Oxymetazoline

Absorption

Imidazole derivatives such as oxymetazoline are readily absorbed across mucosal membranes, especially in children. In adult subjects with erythema associated with rosacea, the mean ± standard deviation (SD) Cmax was 60.5 ± 53.9 pg/mL and the AUC from time 0 to 24 hours (AUC0-24hr) was 895 ±798 pg x hr/mL following topical administration of first-dose oxymetazoline. Following once-daily topical applications for 28 days, the mean ± SD Cmax was 66.4 ± 67.1 pg/mL and the AUC0-24hr was 1050 ± 992 pg x hr/mL. Following twice-daily applications for 28 days, the mean ± SD Cmax was 68.8 ± 61.1 pg/mL and the AUC0-24hr was 1530 ± 922 pg x hr/mL.
Following single-drop ocular administration of oxymetazoline in healthy adult subjects, the mean ± SD Cmax was 30.5 ± 12.7 pg/mL and the area under the concentration-time curve (AUCinf) was 468 ± 214 pg x hr/mL. The median Tmax was 2 hours, ranging from 0.5 to 12 hours.
Following nasal administration of an 0.6 mL combination product containing tetracaine and oxymetazoline in adult subjects, the maximum concentrations of oxymetazoline were reached within approximately 10 minutes. The mean Cmax was 1.78 ng/mL and the AUC0-inf value was 4.24 ng x h/mL, with a median Tmax of 5 minutes.

Toxicity

In rats, the oral LD50 is 680 ug/kg and the subcutaneous LD50 is 1630 ug/kg. In mice, the oral LD50 is 4700 ug/kg, the intraperitoneal LD50 is 48 mg/kg, and the subcutaneous LD50 is 34 mg/kg.
Case reports have documented unintended overdose in both children and adults: overdose has led to dizziness, chest pain, headaches, myocardial infarction, stroke, visual disturbances, arrhythmia, hypertension, or hypotension. Accidental ingestion of topical solutions of imidazoline derivatives, including oxymetazoline, in children has resulted in serious adverse events requiring hospitalization, such as nausea, vomiting, lethargy, tachycardia, decreased respiration, bradycardia, hypotension, hypertension, sedation, somnolence, mydriasis, stupor, hypothermia, drooling, and coma. Possible rebound nasal congestion, irritation of nasal mucosa, and adverse systemic effects (particularly in children), including serious cardiovascular adverse events, have been reported with overdosage as well as prolonged or too frequent intranasal use of oxymetazoline. Overdose should be responded with close monitoring, supportive care, and symptomatic treatment.

Originator

Nasivin,Merck,W. Germany ,1961

The Uses of Oxymetazoline

Oxymetazoline is used for the same indications as naphazoline, primarily for rhinitis.

The Uses of Oxymetazoline

Vasoconstrictor, used as a nasal decongestant.

Indications

Oxymetazoline is indicated for the topical treatment of persistent facial erythema associated with rosacea in adults.
Ophthalmic oxymetazoline is indicated for the treatment of acquired blepharoptosis in adults.
When used in combination with tetracaine intranasally, oxymetazoline is indicated for regional anesthesia when performing a restorative procedure on Teeth 4-13 and A-J in adults and children who weigh 40 kg or more.
Oxymetazoline can be found in over-the-counter nasal products as a nasal decongestant.
For off-label uses, oxymetazoline has been used during nasal intubation and during ear, nose, and throat surgery to improve visualization of the airway and to minimize post-operative bleeding.

Background

Oxymetazoline is an imidazole derivative and a potent, direct-acting alpha (α)-adrenergic agonist with affinity to both α1- and α2-adrenoceptors. Oxymetazoline is available in various formulations with a wide variety of clinical implications. The topical formulation of the drug is used to treat persistent facial redness in adults. As an effective decongestant, oxymetazoline is available in over-the-counter intranasal sprays used to relieve nasal and sinus congestion caused by a wide variety of conditions, such as common cold, hay fever, and upper respiratory allergies. In dentistry, oxymetazoline and tetracaine combination intranasal spray (Kovanaze) is used for regional anesthesia during dental procedures in children and adults. In July 2020, the FDA approved the use of an ophthalmic formulation of oxymetazoline (Upneeq) in adults with acquired blepharoptosis, or ptosis, making it the first FDA-approved medical treatment for this medical condition.

Definition

ChEBI: Oxymetazoline is a member of the class of phenols that is 2,4-dimethylphenol which is substituted at positions 3 and 6 by 4,5-dihydro-1H-imidazol-2-ylmethyl and tert-butyl groups, respectively. A direct-acting sympathomimetic with marked alpha-adrenergic activity, it is a vasoconstrictor that is used (generally as the hydrochloride salt) to relieve nasal congestion. It has a role as an alpha-adrenergic agonist, a sympathomimetic agent, a nasal decongestant and a vasoconstrictor agent. It is a member of phenols, a carboxamidine and a member of imidazolines. It is a conjugate base of an oxymetazoline(1+).

