Lipophilicity protein binding

The pharmacological activity of LAs is determined by several physicochemical properties including lipophilicity, protein binding, and pKa which can be explained by their mechanism of action. A general structure - activity relationship was described by Courtney and Strichartz (1987), according to which an increase in the hydrophobicity leads to a parallel increase in anesthetic... 

The racemic compound bupivacaine, which was first synthesized by Ekenstam et al. in 1957, is an amide-type LA with a high lipophilicity, protein binding and pKa giving rise to an intermediate onset and a long duration of action. At the same time, bupivacaine has a high toxicity potential relatively often associated with convulsions and life-threatening cardivascular collapse (Moore et al., 1978). Levobupivacaine, the (S)-enantiomer of bupivacaine, has recently been developed for clinical use addressing the enantioselectivity of side-effects of bupivacaine (see below). 

The volume of distribution of a peptide or protein drug is determined largely by its physico-chemical properties (e. g., charge, lipophilicity), protein binding, and dependency on active transport processes. Due to their large size - and therefore limited mobility through biomembranes - most therapeutic proteins have small volumes of distribution, typically limited to the volumes of the extracellular space [26, 51]. 

Drug Bio- availability T max (hrs) Lipophilicity Protein binding % Half- life (hrs)... 

Dmg distribution into tissue reservoirs depends on the physicochemical properties of the dmg. Tissue reservoirs include fat, bone, and the principal body organs. Access of dmgs to these reservoirs depends on partition coefficient, charge or degree of ionization at physiological pH, and extent of protein binding. Thus, lipophilic molecules accumulate in fat reservoirs and this accumulation can alter considerably both the duration and the concentration—response curves of dmg action. Some dmgs may accumulate selectively in defined tissues, for example, the tetracycline antibiotics in bone (see Antibiotics,tetracyclines). 

The distribution of a drug in the body is largely driven by its physicochemical properties and in part for some compounds by the contribution of transporter proteins [17]. By using the Oie-Tozer equation and estimates for ionization (pfCj). plasma protein binding (PPB) and lipophilicity (log quite robust predictions for the volume of distribution at steady state (Vdss), often within 2-fold of the observed value, can be made [18]. 

Hansch and Leo [13] described the impact of Hpophihdty on pharmacodynamic events in detailed chapters on QSAR studies of proteins and enzymes, of antitumor drugs, of central nervous system agents as well as microbial and pesticide QSAR studies. Furthermore, many reviews document the prime importance of log P as descriptors of absorption, distribution, metabolism, excretion and toxicity (ADMET) properties [5-18]. Increased lipophilicity was shown to correlate with poorer aqueous solubility, increased plasma protein binding, increased storage in tissues, and more rapid metabolism and elimination. Lipophilicity is also a highly important descriptor of blood-brain barrier (BBB) permeability [19, 20]. Last, but not least, lipophilicity plays a dominant role in toxicity prediction [21]. 

Chou, C. H., Rowland, M. Relationship between lipophilicity and protein binding of a homologous series of barbimrates. Chin. Pharm. f 2002, 54, 87-94. 

Figure 31 Scheme for the protein-binding, diffusional, and partitioning processes and barriers that are encountered by a highly lipophilic and membrane-interactive drug (D) as it permeates through a cell within a continuous monolayer, h and h, thicknesses of the aqueous boundary layers. kd and ka, dissociation and association binding constants, respectively. P, protein molecule. Permeability coefficients Effective, Pe aqueous boundary layer, PABL and PW apical membrane, Pap basolateral membrane, Pbl. 

Raub TJ, CL Barsuhn, LR Williams, DE Decker, GA Sawada, NFH Ho. (1993). Use of a biophysical-kinetic model to understand the roles of protein binding and membrane partitioning on passive diffusion of highly lipophilic molecules across cellular barriers. J Drug Targeting 1 269-286. 

Figure 3.1 shows the appearance of dihydromethysticin in the acceptor well as a function of time [15], The solid curve is a least-squares fit of the data points to Eq. (1), with the parameters Pe = 32 x 10-6 cm s 1, R = 0.42, and t s = 35 min. The membrane retention, R, is often stated as a mole percentage (%R) of the sample (rather than a fraction). Its value can at times be very high - up to 90% for chlor-promazine and 70% for phenazopyridine, when 2% wt/vol DOPC in dodecane is used. Figure 3.2 shows a plot of log %R versus log Ka(7.4), the octanol/water apparent partition coefficient. It appears that retention is due to the lipophilicity of molecules this may be a good predictor of the pharmacokinetic volume of distribution or of protein binding. 

Sawada and coworkers [25-27] studied the iso-pH 7.4 MDCK permeabilities of very lipophilic molecules, including chlorpromazine (CPZ) [25], These authors included 3% wt/vol bovine serum albumin (BSA) on the apical (donor) side, and 0.1-3% BSA on the basolateral (acceptor) side, and found that plasma protein binding greatly affected the ability of molecules to permeate cellular barriers. They observed cell tissue retention of CPZ ranging from 65 to 85%, depending on the... 

Lipooligosaccharide (LOS) bacterial, 25 498 Lipophilic amphiphiles, 24 154-155 Lipophilic interaction dominated substrate recognition, 16 783-786 Lipophilic moieties, 8 706t Lipopolysaccharides (LPS), 4 706 11 47 BPI protein ability to neutralize, 18 257 peptide and protein binding affinity to, 18 256... 

A number of prodrugs in clinical use are esters of fatty acids. For example, haloperidol decanoate is of interest in slow-release preparations. This compound was hydrolyzed by such hydrolases as purified carboxylesterase but was reported to be stable in human blood or plasma and in a variety of rat tissue homogenates [107], The source of this apparent lack of reactivity was competitive binding to blood and tissue proteins. In other words, protein binding sequesters this very lipophilic prodrug and prevents enzymatic hydrolysis, thereby slowing its activation and prolonging its in vivo effects. 

Where Cl = Clg if only one organ is involved in drug clearance. Within this equation Cli is the intrinsic clearance based on total drug concentrations and therefore includes drug bound to protein. Lipophilic drugs bind to the constituents of plasma (principally albumin) and in some cases to erythrocytes. It is a major assumption, supported by a considerable amount of experimental data, that only the unbound (free) drug can be cleared. The intrinsic clearance (C ) can be further defined as ... 

However, the major contributing factor to the decreased renal clearance of total drug was increasing plasma protein binding with increasing lipophilicity. When the extent of plasma protein binding was taken into account, the imbound renal clear-... 

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