Monitoring of Microalgal Processes

Process monitoring, which can be defined as the measurement of process variables with the smallest possible delay, is combined with process models to form the basis for successful process control. Minimizing the measurement delay leads inevitably to employing online, in situ sensors where possible, preferably using noninvasive measurement methods with stable, low-cost sensors. Microalgal processes have similarities to traditional bioprocesses but also have unique monitoring requirements. In general, variables to be monitored in microalgal processes can be categorized as physical, chemical, and biological, and they are measured in gaseous, liquid, and solid (biological) phases. Physical and chemical process variables can be usually monitored online using standard industrial sensors. The monitoring of biological process variables, however, relies mostly on sensors developed and validated using laboratory-scale systems or uses offline methods because of difficulties in developing suitable online sensors. Here, we review current technologies for online, in situ monitoring of all types of process parameters of microalgal cultivations, with a focus on monitoring of biological parameters. We discuss newly introduced methods for measuring biological parameters that could be possibly adapted for routine online use, should be preferably noninvasive, and are based on approaches that have been proven in other bioprocesses. New sensor types for measuring physicochemical parameters using optical methods or ion-specific field effect transistor (ISFET) sensors are also discussed. Reviewed methods with online implementation or online potential include measurement of irradiance, biomass concentration by optical density and image analysis, cell count, chlorophyll fluorescence, growth rate, lipid concentration by infrared spectrophotometry, dielectric scattering, and nuclear magnetic resonance. Future perspectives are discussed, especially in the field of image analysis using in situ microscopy, infrared spectrophotometry, and software sensor systems.

Curdlan sulphate in human severe/cerebral Plasmodium falciparum malaria

Preclinical studies have shown that curdlan sulphate (CRDS), a sulphated 1-->3-beta-D glucan, inhibits Plasmodium falciparum in vitro and down-modulates the immune response. A direct, non-specific effect on cytoadherence and rosetting may be predicted, as has been described with other sulphated polysaccharides, e.g. heparin. The anticoagulant effect of CRDS is 10-fold lower than heparin. Curdlan sulphate has, therefore, emerged as a candidate for adjunct medication in the treatment of severe/cerebral malaria. Two clinical studies were conducted using CRDS as adjunct medication to conventional therapy (artesunate) in patients with severe and severe/cerebral malaria. Both studies were double-blind and placebo-controlled to evaluate the efficacy and safety of the combination. Curdlan sulphate appeared to reduce the severity of the disease process, e.g. fever clearance time was shortened. Due to the small number of patients, there was no difference in mortality. The two treatment arms in both studies showed similar results for all laboratory parameters. The only adverse event recorded during CRDS treatment was an increase in activated partial thromboplastin time. This can be monitored easily. It seems that the patients who may benefit most are severe/cerebral cases with no organ damage on admission.

Seasonal variation in uterotonic activity of Rhoicissus tridentata extracts

BACKGROUND

Rhoicissus tridentata lignotubers are widely used in southern African traditional pregnancy-related remedies.

OBJECTIVES

To determine the seasonal variation in contractile activity of extracts from different parts of the plant.

METHODS

Isolated rat uterus tissue was used to compare the contractile activity of crude aqueous extracts of R. tridentata made from plant material harvested every 3 months over a period of 2 years.

RESULTS AND CONCLUSIONS

The activity of the plant extracts from plants harvested in summer and autumn were 4-5-fold higher than extracts from plants harvested in winter or spring. The tubers stimulated the greatest degree of contractions, followed by the stems, roots and leaves. These results highlight the need to standardise the timing of harvesting R. tridentata.

