Drug excipients

The therapeutical use of drugs involves the application of dosage forms, serving as carrier systems together with several excipients to deliver the active ingredient to the site of action. Drug delivery technology combines an understanding of medicinal chemistry and pharmacology with the skill of formulation, aiming the preparation of improved pharmaceuticals. The recently introduced Biopharmaceutical Classification System provides guidance for dosage form design, taking the molecular and physico-chemical properties of drugs into consideration through their solubility and permeability characteristics. Pharmaceutical excipients used for oral dosage form have been traditionally assumed as being inert. However, recent experience and new results have shown that they can interact with the active drug ingredient, affecting its dissolution, absorption and bioavailability. Classification of the excipients is based on their role in the pharmaceutical formulation and on their interactions influencing drug delivery, based on their chemical and physico-chemical properties. The main classes are the antioxidants, coating materials, emulgents, taste- and smell-improvers, ointment bases, conserving agents, consistency-improvers and disintegrating materials. Some of the excipients may serve multiple purposes; for example, methylcellulose is a coating material, is applied in the preparation of suspensions, to increase viscosity, as a disintegrating agent or binder in tablets. The aim of this paper is to review the drug-excipients with respect to their chemistry, importance and interactions altering the pharmacokinetics of the drug substances. Emphasis will be given to two major classes of excipients: the antioxidants and disintegrants (substances facilitating disintegration of the drug tablets in the gastro-intestinal tract). Details will be given on the mechanisms through which they can alter drug effectiveness and tolerance, and control their application. Examples and references will be given for their analysis.

High-performance liquid chromatographic determination of the plasma concentration of K-27, a novel oxime-type cholinesterase reactivator

A simple and reliable HPLC method for the determination of the plasma level of K-27, an oxime type antidote of use in organophosphorus poisoning is presented. Separation was carried out by HPLC using an octyl silica stationary phase and a mobile phase consisting of 93% phosphate buffer (pH 2.6) containing octane sulfate sodium salt, and 7% methanol. Quantitative absorbance was monitored at 286 nm. The calibration curve was linear through the range of 1.25-200 microg/mL, that is well beyond the detected plasma level range of K-27. Limit of quantitation was 5 microg/mL. Intra-day and inter-day precisions of the HPLC determinations gave standard deviations as 0.77 and 2.67%, respectively. Following intramuscular administration of 50 micromol (22.31 mg) K-27 in rats, the maximum of K-27 concentration in plasma was reached at about 15 min giving 186 microg/mL and the t(1/2) was 85 min. K-27 displays initial (from 15 trough 120 min) zero order elimination kinetics. Similar results have been found after intraperitoneal administration.

HPLC analysis of K-48 concentration in plasma

K-48 is a new oxime-type compound to be used as an enzyme reactivator in the treatment of exposure to organophosphorous compounds. Plasma concentration of K-48 can be determined using reversed-phase HPLC. Analysis using octyl silica stationary phase and ultraviolet-absorbance detection is fast and simple. K-48 displays a relatively high dose-normalized area under the curve as compared to pralidoxime, which might be beneficial for an antidote. After i.m. administration of 50 mumol K-48, the time course of the concentration can be approximated by a straight line between 15 and 120 min meaning the elimination follows zero-order kinetics.

Monitoring the Metabolism of Moexipril to Moexiprilat Using High-Performance Liquid Chromatography-Electrospray Ionization Mass Spectrometry

High-performance liquid chromatography combined with a UV absorbance detector and electrospray ionization mass spectrometer is used for the simultaneous analysis of moexipril and moexiprilat in biological samples. Moexipril and moexiprilat are determined in samples metabolized by rat and human liver microsomal preparations, and also in rat urine. The calibration curve is linear in the ng/mL and microg/mL concentration range of the injected moexipril.

