Partition of alkylsulfates of quaternary ammonium compounds: structure dependence and transport study

Enhanced permeation of methotrexate in vitro by ion pair formation with L-arginine

Ion paired solutions of methotrexate in L-arginine/water/propylene glycol systems were evaluated for their potential to enhance the permeation of methotrexate across rabbit nasal mucosa in vitro. The partition coefficient of methotrexate in the methotrexate: L-arginine ion paired systems was observed to be 24 times greater than that of the methotrexate system without L-arginine. The ion pair formation between methotrexate and L-arginine was confirmed by a decrease in the conductivity of the systems in the presence of propylene glycol, a dielectric constant reducing agent. The permeation of methotrexate across the rabbit nasal mucosa from the ion paired systems was observed to be significantly greater (p < 0.05) as compared to control systems of methotrexate solution in water and a sodium salt. Furthermore, a threefold increase in the flux of methotrexate was observed when propylene glycol was added to the ion paired systems. These results suggest that methotrexate: L-arginine ion paired systems have potential in improving the permeation of methotrexate across rabbit nasal mucosa and may form the basis for further development of an intranasal therapeutic system of methotrexate.

Influence of ion pairing salts on the transcorneal permeability of ionized sulfonamides

The effects of cationic ammonium, phosphonium, and arsonium ion pairing salts as well as anionic organic and inorganic salts on the transcorneal permeability of ionized sulfonamide carbonic anhydrase inhibitors have been studied in the excised rabbit cornea. Benzolamide, trichloromethazolamide (TCM), MK-927, and quaternary ammonium sulfonamide (QAS) were examined. The enhancement in the first-order rate constants (k(in)) for the first compound in the presence of pairing salts was as much as 15 times the basal rate, with smaller increases seen with the remaining three drugs. Ion pairing salts may represent a means for enhancing the transcorneal permeability of highly ionized drugs.

Ion pair transport across membranes

The present review discusses drugs and counter ions suitable for ion pair transport (IPT). Ion pairing is shown to effectively increase the lipophilicity and transport rate of polar drugs across lipid membranes. The proposed mechanisms of IPT are discussed in detail. A marked change in drug properties upon ion pair formation is necessary to improve the bioavailability of hydrophilic ionizable drugs.

Hepatic uptake and biliary excretion of organic cations--II. The influence of ion pair formation

The influence of an anorganic anion iodide (I-) and an organic anion tetraphenylborate (TPB-) on the hepatic uptake and biliary excretion of three organic cations, triethylmethyl ammonium (TEMA), tripropylmethyl ammonium (TPMA) and tri-n-butylmethyl ammonium (TBuMA) was studied. The compounds were injected as a bolus (D = 1 mumole) and studied in isolated perfused livers. In the perfusion medium 25% of the amount of NaCl (3 mmole) was replaced by NaI, whereas in two other experiments TPB- was added to the medium in two concentrations (2 microM and 200 microM). NaI did not affect the biliary output of the three quaternary ammonium compounds (QACs) although an increased net rate of hepatic uptake was found for all compounds, most likely due to a decreased liver to plasma transport. Liver to plasma concentration ratios were increased, while the ratios between bile to liver and bile to plasma were not affected. TPB- in catalytic amounts added to the medium (2 microM) decreased the biliary output of TEMA and TBuMA, whereas the kinetic profile of TPMA was unchanged. The decreased biliary excretion rate of TEMA was explained by a decreased plasma level (due to the increased liver uptake) assuming that the small molecular weight compounds can enter the bile directly from plasma via the junctional complexes between the cells. The bile to plasma (B/P) ratio was not affected. In contrast, the bile to plasma (B/P) ratio and the bile to liver (B/L) ratio of TBuMA were decreased, compared with the control, probably due to an increased reabsorption from the bile, whereas the back transport from the liver into the plasma was also decreased. A large amount of TPB- (200 microM), added to the perfusion medium, dramatically changed the kinetic profile of the three QACs. Ion pair formation between the QACs and TPB- was supposed to be responsible for this effect. Plasma levels dropped more rapidly as a result of an increased rate of liver uptake. The biliary excretion of all compounds was greatly reduced (the excretion rates were 0.022, 0.19 and 0.18 nmole/min, compared with 0.047, 0.71 and 7.5 nmole/min for the controls). It is concluded that ion pair formation may play a role in the hepatobiliary transport. The rate of liver uptake of the QACs is enhanced in the presence of an anion, which is due to an increase in plasma to liver transport (k12) and a reduced liver to plasma transport (k21).(ABSTRACT TRUNCATED AT 400 WORDS)

