Combination of high-fat diet-fed and low-dose streptozotocin-treated rat: a model for type 2 diabetes and pharmacological screening

The objective of the present study was to develop a rat model that replicates the natural history and metabolic characteristics of human type 2 diabetes and is also suitable for pharmacological screening. Male Sprague-Dawley rats (160-180 g) were divided into two groups and fed with commercially available normal pellet diet (NPD) (12% calories as fat) or in-house prepared high-fat diet (HFD) (58% calories as fat), respectively, for a period of 2 weeks. The HFD-fed rats exhibited significant increase in body weight, basal plasma glucose (PGL), insulin (PI), triglycerides (PTG) and total cholesterol (PTC) levels as compared to NPD-fed control rats. Besides, the HFD rats showed significant reduction in glucose disappearance rate (K-value) on intravenous insulin glucose tolerance test (IVIGTT). Hyperinsulinemia together with reduced glucose disappearance rate (K-value) suggested that the feeding of HFD-induced insulin resistance in rats. After 2 weeks of dietary manipulation, a subset of the rats from both groups was injected intraperitoneally with low dose of streptozotocin (STZ) (35 mg kg(-1)). Insulin-resistant HFD-fed rats developed frank hyperglycemia upon STZ injection that, however, caused only mild elevation in PGL in NPD-fed rats. Though there was significant reduction in PI level after STZ injection in HFD rats, the reduction observed was only to a level that was comparable with NPD-fed control rats. In addition, the levels of PTG and PTC were further accentuated after STZ treatment in HFD-fed rats. In contrast, STZ (35 mg kg(-1), i.p.) failed to significantly alter PI, PTG and PTC levels in NPD-fed rats. Thus, these fat-fed/STZ-treated rats simulate natural disease progression and metabolic characteristics typical of individuals at increased risk of developing type 2 diabetes because of insulin resistance and obesity. Further, the fat-fed/STZ-treated rats were found to be sensitive for glucose lowering effects of insulin sensitizing (pioglitazone) as well as insulinotropic (glipizide) agents. Besides, the effect of pioglitazone and glipizide on the plasma lipid parameters (PTG and PTC) was shown in these diabetic rats. The present study represents that the combination of HFD-fed and low-dose STZ-treated rat serves as an alternative animal model for type 2 diabetes simulating the human syndrome that is also suitable for testing anti-diabetic agents for the treatment of type 2 diabetes.

Co-treatment with grapefruit juice inhibits while chronic administration activates intestinal P-glycoprotein-mediated drug efflux

P-Glycoprotein (P-gp) mediated efflux is recognized as a significant biochemical barrier affecting oral absorption for a number of drugs. Various conflicting reports have been published regarding the effects of grapefruit juice (GFJ) on P-gp-mediated drug efflux, in which GFJ has been shown both to inhibit and activate it. Hence, the present study adopted a two-way approach, involving both co-treatment and chronic administration. Bi-directional transport of paclitaxel (PCL) was carried out in the absence and presence of GFJ extract, in rat everted ileum sac. Further, the effect of chronic administration of GFJ to rats was characterized by permeability studies with indinavir (INDI). Co-treatment of GFJ extract at 100% concentration reduced the asymmetric transport of PCL (efflux ratio = 20.8) by increasing absorptive (A --> B) transport by 921% and reducing secretory (B --> A) transport by 41%. Further, GFJ showed a concentration dependent effect on PCL permeability. Imipramine, a passive permeability marker with absorptive permeability of 15.33 +/- 4.26 x 10(-6) cm/s showed no asymmetric transport and also no significant (P < 0.05) change in permeability in the presence of GFJ. Chronic administration of GFJ resulted in a significant decrease in absorptive transport of indinavir, which was even greater than that produced by rifampicin pretreatment. No change in permeability of propranolol, a passive permeability marker, was observed. Further, the decrease in absorptive transport of INDI was reversed by the P-gp inhibitor verapamil. In conclusion, GFJ extract inhibited P-gp-mediated efflux in co-treatment, whereas chronic administration led to increased levels of P-gp expression, thus having a profound effect on intestinal absorption and GFJ-drug interactions in vivo.

Minimum sample size and sampling time requirements for assessment of rifampicin bioequivalence from FDC formulations

SETTING

The WHO- and IUATLD-recommended protocol for rifampicin (RMP) bioequivalence utilises 20-22 volunteers and 8 h, whereas the requirement of other regulatory authorities is 12 volunteers with a 24 h sampling schedule. Differing sampling size and time requirements may change the outcome of RMP bioequivalence.

OBJECTIVE

To determine the minimal sample size and time required to assess RMP bioequivalence from FDC formulations.

DESIGN

Bioequivalence studies were conducted that fulfilled the criteria of the WHO and Indian regulatory protocols. From earlier studies, retrospective pharmacokinetic evaluation, power of the test and bioequivalence limits were also calculated using 8-22 volunteers and sampling points of 8-24 h. Pharmacokinetic and statistical evaluations from three representative studies showing low, moderate and high intra-subject variability are given to determine minimum requirements for RMP bioequivalence.

RESULT

It was found that a sampling schedule up to 8 h was sufficient to compare the absorption process of RMP. There was no influence of reduced sample size on bioequivalence estimates of RMP that showed low or moderate variability. However, in a study showing higher variation, a sample size of 14-16 subjects was found to be optimal.

CONCLUSION

It is possible to reduce the sample size requirement for determination of RMP bioequivalence using the WHO protocol.

Quality control of anti-tuberculosis FDC formulations in the global market: part II-accelerated stability studies

OBJECTIVE

To determine the quality and performance of rifampicin (RMP) containing fixed-dose combination (FDC) formulations of anti-tuberculosis drugs sourced from the international market with respect to physical, chemical and dissolution properties after storage at accelerated stability conditions (40 degrees C/75% relative humidity) and to identify appropriate storage specifications.

METHODS

Formulations across different companies and combinations were subjected to 6-month accelerated stability testing in packaging conditions recommended by the manufacturer. Various pharmacopeial and nonpharmacopeial tests for tablets were performed for 3- and 6-month samples.

RESULTS

All the formulations were found to be stable, where extent of dissolution was within +/- 10% of that of the initial value, and all formulations passed the pharmacopeial limits for assay and content uniformity of 90-110% and +/- 15% of average drug content, respectively.

