Propylhexedrine

Propylhexedrine, commonly sold under the brand name Benzedrex, is an alkylamine primarily utilized as a topical nasal decongestant. Its main indications are relief of congestion due to colds, allergies, and allergic rhinitis.
Medical use
Propylhexedrine is used to treat acute nasal congestion related to common cold, allergies and hay fever. For nasal congestion, the dosage is listed as four inhalations (two inhalations per nostril) every two hours for adults and children 6–12 years of age. Each inhalation delivers 0.4 to 0.5 milligram (400 to 500 μg) in 800 millilitres of air. Use is not to exceed three days.
Historically, it has also been used for weight loss in oral tablet preparations at doses ranging from 5 to 30 milligrams. No medications containing propylhexedrine are currently approved for weight loss in the United States. Such products have been used in European countries, however.
Contraindications
Propylhexedrine should not be used if a MAOI has been used in the past 14 days or is currently in use, for this can result in hypertensive crisis. People with cardiovascular disease should not use propylhexedrine.
Additionally, stimulant drugs and sympathomimetics should not be taken with propylhexedrine. This can lead to a potentially dangerous spike in blood pressure and irregular heart rhythms.
Propylhexedrine is contraindicated in individuals under six years old. There is at least one case of reported accidental poisoning resulting from a child’s access to a propylhexedrine product.
Adverse effects
The most common adverse effects warned about for propylhexedrine inhalers are temporary discomfort (e.g., stinging or burning sensations), worsened nasal congestion, and ill effects if taken internally. The sharing of propylhexedrine inhalers may spread infection. The occurrence of these adverse effects is uncommon as propylhexedrine is generally recognized as safe and effective.
Overdose
Reports of overdoses from propylhexedrine have been documented, but they are uncommon. Most instances of overdoses attributed to propylhexedrine have been the result of intentional misuse or abuse. As noted by the FDA, the most common symptoms of propylhexedrine overdose are the following: "…[R]apid heart rate, agitation, high blood pressure, chest pain, tremor, hallucinations, delusions, confusion, nausea, and vomiting." The use of propylhexedrine products in manners inconsistent with their labeling has proven fatal in some cases. Propylhexedrine products are considered safe and effective if used as intended. Regardless, medical attention should be sought in the case of suspected overdose.
Interactions
As referred to earlier, most of propylhexedrine’s interactions with other medications have to do with its ability to constrict the blood vessels. This means that propylhexedrine may interact adversely with certain stimulants, bronchodilators, sympathomimetics, nasal decongestants, and antidepressants. Caution should be exercised when administering propylhexedrine concurrently with other medicines.
Pharmacology
Mechanism of action
Propylhexedrine works mainly as an adrenergic agonist, when used at therapeutic doses. This restricts the blood vessels in the nose and reduces swelling; thereby, relieving nasal congestion. At higher doses, propylhexedrine affects the central nervous system as a norepinephrine–dopamine releasing agent. Propylhexedrine likely exerts such effects in a manner similar to related alkylamines such as cyclopentamine, methylhexanamine, and tuaminoheptane. In addition, propylhexedrine further releases monoamines through TAAR1 agonism and VMAT2 inhibition. Propylhexedrine also exhibits antihypotensive effects.
Pharmacokinetics
Propylhexedrine undergoes metabolism to form various metabolites such as norpropylhexedrine, cyclohexylacetoxime, cyclohexylacetone, and 4-hydroxypropylhexedrine.
Chemistry
Freebase propylhexedrine is a volatile, oily liquid at room temperature. The slow evaporation of freebase propylhexedrine allows it to be administered via inhalation. The evaporation of the freebase also accounts for the limited shelf-life of propylhexedrine inhalers. Many of the salts of propylhexedrine are stable, clear to off-white crystalline substances that readily dissolve in water.
Propylhexedrine is similar in chemical structure to phenylethylamines. The main difference is the presence of an alicyclic cyclohexyl group instead of the aromatic phenyl group of a phenethylamine.
Propylhexedrine is a chiral compound. The active ingredient contained in Benzedrex inhalers is racemic (RS)-propylhexedrine as the free base. (S)-Propylhexedrine, also known as levopropylhexedrine, is believed to be the more biologically active isomer of the two.
The dextrorotatory counterpart, which is mainly unused, is dextropropylhexedrine.
Propylhexedrine can be synthesized from methamphetamine.
Synthesis
Propylhexedrine can be synthesized from cyclohexylacetone through reductive amination of the intermediate imine.
However, propylhexedrine is more commonly prepared by the hydrogenation of methamphetamine over Adams' catalyst. This transforms methamphetamine's aromatic ring to a cyclohexyl moiety.