Structure-activity relationships and inhibitory effects of various purine derivatives on the in vitro growth of Plasmodium falciparum

The development of novel chemotherapeutic agents has become an urgent task due to the development and rapid spread of drug resistance in Plasmodium falciparum, the protozoan parasite responsible for cerebral malaria. Cyclin-dependent kinases (CDKs) are essential for the regulation of the eukaryotic cell cycle, and several enzymes of this family have been identified in P. falciparum. In recent years, a number of purine-derived kinase inhibitors have been synthesised, some of which display selective activity against CDKs. This report describes a study in which various purine derivatives were screened for in vitro antimalarial activity. The erythrocytic asexual stages of the chloroquine-resistant P. falciparum strain (FCR-3) were cultivated in vitro in the presence of the various purines, and their effect on parasite proliferation was determined by the [3H]hypoxanthine incorporation assay. Our results show considerable variation in the sensitivity of P. falciparum to the different purines, as well as a general independence from their effect on purified starfish CDK1/cyclin B activity, which has been the standard assay used to identify CDK-specific inhibitors. Two subfamilies of purines with moderate to poor activity against CDK1/cyclin B activity showed submicromolar activity against P. falciparum. Structure-activity analysis indicates that certain structural features are associated with increased activity against P. falciparum. These features can be exploited to synthesise compounds with higher activity and specificity towards P. falciparum.

The pharmacological action of Rhoicissus tridentata on isolated rat uterus and ileum

Decoctions and infusions of Rhoicissus tridentata subsp cuneifolia (Vitaceae) roots and lignotubers are widely used in South African traditional herbal remedies during pregnancy. The pharmacological action of an aqueous extract of R. tridentata subsp cuneifolia roots was investigated using isolated rat uterus and ileum. The extract directly stimulated concentration dependent contractions of the uterus and ileum. Pretreatment with the muscarinic antagonist atropine (40 nM) and the cyclooxygenase inhibitor indomethacin (5 microM) both blocked the contractile response to the Rhoicissus extract suggesting that muscarinic receptors and cyclooxygenase metabolites could be involved in the contractile response to the extract. The serotonergic antagonist methysergide (1 microM) and the alpha-adrenoceptor antagonist prazosin (2 microM) had no effect on the direct action of the extract. This infers that the contractile response to the plant extract is independent of serotonin receptors and alpha-adrenoceptors.

The effects of herbal oxytocics on the isolated "stripped" myometrium model

Decoctions of Agapanthus africanus and Clivia miniata are used as oxytocic agents in South African traditional herbal medicine. Aqueous extracts of A. africanus and C. miniata leaves have been shown to possess similar uterotonic activities in the isolated whole uterus preparation. The uterus however, comprises a myometrial and an endometrial layer and the activity of both oxytocin and the prostaglandins differs in these layers. The aim of this study was to determine the uterotonic activity of the herbal remedies in an endometrium-free preparation (i.e. "stripped" myometrium) and, if active, whether this effect could be related to prostaglandin synthesis or to interaction with specific receptors. The effects of the herbal extracts were tested on the isolated "stripped" rat myometrium preparation. Both herbal extracts caused a direct contractile response by the isolated tissue. Pretreatment of the myometrium with either plant extract augmented the initial response to acetylcholine. Preincubation with atropine inhibited the response to cumulative dosage of Agapanthus extract but had no effect on the response to Clivia. Indomethacin administration did not affect the response of the myometrium to cumulative dosage of acetylcholine, oxytocin or Clivia extract but inhibited the response to Agapanthus extract. These results clearly indicate that the Agapanthus and Clivia herbal extracts exhibited uterotonic activity in this model. The study illustrates that the "stripped" myometrium model has successfully differentiated between the mechanisms of action of two herbal oxytocics compared to the whole uterus preparation where their uterotonic activity was thought to be similar.

