Lipophilicity Test on Ibuprofen & Lidocaine Institution Affiliation

Physicochemical Experiment
Experiment Report on Lipophilicity Test on Ibuprofen and Lidocaine
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Lipophilicity Experiment on Ibuprofen & Lidocaine 2
Abstract
Lipophilicity is one of the physicochemical properties of drugs that influence the
operations of medicines in the human system. The flask shake method was used in an
experimental set up to determine the lipophilicity of two substances that is ibuprofen and
lidocaine to find their log P & log D values. Octanol and water were used as the stationary
phases for the analysis. The concentration of acetonitrile was varied in different proportions
to help obtain the calibration curve. Solutions of known Log P was used to facilitate the
analysis and comparison of the values obtained from the experiment. Log P values of
ibuprofen and lidocaine were calculated and analyzed using regression calibration curve RmO
= f (log P. the experimental results when compared to established literature showed a high
level of consistency hence validating the experiment.
Calibration curves for both drugs were generated using the absorption of multiple
dilutions in the appropriate solution. Test samples of ibuprofen and lidocaine for logP
determination were prepared in octanol and a pH 2, pH 11.4 buffers, respectively. LogD
determination samples were prepared in a pH 7.4 buffer for both drugs. UV spectroscopy was
used to analyze the samples

Lipophilicity Experiment on Ibuprofen & Lidocaine 3
INTRODUCTION
Experimentation to determine drugs solubility condition is quite crucial in drug and
medical research since it helps in the development phase and discovery of medicinal use. In
drug research, physicochemical parameters such as ionizations, permeability, solubility and
lipophilicity are often used to screen out drugs to verify its bioequivalence and
biopharmaceutical classification. Ionization and lipophilicity are essential for drug
formulation optimization and use specification. Different methods have been established over
the past few decades to help determine drug lipophilicity and drugs ionizations (Lambert et al.
2017). Among the first methods used for these tests were kinetic tests where the experiments
were based on the turbidity of the drug candidates, UV scanners were used as the detection
system. The study of drugs properties has developed through phases until it reached the
equilibrium phase when equilibrium solubility was used as a method of determining drug
properties (Zhang et al. 2018). However the research phases as evolve through time until now,
with help of advanced technology and creativity in innovations, we have more simple and
basic methods of determining different properties of a drug candidate, among basic methods
are CheqSol or DTT and the most classical of all, the shake-flask method (Amirkhanov et al.
2019).
The classical experimental method of partition coefficient determination is shake-flask
technique. It involves mixing the substance of interest in a mixture of two immiscible
liquids, usually water and octanol, in a flask that is then shaken and left to equilibrate. The
concentration of the substance in each liquid is then measured using a suitable analytical
method
Like UV spectrometry and used to calculate the partition coefficient. Although the shake-
flask technique is the most reliable, it is time-consuming and requires the tested substance to
be soluble in both octanol and water. High-performance liquid chromatography (HPLC) is a

Lipophilicity Experiment on Ibuprofen & Lidocaine 4
faster technique to determine logP experimentally, by correlating the substance retention time
with similar compounds of a known partition coefficient4. Alternatively, the logP can be
calculated theoretically by adding the logP values of each functional group in the compound
from the fragment (Baxevanis et al. 2108).
In this experiment, the lipophilicity of an acidic and a basic drug: ibuprofen and lidocaine
will be measured at different biological pH values using flask-shake technique and to assess
the effect of ionization on lipophilicity (Inoue et al. 2018). The results will be validated by
comparing the experimentally obtained values to the literature values, fragment table values,
Figure 1: chemical structure of ibuprofen6 Figure 2: chemical structure lidocaine7
The logarithmic portion of 1-octanol/water coefficient (Log P) and the acidic
dissociation constant (pKa) the most fundamental parameters in medical, pharmaceutical and
toxicological studies of medicinal organic molecules (Liu et al 2017). Among the drugs
molecules listed in the World Drug Index of 1999, sixty-four per cent are ionizable and
soluble at a pH ranging between pH 2 to pH 12 (Lambert et al. 2017). The ionization property
of drugs is affected by biological, chemical and physical properties of the drug-like candidate,
therefore it is of importance to predict into which ionic form will the molecule have when
tested for lipophilic (Lee et al. 2016). The logarithmic coefficient is often used together with
the constant pKa value to determine the distribution of compounds in the ecological or