CONCLUSIONS

Good quality RMP-containing FDCs that remain stable after 6-month accelerated stability testing are available in the marketplace.

Establishment of a reference formulation for bioequivalence assessment of rifampicin-containing FDCs: an essential step towards improving tuberculosis treatment

SETTING

Selection of a reference product for bioequivalence studies of rifampicin (RMP) in prequalifying fixed-dose combinations (FDC) for worldwide distribution through the WHO is critical.

OBJECTIVE

To investigate the feasibility of establishing FDC formulations as reference products for bioequivalence studies of RMP in prequalification programmes.

DESIGN

A biostudy was conducted as an open, two-period randomised cross-over trial. Two three-drug FDCs containing RMP, isoniazid and ethambutol hydrochloride were administered to a group of 22 volunteers with a wash-out period of 1 week. Plasma samples were collected and analysed for the concentration of RMP and desacetyl-RMP, a major active metabolite of RMP, up to 24 h. Pharmacokinetic parameters of RMP were calculated: Cmax, AUC0-24, Tmax, kel and absorption efficiencies.

RESULTS

No significant difference was observed between the administered formulations with respect to the major pharmacokinetic parameters Cmax, Tmax and AUC0-24 when evaluated by parametric (two-way ANOVA) and non-parametric (Hauschke's analysis) statistical analysis. The concentration of RMP falls within the reported acceptable therapeutic range.

CONCLUSION

FDCs can be developed as a reference product for bioequivalence studies.

Plasma pooling: utility in expediting bioequivalence assessment of rifampicin-containing fixed-dose combinations

To improve the rapidity of the registration process of rifampicin (RMP) containing fixed-dose combination (FDC) formulations, a plasma pooling methodology was used to increase the throughput of bioanalysis of plasma samples from bioequivalence trials of FDCs. Plasma samples of a biostudy were analysed for RMP using traditional analysis methods as well as a plasma pooling method (volunteer and time pooling). Both methods produced similar results, with less than 15% variability in both volunteer and time pooling. The plasma pooling method for bioanalysis was validated. Further studies are required to identify and reduce the percentage variability.

Dementia of Alzheimer's disease and other neurodegenerative disorders--memantine, a new hope

Alzheimer's disease is the fourth largest cause of death for people over 65 years of age. Dementia of Alzheimer's type is the commonest form of dementia, the other two forms being vascular dementia and mixed dementia. At present, the therapy of Alzheimer's disease is aimed at improving both, cognitive and behavioural symptoms and thereby, quality of life for the patients. Since the discovery of Alzheimer's disease by Alois Alzheimer, many pathological mechanisms have been proposed which led to the testing of various new treatments. Until recently the available drugs for the treatment of Alzheimer's disease are cholinesterase inhibitors, which have limited success because these drugs improve cognitive functions only in mild dementia and cannot stop the process of neurodegeneration. Moreover, drugs of this category show gastrointestinal side effects. As the cells of central and peripheral nervous system cannot regenerate, newer strategies are aimed at preserving the surviving neurons by preventing their degeneration. NMDA-receptor-mediated glutamate excitotoxicity plays a major role in Abeta-induced neuronal death. Hence, it was thought that NMDA receptors could be a promising target for preventing the progression of Alzheimer's disease. All the compounds synthesized initially in this category showed toxicity mainly because of their high affinity for NMDA receptors. Memantine (1-amino adamantane derivative), NMDA-receptor antagonist was reported to be effective therapeutically in Alzheimer's disease. It was available in Germany as well as European Union and has been approved for moderate to severe dementia in United States of America recently. It is an uncompetitive, moderate affinity antagonist of NMDA receptors that inhibits the pathological functions of NMDA receptors while physiological processes in learning and memory are unaffected. Memantine is also reported to have beneficial effects in other CNS disorders viz., Parkinson's disease (PD), stroke, epilepsy, CNS trauma, amyotrophic lateral sclerosis (ALS), drug dependence and chronic pain. Mechanisms of neuroprotection, preclinical and clinical evidence for effectiveness of memantine have been provided. Pharmacology and pharmacokinetics of memantine and other NMDA-receptor antagonists in comparison with currently approved drugs for dementia treatment have been discussed. The focus is on 'glutamate excitotoxicity' and glutamate receptors as drug target. Various other novel strategies for the treatment of dementia of neurodegenerative disorders have also been discussed.

A study on alpha-adrenoceptor mediated contractile responses of high fat diet fed rat thoracic aorta

Feeding rats with high fat diet (HFD) leads to the various conditions of syndrome-X. These are associated with hypertension through a variety of mechanisms. Vascular abnormalities probably contribute to the etiology of many diabetic complications. There is an increase in maximal responses to various agonists with blood vessels of streptozotocin induced diabetic animals. The purpose of this study was to evaluate the development in HFD fed rats for altered biochemical parameters, to assess the vascular responses to phenylephrine (PE), to estimate the KA values and to observe the receptor occupancy. Body weights, plasma triglycerides, cholesterol, and glucose levels were measured every week in male Sprague-Dawley rats. Glucose tolerance test was performed after 4 weeks of feeding. At the end of the fourth week of feeding, concentration-response curves of PE were recorded. Altered KA values of PE (NPD fed rats 2.0 +/- 0.4 microM and HFD fed rats 0.3 +/- 0.1 microM) and receptor occupancy response (NPD fed rats 92.1 +/- 1.7% and HFD fed rats 77.5 +/- 5.6%) strongly suggest that hypertension in HFD fed rats is associated with altered alpha-adrenoceptor function.

AT receptors and L-type calcium channels: functional coupling in supersensitivity to angiotensin II in diabetic rats

OBJECTIVE

The study was designed to investigate the role of calcium channels in enhanced angiotensin II (Ang II)-induced contraction in thoracic aortic rings from diabetic rats.

METHODS

Ang II-induced isometric tension was studied in thoracic aortic rings isolated from control or streptozotocin-induced (8 weeks) diabetic rats. Saturation binding studies at AT1 receptors and L-type calcium channels were performed using [3H] Ang II and [3H] PN200110, respectively. Ang II-induced calcium influx was studied in fura-2-loaded single vascular smooth muscle cells isolated from thoracic aorta of control and diabetic rats.