Comparison of the pharmacokinetic profiles of soluble aspirin and solid paracetamol tablets in fed and fasted volunteers

The aim of this study was to investigate the absorption of popular preparations of two common analgesics--soluble aspirin and solid paracetamol tablets. An open, randomised, crossover study design was used to compare the pharmacokinetic parameters of soluble aspirin and solid paracetamol tablets in 16 healthy, male volunteers from the University of the Witwatersrand, South Africa, in both fed and fasted states. Plasma concentrations of paracetamol, aspirin and salicylic acid were measured. It was found that the rate of absorption was significantly faster for soluble aspirin than for solid paracetamol, regardless of fed or fasting state, considering time to maximum concentration (p < 0.01), time to first quantifiable concentrations (p < 0.05) and absorption rate (p < 0.01). Absorption rate was significantly affected by food for both soluble aspirin (p = 0.028) and for solid paracetamol (p = 0.0003). Time to maximum concentration was not significantly affected by food for soluble aspirin (p = 0.17) but significantly lengthened for solid paracetamol (p = 0.0003). The extent of absorption was affected by food in terms of maximum concentration for both drugs (p = 0.0001), with a reduction of 49% in the fed state for solid paracetamol compared to 18% for soluble aspirin, the difference between the drugs being statistically significant (p = 0.0024). The overall bioavailability of soluble aspirin was unaffected by food and the bioavailability of salicylic acid was increased in the fed state, whereas that of solid paracetamol was lowered in the fed state. Greater inter-individual variation was seen in paracetamol concentrations compared with aspirin or salicylic acid levels. In conclusion, these results show that the absorption of soluble aspirin is largely unaffected by food, whereas, in the same volunteers, the absorption of solid paracetamol tablets is greatly affected. In some volunteers, maximum plasma concentrations of paracetamol following food did not reach levels previously reported to be required for effective analgesia, and this may have implications for pain relief in some individuals. The practice in some individuals of taking aspirin tablets after food to minimise potential gastric disturbance should not affect the level of analgesia.

Pharmacological effects of Agapanthus africanus on the isolated rat uterus

The Agapanthus africanus plant is used by South African traditional healers as a phytomedicine in herbal remedies to treat pregnancy-related ailments and to augment labour. It has already been shown that an aqueous extract of A. africanus causes smooth muscle contractions in the isolated uterus and ileum preparations. In the present study, the effects of an aqueous extract of A. africanus leaves was examined on receptor systems involved in contraction of the uterine smooth muscle in order to determine the mechanism of its pharmacological effect relevant to its ethnic use to augment labour. The extract was tested on the isolated rat uterus preparation. The aqueous extract of A. africanus leaves was found to exhibit agonist activity on uterine muscarinic receptors and to promote the synthesis of prostaglandins in the oestrogenized rat uterus. Some pharmacological justification for the ethnic use of A. africanus as a herbal oxytocic in prolonged labour has been provided.

Citalopram enhances the activity of chloroquine in resistant plasmodium in vitro and in vivo

Citalopram, is an extremely potent inhibitor of neuronal serotonin reuptake. It is structurally unrelated to other antidepressants, but it contains the chemical features associated with reversal of drug resistance and exhibits minimal cardiotoxic side effects and fewer of the anticholinergic and adrenolytic side effects associated with other psychotropic agents. Sensitivity tests to citalopram alone and in combination with chloroquine were performed against chloroquine-resistant and chloroquine-sensitive strains of Plasmodium falciparum and Plasmodium chabaudi. Citalopram alone showed intrinsic activity against the chloroquine-resistant strains of P. falciparum (IC50 = 1.51 +/- .6 microM) but only limited activity against the chloroquine-sensitive strain (IC50 = 33.27 +/- 5.87 microM) and no activity in vivo. The interaction of chloroquine and citalopram in vitro resulted in a synergistic response in the chloroquine-resistant strain but there was no interaction between the drugs in the chloroquine-sensitive strain--a pattern found with other reversal agents. Citalopram enhanced chloroquine susceptibility in both strains of P. chabaudi, however, the potentiating effect was seen at lower doses in the chloroquine-resistant strain. The results of this study suggest that citalopram may have potential as a chemosensitizer in Plasmodium infections on the basis of the low toxicity of citalopram at concentrations potentiating chloroquine activity both in vitro and in vivo.

