loxapine

Absorption

Systemic bioavailability of the parent drug was only about one third that after an equivalent intramuscular dose (25 mg base) in male volunteers

Toxicity

LD50=65 mg/kg (Orally in mice)

Originator

Loxitane,Lederle,US,1976

The Uses of loxapine

Tranquilizer (minor).

Background

An antipsychotic agent used in schizophrenia. [PubChem]

Indications

For the management of the manifestations of psychotic disorders such as schizophrenia

Definition

ChEBI: Loxapine is a dibenzooxazepine. It has a role as an antipsychotic agent and a dopaminergic antagonist.

Manufacturing Process

One route is described in US Patent 3,412,193 as follows. To a mixture of o- (p-chlorophenoxy)aniline hydrochloride (prepared from 32 g of the base) in 50 ml of pyridine is added gradually while heating under reflux, 25 ml of ethyl chloroformate. After the addition is completed, the mixture is heated under reflux for one hour longer, and then evaporated under reduced pressure to an oily residue. The residue is taken up in 300 ml of water, and extracted with ether (approximately 200 ml).
The ether extract is separated, dried over sodium sulfate, and evaporated to an oily residue (40 g) which contains ethyl o-(p-chlorophenoxy)carbanilate and is used without further purification. The crude ethyl o-(p-chlorophenoxy) carbanilate is dissolved in 20 ml of benzene, and 20 ml of 1I-methylpiperazine and a small amount of sodium methylate (approximately 25 to 50 mg) are added. Benzene is then removed by slow distillation; and the mixture is heated overnight under reflux (approximately 16 hours).
Evaporation under reduced pressure then gives a solid residue which is dissolved in 400 ml of ether with heating. Concentration to half-volume under reduced pressure produces a precipitate which is collected, washed with petroleum ether and dried (36 g). A second crop of product is isolated from the filtrate. This product is dissolved in 200 ml of chloroform and treated with an excess of anhydrous hydrogen chloride. The resulting precipitate is collected and dried at 50°C (in vacuo), and 4-methyl-2'-(p-chlorophenoxy)-1-piperazinecarboxanilide hydrochloride, MP 210° to 213°C, is thereby obtained.
A mixture of 4-methyl-2'-(p-chlorophenoxy)-1-piperazinecarboxanilide hydrochloride (6 g), 50 ml of phosphorus oxychloride and 10 g of phosphorus pentoxide is heated under reflux for about 24 hours, and then concentrated to a gummy residue by evaporation under reduced pressure. This residue is taken up in 150 ml of ether, 200 g of ice is added, and the mixture is made basic with concentrated aqueous ammonium hydroxide. The ether layer is separated, dried over potassium hydroxide pellets and evaporated to a solid residue (approximately 4 g).
This crude product is dissolved in 100 ml of dilute hydrochloric acid, the acid solution is extracted with ether, and the aqueous layer is made basic with sodium hydroxide solution (3N) in the presence of ether (approximately 250 ml). The ether layer is separated, dried over potassium hydroxide and evaporated to a white solid. Additional purification by repeating the formation of the hydrochloric acid salt and reprecipitation of the base is carried out. When purified in this manner, followed by drying at 80°C in vacuo over phosphorus pentoxide, 2-chloro-11-(4-methyl-1-piperazinyl)dibenz[b,f] [1,4]oxazepine, MP 109° to 111°C, is obtained.

brand name

Loxitane-C Oral Suspension [as hydrochloride] (Wyeth-Ayerst); Loxitane Intramuscular [as hydrochloride] (Wyeth-Ayerst).

Therapeutic Function

Tranquilizer

Biological Activity

loxapine succinate is a d2dr and d4dr inhibitor, serotonergic receptor antagonist and also a dibenzoxazepine anti-psychotic agent [1].

Pharmacokinetics

Loxapine, a dibenzoxazepine compound, represents a subclass of tricyclic antipsychotic agents, chemically distinct from the thioxanthenes, butyrophenones, and phenothiazines. Pharmacologically, Loxapine is a tranquilizer for which the exact mode of action has not been established, however, it is believed that by antagonising dopamine and serotonin receptors, there is a marked cortical inhibition which can manifest as tranquilization and suppression of aggression.

Safety Profile

Poison by ingestion, intraperitoneal, subcutaneous, and intravenous routes. Experimental teratogenic and reproductive effects. A tranquilizer. Many dbenz-azepine compounds have central nervous system effects. When heated to decomposition it emits very toxic fumes of Cl and NOx.

in vitro

loxapine was a typical neuroleptic that showed great structural and functional homology to the atypical antipsychotic clozapine. chronic loxapine treatment was usually associated with extrapyramidal symptoms (eps). loxapineexihibited an extremely strong binding affinity fordopamined4 andserotonin5-ht2receptors, suggesting that both serotonergic and dopaminergic mechanisms contributed to the antipsychotic drug action and eps associated with loxapine in the treatment of schizophrenia [1]. in frontal cortex of brain in human and bovine, in the presence of loxapine, [3h]ketanserin bound to 5-ht2 receptor with ki value of 6.2 nm and 6.6 nm, respectively. in comparing competition experiments involving the human membranes, loxapine exihibited the rank order of potency for the various receptors as follows: 5-ht2≥d4>>>d1>d2 [1]. loxapine administration at 0.2, 2 and 20 μmafter 1 and 3 days of exposure reduced il-1βand il-2 secretion by lps-activated mixed glia cultures. loxapine also decreased il-1βand il-2 secretion in lps-induced microglia cultures [2].

in vivo

chronic administration of loxapine(5 mg/kg) in rats for 4 weeks or 10 weeks significantly reduced more than 50% of serotonin (s2) receptor density. loxapine (5 mg/kg) didn’t change dopamine receptor density but greatly reduced serotonin receptor density by 47% in the brain of rats [3].

Metabolism

Hepatic

References

[1]. singh an1,barlas c,singh s,franks p,mishra rk. a neurochemical basis for the antipsychotic activity of loxapine: interactions withdopamined1,d2, d4 andserotonin5-ht2receptorsubtypes.j psychiatry neurosci.1996 jan;21(1):29-35.
[2]. labuzek k1,kowalski j,gabryel b,herman zs. chlorpromazine and loxapine reduce interleukin-1beta and interleukin-2 release by rat mixed glial and microglial cell cultures.eur neuropsychopharmacol.2005 jan;15(1):23-30.
[3]. lee t,tang sw. loxapine and clozapine decreaseserotonin(s2) but do not elevatedopamine(d2)receptornumbers in the rat brain.psychiatry res.1984 aug;12(4):277-85.