HPLC and HPLC-MS analysis of urinary N(epsilon)-monomethyl-lysine

Administration of (14)C-labelled L-deprenyl to rats results in the urinary elimination of a 14C-labelled compound. The 9-fluorenylmethoxycarbonyl chloride-reacted urine sample is fractionated by high-performance liquid chromatography (HPLC) on an octadecyl silica stationary phase. N(epsilon)-Monomethyl-lysine is identified in the fraction containing the majority of the radioactivity. Structural elucidation is carried out using HPLC-mass spectrometry in atmospheric pressure chemical ionization mode. Identification of the 14C-labelled fragment in Ne-monomethyl-lysine is an experimental proof that an N-methylated amino acid is generated by transmethylation from a well-known drug. This type of transmethylation may have basic importance in the positive side effects of certain drugs.

Detection of Nepsilon-monomethyllysine using high-performance liquid chromatography and high-performance liquid chromatography-mass spectrometry

Nepsilon-Monomethyllysine was identified in the serum, urine, brain, and liver samples of rats treated per os with L-deprenyl. The identification procedure included reaction with Fmoc chloride, clean-up, and analysis using HPLC-UV-MS. Oral administration of (-)-N-14C-methyl-N-propynyl(2-phenyl-1-methyl)ethylammonium hydrochloride L-deprenyl) to rats resulted in transfer of the radiolabelled methyl group to the Nepsilon-amino group of the endogenous lysine. The radiolabelled Nepsilon-monomethyllysine was urinary eliminated together with the other radiolabelled deprenyl metabolites, such as deprenyl-N-oxide and methamphetamine. The presence of Nepsilon-monomethyllysine has also been traced, and its concentrations were compared in the serum, liver and brain of rats subjected to L-deprenyl treatment. Methyl group transfer from the L-deprenyl to endogenous compounds; and the urinary elimination of their products may offer a vital way to eliminate or to decrease the degree of drug transmethylation to the lysine constituents of blood vessels' proteins.

Detection of N-monomethyl-lysine generated by metabolic transmethylation

Administration of radiolabelled deprenyl to rats resulted in the urinary elimination of a (14)C-labelled N(epsilon)-monomethyl-lysine. An increased level of N(epsilon)-monomethyl-lysine was found following an oral dose of another drug, also containing an N-methyl group. The urine sample was treated with 9-fluorenylmethoxycarbonyl chloride and then subjected to high-performance liquid chromatography (HPLC); the radioactive fraction was identified as N(epsilon)-monomethyl-lysine by using HPLC-MS in electrospray mode. Identification of N(epsilon)-monomethyl-lysine in the radioactive fraction gives experimental proof of transmethylation from a well-known drug to an endogenous compound.

Combined effect of promoter polymorphisms in the dopamine D4 receptor and the serotonin transporter genes in heroin dependence

Dopamine D4 receptor (DRD4) and serotonin transporter (SERT) gene polymorphisms were studied, as possible genetic risk factors for substance dependence. The case-control study involved a large cohort (n = 362) of healthy Caucasian population, and an initial sample of 73 substance dependent patients (including a subgroup of 53 heroin dependents). Improved methods were applied for genotype detection of the DRD4 polymorphisms (exon 3 48 bp VNTR; -521 C/T SNP and 120 bp duplication in the 5' flanking region) and the SERT gene polymorphisms (5-hydroxytriptamin transporter linked polymorphic region [5-HTTLPR] in the 5' flanking region and the intron 2 VNTR [STin2]). Association between the -521 C/T SNP of the DRD4 promoter region and substance dependence was significant in the subgroup of heroin dependents (p = 0.044). The other analyzed polymorphisms did not show any significant association, but an interaction between -521 C/T SNP of DRD4 and the 5-HTTLPR polymorphisms was observed. Association between the -521 CC vs. CT or TT genotypes and heroin dependence was enhanced in the presence of short (s or 14-repeat) 5-HTTLPR allele (p 0.01). The odds ratio of 2.14 observed for the -521 CC genotype increased to 4.82 in double homozygotes of -521 CC and 5-HTTLPR ss, emphasizing the importance of combined analysis of polymorphisms in the dopaminergic and serotonergic systems in heroin dependence. However, due to the limited size of our sample these results should be interpreted with caution.

