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Pronunciationklor" fen ir' a meen[1]
Trade namesChlor-Trimeton; Piriton
Other namesChlorpheniramine maleate[1]
  • 3-(4-Chlorophenyl)-N,N-dimethyl-3-pyridin-2-yl-propan-1-amine
Clinical data
Drug class1st-generation antihistamine[2]
Main usesMinor allergies[3]
Side effectsSleepiness, restlessness, weakness[2]
  • AU: A
  • US: B (No risk in non-human studies)
Routes of
By mouth, IV, IM, SC
Onset of actionWith 6 hr[2]
Duration of action~24 hr[2]
Typical dose4 mg up 6x per day[3]
External links
Legal status
Bioavailability25 to 50%
Protein binding72%
MetabolismLiver (CYP2D6)
Elimination half-life13.9–43.4 hours[4]
Chemical and physical data
Molar mass274.79 g·mol−1
3D model (JSmol)
Solubility in water0.55 g/100 mL, liquid mg/mL (20 °C)
  • Clc1ccc(cc1)C(c2ncccc2)CCN(C)C
  • InChI=1S/C16H19ClN2/c1-19(2)12-10-15(16-5-3-4-11-18-16)13-6-8-14(17)9-7-13/h3-9,11,15H,10,12H2,1-2H3 checkY

Chlorphenamine (CP, CPM), also known as chlorpheniramine, is an antihistamine used to treat the symptoms of allergic conditions such as allergic rhinitis (hay fever).[2] It is taken by mouth.[2] The medication takes effect within 6 hours and lasts for about a day.[2]

Common side effects include sleepiness, restlessness, and weakness.[2] Other side effects may include dry mouth and wheeziness.[2] There is no evidence of harm in the first two trimesters of pregnancy; though use is not recommended in later pregnancy.[5][2] It is a first-generation antihistamine and works by blocking the H1 receptor.[2]

Chlorphenamine was patented in 1948 and came into medical use in 1949.[6] It is available as a generic medication and over the counter.[2][7] In the United Kingdom 28 tablets of 4 mg costs the NHS about £2 as of 2021.[5] This amount in the United States costs about 0.80 USD.[8] It is present in many combination products and is commonly used.[1]

Medical uses


The dose in those who weight more than 39 kg is 4 mg up to four to six times per day.[3] In those between 21 and 29 kg 2 mg up to four to six times may be taken.[3] While in those 13 to 21 kg the dose is 1 mg up to six times per day.[3] Treatment should be for as short as possible.[3]

Combination products

Chlorphenamine is often combined with phenylpropanolamine to form an allergy medication with both antihistamine and decongestant properties, though phenylpropanolamine is no longer available in the US after studies showed it increased the risk of stroke in young women.[9] Chlorphenamine remains available with no such risk.

Chlorphenamine may be combined with the opioid hydrocodone. Chlorphenamine/dihydrocodeine immediate-release syrups are also marketed. The antihistamine is helpful in cases where allergy or common cold is the reason for the cough; it is also a potentiator of opioids, allowing enhanced suppression of cough, analgesia, and other effects from a given quantity of the drug by itself. In various places in the world, cough and cold preparations containing codeine and chlorphenamine are available.[citation needed]

In the drug Coricidin, chlorphenamine is combined with the cough suppressant dextromethorphan.

Side effects

Intradermal test-Individual that tests positive for Chlorphenamine hypersensitivity

The adverse effects include drowsiness, dizziness, confusion, constipation, anxiety, nausea, blurred vision, restlessness, decreased coordination, dry mouth, shallow breathing, hallucinations, irritability, problems with memory or concentration, tinnitus and trouble urinating.

A large study on people 65 years old or older, linked the development of Alzheimer's disease and other forms of dementia to the use of chlorphenamine and other first-generation antihistamines, due to their anticholinergic properties.[10]



Site Ki (nM) Species Ref
SERT 15.2 Human [12]
NET 1,440 Human [12]
DAT 1,060 Human [12]
5-HT2A 3,130 Rat [13]
5-HT2C 3,120 Rat [14]
H1 2.5–3.0 Human [15][16]
H3 >10,000 Rat [17]
H4 2,910 Human [18]
M1 25,700 Human [19]
M2 17,000 Human [19]
M3 52,500 Human [19]
M4 77,600 Human [19]
M5 28,200 Human [19]
hERG 20,900 Human [20]
Values are Ki, unless otherwise noted. The smaller the value, the more strongly the drug binds to the site. Values at the mAChRs and hERG are IC50 (nM).