The effect of curdlan sulphate on development in vitro of Plasmodium falciparum

Sulphated glycoconjugates have been reported to inhibit malarial merozoite invasion and interfere with rosetting and adhesion. Curdlan sulphate, a sulphated glycoconjugate with a favourable toxicity profile, exhibits antimalarial activity in vitro. The aim of this study was to characterize the antimalarial activity of curdlan and investigate its effect on adhesion. The antimalarial activity of curdlan at different points in the intraerythrocytic developmental cycle was investigated using morphological observation and radiolabelled hypoxanthine uptake as indices of parasite growth. Effects on adhesion were investigated using a platelet model. Curdlan suphate had no effect on the ability of the parasite to develop through the intraerythrocytic cycle. Inhibition of invasion was dependent on the drug being present at the time of invasion. Curdlan did not interfere with the ability of the parasite to adhere to the C36 receptor in the platelet model. In conclusion, the low toxicity of curdlan and its marked anti-invasion activity on merozoites make curdlan a potential auxiliary treatment for severe malaria.

Preliminary screening of plants used in South Africa as traditional herbal remedies during pregnancy and labour

Agapanthus africanus, Pentanisia prunelloides and Gunnera perpensa are indigenous plants which are used in traditional herbal remedies during pregnancy and childbirth. A crude decoction of each plant was tested on isolated rat uterus and ileum for pharmacological activity. Agapanthus africanus and Pentanisia prunelloides exhibited direct smooth muscle activity on the uterus and ileum preparations, while Gunnera perpensa showed direct smooth muscle activity on the uterus only. All the plant extracts potentiated the initial response of the uterus to oxytocin but Pentanisia prunelloides reduced the maximum response of the uterus to oxytocin. The Agapanthus africanus and Pentanisia prunelloides extracts potentiated the initial response of the ileum to acetylcholine but all the plant extracts inhibited the maximum response of the ileum to acetycholine.

Effect of pH on in vitro potency of amantadine against Plasmodium falciparum

Amantadine is a monoprotic weak base that inhibits intraerythrocytic growth in in vitro cultures of Plasmodium falciparum, specifically chloroquine-resistant strains. Changes in the external PH of the medium are expected to result in a shift in the relative proportion of ionized and unionized species of amantadine by virtue of the weak base characteristic of the drug, influencing passage of the drug through the membrane. The ability of amantadine to alkalinize the food vacuole was determined using the accumulation of acridine orange as a vacuolar probe. Drug sensitivity following alteration of the pH gradient was assessed using the hypoxanthine method. Amantadine was able to alkalinize the food vacuole in the millimolar range; however, since its antimalarial activity is in the micromolar range, alkalinization of the food vacuole is not the primary action of the drug. The pH of the medium profoundly influenced susceptibility to chloroquine; the log of the 50% inhibitory concentration (IC50) values were linearly dependent on the external pH in both chloroquine-resistant and chloroquine-sensitive strains. Log IC50 values of amantadine exhibited a linear dependence on external pH in the chloroquine-sensitive strain, but in the chloroquine-resistant strain, a nonlinear parabolic function was found with the minimum IC50 at pH 7.03. Ammonium chloride did not interfere with the antimalarial activity of amantadine. The presence of the amine group on the hydrocarbon cage is essential for the activity of amantadine in Plasmodium falciparum. These results suggest factors in addition to pH gradient are involved in the effect of amantadine, possibly interactions with membrane phospholipids.

In vitro drug interaction between amantadine and classical antimalarial drugs in Plasmodium falciparum infections

The interactions of amantadine with classical antimalarial drugs were evaluated against a chloriquine-resistant and a chloroquine-sensitive strain of Plasmodium falciparum in vitro. Amantadine potentiated the effect of chloroquine and quinine in both strains; it also potentiated the effect of mefloquine, halofantrine and primaquine in the chloroquine-resistant strain but had no effect in the chloroquine-sensitive strain. Amantadine had no effect on the response to pyrimethamine of either strain. Amantadine does not interfere with the activity of these compounds and may possibly enhance it.

