Quality and functionality of excipients.

The quality of medicines depends not only on the active principles and production processes, but also the performance of the excipients. The traditional concept of the excipient as any component other than the active substance has undergone a substantial evolution from an 'inert' and cheap vehicle to an essential constituent of the formulation. The rapid evolution of scientific, regulatory and economic factors, the introduction of delivery systems and the advance in biopharmaceutics have led to a new interest in the role and functionality of the excipients. More than one thousand raw materials are available from a multitude of sources and are used today in the pharmaceutical industry. Their chemical structures vary from small molecules to complex natural or synthetic polymeric mixtures. Excipients are now chosen to perform a variety of functions to guarantee the stability and bioavailability of the drug substance from the drug product and its manufacturability on a production scale. Beyond the dosage form necessities, excipients are required to perform important and specific technological functions, particularly in the case of solid dosage forms. As a consequence, their characterisation must go beyond the simple tests for identity, purity and strength as prescribed in general by the Pharmacopoeia monographs. With the exception of the Textbook of Pharmaceutical Excipients, not many reference sources describing the physical mechanical characteristics of the powders for a specific role are available. Full physical characterisation of solid materials is now made possible with the help of high resolution analytical techniques on the molecular, particulate and bulk levels. This systematic approach is necessary to guarantee the behaviour of the excipient during the formulation and production phases. Some examples have been chosen in this mini-review in an effort to highlight the emerging trends in the development of 'tailor-made' materials. Three main approaches are followed by the industry: physical or minor chemical manipulation of materials already known, combination of two or more marketed excipients in order to reduce unwanted defects and, finally, preparation of new chemical entities with huge investments for the toxicity studies. Excipient harmonisation, standardised functionality tests, preformulation data bases and expert systems will contribute to change the conventional trial-and-error formulation approach into a far more scientific and technological development.

Drug impurities: problems and regulations.

The matter of impurities is a frequently debated issue, mainly focused on the validation of the analytical methods and on the toxicology of potential impurities. In the first part of the review, the classification, the source and the chemical aspects of impurities are briefly considered according to the current international regulations. A special attention is given to the analytical control, in both qualitative and quantitative terms, of unexpected impurities arising from changes in the manufacturing process or by degradation. The thresholds for identification and qualification of impurities in new drug substances and in new drug products are examined together with the safety studies, when required. Finally, the acceptance limits for four classes of residual solvents are also reported.

Synthesis and anti-ulcer activity of new derivatives of glycyrrhetic, oleanolic and ursolic acids.

A review is made of the literature describing the structural changes to glycyrrhetic, oleanolic and ursolic acids and their influence on anti-ulcer activity. For the glycyrrhetic acid derivatives some analogues were prepared in which the ketonic group in position 11 was removed and the carboxylic function at position 30 was either intact, reduced to alcohol or transformed into ketone. This first series of compounds suggests the possibility of obtaining compounds devoid of the conjugated ketonic group, maintaining anti-ulcer activity but with reduced or lacking mineralocorticoid activity. Based on these findings, a series of carbenoxolone analogues in the beta-amyrin series of glycyrrhetic and oleanolic acid was prepared. In particular, the delta 9,11 unsaturated compounds 14b and 23b and the 11-methylene derivative 18 present advantages in terms of acute toxicity and mineralocorticoid activity as compared to the reference compound. The derivative 14b in the volunteer showed an increase of gastric PGE2 levels with minor pseudoaldosteronic effect. Among the ursolic acid derivatives, the dihemisuccinate sodium salt 35b demonstrated a good separation between anti-ulcer and mineralocorticoid activities. Nevertheless, kidney and liver toxicity was observed in the monkey thus jeopardizing its further development. Better results were obtained with the uvaol dihemiphthalate sodium salt and the diene analogue 39b. In particular, 38b and 39b showed a potent anti-ulcer activity, 3- to 25-fold higher than carbenoxolone. Furthermore, compound 38b does not show signs of liver toxicity in the monkey.

Synthesis and bone resorption effect of alkoxy-substituted xanthones.

A topological modification of ipriflavone 1, a recent antiosteoporotic drug, is described. The flavone moiety of 1 has been replaced by a xanthone one. Among the new derivatives, the 3,6-diisopropoxyxanthone (2a) has shown significant bone resorption inhibition in in vitro and in vivo tests.

Comparative pharmacokinetics and bioavailability of two oral formulations of thiocolchicoside, a GABA-mimetic muscle relaxant drug, in normal volunteers.