Chlorphenamine acts primarily as a potent H1 antihistamine. It is specifically a potent inverse agonist of the histamine H1 receptor.[21][22] The drug is also commonly described as possessing weak anticholinergic activity by acting as an antagonist of the muscarinic acetylcholine receptors. The dextrorotatory stereoisomer, dexchlorpheniramine, has been reported to possess Kd values of 15 nM for the H1 receptor and 1,300 nM for the muscarinic acetylcholine receptors in human brain tissue.[23][24] The smaller the Kd value, the greater the binding affinity of the ligand for its target.

In addition to acting as an inverse agonist at the H1 receptor, chlorphenamine has been found to act as a serotonin reuptake inhibitor (Kd = 15.2 nM for the serotonin transporter).[12][25] It has only weak affinity for the norepinephrine and dopamine transporters (Kd = 1,440 nM and 1,060 nM, respectively).[12] A similar antihistamine, brompheniramine, led to the discovery of the selective serotonin reuptake inhibitor (SSRI) zimelidine.[citation needed]

A study found that dexchlorphenamine had Ki values for the human cloned H1 receptor of 2.67 to 4.81 nM while levchlorphenamine had Ki values of 211 to 361 nM for this receptor, indicating that dexchlorphenamine is the active enantiomer.[26] Another study found that dexchlorphenamine had a Ki value of 20 to 30 μM for the muscarinic acetylcholine receptor using rat brain tissue while levchlorphenamine had a Ki value of 40 to 50 μM for this receptor, indicating that both enantiomers have very low affinity for it.[27]


The elimination half-life of chlorphenamine has variously ranged between 13.9 and 43.4 hours in adults following a single dose in clinical studies.[4]


Chlorphenamine is an alkylamine and is a part of a series of antihistamines including pheniramine (Naphcon) and its halogenated derivatives including fluorpheniramine, dexchlorphenamine (Polaramine), brompheniramine (Dimetapp), dexbrompheniramine (Drixoral), deschlorpheniramine, and iodopheniramine. The halogenated alkylamine antihistamines all exhibit optical isomerism, and chlorphenamine in the indicated products is racemic chlorphenamine maleate, whereas dexchlorphenamine is the dextrorotary stereoisomer.


There are several patented methods for the synthesis of chlorphenamine. In one example, 4-chlorophenylacetonitrile is reacted with 2-chloropyridine in the presence of sodium amide to form 4-chlorophenyl(2-pyridyl)acetonitrile. Alkylating this with 2-dimethylaminoethylchloride in the presence of sodium amide gives γ-(4-chlorphenyl)-γ-cyano-N,N-dimethyl-2-pyridinepropanamine, the hydrolysis and decarboxylation of which lead to chlorphenamine.

Chlorpheniramine synthesis[28]

A second method starts from pyridine, which undergoes alkylation by 4-chlorophenylacetonitrile,[29] giving 2-(4-chlorobenzyl)pyridine. Alkylating this with 2-dimethylaminoethylchloride in the presence of sodium amide gives chlorphenamine.

Chlorpheniramine synthesis[30]

Society and culture


Chlorphenamine is the INN while chlorpheniramine is the USAN and former BAN.

Brand names have included Demazin, Allerest 12 Hour, Codral Nighttime, Chlornade, Contac 12 Hour, Exchange Select Allergy Multi-Symptom, A. R. M. Allergy Relief, Ordrine, Ornade Spansules, Piriton, Teldrin, Triaminic, and Tylenol Cold/Allergy.


The U.S. cost for this medication is $10 (USD) for a supply of 24 tablets (4mg per tablet)[31]


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  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 "Chlorpheniramine Maleate, Dexchlorpheniramine Maleate Monograph for Professionals". American Society of Health-System Pharmacists. Archived from the original on 15 July 2019. Retrieved 15 July 2019.
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External links