Manufacturing Process

10 grams 2,6-dimethyl-3-hydroxy-4-tertiary butylbenzylcyanide (produced by chloromethylation of 2,4-dimethyl-6-tertiary butyl-phenol with formaldehyde and HCl and conversion of the substituted benzyl chloride with NaCN; crystals, from alcohol, melting at 135° to 137°C) and 10.7 grams ethylenediaminemono-p-toluenesulfonate are heated in an oil bath to approximately 235°C for 1? hours, whereby ammonia is evolved. The free base is obtained from the p-toluene-sulfonic acid imidazoline salt which is difficultly soluble in water, by conversion with 50 cc of a 10% NaOH solution. Said base is recrystallized from benzene, and 7.5 grams (62% of the theoretical yield) 2-(2',6'-dimethyl3'-hydroxy-4'-tertiary butylbenzyl)-2-imidazoline, MP 180° to 182°C, are obtained.
By dissolving the free base in an ethyl alcohol solution of hydrochloric acid and adding ether, the hydrochloride can be produced in the usual manner. Said hydrochloride melts, when recrystallized from alcoholic ether, at 300° to 303°C and is decomposed

brand name

Ocuclear (Schering-Plough); Visine (Pfizer).

Therapeutic Function

Nasal decongestant

Pharmacokinetics

Oxymetazoline is an adrenergic α1- and α2-agonist and a direct-acting sympathomimetic drug. By stimulating adrenergic receptors, oxymetazoline causes vasoconstriction of dilated arterioles and reduces blood flow. In a radioligand competition study, oxymetazoline displayed higher affinity at α1A-adrenoceptors compared to α2B-adrenoceptors, but with higher potency at α2B-adrenoceptors. When sprayed intranasally, oxymetazoline relieved relief nasal congestion and improved nasal airflow in patients with acute coryzal rhinitis for up to 12 hours following a single dose.
An early in vitro study demonstrated oxymetazoline to exert anti-oxidant actions, where it inhibited microsomal lipid peroxidation and mediated hydroxyl radical scavenging activity. This suggests that oxymetazoline has a beneficial effect against oxidants, which play a role in tissue damage in inflammation.

Safety Profile

Poison by ingestion and subcutaneous routes. Experimental reproductive effects. When heated to decomposition it emits toxic fumes of NOx.

Synthesis

Oxymetazoline, 6-tert-butyl-3(2-imidazolin-2-ilmethyl)-2,4-dimethylphenol (11.1.39), is synthesized by chloromethylation of 6-tert-butyl-2,4-dimethylphenol and the further transformation of the resulting chloromethyl derivative (11.1.37) into a nitrile (11.1.38). The reaction of this with ethylendiamine gives oxymetazoline (11.1.39) [41,42].

Enzyme inhibitor

This vasoconstrictor and nasal decongestant (FW = 260.38 g/mol; CAS 1491-59-4), systematically named as 6-t-butyl-3-(4,5-dihydro-1H-imidazol- 2-ylmethyl)-2,4-dimethylphenol, is a partial a2A-adrenergic agonist as well as a 5-HT1A, 5-HT1B, and 5-HT1D serotonin receptor agonist. It is an overthe-counter drug that is most often used topically to treat rhinitis and sinusitis. Oxymetazoline exerts a dose-dependent inhibitory effect on total iNOS activity, as indicated by nitrite/nitrate formation, and this effect is attributable to inhibition of enzyme induction rather than direct inhibition of the enzyme itself.

Metabolism

In vitro, oxymetazoline was minimally metabolized by human liver enzymes to produce mono-oxygenated and dehydrogenated metabolites. About 95.9% of the total dose of oxymetazoline remained as an unchanged parent compound after a 120-minute incubation with human liver microsomes. When incubated in rat, rabbit, and human liver post-mitochondrial supernatant fraction from homogenized tissue (S9) fractions, oxymetazoline was more efficiently metabolized by rabbit liver S9 fractions (~65%) than by rat (~20%) or human (~10%) liver S9 fractions. At concentrations (50 μM) at least 130-fold greater than the usual therapeutic intranasal dose (400 nM), CYP2C19 was suggested to be involved in the oxidation of oxymetazoline following intranasal administration; however, metabolites in humans have not been fully characterized up to date and remain speculated based on in vitro studies using rat and rabbit liver S9 fractions and microsomes. The O-glucuronide metabolite catalyzed by UGT1A9 has been identified in vitro.