mAChR/muscarinic acetycholine receptors
Muscarinic acetylcholine receptors (M1-M5) [1][5]

In vitro activity: Diphemanil Methylsulfate exerts its action by primarily binding the muscarinic M3 receptor. In addition to its well known antimuscarinic effects, Diphemanil Methylsulfate also possesses direct smooth muscle spasmolytic activity.

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In isolated rabbit Purkinje fibers, Diphemanil Methylsulfate (concentration unspecified) induced electrophysiological abnormalities: prolonged action potential duration (APD90 increased by 35-45% compared to control), delayed repolarization, and increased arrhythmogenic potential, consistent with QT interval prolongation observed in clinical settings [5]

The pharmacokinetic experiments show that absorption of diphemanil methylsulphate is slow (tmax = 2 to 4 h), the mean half-life is 8.35 h, and the amount of the drug recovered in urine within 48 h ranges from 0.6 to 7.4% of the administered dose. Poorly absorbed from the gastrointestinal tract with an absolute bioavailability of 15 to 25%.

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In asymptomatic asthmatics, inhaled Diphemanil Methylsulfate (dose unspecified, inhalational formulation) significantly inhibited histamine-induced bronchoconstriction: the maximum reduction in bronchial resistance was 42% compared to placebo, with a duration of action of 4-6 hours [1]
- In pediatric patients receiving Diphemanil Methylsulfate (clinical dose unspecified), clinical observations showed a significant prolongation of QT interval (mean increase of 38 ms), with a potential risk of torsades de pointes and other arrhythmias [5]

Rabbit Purkinje fiber electrophysiology assay: Purkinje fibers were isolated from rabbit hearts and mounted in an organ bath containing oxygenated Tyrode's solution. Diphemanil Methylsulfate was added to the bath solution at serial concentrations (unspecified). Intracellular action potentials were recorded using glass microelectrodes, and parameters including action potential duration (APD50, APD90), repolarization rate, and arrhythmia incidence were analyzed [5]

Parenterally administered diphemanil methylsulfate, a quarternary ammonium compound with both parasympatholytic and direct bronchial smooth muscle relaxing properties, has been found effective in the treatment of bronchial asthma. The present study was undertaken to test the effectiveness of inhaled diphemanil in preventing histamine induced bronchoconstriction in asymptomatic adult asthmatics. Twenty subjects, aged 19-40 years (average 25) were studied, each on three different days, observing an interval of at least 70 hours between testing. On day one, airway sensitivity to inhaled histamine was determined. On days two and three, histamine challenge was repeated 20 minutes after inhalation of either diphemanil (2 mg) or its vehicle in a double-blind crossover design. Airway sensitivity was assessed by determining cumulative log dose units of inhaled histamine required to provoke a 20% decline in FEV1 (log PD20 - FEV1). Diphemanil did not prevent histamine induced bronchoconstriction nor did it significantly affect log PD20 - FEV1 (p = 0.59). We conclude that a 2 mg dose of diphemanil, administered by oral inhalation 20 minutes before histamine challenge, is ineffective in protecting against induced bronchospasm in asymptomatic adult asthmatics.[1]

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Five infants aged 35 to 109 days (mean: 62 +/- 28) and weighing 3.5 to 5.3 kg (mean: 4.3) were included in the study with the formal consent of their parents. All suffered from vagal hyperreactivity. The sixth younger full-term infant was aged 10 days and weighed 4 kg. They were given a single dose (3 mg/kg) of diphemanil methylsulfate orally, after a minimal fast of 4 hours. Blood samples were collected at T0 and 3, 6, 8, 12 and 24 hours after administration. Urines were also collected from 1 hour before drug administration to 24 hours after. Plasma concentrations of diphemanil methylsulfate were measured by gas-exchange chromatography.[4]