Detection in bodily fluids
Due to its structure, administration of propylhexedrine can lead to false-positives for phenethylamine-derivatives on urinalysis panels. Propylhexedrine can be differentiated upon further analysis.
History
Propylhexedrine’s medical use as a decongestant evolved from desires to find safer alternatives to previous agents. After searching for such an agent, Dr. Glenn E. Ullyot patented propylhexedrine as a decongestant in 1948. This patent was issued for benefit of Smith, Kline & French. Before it was sold nationally in the United States, propylhexedrine underwent market trials in California. These market trials began on July 15, 1949. Propylhexedrine (under the brand-name Benzedrex) was first introduced into interstate commerce on August 4, 1949. Approval for use in the United Kingdom soon followed in 1956. Later, approval for use in Canada was granted in 1998. In 2023, B. F. Ascher & Co. decreased the amount of propylhexedrine in the Benzedrex inhaler from its historic 250 milligrams down to 175 milligrams.
Barbexaclone, an anticonvulsant containing propylhexedrine, was used in Turkey until its withdrawal from the market in 2009. Barbexaclone’s former niche in Turkish medicine is now largely-occupied by levetiracetam.
Manufacturing
The manufacture of propylhexedrine products is typically performed based on guidelines established in government regulations and pharmacopeial monographs.
Society and culture
Legal status
International control
Propylhexedrine was placed under international control by the Convention on Psychotropic Substances in 1985. This action was reversed in 1991.
Australia
Propylhexedrine is an S4 substance in Australia.
Brazil
Propylhexedrine is a Class B1 substance in Brazil.
Canada
Propylhexedrine is reported to be a Schedule V substance in Canada.
Germany
Propylhexedrine is regulated as a prescription medicine in Germany.
United Kingdom
It was formerly a Class C substance in the United Kingdom, but was deregulated in 1995.
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United States
On the 4th of April 1988, propylhexedrine was designated a controlled substance (Schedule V) in the United States. This was done to satisfy U.S. compliance with an international treaty. However, in 1991, this action was reversed and propylhexedrine was removed from control under the Controlled Substances Act. This was based on the opinion of the Drug Enforcement Administration that propylhexedrine did not warrant control. The substance has remained unregulated under the Controlled Substances Act in the United States ever since. Furthermore, pursuant to 21 C.F.R 1308.22, Benzedrex inhalers are specifically exempt from the Controlled Substances Act.
Recreational use
First reported in the literature as early as 1959, propylhexedrine products have been misused for their monoamine-releasing effects. Recreational misuse can be fatal, its risks are magnified when administering the substance through injection means, and the adverse effects of misuse are similar to that of related substances. The undesirable side effects of propylhexedrine at recreational doses are less tolerable compared to other commonly abused monoaminergic substances; consequently, making it less desirable for recreational use. The fact that propylhexedrine is far less potent than comparable substances also limits recreational use. Even in areas with prevalent substance use, the use of propylhexedrine was reported as not of significant interest. The misuse of nasal decongestant, anorectic, and anticonvulsant preparations have all been reported. The misuse of propylhexedrine products has been on the rise since the early 2000s.
Economics
Propylhexedrine, under the brand name Benzedrex, is sold online by retailers such as Amazon, eBay, and Walmart. Propylhexedrine has been sold in some countries as an anorectic or as part of an anticonvulsant preparation; however, such products are not sold freely to consumers and require a physician’s prescription.
Brand names
Propylhexedrine, as a nasal decongestant, is currently marketed under the trade name Benzedrex. The name Benzedrex was initially trademarked by Smith, Kline & French in 1944. The brand was passed onto Menley James Laboratories in 1990, and was finally acquired by B. F. Ascher & Co. in 1998. Propylhexedrine was also sold in inhaler form by Whitehall Laboratories under the Dristan brand name as an inhaler. In January of 1966, propylhexedrine replaced mephentermine as the active ingredient in the product. The Dristan inhaler has since been discontinued.
Propylhexedrine has also seen use in Europe as an appetite suppressant, under the trade name Obesin. Obesin has been referenced in literature dating back to the 1950s.
Propylhexedrine is a component in the anticonvulsant preparation barbexaclone. Its S-isomer (levopropylhexedrine or L-propylhexedrine) is bonded with phenobarbital for the purpose of offsetting the barbiturate-induced sedation. Barbexaclone has been known under the brand name of Maliasin, manufactured by Abbott Laboratories, as early as 1965. In 2010, Abbott discontinued sale of its barbexaclone preparation in many countries.
Levopropylhexedrine has been used as an appetite suppressant under the brand name Eventin. Eventin’s use has been documented as early as 1958.
References
Anorectics
Cyclohexyl compounds
Decongestants
Norepinephrine-dopamine releasing agents
Sympathomimetics
TAAR1 agonists
Vasoconstrictors
VMAT inhibitors