Active Drug Moiety

In a drug, an active drug moiety is the molecule or ion, responsible for physiological or pharmacological action it excludes those appended portions of the drug compound that cause the drug to be an ester, salt, or other noncovalent derivative (such as a complex, chelate, or clathrate) of the compound. For example, the antidepressant sertraline is available as a salt, sertraline hydrochloride. Sertraline is the active drug moiety of the drug compound, sertraline hydrochloride. The reason an active drug moiety is developed into a drug compound it to accommodate factors such as drug solubility, absorption and dosage considerations. An active drug moiety may be developed into a salt, ester or other chemical form as illustrated in table A.

Table A: Drug Compounds and Their Active Drug Moieties

			Molecular Weight
Drug Compund	Active Drug Moiety	Formula	Drug Compund	Active Drug Moiety
Albuterol sulfate	Albuterol	(C 13H21NO3)2H2SO4	337.4	239.3
Almotriptan malate	Almotriptan	C17H25N3O2S.C4H4O4.H2O	469.5	335.5
Bupropion hydrochloride	Almotriptan	C 13H18ClNO.HCl	276.2	239.7
Pseudoephedrine hydrochloride	Pseudoephedrine	C 10H15NO.HCl	201.7	165.2

Some commercial drug products that are prepared into a salt or other forms are labelled to indicate the equivalent content of active drug moiety for example: In the drug label below each ml contains 1 mg of albuterol sulfate equivalent to 0.83 mg of albuterol.

The pharmacist may need to calculate the active drug moiety in a given preparation and or compare two pharmaceutically equivalent compounds (for e.g. tetracycline hydrochloride and tetracycline phosphate)