DIMETHINDENE

Toxicity

As with other antihistaminic drugs, overdosage can produce the following symptoms: CNS depression accompanied by drowsiness (especially in adults), CNS stimulation and antimuscarinic effects (especially in children) including the following: excitation, ataxia, hallucinations, tonic or clonic spasms, mydriasis, dryness of the mouth, redness of the face, urine retention, fever and tachycardia. Blood hypotension is also possible. In its terminal phase, coma can be aggravated by cardiorespiratory colapse and death. There has been no report of a fatal outcome of Dimethindene overdosage.

Originator

Fenistil,Zyma,W. Germany,1961

Background

Dimetindene (Fenistil) is an antihistamine/anticholinergic used orally and locally as an antipruritic.

Indications

Indicated as symptomatic treatment of allergic reactions: urticaria, allergies of the upper respiratory tract such as hey fever and perennial rhinitis, food and drug allergies; pruritus of various origins, except pruritus due to cholestasis; insect bites. Dimethindene is also indicated for pruritus in eruptive skin diseases such as chicken-pox. Dimethindene can also be used as an adjuvant in eczema and other pruriginous dermatoses of allergic origin.

Definition

ChEBI: Dimetindene is an indene.

Manufacturing Process

26 grams of 2-ethylpyridine is added dropwise with cooling to 20°C and in an atmosphere of nitrogen to a stirred solution of 650 ml of an 0.37 molar solution of phenyl lithium in benzene. After two hours a solution of 10 grams of 2-(2-dimethylaminoethyl)-indan-1-one in 50 ml of dry ether is added over a period of five minutes while stirring and cooling to room temperature. After standing for 24 hours the organo-lithium compounds are decomposed by the addition of 50 ml of water with external cooling. After separating the water phase from the organic solution, the latter is washed several times with 50 ml of water, and then extracted with a mixture of 40 ml of concentrated hydrochloric acid and 100 ml of water.
The acidic solution, containing the 2-(2-dimethylaminoethyl)-1-[1-(2-pyridyl)- ethyl]-indan-1-ol is heated on the steam bath for thirty minutes to effect dehydration to the desired indene derivative. The solution is cooled, made strongly basic with an aqueous solution of ammonia and then extracted with ether. The ether phase is dried over sodium sulfate, filtered, evaporated and the residue distilled.
At 15 mm pressure the excess of 2-ethylpyridine is removed, at 120°C/0.5 mm some unreacted 2-(2-dimethylaminoethyl)-indene distills and at 165°- 175°C/0.5 mm the 2-(2-dimethylaminoethyl)-3-[1-(2-pyridyl)-ethyl]-indene is collected. It may be converted to an aqueous solution of the dihydrochloride by dissolving it in the appropriate amount of dilute hydrochloric acid.
To a solution of 1.0 gram of 2-(2-dimethylaminoethyl)-3[1-(2-pyridyl)-ethyl]- indene in 10 ml of ethanol is added while stirring and heating 0.4 gram of maleic acid. On cooling the 2-(2-dimethylaminoethyl)-3-[1-(2-pyridyl)-ethyl]- indene maleate crystallizes, is filtered off, washed with a small amount of ethanol and recrystallized from ethanol, MP 158°C.

Therapeutic Function

Antihistaminic

Pharmacokinetics

Dimethindene occurs as a racemic mixture. The (S)-(+)-dimethindene is a potent M2-selective muscarinic receptor antagonist (with lower affinity for M1, M3, and M4 muscarinic receptors). The (R)-(-)-enantiomer is the eutomer (responsible for bioactivity) for histamine H1 receptor binding.

Synthesis

Benzylmalonic acid is esterified with dihydropyran and reacted with sodium hydride and 2-dimethylaminoethyl chloride in toluene to give ditetrahydropyranyl-2-benzyl-2- (2-dimethylaminoethyl)malonate, which is cyclized with the help of polyphosphoric acid to 2-(2-dimethylaminoethyl)-indan-1-one. This compound reacts with 2-ethylpyridine and phenyllithium to give the carbinol, which is dehydrated by heating to dimetindene .

Metabolism

Not Available