Structure-pharmacokinetics relationship of quaternary ammonium compounds. Correlation of physicochemical and pharmacokinetic parameters

Correlations between lipophilicity or molecular weight and some pharmacokinetic parameters such as clearance (Cl), elimination rate constant (k10), volume of distribution (V), and terminal half life (lambda z) are presented for a series of structurally related quaternary ammonium cations (QACs). The structure-pharmacokinetics relations were fitted using the computer program NONLIN and were represented by linear, parabolic or S-shaped curves. The relationship between total plasma clearance or hepatic, renal and intestinal clearance and lipophilicity for the present set of data could be described most properly by the equation Y = 1/(aXb + c), where Y stands for the logarithm of the pharmacokinetic parameters and X represents the logarithm of the values of some physicochemical parameters, such as the partition coefficient (P), the (HPLC) capacity factor k' (another lipophilicity parameter) and molecular weight (MW). On the basis of this relationship, correlations of the hepatic or intestinal clearances with the lipophilicity parameters were good (r = 0.98 and r = 0.95 respectively). Curves relating values for partition coefficients and clearance via liver and intestine (expressed relative to the most simple QAC tetramethyl ammonium) showed S-shaped correlation patterns, in contrast to the renal clearance, which correlated poorly (r = 0.54) with lipophilicity. The extent of biliary output of the organic cations shows a threshold phenomenon, sharply increasing at log P greater than 1.5 to a maximum at P greater than 2.5. This pattern was less pronounced in the case of intestinal elimination and absent in the case of renal clearance. The apparent maximum in the hepatic and intestinal clearance for the most lipophilic organic cations is probably due to limitation by organ blood-flow and/or plasma protein binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Ion pair absorption of ionized drugs--fact or fiction?

The lipophilicity of some highly ionized drugs at physiological pH is very low. Gastro-intestinal absorption of such compounds cannot be explained by the 'pH-partition' hypothesis. Ion pair formation between a drug and an endogenous counter ion alone resulting in an electrically neutral and potentially more lipophilic species has been proposed as a mechanism to explain the observed, though deficient, absorption of ionic drugs. The concept of ion pair formation between an ionic drug and an exogenous counter ion has been the rationale for attempts to improve penetration of biological membranes and, specifically, result in increased absorption from the gastro-intestinal tract. The validity of the 'ion pair absorption hypothesis' is re-evaluated in the context of a conceptual review of relevant literature.

Determination of sigma and pi constants of quinolinium acid derivatives

The apparent partition coefficients of 10 quinoline monocarboxylic acid derivatives in a chloroform-water system were determined. From these data, Hammett's sigma and Hansch's pi values were calculated.

Determination of thermodynamics of halogen groups in solutions of drug molecules

The contribution of the halogen groups (F, Cl, Br, I) to solute activity and partition coefficients has been investigated using literature data. The activity coefficient for an aromatic solute at infinite dilution is increased as the size of the halogen group increases. Partition coefficients are affected similarly but there is variation among group values for a given halogen. This is related to group position and the partition solvent. Preferred group values for partition have been selected and for different solvent systems mean preferred values can be calculated for two general solvent classifications; polar and non-polar. There is excellent correlation between group values and the size of the halogen function as given by surface area. The group values for non-polar solvents are related to those of the polar solvents through the Hammett electronic substituent constant. The use of the group values in structure-activity relations is discussed with reference to the thermodynamic model of Higuchi and Davis.

Determination of the thermodynamics of the methyl group in solutions of drug molecules

The contribution of the CH3 group to the solution thermodynamics of drug molecules is dependent on whether it is attached to a ring system or is in the terminal position in an aliphatic chain. In the former case group contributions for CH3 are very similar to those found for the CH2 group. For instance, in partition, the CH3 group contribution (log Fch3) is in the range 0.65 to 0.28 (ΔG = 2.303 RT log Fch3) and is dependent on the polarity of the organic solvent. The contribution for the terminal aliphatic CH3 is not equivalent to the mid chain CH2 and a CH3 correction factor or 1.14 to 1.34 kcalmol−1 (4.77 to 5.61 kJmol−1), has been calculated from alkane solubility data and partition studies. The additivity of group contributions and the correct choice of reference state are also discussed.