P. N. Shaw

The effect of temperature and pH on the deacetylation of diamorphine in aqueous solution and in human plasma

Abstract— The effect of temperature on the kinetics of the deacetylation of diamorphine and 6‐monoacetylmorphine was studied in human plasma. Diamorphine was rapidly and quantitatively degraded to 6‐monoacetylmorphine with initial half‐lives of 354, 18 and 3 min at temperatures of 4, 25 and 37°C, respectively. Further deacetylation to morphine was not detected. In aqueous solution, diamorphine was quantitatively degraded to give 6‐monoacetylmorphine as the major product and morphine as a minor product, the rate of deacetylation being dependent on temperature and pH. At pH 4·0 and 5·6 diamorphine had a half‐life of greater than 14 days at all temperatures but at alkaline pH diamorphine was rapidly deacetylated. The rate of deacetylation of 6‐monoacetylmorphine was consistently slower than that of diamorphine under identical conditions of pH and temperature. A method is described for the rapid stabilization and subsequent assay of diamorphine in plasma which will prevent errors in estimation of the drug due to unwanted hydrolysis.

Phytochemical extraction, characterisation and comparative distribution across four mango (Mangifera indica L.) fruit varieties

In this study we determined the qualitative composition and distribution of phytochemicals in peel and flesh of fruits from four different varieties of mango using mass spectrometry profiling following fractionation of methanol extracts by preparative HPLC. Gallic acid substituted compounds, of diverse core structure, were characteristic of the phytochemicals extracted using this approach. Other principal compounds identified were from the quercetin family, the hydrolysable tannins and fatty acids and their derivatives. This work provides additional information regarding mango fruit phytochemical composition and its potential contribution to human health and nutrition. Compounds present in mango peel and flesh are likely subject to genetic control and this will be the subject of future studies.

Intestinal lymphatic transport of three retinoids in the rat after oral administration: Effect of lipophilicity and lipid vehicle

The retinoids are highly lipophilic molecules and are known to be transported in the intestinal lymph after oral administration. Three retinoids, isotretinoin, etretinate and temarotene were used to study the effects of solubility and lipophilicity on lymphatic uptake in the rat after oral administration in each of three oily vehicles, cottonseed oil, Miglyol 812 and linoleic acid. Lipid solubility showed a general increase with increasing log P of the retinoid. The most lipophilic retinoid, temarotene, showed solubilities between 109.5 mg/ml (linoleic acid) and 170.6 mg/ml (Miglyol 812), whereas the least lipophilic retinoid, isotretinoin showed much lower solubilities between 5.1 (cottonseed oil) and 30.5 mg/ml (linoleic acid). Lymphatic uptake of temarotene was 4000-times and from etretinate 1000-times greater than that for isotretinoin after administration in linoleic acid. The lymphatic uptake of temarotene and etretinate from cottonseed oil were 27- and 26-times greater than that for isotretinoin and from Miglyol 812, 22-and 10-times greater than isotretinoin. These decreases in absorption via the lymphatic route reflect a decrease in log P value from temarotene (log P ≈ 8.7) to etretinate (log P ≈ 7.8) to isotretinoin (log P ≈ 6.8). The rank order of increasing lymphatic uptake from each of the three oils shows an inverse relationship with solubility of the retinoid in each of the oils

Quantification of clarithromycin, its 14-hydroxy and decladinose metabolites in rat plasma, gastric juice and gastric tissue using high-performance liquid chromatography with electrochemical detection.

A rapid, selective and sensitive HPLC assay has been developed for the simultaneous analysis of clarithromycin, its 14-hydroxy-clarithromycin metabolite, and its decladinose acid degradation product, in small volumes of rat gastric juice aspirate, plasma and gastric tissue. Sample were extracted with n-hexane/2-butanol (4:1) and the internal standard was roxithromycin. A Kromasil ODS 5 micrometer(75x4.6 mm I.D.) column was used with a mobile phase consisting of acetonitrile/aqueous phosphate buffer (pH 7, 0.086 M) (45:55 v/v). The column temperature was 30 degrees C and coulometric detection was used at 850 mV using a screen voltage of 600 mV. The analysis time was less than 8 min. The limits of quantitation for clarithromycin, 14-OH clarithromycin and decladinose clarithromycin were 0.15 microgram ml(-1) or lower in plasma (0.05 ml); 0.16 microgram ml(-1) or lower in gastric juice (0.2 ml); and 0.51 microgram g(-1) or lower for gastric tissue (0.25 g). The method was linear up to at least 20.3, 15.4 and 12.5 microgram ml(-1) for clarithromycin, 14-OH-clarithromycin and decladinose, respectively, in gastric juice aspirate and plasma and up to 40.6, 30.9 and 25.0 microgram g(-1) in gastric tissue. The assay was applied to the measurement of clarithromycin, 14-OH-clarithromycin and, for the first time, decladinose clarithromycin in pharmacokinetic studies of gastric transfer of clarithromycin in individual rats.

Major Australian tropical fruits biodiversity: Bioactive compounds and their bioactivities

The plant kingdom harbours many diverse bioactive molecules of pharmacological relevance. Temperate fruits and vegetables have been highly studied in this regard, but there have been fewer studies of fruits and vegetables from the tropics. As global consumers demand and are prepared to pay for new appealing and exotic foods, tropical fruits are now being more intensively investigated. Polyphenols and major classes of compounds like flavonoids or carotenoids are ubiquitously present in these fruits, as they are in the temperate ones, but particular classes of compounds are unique to tropical fruits and other plant parts. Bioactivity studies of compounds specific to tropical fruit plants may lead to new drug discoveries, while the synergistic action of the wide range of diverse compounds contained in plant extracts underlies nutritional and health properties of tropical fruits and vegetables. The evidence for in vitro and animal bioactivities is a strong indicator of the pharmacological promise shown in tropical fruit plant biodiversity. In this review, we will discuss both the occurrence of potential bioactive compounds isolated and identified from a selection of tropical fruit plants of importance in Australia, as well as recent studies of bioactivity associated with such fruits and other fruit plant parts.

