestinal propulsion (which amounted to an average distance of 91% of the total length of the small intestine in 90 min). Paraffin oil propulsion was blocked (to values less than 60%) by all opioids tested with the exception of the gut-selective compounds loperamide, loperamide oxide and fluperamide oxide (ED50s: greater than or equal to 160 mg/kg). Castor oil diarrhea was antagonized by all opioids tested and, at comparable but slightly (1.3-2.6 times) higher doses, propulsion was normalized to values (less than 100%) comparable to those measured in paraffin oil-challenged control rats. Castor oil propulsion was further reduced to subnormal values (less than 60%) by still higher doses of the opioids, comparable to those that blocked propulsion after paraffin oil. However, the required dose increment varied consistently among the opioids tested and ranged, depending on gut selectivity, from a factor 2.3 times the antidiarrheal dose for narcotic analgesics such as pethidine and dextromoramide to greater than 300 for antidiarrheals such as loperamide, loperamide oxide and fluperamide oxide. Protection from diarrhea and normalization of propulsion showed a close correlation; both failed to correlate with central analgesic activity and are thought to be mediated via peripheral opioid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesics

Antidiarrheal properties of supraspinal mu and delta and peripheral mu, delta and kappa opioid receptors: inhibition of diarrhea without constipation.

We evaluated the ability of mu [morphine, Tyr-Pro-N-MePhe-D-Pro-NH2 (PLO17)], delta (Tyr-D-Pen-Gly-Phe-D-Pen) (DPDPE) and kappa [U50,488H, (trans-3,4-dichloro-N-methyl-N-(2-(1-pyr-rolidinyl) cyclo-hexyl)benzeneacetamine)] opioid receptor selective agonists to inhibit diarrhea induced by castor oil (0.6 ml p.o.) in mice after supraspinal (i.c.v.) and peripheral (s.c.) administration. The antidiarrheal potency of each compound was compared to its analgesic and gastrointestinal antitransit potency when given by the same route of administration. When administered i.c.v., morphine, PLO17 and DPDPE inhibited diarrhea in a dose-related fashion. The mu agonists, morphine and PLO17, given i.c.v, inhibited diarrhea at doses much lower than those needed to produce analgesia or to inhibit gastrointestinal transit. DPDPE (i.c.v.) was equipotent in inhibiting diarrhea and in eliciting analgesia, but did not effect the rate of transit. U50,488H (i.c.v.) inhibited diarrhea only at extremely high doses which also caused profound postural-motor incapacitance. U50,488H given i.c.v. had no effect on transit at any dose. When given peripherally, morphine, PLO17, DPDPE and U50,488H all inhibited diarrhea in a dose-related fashion. All four compounds inhibited diarrhea at doses much below those needed to cause analgesia. Morphine s.c. and PLO17 s.c. both inhibited diarrhea at doses lower than those required to inhibit transit. DPDPE s.c. and U50,488H s.c. had no effect on transit at any dose. The antidiarrheal effects of i.c.v. morphine, i.c.v. PLO17 and i.c.v. DPDPE were antagonized by pretreatment with 1 microgram i.c.v. of naltrexone.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh

WHR 1049, a potent metabolite of lidamidine, has antidiarrheal and antimotility effects on the small intestine in rats.

Lidamidine HCl has been suggested to be effective in treating certain motor disorders of the gastrointestinal tract. Lidamidine has alpha-2 agonist as well as local anesthetic properties. We studied the antimotility and antidiarrheal activity of WHR 1049, a hepatic metabolite of lidamidine known to have some activity and to persist longer in the serum than does lidamidine. We recorded the intestinal myoelectric activity of fasted unanesthetized rats with bipolar electrodes implanted on their proximal jejunum. We found that lidamidine HCl, given by gavage, inhibited fasting myoelectric activity in a dose-dependent manner (using 0.5-4.0 mg/kg). Neither saline nor tetracaine inhibited myoelectric activity. WHR 1049 given by gavage also inhibited myoelectric activity and was 30 times as potent as lidamidine (milligram per milligram, using 0.0625- to 0.25-mg/kg doses). Pretreatment with yohimbine (5 mg/kg s.c.), before administration of WHR 1049, decreased the myoelectric activity inhibition by two-thirds (but did not completely block it). Castor oil (1 ml/200 g b.wt.) was given to induce diarrhea and did so when given alone or with saline (vehicle) pretreatment. When these animals were pretreated with 0.25 mg/kg of WHR 1049, the same dose of castrol oil did not induce diarrhea for a 6-hr observation period. We conclude that WHR 1049 is a potent metabolite of lidamidine that inhibits myoelectric activity, has significant alpha-2 agonist activity and blocks induced diarrhea. Because tetracaine does not inhibit myoelectric activity we suggest that the local anesthetic properties of lidamidine do not account for any of the myoelectric activity inhibition. WHR 1049 may account for much of the antimotility and antidiarrheal activity of lidamidine.

Action Potentials

Different actions of 2 antidiarrheal agents, lidamidine and loperamide, on motility of the isolated cat colon muscle.

Besides their action on intestinal absorption and secretion antidiarrheal agents may affect gastrointestinal motility. Little is known about motor actions in the large intestine. Therefore, the effects of loperamide and lidamidine on contractile and myoelectrical activity were studied in strips of the circular muscle of the cat colon in vitro. Both drugs caused a concentration dependent increase in spontaneous contractions, but the potency of loperamide was greater than that of lidamidine and the efficacy of lidamidine greater than that of loperamide. The corresponding EC50 were 2.9 X 10(-9) M and 1.4 X 10(-5) M, respectively, and the EC100 2.7 X 10(-7) M and 10(-4) M, respectively. In the myoelectrical tracings loperamide stimulated predominantly spike activity, lidamidine oscillatory potentials. The effect of loperamide was antagonized by naloxone, thus indicating an action on opiate receptors. The effect of lidamidine was not inhibited by a variety of drugs. Tetrodotoxin and alpha-adrenergic inhibitors even exaggerated the lidamidine effect, probably by a suppression of tonic nervous inhibition. The receptor for the lidamidine action has yet to be determined. In conclusion, the motor effects may play an important role in the antidiarrheal action of loperamide, but probably not in that of lidamidine, at least not within the range of clinically used doses.

Animals