Hydrocortisone and tumor necrosis factor in severe community-acquired pneumonia. A randomized controlled study

BACKGROUND

Community-acquired pneumonia is a major cause of death in third world countries. Antimicrobial therapy may have little impact on the natural history of patients with severe pneumonia. We hypothesized that the intrapulmonary production of tumor necrosis factor-alpha (TNF-alpha) may be responsible for the progressive lung injury and shock commonly seen in patients with severe pneumonia after commencing antibiotic therapy.

AIM

To investigate the effects of a single bolus of hydrocortisone on the clinical course and serum TNF-alpha levels of patients with severe community-acquired pneumonia.

DESIGN

Randomized placebo-controlled study.

SETTING

Multidisciplinary ICU of a tertiary care teaching hospital.

PATIENTS AND METHODS

Patients with three or more British Thoracic Society criteria of severe pneumonia were studied. Patients were randomized to receive either a single dose of hydrocortisone (10 mg/kg) or placebo 30 min prior to commencing antibiotic therapy. Patients were treated with cefotaxime and other antibiotics as clinically indicated. Blood for TNF-alpha was taken at the time of hospital admission and repeated 2, 6, and 12 h after starting antibiotic therapy.

RESULTS

Thirty patients were studied: 16 received placebo and 14 received hydrocortisone. The patients who received placebo tended to be sicker than the patients who received hydrocortisone. The baseline TNF-alpha value was 989 +/- 374 pg/ml in the placebo group and 827 +/- 394 pg/ml in the hydrocortisone group. In both groups of patients, the TNF-alpha levels did not change significantly with time. There was no correlation between the TNF-alpha levels and the APACHE II score, lung injury score, or outcome. The only variable that predicted outcome was the APACHE II score.

CONCLUSION

Bactericidal antibiotics do not increase serum TNF-alpha levels in patients with severe pneumonia. Hydrocortisone given prior to antibiotic treatment had no effect on the serum TNF-alpha levels or the clinical course of patients with severe community-acquired pneumonia.

Malaria pigment and extracellular iron. Possible target for iron chelating agents

Extracellular iron is necessary for many biochemical reactions involved in Plasmodium falciparum growth and multiplication. The incorporation of radioactive iron taken up by the parasite was found, electrophoretically and via gamma counting, to be mainly associated with the haemozoin only in the presence of the active metabolism of the parasite. The potent antimalarial activity of desferrioxamine, a ferric iron chelating agent, has shown that iron deprivation is inhibitory to the parasite. We propose that the mechanism of action of desferrioxamine in addition to the chelation of iron from the parasitic compartment, chelates iron from the haemozoin crystal resulting in free radical generation and parasite death. The ability of desferrioxamine and not the ferrous iron chelating agent, 2,2'-bipyridyl, to chelate the non-haem iron from the haemozoin structure indicates that the oxidative state of iron associated with the haemozoin structure is ferric in nature.

Plasmodium falciparum: effects of amantadine, an antiviral, on chloroquine-resistant and -sensitive parasites in vitro and its influence on chloroquine activity

The lysosomotropic nature of amantadine suggested potential as an antimalarial. Sensitivity tests to amantadine hydrochloride alone and in combination with chloroquine were carried out in 96-well microtitre plates using the tritiated hypoxanthine uptake method to measure parasite growth. Amantadine alone has antimalarial activity. Amantadine is more potent against chloroquine-resistant strains. Combinations of amantadine and chloroquine result in slight synergy in both resistant and sensitive strains.