Retention behavior of morphine and its metabolites on a porous graphitic carbon column

SummaryThe chromatographic behaviour of a series of morphine-based opiates has been investigated using a porous graphitic carbon packing material at acid and alkaline pH. The effects of mobile phase pH, mobile phase organic percentage, column temperature and ionpairing agents were studied. All six opiates were separated within a close retention window despite large differences in measured lipophilicities of the individual opiates. The retention order was not related to the log P values of the opiates and strong retention of the fully ionised compounds was observed, particularly those with acidic functional groups. The effect of pH on the retention of the compounds indicated that the degree of ionisation of the individual compounds was important in the separation mechanism, suggesting that hydrophobic interactions were present in addition to the polar retentive effects observed above. The strong retention of the ionised glucuronide and sulphate conjugates of morphine is a particularly useful feature of the porous graphitic carbon packing material which has general applicability to the analysis of polar or ionised drug metabolites.

Rapid and selective high-performance liquid chromatographic method for the determination of metronidazole and its active metabolite in human plasma, saliva and gastric juice

A rapid and selective HPLC method has been developed for the separation and quantitation of metronidazole and its hydroxylated metabolite in human plasma, saliva and gastric juice. The assay requires a simple protein precipitation step prior to analysis and is selective, sensitive and reproducible. The limits of quantitation (0.5-ml sample) were at least 0.25 microgram/ml for metronidazole and 0.20 micrograms/ml for its hydroxy metabolite. A Hypersil ODS 5 micron (150 x 4.5 mm I.D.) column was used with a mobile phase of acetonitrile-aqueous 0.05 M potassium phosphate buffer (pH 7) containing 0.1 % triethylamine (10:90) delivered at a flow-rate of 1.0 ml/min.

Randomised, double blind trial of two loading dose regimens of diamorphine in ventilated newborn infants.

AIMS--To compare the safety and efficacy of two loading doses of diamorphine in 27 ventilated newborn infants in a randomised double blind trial. METHODS--Fifty or 200 mcg/kg were infused intravenously over 30 minutes, followed by a 15 mcg/kg/hour continuous infusion. Serial measurements were made of physiology, behaviour, and stress hormones. RESULTS--Both loading doses produced small but significant falls in blood pressure. The 200 mcg/kg dose produced greater respiratory depression, and two infants deteriorated clinically, requiring resuscitation. Loading reduced respiratory effort in most of the infants, but had little effect on behavioural activity. Stress hormone concentrations were reduced at six hours in both dosage groups; differences between loading doses were not significant. Morphine, morphine-3-glucuronide, and morphine-6-glucuronide were detected in the plasma of all patients. No significant differences in concentrations between loading doses were found. CONCLUSIONS--Diamorphine reduces the stress response in ventilated newborn infants. A high loading dose confers no benefit, and may produce undesirable physiological effects. A 50 mcg/kg loading dose seems to be safe and effective.

Impact of acid secretion, gastritis, and mucus thickness on gastric transfer of antibiotics in rats

Background and aims: The success of Helicobacter pylori eradication regimens depends on gastric pH, inflammation, and mucus thickness. Our aim was to investigate the effects of acid secretion, inflammation, and mucolysis on gastric antibiotic transfer. Subjects and methods: A total of 134 anaesthetised rats were given metronidazole, amoxicillin, or clarithromycin intravenously and gastric contents were aspirated via an indwelling cannula. Acid secretion was controlled by either omeprazole or pentagastrin while gastritis was induced by infection with H pylori or dosing with iodoacetamide. Mucolysis was achieved by instilling pronase into the gastric lumen. Results: Metronidazole transfer increased with acid secretion and fell with omeprazole, independently of gastric pH. Clarithromycin was also transferred with acid but was then rapidly degraded. Omeprazole prevented this degradation, raising gastric luminal concentrations. Omeprazole did not alter amoxicillin transfer. Gastritis induced by H pylori did not alter gastric transfer of metronidazole and amoxicillin but that of clarithromycin was increased by 23%. However, gastritis induced by iodoacetamide reduced clarithromycin transfer without any effect on metronidazole or amoxicillin transfer. Pronase treatment increased amoxicillin transfer fourfold and metronidazole by 66% but reduced clarithromycin transfer by 35%. Conclusions: Metronidazole and clarithromycin are predominantly transferred with gastric acid rather than by an acid trapping mechanism. Pronase increases the appearance of amoxicillin and metronidazole in gastric secretions.

Ion-pair high-performance liquid chromatographic assay method for the assessment of clarithromycin stability in aqueous solution and in gastric juice

A simple and selective ion-pair HPLC method has been developed for the analysis of clarithromycin in aqueous solutions and in gastric juice. A Hypersil ODS 5-microns (150 x 4.6 mm I.D.) column was used with a mobile phase consisting of acetonitrile-aqueous 0.05 M phosphate buffer (pH 4.6) containing 5 mM l-octanesulphonic acid (50:50, v/v). The column temperature was 50 degrees C and detection was by UV absorption (210 nm). The limits of detection of 50-microliters samples were 0.4 microgram/ml (aqueous) and 0.78 microgram/ml (0.5 ml gastric juice) or better. The assay was linear in the range of 1.56 to 100 micrograms/ml with r2 values greater than 0.99. The recovery from the gastric juice samples was 98.5 +/- 2.9%. The method was applied successfully to determine the stability of clarithromycin in 0.01 M HCl and gastric juice.