Surface electrical charge of ionic drugs

The surface electrical charge of ionic drugs is a fundamental physicochemical property rather than a biological target or receptor. It refers to the net electrostatic charge a drug molecule carries at a specific physiological pH, which is determined by the molecule's acid dissociation constants (pKa) and the surrounding environmental pH [1][2]. Most pharmaceutical agents are weak acids or bases, existing in an equilibrium between ionized (charged) and unionized (neutral) states according to the Henderson-Hasselbalch equation [3]. This charge state significantly influences the drug's ability to traverse lipid bilayers, as neutral forms typically pass through membranes more readily than their charged counterparts [1]. Cationic drugs often exhibit high volumes of distribution and may undergo 'ion trapping' in acidic organelles such as lysosomes, a process that can lead to intracellular accumulation and specific toxicities [4]. Conversely, the charge state also dictates the affinity of drugs for plasma proteins, such as the binding of anionic drugs to human serum albumin [5]. Understanding the surface charge is therefore essential for predicting a drug's absorption, distribution, metabolism, and excretion (ADME) profile during the drug development process [2][3].

Other names

Net molecular chargeIonization statepKa-dependent chargeSurface charge densityZeta potential of drug particles

The surface electrical charge governs the electrostatic interactions between a drug and its biological environment, influencing passive transport across membranes and binding to target sites or carrier proteins.