Enhancement of Bioavailability and Determination of Some Fluoroquinolones Antibiotics; Application to U A E Market

Moza Rashed Sultan Al-Zaabie


Chapter 1 of this thesis includes the importance of fluroquinolone as one of the most impressive antibacterial drugs. Also, a complete picture about the selective molecules named cyclodextrins (CDs) is drawn. Such molecules are able to form inclusion complexes with a wide variety of lipophilic drugs. That is why CDs act as drug carriers through an aqueous media to the lipophilic cell membrane and delivers them to cell. Which results in enhancing the bioavailability of drug with low aqueous solubility. Moreover, an explanation of the DNA/drug interactions is proposed. These are extremely useful in understanding the DNA sequence recognition by drugs as well as by proteins. Finally, the objective of the present work is included.

Chapter 2 explains in detail the experimental part. It includes the chemicals and the materials used, the methods of preparation of the various solutions such as DNA, cyclodextrins, drugs, buffers and metal salt. Also, the instruments used such as voltammetric and spectrophotometric techniques were included. The general procedures for all the measurements were described in detail.

The results and discussion are presented in chapters 3, 4 and 5. In chapter 3 the quantitative determination of nalidixic acid in pharmaceutical samples, human urine and serum are described. The quinolone antibacterial agent nalidixic acid (NAL) was studied by cyclic voltammetry (CV) and differential pulse stripping voltammetry (DPSV). A sensitive method is described for the determination of NAL in its pure form, dosage forms and biological fluids. Controlled adsorptive accumulation of NAL on a hanging mercury drop electrode provides the basis for the direct stripping measurement of that drug in the nanomolar concentration level. Different variables were studied and optimized. The proposed method depends upon the voltammetric activity of NAL in Britton-Robinson buffer, whereby a well-defined cathodic peak is produced at pH 5.0 in presence of NO3-. The calibration graph to determine NAL was linear in the range 2.9 x 10-8 to 2.5 x 10-5 M by DPSV with detection limit (s/n=3) of 0.766 ng ml-1 (3.3x10-9 M). The relative standard deviation (n=5) was 5.2% at concentration level of 1.0 x 10-7 M NAL. The degree of interference from coexisting metal ions on the DPSV signal for NAL was evaluated. The method was applied to two different commercial pharmaceutical products (Negram tablets and suspension) with very good recoveries. It was also shown that the method was successfully applied to the determination of NAL in human urine and blood serum. Mean recoveries were 98.8±0.3% and 98.9±0.41%, respectively. Also, the inclusion of the antibacterial drug, nalidixic acid (NAL), in α-, and β-cyclodextrins (CDs) cavities is studied using UV -Vis absorption and the voltammetric methods. It was corroborated that the UV absorption bands of NAL are intensified in the presence of α-, and β-CDs. Also, a pronounced decrease in the peak currents of NAL was noticed upon the addition of α-, and β-CDs. From the changes in the peak currents, it was concluded that NAL form 1: 1 inclusion complex with the various hosts, which is revealed from the phase solubility profile of NAL-β-CD system, as a representative example. Furthermore, from voltammetric data, the logarithm of the binding constants were calculated to be 2.60 and 3.20 for α-, and β-CDs, respectively. The magnitude of the formation constants as well as the Gibbs free energies, for NAL with α-, and β-CDs shows a trend that NAL is bound more strongly to β-CD, with more apolar cavity, than α-CD. These observations suggest that the hydrophobic interaction is the most important recognition element in the binding process. With the purpose of characterizing the inclusion complex of NAL with CD, all orientations of entering NAL into the cavity are proposed. Combining the experimental results and molecular modeling and energy calculations on the inclusion complexes yield a more detailed picture of the solution structure of the complex formed between NAL and either α-CD or β-CD. It was inferred that the inclusion process can occur through 2-methyl-pyridine side. Also, an additional hydrogen bond was found to be formed between the carboxyl group of NAL, that remain outside the β-CD cavity, and the secondary hydroxyl group of β-CD. Therefore, this hydrogen bond should be operating as an important second recognition element in case of NAL-β-CD system. Furthermore, the interaction on NAL with DNA was investigated by cyclic voltammetry and differential pulse stripping voltammetry. It was found that the stoichiometry of the NAL-DNA is 1: 1 and the binding constant was calculated to be 1.84 x 105 M-1, revealing the strong binding affinity of NAL to DNA.

In chapter 4 the determination of norfloxacin (NOR) and its interaction with DNA and CDs are reported. The dependence of differential pulse stripping peak of NOR on different variables are studied in order to choose the optimum conditions for the analytical determinations by DPSV at HMDE. Under the optimum coditions (phosphate buffer, pH = 11 in presence of ClO4-, 100 mV pulse amplitude, 20 mVs-1 scan rate, 30 s accumulation time and -0.6 V accumulation potential) the NOR can be accurately determined over the range from 1.47x10-7 M to 2.3x10-6 M NOR. The detction limit, the percentage relative error and percentage relative standard deviation are 5 x10-9 M, 3.1 % and 4.2%, respectively. According to this proposed method the NOR in Noroxin tablets was succefully determined with excellent spike recovery (close to 100%) and high precision (%RSD ≥ 3.5).

Finally, in chapter 5 the determination of ciprofloxacin (CIP) and its interaction with DNA and CDs are reported and discussed. The optimum conditions for the voltammetric determination of CIP were evaluated from comprehensive study on the factors affecting the electrochemical behavior of CIP such as pH, anions of the supporting electrolyes, scan rate, adsorption potential, pulse amplitude and adsorption time. Thus, quantitative trace determination of CIP in model samples as well as in pharmaceutical formulations was succesfully done using the following optimum conditions: phosphate buffer (PH = 7) in presence of NO3-, 100 mV pulse amplitude, 20 mVs-1 scan rate, 60 s accumulation time and -DA V accumulation potential. Under these conditions the CIP concentration is linear over the range 1.5 x10-8 M - 1.2 x10-7 M CIP with regresion coefficient equal 0.996. The detection limit, percent relative error and %RSD are 6x10-9 M, 3.1 % and 4.2%, respectively. Also, the proposed method was succesfully applied for the determination of CIP in Bactiflox-250 tablets with high accurately and precesion (average recovery 105% and % RSD = 3.2%). Moreover, the interaction of CIP with both DNA and CDs are studied. It was inferred that the binding complex of CIP molecule with either DNA or CD was 1:1 association complex. The binding constant for these complexes were calculated and indicated that the CIP molecule has a high affinity for DNA.