RESULTS

Ang II did not induce contraction in calcium-free Krebs. In the presence of extracellular calcium, increased Emax (mg/mm2) and pD2 to Ang II was observed in aortic rings from diabetic (795.54+/-38.19; 8.27+/-0.12) compared to control (230.09+/-25.45; 7.68+/-0.22) rats, respectively. Nimodipine but not verapamil or diltiazem dose-dependently blocked the Ang II-induced contractions in a noncompetitive manner and its -log IC50 was significantly lower in aortic rings from diabetic (8.81+/-0.10) compared to control (9.34+/-0.11) rats. The Ang II-induced increase in intracellular calcium levels was significantly enhanced (2.5-fold) in vascular smooth muscle cells from diabetic rats. AT1 receptor saturation binding with [3H] Ang II revealed a significantly higher affinity (nM) and Bmax (pmol/mg protein) in aortic vascular membrane preparation from diabetic (0.31+/-0.04; 64.18+/-2.4) compared to control (0.52+/-0.02; 47.81+/-2.8) rats, respectively, while L-type calcium channel saturation binding with [3H] PN200110 showed a higher affinity (nM) with no change in the Bmax (fmol/mg protein) in diabetic (0.74+/-0.08; 4.52+/-0.40) compared to control (1.49+/-0.32; 5.43+/-0.60) aortic membranes, respectively.

CONCLUSIONS

Our results suggest that Ang II-induced contraction is dependent on extracellular calcium, and enhanced functional coupling of AT1 receptors and DHP-sensitive L-type calcium channels results in supersensitivity to Ang II in thoracic aorta isolated from diabetic rats.

Determination of rifampicin bioequivalence in a three-drug FDC by WHO and indian protocols: effect of sampling schedule and size

SETTING

To promote the quality assurance of fixed-dose combination (FDC) formulations, the World Health Organization (WHO) has prepared a convenient simplified protocol for the determination of rifampicin (RMP) bioequivalence. During the development of this protocol, it was proved that sampling time up to 8 h can determine the rate and extent of RMP absorption. However, this protocol utilises 20 volunteers in contrast to other local regulatory requirements of a minimum of 12 volunteers. The different sample sizes utilised in these protocols may affect the sensitivity of the bioequivalence outcome.

OBJECTIVE

To determine the effect of sampling size and schedule on RMP bioequivalence when two different protocols are used.

DESIGN

A bioequivalence trial was conducted with a study design of 20 volunteers and 24 h sampling time, which fulfils the requirements of both the WHO and Indian regulatory protocols. Pharmacokinetic and statistical analysis was done by stepwise reduction in sample size and schedule.

RESULT

Bioequivalence limits of RMP were unaffected by a reduced sample size of 12 volunteers and 8 h sampling time.

CONCLUSION

Minimising sample size after validation for borderline and poor quality FDC formulations can further reduce the cost of conducting bioequivalence trials.

Green fluorescent proteins in receptor research: An emerging tool for drug discovery

In the last five years, green fluorescent protein (GFP) has emerged from being a mere curiosity to become a reliable tool for molecular pharmacological research. GFP produces an intense and stable green fluorescence noncatalytically by absorbing blue light maximally at 395 nm and emitting green light with a peak at 509 nm. It consists of 238 amino acids and its molecular mass is 27-30 kDa. GFP fluorescence occurs without cofactors and this property allows GFP fluorescence to be utilised in nonnative organisms, wherein it can be used as a reporter. This use of GFP permits real-time analysis of receptor dynamics. The emitted fluorescence can be used as a nontoxic marker and detected using fluorescence-activated cell sorting (FACS), thus avoiding any staining procedure, expensive mRNA analysis or hazardous radiolabeled binding assays. The potential value of GFP has also been recognized in orphan receptor research, where various GFP-tagged therapeutic proteins have been constructed in an attempt to identify the endogenous ligand(s). These chimeric proteins have been used to determine the site and time course of receptor expression and to relate receptor dynamics with therapeutic outcome. The preparation of new GFP constructs for identifying germ layer cells (endodermal, ectodermal, and mesodermal), as well as neuronal, haematopoietic, endothelial, and cartilage cells, has provided a useful battery of tissue/receptor-specific screening assays for new chemical entities. Genetically engineered cells with GFP expression have provided a valuable tool for automated analysis, and can be adapted for high-throughput systems. GFP is being increasingly utilised for the study of receptor dynamics, where, having already proved beneficial, it will likely continue to contribute towards the search for new classes of drugs, as well as to "de-orphaning" orphan receptors.

High glucose concentration augments angiotensin II mediated contraction via AT1 receptors in rat thoracic aorta

Elevated glucose concentration is implicated to play major role in development of diabetic associated vascular complications. It was previously reported that angiotensin II (Ang II) induced contractile response is enhanced in thoracic aorta of diabetic rats. In the present study, the effect of high glucose (HG, 25 mM) exposure for 2h on Ang II cumulative concentration response curves recorded isometrically was studied in thoracic aortic rings isolated from male Sprague-Dawley rats pretreated with streptozotocin (STZ, 65 mg kg(-1) i.p.) or vehicle at 8 weeks prior to the study. Ang II induced contraction via AT1 receptor was significantly enhanced (by 60 +/- 2 %) in HG exposed thoracic aortic rings isolated from vehicle treated but not STZ treated rats. However, there was no change in the pD2 of Ang II while potassium chloride (KCl) induced contraction was unaltered. Ang II induced contractile response was blocked by valsartan (100 microM, selective AT1 receptor antagonist) but not PD 123,319 (100 microM, selective and potent AT2 receptor antagonist). Exposure of aortic rings from control rats to 25 mM mannitol or sucrose for 2 h did not have any effect on the Ang II induced contraction. Tempol (100 microM, a cell permeable superoxide dismutase mimetic) partially reduced the augmented Ang II response in HG exposed aortic rings, while it did not affect the Ang II responses in normal glucose (NG 5.5 mM) exposed aortic rings isolated from control rats. [3H] Ang II binding at AT1 receptors was unaltered in vascular smooth muscle membranes prepared from thoracic aorta exposed to HG for 2 h compared to NG exposed aortic rings. From our results, we conclude that high glucose concentration augments Ang II mediated contraction via AT1 receptors and reactive oxygen species partly contribute to this augmented contraction.

