Pheniramine

Pheniramine is a first-generation antihistamine (antiallergic) with anticholinergic activity. Although it counts as an anti-allergic for the treatment of allergic rhinitis and itching, it is no longer commercially available as such. Instead, pheniramine is primarily used as a combination preparation with other active ingredients for the treatment of influenza.

Therapeutically, the pheniramine maleate, or salt, is used because it is more water-soluble than pheniramine and thus can be dissolved and absorbed more rapidly in the digestive tract after ingestion.

Applications and indications

In Austria and Switzerland, pheniramine is now only available as the combination preparation NeoCitran with other active ingredients such as paracetamol and phenylephrine as well as vitamin C. This is used for the symptomatic treatment of cold symptoms in flu-like infections.

History

Originally, the 1st generation antihistamines - which include pheniramine - were developed for the treatment of typical allergic symptoms such as hay fever. Over time, the strong sedative effect of these substances came more and more to the fore.

Due to their lipophilic nature, the active ingredients of this group are able to cross the blood-brain barrier and thus enter the brain. Once there, they block the H1 receptors, causing drowsiness and sleepiness.

Another disadvantage was that they had a short duration of action and thus had to be administered more often. As a result, antihistamines of this generation are rarely used for their intended purpose anymore. Instead, only 2nd generation antihistamines are used today, which are more mature and are characterized by fewer side effects.

Pharmacodynamics/mechanism of action

Pheniramine acts as an inverse agonist, which means that it binds to the histamine H1 receptor and attenuates its activity.

Histamine is an important messenger in the human body involved in many processes such as allergic reactions, inflammation, and sleep-wake cycle. It also supports the immune system in its defense against foreign substances.

Thus, by weakening the effect of histamine, the occurrence of allergic reactions is reduced or prevented. Thus, if pheniramine binds to the receptor instead of histamine, it has an anti-allergic effect.

In combination preparations, pheniramine has a decongestant effect, which causes the nasal mucosa to recede, making breathing easier.

Pharmacokinetics

Pheniramine is degraded in the liver by various processes such as hydroxylation, demethylation, etc., and is subsequently excreted renally.

Interactions

Pheniramine as an H1 antihistamine enhances the effects of the following drugs:

• Analgesics
• Hypnotics
• Narcotics
• Psychotropic drugs

Another interaction occurs with CYP3A4 inhibitors.

Moreover, pheniramine enhances the effect of alcohol, therefore concomitant use is not recommended.

Contraindications & precautions

Pheniramine impairs driving ability due to its sedative effects. Due to this you should not drive a car after taking it.

If you suffer from glaucoma, asthma or high blood pressure you should inform your doctor before using the medication as it is a contraindication.

Side effects

H1 1st generation antihistamines all have central depressant effects that may cause somnolence (drowsiness).

Other side effects that may occur are:

• Fatigue, drowsiness
• Gastrointestinal distress
• bradycardia (slowing of the heartbeat)

Pregnancy and lactation

No information is available regarding the use of pheniramine as active ingredient during pregnancy/breastfeeding, therefore a medical consultation is recommended before use.

During breastfeeding, the active ingredient poses no significant risks to the newborn, but larger doses of pheniramine or prolonged use may cause drowsiness and other effects.