Propylhexedrine (Benzedrex, Obesin) is a stimulant drug used mainly to provide temporary symptomatic relief of nasal congestion due to colds, allergies and allergic rhinitis. Being a vasoconstrictor used to decongest nasal mucosa, it is administered by inhalation.
Propylhexedrine is most commonly found in over-the-counter Benzedrex inhaler. Benzedrex was first manufactured by Smith, Kline and French after the Benzedrine inhaler, which contained racemic amphetamine, became unavailable following the placement of amphetamines on the US Schedule II status (second highest abuse potential with limited medicinal use). Benzedrex is currently manufactured by B.F. Ascher & Co. Inc. Pharmaceuticals. Propylhexedrine has also seen use in Europe as an appetite suppressant under the trade name Obesin and 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. Levopropylhexedrine is also used as an anorectic under the brand name Eventin.
Chemistry
Free base propylhexedrine is a volatile, oily liquid at room temperature. The slow vaporization of free base propylhexedrine allows it to be administered via inhalation. Acid salts of propylhexedrine (such as propylhexedrine HCl) often present as a stable, clear to off-white crystalline powder that readily dissolves in water.
Propylhexedrine is structurally similar to methamphetamine and other phenylethylamines, with the only structural difference being the substitution of an alicyclic cyclohexyl group for the aromatic phenyl group of phenethylamine. Propylhexedrine is not an amphetamine, nor even a phenethylamine, but instead can be referred to as a cycloalkylamine. Because propylhexedrine is not an amphetamine, it is somewhat less potent than structurally similar amphetamines such as methamphetamine.
Propylhexedrine is a chiral compound (the α-carbon is chiral), and 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. (S)-Propylhexedrine can be synthesized from dextromethamphetamine.
Synthesis
Propylhexedrine can be synthesized starting with cyclohexylacetone in a similar fashion to the phenylacetone synthesis of methamphetamine. However, more commonly propylhexedrine is prepared by reacting methamphetamine with Adams' catalyst, reducing methamphetamine's aromatic ring to a cyclohexyl moiety.
Pharmacology
Propylhexedrine is a TAAR1 agonist like amphetamine. Consequently, it reverses the transporters for dopamine, norepinephrine and serotonin, leading to a release of monoamines from presynaptic vesicles into the synaptic cleft. The increased level of monoamines within the synapse results in increased activity at these receptors. Additionally, propylhexedrine appears to antagonize the VMAT2 transporter, leading to a further increase in the aforementioned monoamines. The pharmacological actions of propylhexedrine are similar to that of structurally similar stimulant phenethylamines, such as amphetamine.
Metabolism
Propylhexedrine undergoes metabolism to form various metabolites including norpropylhexedrine, cyclohexylacetoxime, cis- and trans-4-hydroxypropylhexedrine.
Contraindications
Propylhexedrine should not be used if an MAOI has been used in the past 14 days, or is being currently used, as this can lead to a hypertensive crisis. People with cardiac disease should not use propylhexedrine.
Additionally, drugs such as stimulants and sympathomimetics should not be taken along with propylhexedrine, as this can lead to potentially dangerous spikes in blood pressure and irregular heart rhythms.
There is one case of death resulting from the combination of propylhexedrine and kratom.
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 two inhalations (one inhalation per nostril) every two hours for adults and children 6â€"12 years of age. Each inhalation delivers 0.4 to 0.5 milligrams (400 to 500 μg) in 800 millilitres of air. Historically, it has also been used for weight loss.
Recreational use
Propylhexedrine has been reported to be used recreationally, obtained as free base from the cotton rods that Benzedrex inhalers contain.
Effects
Propylhexedrine has sympathomimetic, adrenergic, vasocontricive and psychostimulant effects when taken above the medical dosage. Effects include increased sweating, talkativeness, euphoria, mydriasis, emotional lability, anorexia, tachycardia, palpitations, dry mouth, bruxism, anxiety, dysphoria, increased aggressiveness, paranoia, headache, dizziness, psychosis, slurred or impaired speech, rarely convulsions and serious heart problems. Propylhexedrine can also cause swelling, dryness and irritation of mucous membranes.
Withdrawal effects can occur and include fatigue, depression, suicidal tendencies, hunger and extreme desire for sleep.
Recreational use potential
Propylhexedrine has a lower potential for abuse than other stimulants, partially because methods of its use are limited, unlike more commonly abused amphetamine, methamphetamine and methylphenidate. It has gained popularity as an over the counter high, but it is not as popular as other OTC drugs with abuse potential, such as dextromethorphan and diphenhydramine. Oral ingestion being the most practical method of consumption, the inactive ingredients in a Benzedrex inhaler (menthol and lavender oil) are also ingested - most users report the taste and smell to be very unpleasant, resulting in "menthol burps" (frequent belching releasing the smell of the two) that often cause the user discomfort and sometimes nausea. Many drug users find propylhexedrine has a very heavy comedown compared to the "high" it causes. The abuse potential is considered to be low enough that neither the DEA nor the WHO consider it a drug of concern at the present, unlike ephedrine and its salts, which are known to be used as precursor chemicals in illicit manufacture of methamphetamine (and occasionally amphetamine). Propylhexedrine is controlled in some jurisdictions - for example, placed behind the counter like ephedrine to combat theft.
Injection risks
While propylhexedrine is limited in a number of administration routes, attempts to extract the drug from the nasal inhaler and then inject it have been reported. Recreational use by intravenous injection (IV) is dangerous and could result in serious bodily harm or death. IV use of propylhexedrine is known to cause transient diplopia and brainstem dysfunction, and deaths have been recorded in the medical literature. Typically, recorded cases of IV use are prepared by forming propylhexedrine HCl in a solution with hydrochloric acid, the solution is then heated to evaporate and the resulting crystals are dissolved in water for injection.
Drug risks
As with similar drugs, using propylhexedrine to keep oneself awake for extended times can lead to a temporary state of sleep deprivation, during which an individual may experience hallucinations, including auditory, visual and tactile sensations (formication), paranoia, irritability and impaired memory. Ingestion of the cotton rod can cause bowel obstruction and various conditions involving the lower intestine.
Propylhexedrine, being a vasoconstrictor and a stimulant, may carry a further risk as blood pressure and heart rate are raised, sometimes severely. Hypertension experienced by users of propylhexedrine can be dangerous, especially in those who have pre-existing blood pressure problems. The increase in heart rate can lead to lower levels of oxygen, discomfort, panic, and in severe cases, heart attack or serious arrhythmias. Again, this risk is higher if the user has existing heart problems.
The use of all inhaled vasoconstrictors in the nose risks desensitizing the nose both to natural and therapeutic levels of decongestants. Desensitization is accompanied by "rebound" increase in congestion. Short acting decongestants, requiring frequent dosing, carry a high risk of dependency.
See also
- Amphetamine
- Benzedrine
- Cyclopentamine
- Cypenamine
- Methamphetamine
- Tranylcypromine