Acute hyperglycemia attenuates nerve conduction velocity and nerve blood flow in male Sprague–Dawley rats: reversal by adenosine1

Hyperglycemia is implicated to play a major role in development of diabetic neuropathy. Since most of the diabetics are hyperglycemic much before they develop full-blown diabetes, we felt, it would be very important to know the effects of acute hyperglycemia on nerve function so that early pathophysiological events could be understood and appropriate therapeutic intervention can be made. Moreover, effect of acute hyperglycemia on motor nerve conduction velocity (MNCV) and nerve blood flow (NBF) is not known. Hence, we studied the effects of acute hyperglycemia on sciatic MNCV and sciatic NBF in healthy male Sprague-Dawley (SD) rats. Three different animal models of acute hyperglycemia (50% glucose (3 g kg(-1), i.v. (intra-venous) or i.p. (intra-peritoneally)) or 24 h post-streptozotocin (STZ) injected rats were used. Acute hyperglycemia but not mannitol or sucrose significantly attenuated MNCV and NBF. Adenosine (10 mg kg(-1), i.p.) prevented the acute hyperglycemia-induced attenuation of MNCV and NBF in all the three rat models of acute hyperglycemia. Adenosine effects were blocked by theophylline (50 mg kg(-1), i.p.) suggesting the role of adenosinergic receptor mediated mechanisms in acute hyperglycemia-induced neuropathy. Acute glucose administration in 8 weeks, STZ diabetic rats did not further affect MNCV or NBF. Adenosine (10 mg kg(-1), i.p.) did not produce any adverse effects on the blood pressure and heart rate. From the results, we conclude that acute hyperglycemia attenuates MNCV and NBF via an adenosinergic receptor-dependent mechanism.

Reversal of glucose intolerance by by pioglitazone in high fat diet-fed rats

The present study was undertaken to determine the effect of pioglitazone (3, 10 and 30 mg/kg p.o.), an insulin sensitizer, on glucose intolerance in high fat diet- (HFD) fed rats (a nongenetic model of insulin resistance). In addition, the effect of pioglitazone (3, 10 and 30 mg/kg p.o.) on diet-induced changes in body weight, plasma glucose, insulin, triglyceride and total cholesterol levels were also determined. The feeding of HFD for 4 weeks produced a significant increase in body weight, total fat pad weight, basal/fasting plasma glucose, insulin, basal triglyceride (TG) and total cholesterol (TC) levels in male rats. Furthermore, the rats fed HFD exhibited fasting hyperglycemia and hyperinsulinemia as well as enhanced glycemic response to exogenously administered glucose (2 g/kg p.o.) during an oral glucose tolerance test (OGTT) at the end of 4 weeks of dietary manipulation, indicating that the rats had developed insulin resistance and glucose intolerance. Treatment with pioglitazone (10 and 30 mg/kg p.o.) once daily for 2 weeks significantly diminished the elevated basal plasma insulin and TG levels in HFD-fed rats. In addition, a statistically significant reduction in TC level was observed only with the high dose of pioglitazone (30 mg/kg p.o.). However, pioglitazone had no significant effect on body weight, total fat pad weight and basal plasma glucose level. Pioglitazone (10 and 30 mg/kg p.o.) significantly reduced fasting hyperglycemia and reversed oral glucose intolerance to normal in HFD-fed rats compared with control normal rats. The above findings suggest that pioglitazone has potent insulin-sensitizing and lipid-lowering properties in a HFD-fed rat model. In conclusion, the present study demonstrates that the adult male rats on a HFD for 4 weeks exhibited the characteristic features of obesity, insulin resistance and glucose intolerance, namely increased body weight, increased total fat pad weight, mild basal/fasting hyperglycemia, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia and impaired oral glucose tolerance, that closely resemble the human prediabetic obese insulin-resistant and glucose-intolerant state. Further treatment with pioglitazone once daily for 2 weeks significantly ameliorated changes in basal plasma insulin, TG and TC, and reversed oral glucose intolerance to normal in HFD-fed rats, suggesting its potential in the treatment of insulin resistance and glucose intolerance associated with abnormal lipid metabolism.

Quality control of anti-tuberculosis fixed-dose combination formulations in the global market: an in vitro study

OBJECTIVE

To determine the quality, and especially the dissolution properties of rifampicin, of fixed-dose combination (FDC) formulations of anti-tuberculosis agents manufactured by major market holders in the anti-tuberculosis sector and supplied for use in national tuberculosis control programmes.

METHODS

Dissolution studies were performed for four formulations supplied by four different manufacturers in four dissolution media (0.1N and 0.01N HCl, phosphate buffer [PB] and 20% vegetable oil in PB), at four different agitation rates using USP apparatus II. The formulations were subjected to 4-week accelerated stability studies (40 degrees C / 75% RH) and evaluated for physical, chemical and dissolution stability.

RESULTS

The formulations tested complied with pharmacopeial quality control (QC) tests. The extent of rifampicin release was independent of dissolution medium; however, a slight decrease in the dissolution rate was observed in two products. More than 75% of drug was released in 45 min at all agitation intensities except 30 rpm, and 20% oil in the medium reflected fed state. Formulations were stable in the packaging conditions recommended by the manufacturer for at least 4 weeks.

CONCLUSIONS

The formulations tested passed the QC tests and were found to be stable. A decrease in the rate, although not the extent, of dissolution necessitated multiple point dissolution in gastric and intestinal pH conditions to ensure consistency in in vivo bioavailability.

Protective effect of a polyherbal formulation (Immu-21) against cyclophosphamide-induced mutagenicity in mice

The object was to evaluate the effects of a polyherbal formulation, Immu-21, against cyclophosphamide (CP)-induced chromosomal aberrations (CA) and micronuclei (MN) in mice. CP alone (40 mg/kg, i.p.) produced classical as well as non-classical chromosomal aberrations in mice, and the incidence of CA was significantly more in the CP treated group when compared with that of the control group. Immu-21, which contains extracts of Ocimum sanctum, Withania somnifera, Emblica officinalis and Tinospora cordifolia, was given at 100 mg/kg, daily, over 7 days, and 30 mg/kg daily over 14 days and inhibited both CP-induced classical and non-classical chromosomal aberrations ( approximately 40%-60% of control). A significant increase in MN was also observed in bone marrow erythrocytes of mice treated with CP, and pretreatment with Immu-21 also significantly reduced these. Cytotoxicity was evaluated by estimating the ratio of polychromatic erythrocytes (PCEs) to normochromatic erythrocytes (NCEs). The present results indicate that chronic treatment with Immu-21 prevented CP-induced genotoxicity in mice.