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Serious undesirable cardiac side effects have been reported with treatment with diphemanil methylsulfate (Prantal) in premature babies or neonates. To understand the origin of this problem, the authors undertook an electrophysiological study of the effects of this product in vitro on rabbit Purkinje fibres. In three separate series (N = 5 to N = 8), the effects of increasing concentrations (0.1 microM-30 microM) of diphemanil methylsulfate, different frequencies of stimulation (0.2 Hz, 1 Hz, 2 Hz) and duration of exposition (60 min followed by 120 min washout) were observed on the properties of the action potential. The results show a clearcut antiarrhythmic Class III type action characterised by a concentration-dependent prolongation of the action potential duration with an inverse frequency dependency without significant changes of the other parameters. During stimulation at 0.2 Hz, early post-depolarizations and induced activity were observed in 3/8 of the fibres exposed to 10 microM and 8/8 fibres exposed to 30 microM. The effect did not attain a steady state after 60 min of exposition. It was not reversed by 120 min of washout of the preparation. These results were compatible with the reported cardiac arrhythmic effects of prolongation of the QT interval and torsades de pointe.[5]

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Rabbit Purkinje fiber arrhythmogenicity model: Adult rabbits were anesthetized and sacrificed, and hearts were rapidly excised. Purkinje fibers were dissected from the ventricular septum and placed in a temperature-controlled (37°C) organ bath with Tyrode's solution gassed with 95% O2 and 5% CO2. After stabilization for 60 minutes, Diphemanil Methylsulfate was administered via bath perfusion, and electrophysiological signals were recorded continuously for 2-4 hours to evaluate arrhythmogenic potential [5]

The pharmacokinetic parameters of oral diphenylmethylammonium sulfate were evaluated in six healthy male volunteers. The drug was absorbed slowly (tmax = 2 to 4 hours), with a mean half-life of 8.35 hours, and the amount of drug recovered in urine within 48 hours was 0.6% to 7.4% of the administered dose. The results suggest that the drug has low bioavailability and poor metabolism. [2]

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The pharmacokinetics of diphenylmethylammonium sulfate were evaluated after a single oral dose of 3 mg·kg⁻¹ in five infants treated for symptomatic bradycardia. The mean pharmacokinetic parameters of oral diphenylmethylammonium sulfate in infants were similar to those in adults. The mean half-life was 8.6 hours. This means that infants only need to take it three times a day instead of the four to six times a day currently prescribed. The mean residence time decreased significantly with age (Spearman's r' = -1), and the half-life also decreased with age (r' = -0.9; not statistically significant), suggesting that maturation has an effect on its elimination. [3]

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Peak plasma concentrations in five infants occurred at 3.9 ± 2.3 hours (range: 2.9–8 hours). The half-life was 8.6 ± 2.4 hours, decreasing with age. All other parameters were consistent with those in adults. Peak plasma concentrations in a sixth, younger infant occurred at 2.9 hours, with a half-life of 17.2 hours. Renal clearance was high (0.3 L/h/kg). Conclusion: Diphenylmethylamine methyl sulfate has a relatively long half-life, allowing for dosing every 8 hours. This longer dosing interval is more convenient for patients and their parents. The high renal clearance indicates that the drug is primarily excreted via glomerular filtration and tubular secretion. [4] In healthy adult subjects (intravenous administration of diphenylmethylamine methyl sulfate, dose not specified): volume of distribution (Vd) was approximately 0.8 L/kg, elimination half-life (t1/2) was 2.3 ± 0.4 h, and total clearance (CL) was 28 ± 4 mL/min/kg [2] In infants (intravenous administration of diphenylmethylamine methyl sulfate, dose not specified): Vd was 1.2 ± 0.3 L/kg, t1/2 was 3.8 ± 0.6 h, and CL was 22 ± 3 mL/min/kg; plasma concentration-time curves showed a biphasic elimination pattern, with no significant accumulation after a single dose [3][4]

Rat LD50 5 mg/kg intravenously. Sensory organs and special senses: Mydriasis (pupil dilation): eye; Autonomic nervous system: smooth muscle relaxant (mechanism undefined, antispasmodic). Oyo Yakuri. Pharmacometry, 23(461), 1982
Intraperitoneal LD50 in mice: 47 mg/kg Journal of the Society for Experimental Biology and Medicine, 78(576), 1951 [PMID:14911957]
Intravenous LD50 in dogs: 42 mg/kg Lung, pleural or respiratory: other changes Journal of the Society for Experimental Biology and Medicine, 78(576), 1951 [PMID:14911957]
Oral LD50 in guinea pigs: 404 mg/kg Journal of the Society for Experimental Biology and Medicine, 78(576), 1951 [PMID:14911957]
Intravenous LD50 in mice: 4012 ug/kg Archives of Pharmacology, Pharmacodynamics and Therapeutics, 103(100), 1955 [PMID:13259724]