The combined effect of iron chelators and classical antimalarials on the in-vitro growth of Plasmodium falciparum

The emergence of drug resistant malaria has prompted an intensified search for new antimalarials or combinations of such drugs. Iron chelating agents may represent a new approach to antimalarial treatment and could possibly be used in combination with classical antimalarials. Plasmodium falciparum (FCR-3) strain used at a 1% haematocrit, was subjected to various combinations of the classic antimalarials (chloroquine, pyrimethamine and quinine) and iron chelating agents (desferrioxamine and 2,2'-bipyridyl) in vitro. Tritiated hypoxanthine incorporation was used to determine the growth of the malarial parasites. The iron chelating agents and classic antimalarials when tested alone were found to inhibit the growth of the late stages of the parasite. The combination of the classic antimalarials and iron chelating agents resulted in additive effects on the in-vitro growth of P. falciparum.

Cardiac glycoside poisoning involved in deaths from traditional medicines

Autopsy cases (from all areas of South Africa except the Cape Province) are referred for chemical investigation to the Johannesburg Forensic Chemistry Laboratory of the State Health Department. Over a 1-year period in 41 autopsies where death was presumed to have been caused by a herbal medicine, the presence of cardiac glycosides was sought and was found in 44%. Most of the cases were from the Transvaal, followed by Natal. Clinical histories of the patients revealed that gastrointestinal irritation was the most common syndrome experienced after traditional medicine administration (54%). It is concluded that in patients presenting with gastro-intestinal symptoms, presumably due to poisoning by traditional medicines, cardiac glycoside poisoning should be suspected.

The pharmacokinetic of amikacin in critically ill adult and paediatric patients: comparison of once- versus twice-daily dosing regimens

The pharmacokinetic profile of amikacin was analysed by a two-compartment model in 100 critically-ill adult and paediatric patients with normal renal function. In addition the serum amikacin levels in 200 patients randomized to receive a once- or twice-daily dosing regimen are reported. The mean volume of distribution (Vdt) was 0.33 l/kg in the adult patients, 0.50 l/kg in patients 6 to 12 months of age and 0.58 l/kg in patients less than 6 months old. The elimination half-life was prolonged, being 3.45, 2.86 and 5.02 h for the respective age groups (normal 2 h). The clearances dose/AUC) were 0.051, 0.068 and 0.063 l/h/kg respectively. Within each group of patients there was a large variation in the pharmacokinetic parameters, with the Vdt varying by a factor of 6 and the elimination half-life by a factor of 10. All patients receiving a once-daily dose of amikacin had therapeutic peak concentrations. In comparison, therapeutic concentrations were achieved in only 48% of adult and 44% of the paediatric patients receiving the twice-daily dosing regimen. Furthermore the amikacin trough concentrations were significantly higher in the patients who received a divided daily dose. As a consequence of the pharmacokinetic profile of amikacin in critically ill patients a once-daily dosing regimen may be more effective and less toxic than the conventional twice-daily dosing regimen.

On the prenatal noxious effects of trypan blue and of a related azo dye

Since 1948 trypan blue has been a well-known and extensively used experimental teratogen, belonging to the group of azo dyes. Chemically, trypan blue consists of a biphenyl molecule (0-tolidine or benzidine) combined by means of azo linkages with two molecules of a substituted naphthalene. Between 1987-89 the effect of the replacement of the biphenyl molecule by a molecule of p,p'-diaminobenzanilide upon the prenatal noxious action of trypan blue has been controlled. Investigations were carried out on three species: chick embryos, albino rats and albino mice. In the species used, the replacement annihilates the teratogenic properties of the dye, with the persistence of some embryotoxic effects. On the other hand, the control of o-tolidine and of p,p'-diaminobenzanilide revealed that no one had teratogenic properties (only some embryotoxic effect, more marked in the case of o-tolidine). It results that the teratogenic action of trypan blue cannot be attributed to the o-tolidine molecule proper but to an effect which results (in a for the moment unknown manner) from its combination with the other parts of the dye molecule.