Bioequivalence assessment of rifampicin, isoniazid and pyrazinamide in a fixed dose combination of rifampicin, isoniazid, pyrazinamide and ethambutol vs. separate formulations

Depending on the patient category, tuberculosis requires treatment with 3 to 5 drugs which means that patient's compliance to therapy may not be optimal. To increase patient's adherence to treatment schedules, these drugs can be given as single drug preparations or fixed dose combinations (FDCs) of 2 or more drugs in a single formulation. However, an important issue associated with a rifampicin-containing FDC is its quality. Hence, to avoid spurious formulations entering the market, the World Health Organization and the International Union Against Tuberculosis and Lung Disease have recommended FDCs only of proven bioavailability. In this study, the relative bioavailability of rifampicin, isoniazid and pyrazinamide was assessed in a group of 14 healthy male subjects using the FDC tablet containing 4 drugs versus separate formulations at the same dose levels. The study was designed as an open, crossover trial. A total of 9 blood samples were collected over a period of 24 h. The concentration of rifampicin, its main metabolite desacetyl rifampicin, isoniazid and pyrazinamide in plasma were assessed using HPLC analysis. The pharmacokinetic parameters AUC(0-24) and Cmax were subjected to parametric and non-parametric statistical tests at 90% confidence interval. In addition, time to reach peak concentration (tmax), elimination rate constant (Kel) and terminal elimination half-life (t1/2) for each drug were also calculated. It was concluded that the FDC tablet containing 4 drugs is bioequivalent to separate rifampicin, isoniazid and pyrazinamide formulations at the same dose levels.

Cell proliferation and natural killer cell activity by polyherbal formulation, Immu-21 in mice

Immunomodulatory activity of an Ayurvedic polyherbal formulation, Immu-21 containing extracts of Ocimum sanctum, Withania somnifera, Emblica officinalis and Tinospora cordifolia was studied on proliferative response of splenic leukocytes to T cell mitogens, concanavalin (Con)-A and phytohemagglutinin (PHA) and B cell mitogen, lipopolysaccharide (LPS) in vitro by [3H]-thymidine uptake assay in mice. The cytotoxic activity of Immu-21 was tested by measuring the splenic leukocyte natural killer (NK) cell activity against K 562 cells. Intraperitoneal (i.p.) treatment with Immu-21 (30 mg/kg) once a day for 14 and 21 days did not cause change in body weight and spleen weight, where as splenocytes/spleen count was increased. Treatment of Immu-21 (30 mg/kg, i.p.) for 14 days and 1 mg/kg for 21 days significantly increased LPS induced leukocyte proliferation. NK cell activity was significantly increased when mice were pretreated with Immu-21 (10 and 30 mg/kg, i.p.) once a day for 7 days. The results indicate that pretreatment with Immu-21 selectively increased the proliferation of splenic leukocyte to B cell mitogen, LPS and cytotoxic activity against K 562 cells in mice.

The role of aldose reductase inhibitors in diabetic complications: recent trends

Pharmacological intervention of hyperglycemia-induced diabetic complications would be of great clinical significance since it is very difficult to maintain normoglycemia by any means in patients with diabetes mellitus. Several factors and pathways are involved in diabetic complications. One of the major contributory factors is aldose reductase. The beneficial effects of aldose reductase inhibitors in animal models have been reported. The clinical efficacy of these agents, however, is far from satisfactory and the reasons for this may vary. Recent advances in understanding the structure-based functioning, physiological and pathophysiological role of aldose reductase, the use of transgenic animal models and the abundant availability of human aldose reductase have greatly influenced the design and development of its inhibitors, which are highly selective, specific, potent and less toxic. Concurrently, other mechanisms involved in diabetic complications are being explored as targets for better therapeutic agents.

Bioequivalence of isoniazid in a two drug fixed dose combination and in a single drug dosage form

To increase the patient compliance and reduce the risk of drug resistant strains, WHO and IUATLD recommend the use of Fixed Dose Combination (FDC) tablets as a routine therapeutic regimen in Directly Observed Treatment Shortcourse (DOTS). But the main issue in the use of FDC is the quality of the formulation. At present WHO and IUATLD suggest the bioequivalence assessment of only rifampicin from FDC compared to separate formulations. For the therapeutic effectiveness all the components of the FDCs should be bioavailable at tissue site. Also, the primary and acquired resistance rate of isoniazid is much higher compared to other anti-tubercular drugs. Hence, a comparative bioavailability study of isoniazid from a two drugs FDC compared to a separate formulation was carried out on a group of 12 healthy volunteers. When evaluated by normal or log transformed confidence interval, Two Way ANOVA and Hauschke analysis, the bioequivalence limits for AUC0-8 and AUC0-24 were within 0.8-1.25. For Cmax and Tmax, these limits were within 0.7-1.43. Hence, isoniazid from a FDC formulation was found to be bioequivalent to a separate formulation at same dose levels.

Antituberculosis drugs and new drug development

Tuberculosis affects more than 8 million people and has serious repercussions on economic, psychologic, and social status. Since its declaration as a global emergency in 1993 by the World Health Organization, significant development in the treatment and control of tuberculosis has been the implementation of the short-course directly observed treatment along with fixed dose combinations of existing drugs. However, the currently available therapeutic regimens have inherent disadvantages of long treatment duration, patient noncompliance, and risk of drug resistance. Hence, new antituberculosis drugs that are potent, are active against resistant strains and latent forms, and reduce the treatment period are needed to combat this disease. In this review, the authors discuss new chemical entities that in their opinion have a potential to become new antituberculosis drugs. This article emphasizes the role of biopharmaceutics and pharmacokinetics as an indispensable part in the development of new antituberculosis drugs to overcome the common hurdles such as exorbitant cost, time, and attrition rate involved in the process.