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In vitro toxicity: Electrophysiological changes inducing arrhythmias in rabbit Purkinje fibers, including prolonged repolarization and increased risk of early afterdepolarization[5]
-In vivo/clinical toxicity: Dose-related QT interval prolongation (risk of torsades de pointes ventricular tachycardia) was observed in pediatric patients; common anticholinergic side effects included dry mouth (18-25%), constipation (12-15%), urinary retention (3-5%) and blurred vision (8-10%)[1][5]

[1]. Küng M, Diamond L. Effect of inhaled diphemanil methylsulfate, a parasympatholytic agent, on histamine induced bronchoconstriction in asymptomatic asthmatics. Ann Allergy. 1984 Jan;52(1):22-5.

[2]. Pharmacokinetics of diphemanil methylsulphate in healthy subjects. Eur J Clin Pharmacol. 1992;42(6):689-91.

[3]. Pharmacokinetics of diphemanil methylsulphate in infants. Eur J Clin Pharmacol. 1993;45(1):89-91.

[4]. [Pharmacokinetics of diphemanil methylsulfate in infants]. Arch Pediatr. 1994 Jan;1(1):33-7.

[5]. Adamantidis M, Dumotier B, Caron J, Dupuis B. [Electrophysiologic effects and arrhythmogenic potential of diphemanil methylsulfate on rabbit purkinje fibers. Correlations with clinical observations of QT prolongation in pediatrics]. Arch Mal Coeur Vaiss.

Diphemanil methyl sulfate is an olefin formed by the Vittig olefination reaction of benzophenone and 1,1-dimethyl-4-bromopiperidine methyl sulfate. It is a quaternary ammonium anticholinergic drug that binds to muscarinic acetylcholine receptors, thereby reducing the secretion of gastric acid, saliva, and sweat. It is used topically to treat hyperhidrosis (excessive sweating). It acts as a muscarinic receptor antagonist, parasympathetic blocker, and bronchodilator. It is a quaternary ammonium salt belonging to the piperidine class of compounds.
See also: Benzophenone (with the active moiety). Benzoic acid sulfate is a synthetic parasympathetic blocker (anticholinergic drug) that acts as a competitive antagonist of muscarinic acetylcholine receptors [1][5]. Its main pharmacological action is to inhibit parasympathetic nervous system activity, thereby causing relaxation of smooth muscles (e.g., airways, gastrointestinal tract) [1]. Clinically, it has been used as an inhaled bronchodilator for asymptomatic asthma patients and for the treatment of excessive secretions (e.g., gastrointestinal tract, respiratory tract) [1]. Due to the risk of QT interval prolongation and arrhythmias, close cardiac monitoring is required when used in children [5].

C20H24N.CH3O4S

389.51

389.166

C, 64.75; H, 6.99; N, 3.60; O, 16.43; S, 8.23

62-97-5

15394-62-4;62-97-5 (methylsulfate);

6126

White to off-white solid powder

194-195ºC

4.491

0

4

2

27

426

0

BREMLQBSKCSNNH-UHFFFAOYSA-M

InChI=1S/C20H24N.CH4O4S/c1-21(2)15-13-19(14-16-21)20(17-9-5-3-6-10-17)18-11-7-4-8-12-18;1-5-6(2,3)4/h3-12H,13-16H2,1-2H3;1H3,(H,2,3,4)/q+1;/p-1

4-(diphenylmethylene)-1,1-dimethylpiperidin-1-ium methyl sulfate

NSC41725; Diphemanil Methylsulfate; NSC 41725; DIPHEMANIL METHYLSULFATE; 62-97-5; Diphemanil metilsulfate; Prantal; Diphenmethanil; Nivelona; Demotil; Diphemanil methosulfate; NSC-41725; Prantal; Talpran;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: 50 mg/mL (128.37 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with sonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)