Volume 58 (2008): Issue 3 (September 2008)

A rapid resolution reversed-phase high performance liquid chromatographic (RR RP-HPLC) method has been developed and validated for simultaneous determination of haloperidol and six related compounds. Investigated matrix was a laboratory mixture of a therapeutic active substance haloperidol and its six related compounds in concentration ratio 300:1. Experimental design was used during method optimization (full factorial 2³ design) and robustness testing (Central Composite Circumscribed design). Three factors: organic phase variation during gradient elution, flow rate and gradient rise time were independent variables. To estimate the system response during the optimization procedure and robustness testing, resolution (R_s) and a chromatographic response function (CRF) were used. Chromatography was performed with the mobile phase containing phosphate buffer pH 6.5 and acetonitrile as organic modifier. Separation was achieved using gradient elution (organic phase fraction changed linearly from 20 to 72 %) over 7 min. A Zorbax Eclipse XDB C18 Rapid Resolution HT 4.6 mm x 50 mm, 1.8 μm particle size, column was used at 25 °C at a flow rate of 1.5 mL min^-1. UV detection was performed at 230 nm. The total time for chromatographic separation was 5.5 min with a total analysis time of 7.0 min. The method was validated for its linearity, precision, modal recovery and robustness.

Irbesartan (IBS) is a hydrophobic drug with poor aqueous solubility and dissolution rate. Solid dispersions (SDs) of IBS were prepared with both small molecules (tartaric acid and mannitol) and polymeric additives (polyvinyl-pyrrolidone, PVP, and hydroxypropyl methylcellulose, HPMC). A 9.5 and 7 folds enhancement in solubility over the crystalline form (14.6 μg mL^-1) was observed for tartaric acid (138 μg mL^-1) and PVP (103 μg mL^-1), respectively. Powder X-ray diffraction confirmed that IBS existed in the glassy state in all cases, even with excipients having low glass transition temperature. Thermal methods (differential scanning calorimetry and hot stage microscopy) were used to evaluate the miscibility of the drug and additives. These techniques suggested that tartaric acid led to generation of >amorphous solutions< in contrast to >amorphous suspensions< in other three cases. The in vitro dissolution of IBS depended on the additive load and increased with increasing concentration in the case of tartaric acid, an acidifying excipient. The results indicate the suitability of even small molecules for providing solubility benefits, which can be attributed to the good glass forming ability and reasonable ability of IBS to remain in the glassy state.

Two spectrophotometric methods for the determination of ceftazidime (CFZM) in either pure form or in its pharmaceutical formulations are described. The first method is based on the reaction of 3-methylbenzothiazolin-2-one hydrazone (MBTH) with ceftazidime in the presence of ferric chloride in acidic medium. The resulting blue complex absorbs at λ_max 628 nm. The second method describes the reaction between the diazotized drug and N-(1-naphthyl)ethylenediamine dihydrochloride (NEDA) to yield a purple colored product with λ_max at 567 nm. The reaction conditions were optimized to obtain maximum color intensity. The absorbance was found to increase linearly with increasing the concentration of CFZM; the systems obeyed the Beer's law in the range 2-10 and 10-50 μg mL^-1 for MBTH and NEDA methods, resp. LOD, LOQ and correlation coefficient values were 0.15, 0.79 and 0.50, 2.61. No interference was observed from common excipients present in pharmaceutical formulations. The proposed methods are simple, sensitive, accurate and suitable for quality control applications.

The present study is mainly aimed at delivering a drug into the brain via the intranasal route using a liposomal formulation. For this purpose, rivastigmine, which is used in the management of Alzheimer's disease, was selected as a model drug. Conventional liposomes were formulated by the lipid layer hydration method using cholesterol and soya lecithin as lipid components. The concentration of rivastigmine in brain and plasma after intranasal liposomes, free drug and per oral administration was studied in rat models. A significantly higher level of drug was found in the brain with intranasal liposomes of rivastigmine compared to the intranasal free drug and the oral route. Intranasal liposomes had a longer half-life in the brain than intranasally or orally administered free drug. Delivering rivastigmine liposomes through the intranasal route for the treatment of Alzheimer's disease might be a new approach to the management of this condition.

Multi-drug tablets of amlodipine besylate and atenolol were prepared as either mono-layer (mixed matrix) or bilayer tablets containing each drug in a separate layer by using similar excipients and processing. Each tablet batch was packed in strip and blister packs and kept under accelerated temperature and humidity conditions. The stability of two tablet and packaging types was compared by HPLC analysis after 0, 1, 3 and 4.5 months and expressed as the content of intact amlodipine and atenolol. The content of atenolol did not decline regardless of tablet and packaging type. Amlodipine content in bi-layer tablets decreased to about 95 and 88% when packed in strips and blisters, respectively. When prepared as mono-layer tablets, the content decreased to 72 and 32%, respectively.