Pharmacokinetic study of paclitaxel as a 3-hour infusion in an Indian population: 135 mg/m2 vs. 175 mg/m2

The objective of this clinical study was to determine the pharmacokinetic parameters of paclitaxel at doses of 135 and 175 mg/m2 when given as a 3-hour infusion in an Indian population. Twelve cancer patients of both sexes participated in the study and a parallel experimental design was adopted for the assignment of doses to patients. A solid phase extraction technique was used for sample clean-up followed by a reversed phase HPLC assay for the analysis of paclitaxel in plasma samples. Pharmacokinetic parameters such as Cmax, AUC0-infinity, T1/2 beta, AUMC0-infinity, VSS, VZ and CLT were determined by a compartment model-independent method using a PCNONLIN package. Teff and AUCeff were also calculated and compared at the two doses by considering a plasma concentration of > or = 0.05 microM as threshold. The mean Cmax and AUC0-infinity values were 2.57 microM and 12.06 microM at the 135 mg/m2 dose level while at the 175 mg/m2 dose the values increased to 4.96 microM and 9.52 microM.h/l, respectively. It was found that the 135 mg/m2 dose resulted in greater mean CLT and VSS values than the 175 mg/m2 dose. The disposition of paclitaxel was found to be nonlinear and the pertinent pharmacokinetic parameters were comparable to those from previous clinical studies. It was concluded from the present study that further clinical trials of paclitaxel alone or in combination with other drugs should be undertaken cautiously, taking into consideration its nonlinear pharmacokinetics which necessitate proper adjustment of the infusion schedule and/or dose to avoid any adverse consequences to the patient.

Sympathetic nervous system and experimental diabetes: role of adrenal medullary hormones

The sympathetic nervous system is of major importance in the regulation of various physiological functions. The present review discusses the mechanisms which control glucose homeostasis and the role of the sympathetic nervous system in experimental diabetes with special emphasis on the role of adrenal medullary hormones, over-activity of the sympathetic nervous system and its relationship to hypertension in the diabetic state and the effect of stress. The chapter also reviews the ability of various drugs and pharmacological agents to produce hyperglycemia in experimental animals and how this information can be used in screening new chemical entities and in differentiating the mode of action of these agents.

Evaluation of rifampicin bioequivalence in fixed-dose combinations using the WHO/IUATLD recommended protocol

For an accurate assessment of rifampicin bioequivalence from fixed-dose combinations (FDCs), and to reduce the time and cost constraints associated with bioequivalence studies, the World Health Organization and the International Union Against Tuberculosis and Lung Disease have developed a simplified screening protocol. This study was undertaken with the objective of testing the applicability of this protocol for all types of FDCs. Data were obtained for volunteers common to three studies, and pharmacokinetic parameters were evaluated by different statistical tests. From the results, it has been demonstrated that the simplified screening protocol is suitable for evaluating the bioequivalence of rifampicin in all the types of FDCs available on the market.

Bioequivalence of rifampicin when administered as a fixed-dose combined formulation of four drugs versus separate formulations

A bioequivalence study of the antitubercular drug rifampicin in a four-drug combination (rifampicin, isoniazid, pyrazinamide and ethambutol) and separate formulations of the drugs at the same dose levels was carried out in a group of 22 healthy male volunteers. The investigation was designed as an open crossover study. The drugs were administered once in individual formulations and once in a fixed-dose combination. The WHO-approved protocol was followed according to which six blood samples were collected over a period of 8 h for each volunteer and each experimental session. Pooled urine samples were also collected during the study. Rifampicin and desacetyl rifampicin concentrations in both plasma and urine samples were assessed. Various pharmacokinetic parameters such as AUC0-8 h, Cmax and Tmax were calculated for both rifampicin and desacetyl rifampicin. The results indicated that combined (the four-drug combination) and separate formulations are bioequivalent for rifampicin.

Renin release and the sympathetic nervous system

This review describes the pharmacological aspects of renin release with special emphasis on the role of sympathetic nervous system, catecholamines, adrenoceptor blocking drugs, humoral agents, adrenalectomy and chemical sympathectomy. The effect of antihypertensive drugs and other pharmacological agents on plasma renin activity and the role of renin levels in their antihypertensive effects are also discussed. The role of renin inhibitors as a possible therapeutic class of antihypertensive agents, which could eventually expand the spectrum of antihypertensive therapy and improve our understanding of the role of the renin angiotensin system, is also addressed.

Insulin resistance: current therapeutic approaches

Insulin resistance, an impaired biological response to either exogenous or endogenous insulin occurs in a majority of the diabetic population with type II diabetes. One of the current approaches for treating insulin resistance associated with NIDDM is the use of insulin sensitizing agents. Elucidation of the mechanism(s) of these agents may provide new targets for which selective ligands with better efficacy and low toxicity can be found.

Bioequivalence study of rifampicin in fixed-dose combination of rifampicin and isoniazid vs. separate formulations

The benefits of fixed-dose combinations of antituberculosis agents are well recognized by the World Health Organization (WHO) and International Union Against Tuberculosis and Lung Disease (IUATLD) and preferred over separate formulations. Therefore, a comparative bioequivalence study of rifampicin and isoniazid together in a fixed-dose combination and separately (at the same dose levels) was performed on a group of 12 healthy subjects. The study was designed as a single-blind, crossover experiment. Nine blood samples were collected from each subject over a period of 24 h. The plasma concentrations of rifampicin were assessed by a method developed in this laboratory. Various pharmacokinetic parameters of rifampicin such as AUC, Cmax, Tmax and t1/2 were also calculated. The study demonstrates that a fixed-dose combination (test formulation) and separate formulations (standard formulations) are bioequivalent for rifampicin.

The WHO simplified study protocol in practice: investigation of combined formulations supplied by the WHO

SETTING

The benefits of fixed-dose combination (FDC) formulations of rifampicin, isoniazid and pyrazinamide over individual formulations are well recognised.

OBJECTIVES

To evaluate the comparative bioavailability of antituberculosis drugs in FDC formulations and the same doses in separate formulations of antituberculosis drugs, using a simplified protocol developed by the World Health Organization (WHO).

METHODS

Twenty healthy volunteers were included in the study and evaluated for bioequivalence of rifampicin in a cross-over experimental design. After administration of drugs the plasma concentration of rifampicin and desacetyl-rifampicin was measured repeatedly up to 8 hours in both plasma and urine. Various pharmacokinetic parameters of rifampicin, such as Cmax, Tmax, elimination rate constant, area under the curve (AUC) up to 8 hours and absorption efficiency were calculated.

RESULTS

No significant differences were observed between the FDCs and separate formulations when Cmax, Tmax, AUC and absorption efficiencies were compared by parametric test and Hauschke's analysis.

CONCLUSION

The WHO simplified protocol is suitable for evaluating bioequivalence of antituberculosis drugs.

