Ionization, lipophilicity, and molecular modeling to investigate permeability and other biological properties of amlodipine

Conformational Effects on the Passive Membrane Permeability of Synthetic Macrocycles

Macrocyclic compounds (MCs) can have complex conformational properties that affect pharmacologically important behaviors such as membrane permeability. We measured the passive permeability of 3600 diverse nonpeptidic MCs and used machine learning to analyze the results. Incorporating selected properties based on the three-dimensional (3D) conformation gave models that predicted permeability with Q² = 0.81. A biased spatial distribution of polar versus nonpolar regions was particularly important for good permeability, consistent with a mechanism in which the initial insertion of nonpolar portions of a MC helps facilitate the subsequent membrane entry of more polar parts. We also examined effects on permeability of 800 substructural elements by comparing matched molecular pairs. Some substitutions were invariably beneficial or invariably deleterious to permeability, while the influence of others was highly contextual. Overall, the work provides insights into how the permeability of MCs is influenced by their 3D conformational properties and suggests design hypotheses for achieving macrocycles with high membrane permeability.

Extemporaneous Compounding and Physiological Modeling of Amlodipine/Valsartan Suspension

Method

Amlodipine/valsartan extemporaneous suspension was prepared from available commercial tablets such as Valzadepine^®. The dissolution profiles for the extemporaneous preparation and the commercial tablet were determined in different pH media. The physical, chemical, and microbial stability of the compounded formulation was evaluated over one-month period at room temperature. Moreover, in silico modeling using GastroPlus™ software was used to build absorption models for both drugs based on the in vitro dissolution data. The simulated plasma profiles for both active ingredients were compared with the in vivo plasma profiles to examine the similarity of the extemporaneous suspension and the commercial tablets.

Results

The amlodipine/valsartan extemporaneous suspension was successfully prepared with acceptable organoleptic properties. The suspension was stable for four-week period preserving its physical and chemical features. The release profiles of valsartan and amlodipine from the suspension were similar to those from source tablet Valzadepine^®. In silico modeling predicted the similarity of the extemporaneous suspension and the commercial tablets.

Conclusion

Amlodipine/valsartan extemporaneous suspension could be prepared from available commercial tablets. Moreover, GastroPlus™ can be applied along with the in vitro dissolution in order to affirm similarity in extemporaneous compounding situations.

A Physiologically Based Pharmacokinetic Model for Pregnant Women to Predict the Pharmacokinetics of Drugs Metabolized Via Several Enzymatic Pathways

BACKGROUND

Physiologically based pharmacokinetic modeling is considered a valuable tool for predicting pharmacokinetic changes in pregnancy to subsequently guide in-vivo pharmacokinetic trials in pregnant women. The objective of this study was to extend and verify a previously developed physiologically based pharmacokinetic model for pregnant women for the prediction of pharmacokinetics of drugs metabolized via several cytochrome P450 enzymes.

METHODS

Quantitative information on gestation-specific changes in enzyme activity available in the literature was incorporated in a pregnancy physiologically based pharmacokinetic model and the pharmacokinetics of eight drugs metabolized via one or multiple cytochrome P450 enzymes was predicted. The tested drugs were caffeine, midazolam, nifedipine, metoprolol, ondansetron, granisetron, diazepam, and metronidazole. Pharmacokinetic predictions were evaluated by comparison with in-vivo pharmacokinetic data obtained from the literature.

RESULTS

The pregnancy physiologically based pharmacokinetic model successfully predicted the pharmacokinetics of all tested drugs. The observed pregnancy-induced pharmacokinetic changes were qualitatively and quantitatively reasonably well predicted for all drugs. Ninety-seven percent of the mean plasma concentrations predicted in pregnant women fell within a twofold error range and 63% within a 1.25-fold error range. For all drugs, the predicted area under the concentration-time curve was within a 1.25-fold error range.

CONCLUSION

The presented pregnancy physiologically based pharmacokinetic model can quantitatively predict the pharmacokinetics of drugs that are metabolized via one or multiple cytochrome P450 enzymes by integrating prior knowledge of the pregnancy-related effect on these enzymes. This pregnancy physiologically based pharmacokinetic model may thus be used to identify potential exposure changes in pregnant women a priori and to eventually support informed decision making when clinical trials are designed in this special population.

Intramolecular hydrogen bonding: An opportunity for improved design in medicinal chemistry

Recent literature shows that intramolecular hydrogen bond (IMHB) formation can positively impact upon the triad of permeability, solubility, and potency of drugs and candidates. IMHB modulation can be applied to compounds in any chemical space as a means for discovering drug candidates with both acceptable potency and absorption, distribution, metabolism, and excretion-Tox profiles. Integrating IMHB formation in design of drugs is, therefore, an exciting and timely challenge for modern medicinal chemistry. In this review, we first provide some background about IMHBs from the medicinal chemist's point of view and highlight some IMHB-associated misconceptions. Second, we propose a classification of IMHBs for drug discovery purposes, review the most common in silico tactics to include IMHBs in lead optimization and list some experimental physicochemical descriptors, which quantify the propensity of compounds to form IMHBs. By focusing on the compounds size and the number of IMHBs that can potentially be formed, we also outline the major difficulties encountered when designing compounds based on the inclusion of IMHBs. Finally, we discuss recent case studies illustrating the application of IMHB to optimize cell permeability and physicochemical properties of small molecules, cyclic peptides and macrocycles.