The study revealed that the bi-layer tablet formulation was more stable than the mono-layer type. Further, the stability was increased when the tablets were packed in aluminium strips as compared to PVC blisters.

The objective of the present investigation was to prepare and evaluate an ispaghula husk based directly compressible (DC) adjuvant that can be used as matrixing agent using an agglomeration technique. Addition of hydroxypropyl methylcellulose was found necessary to improve cohesion. Lactose (X1), calcium hydrogen phosphate dihydrate (X2) and Avicel PH101 (X3), used along with ispaghula in preparation of agglomerates, were selected as three independent variables in a simplex lattice design affecting compressional and dissolution characteristics of the drug from the DC adjuvant. The agglomerates were evaluated for their flow properties. Tablets were prepared using 70% agglomerates and 30% acetaminophen, a poorly compressible drug, and were subjected to in vitro drug release study. Amounts of the drug released at the end of 60 min (Y60), 300 min (Y300) and 480 min (Y480) were selected as dependent variables in a simplex lattice design. Batch IH05 that contained lactose and calcium hydrogen phosphate dihydrate in a 1:2 ratio could control the release for 12 hours and thus form the basis for twice a-day-dosing.

A new series of cyclooxygenase-2 inhibitors with 2-amino--5-sulfanyl-1,3,4-thiadiazole as the central scaffold unit has been synthesized. The newly synthesized compounds were characterized by analytical and spectral methods. Compounds were screened for cyclooxygenase inhibitory activity by the colorimetric COX (ovine) inhibitor screening assay, anti-inflammatory activity by the carrageenean induced rat paw oedema test and analgesic activity by the tail flick method. Some compounds exhibited significant biological activity.

Selective UV-spectrophotometric methods for determination of iron(III) in iron(II) samples have been developed. The methods are based on the interaction of Fe(III) with quercetin and morin, compounds of the flavonoid group. Redox reactions occurring between Fe(III) ions and the reagents used make the basis for the detection. Iron(II) does not react with quercetin and morin under the conditions applied [aqueous-methanolic (3:2) soluions, 0.3 mol L^-1 HCl, 1.2 x 10^-4 mol L^-1 quercetin (morin)] and does not interfere with the determination of Fe(III). Iron(III) can be determined up to 15 μg mL^-1 using both the examined systems. The detection limits are 0.06 and 0.38 μg mL^-1 when using quercetin or morin, respectively. The method with quercetin was applied to the determination of Fe(III) (ca. 0.2%) in a Fe(II) pharmaceutical product.

An approach for binding affinity evaluation is suggested and exemplified using a set of triazolo [1,5-a] quinoxaline for the (R, S)-2-amino-3-(3-hydroxy-5-methylisoxazol--4-yl)-propionic acid (AMPA) receptor. Biological activity toward the AMPA receptor (expressed as --log IC₅₀) was taken as a dependent variable for building Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA) models. The resulting models show the ways of increasing the binding affinity to the AMPA receptor as a potential target for epilepsy. The statistically significant results show that the cross-validated r²_CV value (0.766) for the CoMFA model is greater than (0.758) for the CoMSIA model. The non-cross validated run giving the coefficient of determination r² values of 0.944 and 0.919 for CoMFA and CoMSIA, respectively, provided good correlation between the observed and computed affinities of the training set compounds. The resulting CoMFA and CoMSIA models indicate that steric, electrostatic, hydrophobic (lipophilic), hydrogen bond donor and acceptor substituents play a significant role in increasing the binding affinity and selectivity of the compounds toward the AMPA receptor.

A rapid, sensitive and selective method for the determination of raloxifene hydrochloride (RLX) in pure drug and in tablets was developed using gradient high performance liquid chromatography (HPLC). The devised method involved separation of RLX on a reversed phase Hypersil ODS column and determination with UV detection at 284 nm. The standard curve was linear (R = 0.999) over the concentration range of 50--600 μg mL^-1 with a detection limit of 0.04 μg mL^-1 and a quantification limit of 0.16 μg mL^-1. Intra-day and inter-day precision and accuracy of the method were established according to the current ICH guidelines. Intra-day RSD values at three QC levels (250, 450 and 550 μg mL^-1) were 0.2--0.5%, based on the peak area. The intra-day relative error (e_r) was between 0.2 and 0.5%. The developed method was successfully applied to the determination of RLX in tablets and the results were statistically compared with those obtained by a literature method. Accuracy, evaluated by means of the spike recovery method, was the excellent with percent recovery in the range 97.7--103.2 with precision in the range 1.6--2.2%. No interference was observed from the co-formulated substances. The method was economical in terms of the time taken and the amount of solvent used.