The comparative pharmacokinetic and bioavailability profile of two different formulations (tablets and capsules) of thiocolchicoside was investigated in 8 healthy male volunteers after administration of single oral 8 mg doses. Plasma samples were assayed by a capillary gas chromatography--mass spectrometry (GC-MS) method following enzymatic hydrolysis of thiocolchicoside to its aglycone (3-demethylthiocolchicine) and no attempt was made to account for the possible occurrence of hydrolysis in vivo. Irrespective of the formulation used, the drug was rapidly absorbed from the gastrointestinal tract, peak levels of about 17 ng/ml being detected within 1 h in most subjects. Elimination was rapid, with mean MRT values of 5-6 h. All kinetic parameters showed considerable interindividual variability but none differed significantly between the two formulations. Relative to the tablet formulation, the oral bioavailability of the capsule formulation was 1.06 +/- 0.39.

The cost benefit ratio of enantiomeric drugs.

Several drugs possess a chiral structure, i.e. they contain one or more stereogenic centres in their molecule. While naturally occurring active principles usually contain a single enantiomer, most chiral drugs produced by chemical synthesis are used in the form of racemic mixtures of two or more diastereoisomers. These stereoisomers (including enantiomers) may interact in different ways with biological structures and, therefore, may exhibit widely different pharmacokinetic properties. In the pharmaceutical industry, partly in response to increasing demands raised by regulatory authorities, these considerations justify the current trend to develop the single enantiomer characterized by the most favourable profile of activity (eutomer). The availability of new chemical and analytical technologies facilitates stereoselective synthetic processes and separation of individual enantiomers from racemic mixtures. Any decision to develop a drug as a single enantiomer, however, should be made only after careful evaluation of the cost-benefit ratio, i.e. when the advantages of the eutomer in terms of efficacy and tolerability outweigh the associated increase in production and development costs with respect to the racemic drug. This article takes into consideration synthetic procedures and pharmacological profiles for a number of chiral drugs in therapeutic use (naproxen, labetalol, and warfarin) or selected for clinical development, such as the beta-blocker dilevalol or the mucokinetic agent 3'-hydroxyfarrerol. These examples demonstrate that the kinetic, pharmacological and toxicological properties of individual enantiomers need to be clearly characterized before any decision can be made concerning the development of a chiral drug. The choice of preferentially developing a single enantiomer should be based on careful consideration of production and development costs and actual therapeutic advantages especially in terms of improved safety.

Synthesis and biotransformation of 3-hydrazinopyridazine drugs.

Several derivatives of 3-hydrazinopyridazine are reported to possess interesting biological properties as chemotherapeutics, anti-inflammatory agents, CNS depressants and stimulants and anti-hypertensives. In particular, variously substituted 3-hydrazinopyridazines raised considerable interest as peripheral vasodilators with improved potency and safety compared to hydralazine and dihydralazine. More recently, some compounds bearing substituents which may also account for beta-adrenoceptor blocking properties were prepared and studied in approaches aimed at combining in single molecules both the vasodilating and the beta-adrenoceptor blocking activity in an appropriate balance. When substituents are alkylic or arylic, the pyridazine nucleus is synthesized through the appropriate 4-oxoacid, otherwise 3,6-dichloropyridazine is generally used as starting compound. In the latter case, while the nucleophilic substitution of the first chlorine atom is easily obtained, the reactivity of the second chlorine is considerably reduced when the first group introduced has electro-donating properties (alkoxy or alkylamino groups) and an excess of hydrazine is required under forcing conditions. Since 3-chloro-6-hydrazinopyridazine is practically unreactive, it was found to be convenient to convert it to 3-chloro-6-(triphenylmethylazo)pyridazine, whose halogen atom is activated towards nucleophiles, and to restore the hydrazino group after the substitution. 3-Hydrazinopyridazines are extensively metabolized, mainly by acetylation of the free hydrazino group, followed by cyclization, or by reaction with endogenous carbonyl compounds and, to a lower extent, by hydrolysis or oxidation. When the hydrazino group is protected, biotransformation is generally less extensive, giving rise to an active metabolite which in turn follows the metabolic pathways outlined above. Interestingly, pharmacokinetic studies on cadralazine (a 3-hydrazinopyridazine protected as ethoxycarbonyl derivative) support the attractive hypothesis that the pro-drug is biotransformed topically to the active metabolite in the endothelium of arterial vessels, close to the site at which smooth muscle relaxation is required.

Synthesis of imidazo[2,1-b]thiazoles and thiazolines as potential antiulcer agents.

The replacement of the imidazole ring of cimetidine with a bicyclic system (imidazo[1,2-a]pyridine), reported in the literature, produced compounds endowed with potent antiulcer activity. In this paper we describe the synthesis of imidazo [2,1-b]thiazoles and thiazolines bearing the side chain of metiamide, cimetidine and ranitidine: the compounds obtained, tested on gastric lesions induced in rats by ethanol and by stress, were devoid of antiulcer activity.