Effect of drug amlodipine on the charged lipid bilayer cell membranes DMPS and DMPS + DMPC: a molecular dynamics simulation study

In this work, the effects of the anti-hypertensive drug amlodipine in native and PEGylated forms on the malfunctioning of negatively charged lipid bilayer cell membranes constructed from DMPS or DMPS + DMPC were studied by molecular dynamics simulation. The obtained results indicate that amlodipine alone aggregates and as a result its diffusion into the membrane is retarded. In addition, due to their large size aggregates of the drug can damage the cell, rupturing the cell membrane. It is shown that PEGylation of amlodipine prevents this aggregation and facilitates its diffusion into the lipid membrane. The interaction of the drug with negatively charged membranes in the presence of an aqueous solution of NaCl, as the medium, is investigated and its effects on the membrane are considered by evaluating the structural properties of the membrane such as area per lipid, thickness, lipid chain order and electrostatic potential difference between bulk solution and lipid bilayer surface. The effect of these parameters on the diffusion of the drug into the cell is critically examined and discussed.

Guiding dose adjustment of amlodipine after co-administration with ritonavir containing regimens using a physiologically-based pharmacokinetic/pharmacodynamic model

Amlodipine, a commonly prescribed anti-hypertensive drug, shows increased systemic exposure with cytochrome P450 (CYP) 3A inhibitors. Ritonavir (RTV) is a potent mechanism-based and reversible CYP3A inhibitor and moderate inducer that is used as a pharmacokinetic enhancer in several antiviral treatment regimens. Drug-drug interaction (DDI) between RTV and amlodipine is due to mixed inhibition and induction of CYP3A4, which is challenging to predict without a mechanistic model that accounts for the complexity of both mechanisms occurring simultaneously. A novel physiologically-based pharmacokinetic (PBPK) model was developed for amlodipine, and the model was verified using published clinical PK and DDI data. The verified amlodipine PBPK model was linked to a pharmacodynamics model that describes changes in systolic blood pressure (SBP) during and after co-administration with RTV. The magnitude and time course of RTV effects on amlodipine plasma exposures and SBP were evaluated, to provide guidance on dose adjustment of amlodipine during and after co-administration with RTV-containing regimens. Model simulations suggested that the increase in amlodipine's plasma exposure by RTV diminishes by approximately 80% within 5 days after the last dose of RTV. PBPK simulations suggested that resuming a full dose of amlodipine [5 mg once daily (QD)] immediately after RTV's last dose would decrease daily average SBP by a maximum of 3.3 mmHg, while continuing with the reduced dose (2.5 mg QD) for 5 days after the last dose of RTV would increase daily average SBP by a maximum of 5.8 mmHg. Based on these results, either approach of resuming amlodipine's full dose could be appropriate when combined with appropriate clinical monitoring.

Predicting the Oxidative Metabolism of Statins: An Application of the MetaSite® Algorithm

PURPOSE

This study was undertaken to examine the MetaSite algorithm by comparing its predictions with experimentally characterized metabolites of statins produced by cytochromes P450 (CYPs).

METHODS

Seven statins were investigated, namely atorvastatin, cerivastatin, fluvastatin, pitavastatin and pravastatin which are (or were) used in their active hydroxy-acid form, and lovastatin and simvastatin which are used as the lactone prodrug. But given the fast lactone-hydroxy-acid equilibrium undergone by statins, both forms were investigated for each of the seven drugs. The MetaSite version 2.5.3 used here contains the homology 3D-models of CYP1A2, CYP2C19, CYP2C9, CYP2D6 and CYP3A4. In addition, we also used the crystallographic 3D-structure of human CYP2C9 and CYP3A4. To allow a better interpretation of results, the probability function PsMi calculated by MetaSite (namely the probability of atom i to be a site of metabolism) was explicitly decomposed into its two components, namely a recognition score Ei (the accessibility of atom i) and the chemical reactivity Ri of atom i toward oxidation reactions.

RESULTS

The current version of MetaSite is known to work best with prior experimental knowledge of the cytochrome(s) P450 involved. And indeed, experimentally confirmed sites of oxidation were correctly given a high priority by MetaSite. In particular 77% of correct predictions (including false positive but, as discussed, this is not necessarily a shortcoming) were obtained when considering the first five metabolites indicated by MetaSite.