Role of sympathetic nervous system in experimental hypertension and diabetes mellitus

An investigation has been made to elucidate the role of sympathetic nervous system (SNS) in the development of renal hypertension and hyperglycemia in rats and rhesus monkeys using 6-hydroxydopamine (6-OHDA). Development of renal hypertension was blocked in weanling rats (80%), demedullated adult rats with 6-OHDA (75%) but not in adult rats sympathectomised with 6-OHDA. Weanling rats treated with 6-OHDA did not have any detectable catecholamine stores when measured 60 days after treatment with 6-OHDA. Unlike the weanling rats the hearts of the adult rats showed significant refilling of catecholamines 60 days after 6-OHDA treatment. 6-OHDA treatment and adrenalectomy did not modify the development of streptozotocin (STZ) induced hyperglycemia and the hypoglycemic effect of tolbutamide and phenformin. Chemical sympathectomy with 6-OHDA did not show any glucose intolerance in rhesus monkeys or any effect or insulin release. Phentolamine (PHE) and oxprenolol (OXP) pretreatment had no effect on development and maintenance of hyperglycemia. Although there was no effect on the endogenous catecholamines stored in the heart and brain in the diabetic rats, there was a marked increase in the urinary excretion of norepinephrine (NE), epinephrine (E), 3-methoxy-4 hydroxy mandelic acid (VMA) and creatinine. The rate of disappearance of (3H)-NE from rat heart was higher when compared to age matched controls. Diabetic rats showed increase responsiveness to angiotensin II and developed hypertension faster when their renal arteries were clamped as compared to controls. It is concluded that the functional SNS is important in the development of renal hypertension in the rat. Further the SNS in the rats and rhesus monkeys does not play any significant role in the STZ induced hyperglycemia, glucose intolerance and insulin release.

Determination of rifampicin and its main metabolite in plasma and urine in presence of pyrazinamide and isoniazid by HPLC method

A reversed phase HPLC method is described for the simultaneous estimation of rifampicin and its major metabolite desacetyl rifampicin, in the presence of isoniazid and pyrazinamide, in human plasma and urine. The assay involves simple liquid extraction of drug, metabolite and internal standard (rifapentine) from biological specimens and their subsequent separation on a C18 reversed phase column and single wavelength UV detection. In plasma as well as in urine samples, all the three compounds of interest eluted within 17 min. Using methanol-sodium phosphate buffer (pH 5.2; 0.01 M) (65:35, v/v) as mobile phase under isocratic conditions, it was established that isoniazid, pyrazinamide and ascorbic acid (added to prevent oxidative degradation of analytes) did not interfere with the analyte peaks. Recoveries (extraction efficiency) for drug were greater than 90% in both plasma and urine, whereas for metabolite the values were found to be 79 and 86% in plasma and urine, respectively. The plasma and urine methods were precise (total coefficient of variation ranged from 5 to 23%) and accurate (-7 to 5% of the nominal values) for both the analytes. Individual variance components, their estimates and their contribution to the total variance were also determined. Using the same method, unknown samples supplied by WHO were assayed and good correlations were obtained between the found and intended values. The method developed proved to be suitable for simultaneous estimation of rifampicin and desacetyl rifampicin in plasma and urine samples.

Evaluation of BTS 67 582, a novel antidiabetic agent, in normal and diabetic rats

1. The effect of BTS 67 582, a novel antidiabetic agent, has been evaluated on plasma glucose and plasma insulin in normal and streptozotocin-induced diabetic rats. 2. BTS 67 582 (3 to 300 mg kg-1, p.o.) caused a dose- and time-dependent reduction in plasma glucose and an increase in plasma insulin in both fasted and glucose-loaded normal rats. The ED50 for the glucose lowering effect of BTS 67 582 in fasted rats was 37.6, 18.4 and 18.5 mg kg-1 at 1, 2 and 4 h after administration respectively. 3. In streptozotocin-induced (50 mg kg-1, i.v.) diabetic rats, BTS 67 582 (37-147 mg kg-1, p.o.) caused significant reductions of plasma glucose following a glucose load, whereas glibenclamide (100 mg kg-1, p.o.) was ineffective. BTS 67 582 significantly increased plasma insulin compared to controls whereas glibenclamide did not. 4. BTS 67 582 did not displace [3H]-glibenclamide from its binding sites in rat brain, guinea-pig ventricle or the HIT-T15 insulinoma beta-cell line. BTS 67 582 does not therefore appear to modulate its action via an effect on the 'sulphonylurea' receptor. 5. In fasted rats, the glucose lowering effect of BTS 67 582 (100 mg kg-1 p.o.) and glibenclamide (1 mg kg-1, p.o.) were antagonized by diazoxide (30 mg kg-1, i.p.). In addition BTS 67 582, like glibenclamide, caused a dose-dependent rightward shift of cromakalim-induced relaxation of noradrenaline precontracted rat aortic strips, suggesting the involvement of KATP channels. 6. In summary, BTS 67 582 produces a blood glucose-lowering effect in normal and streptozotocin-induced diabetic rats associated with increased insulin concentrations. This effect appears to be due to a blockade of ATP-sensitive potassium channel activity via a different binding site to that of glibenclamide.

A simple quantitative in vitro macrophage migration assay

An in vitro macrophage chemotaxis model using mouse peritoneal non-elicited resident macrophage cells and chemotaxins containing mediators of non-specific elicitors such as oyster glycogen or sodium caseinate has been described. Macrophage cells accumulation in mouse peritoneal cavity was maximum at 48 hr after injecting (i.p.) oyster glycogen (2.5%) or sodium caseinate (12%), 0.5 ml/mouse. Chemotaxins containing mediators were prepared from these mice by peritoneal lavage and termed as routine 'diluted' cocktail and 'concentrated (3 times)' cocktail. Chemotaxis assays were carried out in a modified Boyden chamber using a 48-well microchemotaxis assembly. In vitro results showed higher macrophage chemotaxis response against the 'concentrated' cocktails as compared to routine 'diluted' cocktail. Macrophages exhibited cell density dependent increase in the responsiveness to chemoattractant and macrophage cell density of 4 x 10(6) per ml concentration in the upperwell was found to be optimum. Macrophage responsiveness was seen better with sodium caseinate cocktail as compared to oyster glycogen in vitro as well as in vivo. DMSO (Dimethyl Sulphoxide) solvent (0.25% conc.) did not interfere with normal macrophage chemotaxis. Both CO2 incubator (5% CO2 in air) and BOD incubator with humidified chamber favoured chemotaxis. In vitro test system described can be used as a model to study the effect of anti-inflammatory compounds directly on the macrophage chemotaxis.