Synthesis and muscle relaxant activity of cyclic baclofen analogues.

Some new cyclic analogues of baclofen have been prepared and characterized, starting from 4-(4-chlorophenyl)-pyrrolidone. When tested in comparison with the parent compound, they exhibited only a moderate muscle relaxant activity.

A novel antioxidant flavonoid (IdB 1031) affecting molecular mechanisms of cellular activation.

In searching for new drug candidates which could help bridge the gaps between free radical oxidations, pathophysiological responses, and pharmacological treatment, a series of flavonoids was screened. The most interesting compound emerging from this screening, the flavone 3'-hydroxyfarrerol (IdB 1031), is presented in this article. This compound is a good inhibitor of microsomal lipid peroxidation induced by either iron-adenosine 5'-diphosphate (ADP) or carbon tetrachloride. The elevated rate constant for the interaction with peroxyl radicals, analysed by the kinetics of inhibition of crocin bleaching in the presence of a diazo initiator, gives an account for the observed antioxidant capacity. When tested on human neutrophils activated by fMLP, IdB 1031 inhibits (ID50:20 microM) respiratory burst. This effect, which is possibly linked to the observed inhibition of protein-kinase C (ID50:50 microM), seems rather specific since IdB 1031 does not inhibit tyr-kinases and casein-kinase-2, while Quercetin and other flavonoids inhibit unspecifically all these enzymes. These effects, as a whole, depict this compound as a drug candidate for diseases in which peroxidative damage is associated with the induction of inflammatory responses and specifically with activation of a respiratory burst of leucocytes.

Synthesis and diuretic activity of (E)-2-methyl-6-phenylimidazo[2,1-b]-1,3,4-thiadiazole-5-carboxald ehyde dimethylaminoacetohydrazone.

(E)-2-Methyl-6-phenylimidazo[2,1-b]-1,3,4-thiadiazole-5-carboxalde hyde dimethylaminoacetohydrazone was synthesized and its configuration determined. The diuretic activity of this compound, evaluated in rats in a dosage range of 2.5, 10 and 40 mg/kg, was higher than that of the reference compounds hydrochlorothiazide and furosemide.

Synthesis and antiulcer activity of uvaol hemiphthalate derivatives.

Disodium salts of the dihemiphthalates of urs-12-ene-3 beta, 28-diol 3b and of ursa-9(11), 12-diene-3 beta,28-diol 4b were synthesized from uvaol and examined for their gastroprotective activity in rats. The effects showed by 3b and 4b, given p.o. in two antiulcer tests (ethanol induced gastric lesions and diclofenac induced gastric ulcers), were 5-25 times better than those of carbenoxolone. When given p.o. in the rat once a day for 5 days at a gastroprotective dose, 3b and 4b did not induce any change in urine excretion, whereas carbenoxolone significantly reduced urine volume, Na+ excretion and Na+/K+ ratio. In conclusion, 3b and 4b are effective antiulcer agents, devoid of mineral-corticoid activity and therefore provided with a good therapeutic index.

Synthesis and antihepatotoxic activity of silybin 11-O-phosphate.

Silybin 11-O-phosphate 3 was synthesized by selective phosphorylation of silybin with POCl3. The pharmacological activity of 3 was evaluated in the rat by using the praseodymium poisoning test. Preliminary results showed that the compound possesses antihepatotoxic activity, possibly with lower potency compared to the reference drug silybin hemisuccinate.

Comparative pharmacokinetics of silipide and silymarin in rats.

The plasma level profile and the biliary excretion of silybin, the main flavanolignan component of silymarin, were evaluated in rats after single equimolar oral doses (200 mg/kg, expressed as silybin equivalents) of the silybin-phosphatidylcholine complex silipide (laboratory code IdB 1016) and of silymarin. Silybin was assayed by using a specific HPLC method which allowed also the determination of other flavanolignans present in the biological fluids after administration of silymarin (i.e. silydianin, silycristin and isosilybin). After oral silipide, silybin reached peak plasma levels within 2 h, with a Cmax of 9.0 +/- 3.0 micrograms/ml for unconjugated drug and 93.4 +/- 16.7 micrograms/ml for total (free + unconjugated drug). Maximum total biliary concentrations of silybin (2989 +/- 568 micrograms/ml) were observed within 2 h and the biliary recovery after 24 h accounted for about 13% of the administered amount. After administration of silymarin, unconjugated and total plasma silybin levels as well as biliary excretion were several-fold lower than those observed after treatment with silipide. Silybin recovered over a 24 h period after silymarin intake accounted for about 2% of the administered dose. Plasma and bile obtained after administration of silymarin contained also silydianin, silycristin and, to a greater extent, isosilybin. The concentrations of the latter compound in plasma and in bile were higher than those of silybin itself. The relative bioavailability of silipide (calculated in the target organ as the ratio between AUCs of cumulative biliary excretion curves) was 10-fold higher than that of silymarin.

