MEHISDIN-P

Dexchlorpheniramine, the d-isomer of the racemic compound chlorpheniramine, is two times more active than chlorpheniramine. Dexchlorpheniramine does not prevent the release of histamine, but rather, competes with free histamine for binding at the H₁-receptor sites, and competitively antagonizes the effects of histamine on H₁-receptors in the GI tract, uterus, large blood vessels, and bronchial muscle. Blockade of H₁-receptors also suppresses the formation of oedema, flare, and pruritus that result from histaminic activity. Since dexchlorpheniramine binds to central and peripheral H₁-receptors, sedative effects are likely to occur. Dexchlorpheniramine has high antihistaminic activity, moderate anticholinergic effects and minimal sedative effects.

Phenylephrine is a sympathomimetic agent with mainly direct effects on adrenergic receptors. It has predominantly alpha adrenergic activity and is without stimulating effects on the central nervous system. The sympathomimetic effect of phenylephrine produces vasoconstriction which in turn relieves nasal congestion.

Sodium citrate has no relevant pharmacodynamic activity other than that caused by its alkalinity (e.g. its gastric acid neutralising capacity). Sodium citrate is a non-particulate antacid for use by mouth to prior to general anaesthesia for caesarean section.