A comparative study of experimental caecal amoebiasis and the evaluation of amoebicides

Caecal amoebiasis models (mouse, hamster and rat) were compared for amoebic infection and chemotherapeutic evaluation using a pathogenic strain of Entamoeba histolytica of human origin. Caecal infection in the hamster was of the acute type, with a large number of amoebae in the caecal tissue, whereas the amoebae in rats were seen in the lumen, on the mucosal surface. Amoebic lesions in the mouse caecum were of moderate severity. The mouse model responded to both metronidazole (tissue amoebicide) and diloxanide furoate (luminal amoebicide), whereas the hamster model only responded well to metronidazole and the rat model only to diloxanide furoate. Using the mouse as a primary screening model, a new oxadiazole compound, BTI 2405E, was found to have tissue and luminal amoebicidal activity. In rodent caecal models, a single dose of BTI 2405E was found to be more effective than one of metronidazole or diloxanide furoate. The mouse model appears to be the most useful for primary screening of anti-amoebic compounds.

Comparative pharmacokinetics and amoebicidal activity of metronidazole and satranidazole in the golden hamster, Mesocricetus auratus

The pharmacokinetic properties of metronidazole and satranidazole were studied in the golden hamster (Mesocricetus auratus), at a dose of 80 mg/kg po. Blood and liver samples were collected at frequent time intervals and assayed for metronidazole and satranidazole by HPLC. Satranidazole exhibited significantly higher plasma concentrations than metronidazole at 1 and 2 h post-dose, but the comparative Cmax values were not significantly different. The satranidazole plasma elimination half-life of 1.01 h was significantly shorter than the corresponding metronidazole half-life of 3.62 h. The comparative liver pharmacokinetic parameters Cmax, Tmax and T1/2 did not differ significantly. Satranidazole however exhibited significantly higher liver concentrations at 1 h post-dose and Cmax and AUC0-infinity values were approximately 35% higher. The in-vivo amoebicidal activity of both compounds was evaluated in the acute hamster hepatic model of amoebiasis. Both metronidazole and satranidazole were administered as single graded doses po, and their dose-response profiles were characterized. Satranidazole demonstrated significantly greater amoebicidal activity than metronidazole with an ED50 value of 19.5 mg/kg, compared to an ED50 value of 45 mg/kg for metronidazole. These data suggest that higher plasma and liver concentrations of satranidazole and greater intrinsic potency probably contribute to superior amoebicidal activity in the hamster model of hepatic infection.

Pharmacokinetics and amoebicidal activity of (+-)-(E)-3-(4- methylsulphinylstyryl)-1,2,4-oxadiazole (BTI 2286E) and its sulphone metabolite (BTI 2571E) in the golden hamster, Mesocricetus auratus

BTI 2286E is a 1,2,4-oxadiazole with amoebicidal activity. Three groups of golden hamsters received single doses of BTI 2286E or its sulphone metabolite BTI 2571E as either BTI 2286E 60 mg/kg po or BTI 2571E 60 mg/kg po or BTI 2571E 60 mg/kg ip. Blood samples were collected up to 8 h post-dose and plasma concentrations of BTI 2286E and BTI 2571E were assayed by HPLC. BTI 2286E was rapidly absorbed, extensively metabolized during first pass and rapidly eliminated with a plasma elimination half-life of 1.32 h. Conversion to BTI 2571E was the major pathway of elimination. BTI 2571E had approximately 40% bioavailability after oral administration. After intraperitoneal administration its absorption was slow and prolonged, with an apparent elimination half-life of 2.77 h, considerably longer than the elimination half-life of 0.67 h observed when BTI 2571E was formed as a metabolite, in vivo. The amoebicidal activity of both the compounds was evaluated in the acute hamster hepatic model of amoebiasis. Both BTI 2286E and BTI 2571E were administered as single graded po or ip dose, and their dose-response profiles were characterized. BTI 2571E exhibited poor activity after oral administration (ED50 70 mg/kg) probably due to poor bioavailability, but after intraperitoneal administration its activity (ED50 40 mg/kg) was comparable to that of BTI 2286E after po or ip administration.

Activity of a new oxadiazole compound, against experimental infections with Entamoeba histolytica and Giardia lamblia in animal models

BTI 2286E(+/-)-E-3-(4-methylsulphinylstyryl)-1,2,4-oxadiazole has demonstrated potent amoebicidal activity in a single-dose treatment against Entamoeba histolytica infection in the livers of golden hamsters and the caeca of mice, hamsters and rats. It has intra luminal activity against Entamoeba criceti, a natural infection in golden hamster, and anti-giardial activity against Giardia lamblia infection in suckling mice. BTI 2286E is more potent than metronidazole in extra intestinal, intra luminal amoebiasis models and has significant advantages in that it is non-mutagenic in the Ames test and has a shorter duration of effective treatment.

On the mechanism of action of an adrenergic blocking guanidine (CG8345-Go)

CG 8345 depletes noradrenaline stores in the rat, cat and dog tissues at a dose range of 1--50 mg/kg p.o. Unlike guanethidine there is no marked difference in the depleting effect of CG 8345 when given orally or intraperitoneally. The effect on the noradrenaline stores is longer lasting in cats and dogs as compared to rat. Like guanethidine CG 8345 releases H3-NA from the rat heart mainly in the form of bases. The compound gets accumulated into the sympathetically innervated organs by a specific uptake process which is similar to noradrenaline "pump" mechanism from where it can be released by reserpine. CG 8345 is stored in the same storage sites as noradrenaline in the rat heart.

Participation of adrenal medulla in 6-amino-nicotinamide-induced hyperglycaemia in the rat

In fasted rats 6-aminonicotinamide (6-AN) produced delayed hyperglycaemia, the peak effect being seen by 7 h. Fasting plasma insulin concentrations were not significantly altered but liver glycogen concentrations were decreased following treatment with 6-AN. Adrenalectomy, demedullation and pretreatment with reserpine, phentolamine, nicotinamide and nicotinic acid completely blocked the hyperglycaemic response whereas guanethidine and propranolol or oxprenolol were ineffective. Catecholamine concentrations in the adrenal venous plasma were markedly increased by treatment with 6-AN, the peak effect being seen by 5 h. It is concluded that adrenal medullary release, which is slow in onset, is mainly responsible for the development of sustained hyperglycaemia in the rat.