CONCLUSION

To the best of our knowledge, this is the first independent report on the software. It is expected to contribute to the development of improved versions, but above all it demonstrates that the usefulness of such softwares critically depends on human experts.

Classification of α-cyclodextrins inclusion complexes into Type 1 and Type 2: A prelude to logK prediction

Molecular Interaction Fields (MIFs) were used in combination with a small number of geometrical descriptors to separate nine alpha-CD complexes into Type 1 and Type 2, two classes, respectively, containing complexes having high log K and low log K values (stoichiometry of 1:1). Calculations were performed on the crystallographic conformations of alpha-CDs after their separation from the ligand and without minimization. The results show that the computational strategy adopted is able to distinguish Type 1 from Type 2 complexes and that it can be applied to all CD families.

A combined in silico strategy to describe the variation of some 3D molecular properties of β-cyclodextrin due to the formation of inclusion complexes

A powerful in silico strategy based on the combined use of two computational tools (MLP and MIFs) able to calculate and visualize 3D molecular fields can give useful information about surface properties of macromolecules involved in the mechanisms of formation of complexes. In particular, this study investigated the variation in polar/hydrophobic pattern induced on the beta-CD alone (i.e. =without the ligand) by the inclusion of four ligands having different lipophilicities and small size. Results indicate that, in the presence of guests with P>0, the hydrophobicity of beta-CD increases in the cavity and its surroundings on the primary face.

Intestinal permeability and excretion into bile control the arrival of amlodipine into the systemic circulation after oral administration

The objective of this study was to identify the factors controlling the arrival of amlodipine into the systemic circulation after oral administration in the fasting state. Dissolution data were collected with the rotating paddle and the flow-through apparatus. Caco-2 cell lines were used to assess the intestinal permeability characteristics. Actual in-vivo data were collected in 24 fasted healthy subjects after single-dose administration of the same amlodipine besylate tablet formulation used in the in-vitro dissolution studies. Regardless of the hydrodynamics, dissolution of amlodipine besylate tablets was rapid and complete in media simulating the contents of the upper gastrointestinal tract in the fasting state. Permeability of amlodipine through Caco-2 cell lines was lower than propranolol's and higher than ranitidine's, indicating that transport through the intestinal mucosa may be one process that limits the arrival into the systemic circulation. Indeed, the de-convoluted profile indicated that arrival into portal blood occurs at rates much slower than gastric emptying or dissolution rates. However, prediction of amlodipine's mean plasma profile after oral administration became possible only after additionally assuming excretion of amlodipine into the bile and a reasonable gastrointestinal residence time. Interestingly, in-vitro permeability data collected in this or in previous studies were inappropriate for simulating the mean actual plasma profile.

The rise of PAMPA

The parallel artificial membrane permeability assay (PAMPA), as a passive-permeability screen, is a possible low-cost alternative to cellular models for the earliest ADME primary screening of research compounds. Its popularity in the industry has risen rapidly. This review examines state-of-the-art PAMPA methods. The various covered topics include: different lipid formulations, the quantitative relationships between hexadecane, dioyleyoylphosphatidycholine and Double-Sink PAMPA measurements, the use of individual-well stirring, issues of ultraviolet sensitivity, timing strategies, reproducibility of measurements, the correct pH to perform the measurement to avoid aqueous boundary layer problems, the pKa(flux) method for determining intrinsic permeability coefficients and the cosolvent method for very insoluble molecules. Examples of the determination of permeability of very difficult molecules, but molecules that are well absorbed, are given. Carefully gathered evidence in support of the use of the Double-Sink PAMPA model is presented. The review concludes with a binning strategy to predict human intestinal absorption, based on the use of the sum of permeability coefficients, measured at gradient pH 5.0, 6.2 and 7.4. Opinions regarding the future of PAMPA are offered.

Calculating Virtual log P in the Alkane/Water System (log PNalk) and Its Derived Parameters Δlog PNoct-alk and log DpHalk

Growing interest in the use of both the logarithm of the partition coefficient of the neutral species in the alkane/water system (log P(N)(alk)) and the difference between log P(N)(oct) (the logarithm of the partition coefficient of the neutral species in the n-octanol/water system) and log P(N)(alk) (Deltalog P(N)(oct-alk)) in the early stages of drug design has stimulated development of a computational tool based on the Volsurf software to predict virtual (=of each conformer) log P(N)(alk) and virtual log P(N)(oct). From these two pieces of data, it is then possible to calculate Deltalog P(N)(oct-alk) for a given compound as the difference between log P(N)(oct) and log P(N)(alk). Once the pK(a) is known and the legitimacy of neglecting the contribution made by the ionized species has been checked, it is also possible to calculate log D(pH)(alk), which might be an important lipophilicity descriptor in absorption, distribution, metabolism, and excretion (ADME) prediction, from log P(N)(alk).