[Chemical-physical compatibility of thiocolchicoside and nonsteroidal anti-inflammatory drugs]. / Compatibilità chimico-fisica tra tiocolchicoside e farmaci antinfiammatori non steroidei.

The combined therapy requires the knowledge of possible interactions between the drugs used. In the case of parenteral formulations the physiochemical stability must be preliminarily verified in an extemporary mixture. The study protocol should be able to make evident possible variations of the main physicochemical parameters at room temperature and in stress conditions. Examples of drug-drug interactions are taken from literature to better define the issue of compatibility in solution. The results of an experimental study between an injectable thiocolchicoside, a well-known miorelaxants and some non-steroidal antiinflammatory drugs are also reported.

Synthesis and antihypertensive activity of imidazo[2,1-b]-thiazoles bearing a 2,6-dichlorophenyl group.

A number of imidazo[2,1-b]thiazoles bearing a 2,6-dichlorophenyl group as hydrazone or as amide were prepared and tested in rats as antihypertensive agents. Only compounds bearing a chlorine at position 6 were active.

Synthesis and pharmacological activity of imidazo [2,1-b] thiazole nitriles, amides and p-sulfamidophenylhydrazones.

The synthesis of three series of new imidazo [2,1-b] thiazoles (nitriles 1-7, amides 8-14 and p-sulfamidophenylhydrazones 15-24) is reported. Among the compounds tested, only 12 showed a borderline diuretic activity. Compounds 15-24, possible prodrugs of sulfanilamide, were devoid of antibacterial activity.

Assay of hydroxyfarrerol in biological fluids.

A high-performance liquid chromatographic method for the determination of hydroxyfarrerol (IdB 1031) in biological samples was developed. IdB 1031 was first extracted by liquid-solid partition and the extracts were evaporated and analysed on a reversed-phase column under isocratic conditions, using either an electrochemical or a UV detector. The detection limit was ca. 5 ng/ml. Preliminary pharmacokinetic data showed that rats treated orally with 500 mg/kg had an average peak plasma concentration (Cmax) of 497 ng/ml after 2 h.

Pharmacokinetic studies on IdB 1016, a silybin- phosphatidylcholine complex, in healthy human subjects.

IdB 1016 is a complex of silybin (the main active component of silymarin) and phosphatidylcholine, which in animal models shows greater oral bioavailability and therefore greater pharmacological activity compared with pure silybin and silymarin. In order to assess its pharmacokinetic profile in man, plasma silybin levels were determined after administration of single oral doses of IdB 1016 and silymarin (equivalent to 360 mg silybin) to 9 healthy volunteers. Although absorption was rapid with both preparations, the bioavailability of IdB 1016 was much greater than that of silymarin, as indicated by higher plasma silybin levels at all sampling times after intake of the complex. Regardless of the preparation used, the terminal half-life was relatively short (generally less than 4 h). In a subsequent study, 9 healthy volunteers received IdB 1016 (120 mg b.i.d., expressed as silybin equivalents) for 8 consecutive days. The plasma silybin level profiles and kinetic parameters on day 1 were similar to those determined on day 8. Most of the silybin present in the systemic circulation was in conjugated form. Less than 3% of the administered dose was accounted for by urinary recovery of free plus conjugated silybin, a significant proportion of the dose probably being excreted in the bile. It is concluded that complexation with phosphatidylcholine in IdB 1016 greatly increases the oral bioavailability of silybin, probably by facilitating its passage across the gastrointestinal mucosa.

[Characterization of plant extracts and registration requirements]. / Caratterizzazione di estratti vegetali e requisiti registrativi.

The extracts of vegetable origin, obtained by extraction, pressing and subsequent processing from whole plants or from their fresh or dried parts, contain the active principles in admixture with secondary constituents in the natural ratio. The quali-quantitative characterization of such extracts, as active ingredients for the formulation of proprietary medicinal products, requires therefore, if compared with that of pure products, to set up a specific analytical development in relation to the complexity and the grade of refinement attained by the multicomponent mixture. In respect of the existing European Community provisions for the control of pharmaceutical starting materials, the problems relevant to nomenclature, description, manufacture and quality control for the scientific documentation of the various extracts, are discussed in comparison with those of pure products.