Pharmacological Aspects of (-)-Deprenyl

Deprenyl, the selective irreversible inhibitor of monoamine oxidase-B (MAO-B), has been synthesised as a potential antidepressant, however, due to its dopamine potentiating capacity, became a registered drug in the treatment of Parkinson's disease. Deprenyl possesses a wide range of pharmacological activities; some of them are not related to its MAO-B inhibitory potency. Beside its dopamine potentiating effect, it renders protection against a number of dopaminergic, cholinergic and noradrenergic neurotoxins with a complex mechanism of action. By inducing antioxidant enzymes and decreasing the formation of reactive oxygen species, deprenyl is able to combat an oxidative challenge implicated as a common causative factor in neurodegenerative diseases. In a dose substantially lower than required for MAO-B inhibition (10(-9)-10(-13) M), deprenyl interferes with early apoptotic signalling events induced by various kinds of insults in cell cultures of neuroectodermal origin, thus protecting cells from apoptotic death. Deprenyl requires metabolic conversion to a hitherto unidentified metabolite to exert its antiapoptotic effect, which serves to protect the integrity of the mitochondrion by inducing transcriptional and translational changes. Pharmacokinetic and metabolism studies have revealed that deprenyl undergoes intensive first pass metabolism, and its major metabolites also possess pharmacological activities. The ratio of the parent compound and its metabolites reaching the systemic circulation and the brain are highly dependent on the routes of administration. Therefore, in the treatment of neurodegenerative diseases, reconsideration of the dosing schedule, by lowering the dose of deprenyl and choosing the most appropriate route of administration, would diminish undesired adverse effects, with unaltered neuroprotective potency.

Biological role of formaldehyde, and cycles related to methylation, demethylation, and formaldehyde production

An overview is given on the analysis, formation, role and occurrence of formaldehyde in living organisms. Various methods have been used for the determination of formaldehyde in tissues and body fluids. Gas chromatography, thin-layer chromatography and HPLC were employed for the analysis of formaldehyde, mainly after derivatization. The formaldehyde level of human blood and urine was found at the low ppm level. The formaldehyde level could be increased upto several ten micro g/mL(-1) following special dietary supply. Biochemical pathway of both the formaldehyde production and demethylation/methylation processes is generally connected to the methionine - homocysteine cycles. Another important way of demethylation generated formaldehyde production is given by microsomal cytochrome P-450 dependent oxidation of xenobiotics, such as various drugs prescribed by doctors. Semicarbazide sensitive amine oxidase also produces formaldehyde. Increased level of formaldehyde may be the indication of either patho-physiological processes, or environmental contamination, or malnutrition. The formaldehyde-related methylation and demethylation procedures are also detailed. DNA methylation may have an important role in the pathogenesis of certain diseases.

HPLC analysis of metabolically produced formaldehyde

Radiolabelled (-)-deprenyl is orally administered to rats, and urinary elimination of radiolabelled formaldehyde is detected. The separation is performed using high-performance liquid chromatography on octadecyl-silica stationary phase. Both the radioactivity and the UV absorbance of the dinitrophenylhydrazine formaldehyde peak are determined. Formaldehyde generation takes place by N-demethylation. Low levels of formaldehyde may have a beneficial role in counterbalancing the oxidative stress of the everyday person's life.

5-Alpha- and 5-beta-2-deoxyintegristerone A, a 5-alpha and 5-beta isomer pair of ecdysteroids isolated from the Silene genus

5-Alpha-2-deoxyintegristerone A and 5-beta-2-deoxyintegristerone A were isolated from the aerial parts of Silene italica ssp. nemoralis (Waldst. and Kit.) Nyman using a specific combination of absorption column chromatography, preparative thin-layer chromatography and preparative HPLC. Both normal-phase and reversed-phase modes of HPLC were employed for isolation. Structural elucidation of 5-alpha-2-deoxyintegristerone A was completed by X-ray diffraction. Both 5-alpha-2-deoxyintegristerone A and 5-beta-2-deoxyintegristerone A were firstly isolated from this plant. We propose that 5-alpha-2-deoxyintegristerone A is not an artifact but an integral part of the ecdysteroid spectrum of Silene italica ssp. nemoralis (Waldst. and Kit.) Nyman.