Malaria at Johannesburg Hospital. A retrospective study

A total of 43 patients diagnosed as having malaria were admitted to Johannesburg Hospital during 1988; 40 (94%) were infected with Plasmodium falciparum. Only 26 patients (60%) were recorded as having used prophylaxis of any kind; chloroquine alone and in combination was used as prophylaxis by 17. Patients were treated with quinine (alone or in combination) in 67% of cases. In 42% of patients chloroquine-resistant malaria was considered a possibility.

Adriamycin cellular transport: methodological aspects

A rapid and simple method for determination of cellular uptake of adriamycin is described. The method is based on the principle that active uptake is proportional to alterations of drug distribution, measured as a fraction of time, between suspending medium and cells, the volume of each having been accurately determined. Cellular drug uptake can be calculated by the use of a simple distribution formula. This method represents a compromise between indirect measurement of the loss of drug from suspending medium and direct measurement of drug uptake following cell separation, washing, and lysis. This method should be applicable to the measurement of cellular uptake of a wide range of drugs.

Solubility changes on mixing short- and long-acting insulin preparations

The loss of solubility of short-acting insulins when mixed in a ratio of 1:1 with intermediate-acting insulins in vitro was determined using high-performance liquid chromatography. Insulin preparations (porcine and human) from three different manufacturers were tested and various times of mixing (0-24 h) were investigated. The loss of solubility with mixtures of human insulins and with mixtures of porcine Velosulin (Nordisk) and Insulatard (Nordisk) was small at all the times used. A mixture of porcine Actrapid MC (Novo) and Monotard MC (Novo) led to a 60-95% loss of the soluble component, depending on the duration of mixing. The greater the time the greater the loss. These in vitro data indicate that short-acting insulins may lose solubility when mixed with long- or intermediate-acting ones. This phenomenon could be clinically relevant when patients are changed from mixtures of monocomponent to human insulins.

[Simulation of kinetics of phenazepam and its metabolite 3-hydroxyphenazepam in cat blood]

The pharmacokinetics of the tranquilizer phenazepam and its high-active metabolite 3-hydroxyphenazepam in the cat blood was studied in experiments using gas liquid chromatography and mathematic simulation. The experimental findings were computer-processed. An appreciable quantity of 3-hydroxyphenazepam was found in the blood in addition to the unchanged drug at any times after oral administration of phenazepam (2 mg/kg). Joint modelling of the kinetics of phenazepam and 2-hydroxyphenazepam within the same metabolic model allowed calculating the kinetic parameters of both the compounds. The elimination constant of the metabolite in cats was found to be twice as high on the average as compared to that of the unchanged drug.

Effects of potassium ethylxanthogenate and 2,3-dimercaptopropane sulphonate sodium on the pentobarbital pharmacokinetics and metabolism in male mice

The effects of potassium ethylxanthogenate (PEX) and 2,3-Dimercaptopropane sulphonate sodium (Unithiol) on the pentobarbital (40 mg/kg, body weight i.v.) (PB) sleeping time, pharmacokinetics, and metabolism, were studied in comparative experiments on male albino mice. It was established that the pretreatment of animals with PEX (80 mg/kg of body weight s.c.) potentiated the PB sleeping time. Unithiol in an equimolar dose (105.2 mg/kg of body weight s.c.) had no effect. The pharmacokinetics of PB could be fitted to be a biexponential equation of the type Cp(t) = A.e-alpha t + B.e-beta t. PEX caused an almost two-fold decrease in the elimination rate constant of plasma PB, which led to a higher half-time and a lower total clearance compared with the controls. The curve for the plasma PB metabolites in the PEX-pretreated mice was significantly lower than of the controls. A higher PB level and decreased rate of elimination in PEX-pretreated animals was observed also in the: liver, lungs, kidney, and brain. A conclusion was drawn that the potentiating effect of PEX on the PB sleeping time is mainly due to inhibition of PB liver metabolism. It was suggested that the differences in the biological effects of the two thiol compounds are due to the differences in their chemical structures: PEX possesses a C = S group but Unithiol lacks this group.