Pharmacodynamics +<unk>  Site Ki (nM) Species Ref 15.2 Human 1,440 Human 1,060 Human 5-HT2A 3,130 Rat 5-HT2C 3,120 Rat H1 2.5–3.0 Human H2 H3 >10,000 Rat H4 2,910 Human M1 25,700 Human M2 17,000 Human M3 52,500 Human M4 77,600 Human M5 28,200 Human 20,900 Human Values are Ki, unless otherwise noted. The smaller the value, the more strongly the drug binds to the site. Values at the and are IC50 (nM).<unk>  acts primarily as a potent H1 antihistamine. It is specifically a potent inverse agonist of the histamine H1 receptor. 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. 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,<unk>  has been found to act as a serotonin reuptake inhibitor (Kd = 15.2 nM for the serotonin transporter). It has only weak affinity for the norepinephrine and dopamine transporters (Kd = 1,440 nM and 1,060 nM, respectively). A similar antihistamine, brompheniramine, led to the discovery of the selective serotonin reuptake inhibitor (SSRI) zimelidine. 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. 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. Pharmacokinetics The elimination half-life of<unk>  has variously ranged between 13.9 and 43.4 hours in adults following a single dose in clinical studies.
Chlorphenamine
Phenethylamine
Methoxyphenamine
Beclamide
Nicergoline
Phenoxypropazine
Mephentermine
Brompheniramine