Application of hot melt extrusion for improving bioavailability of artemisinin a thermolabile drug

Hot melt extrusion has been used to produce a solid dispersion of the thermolabile drug artemisinin. Formulation and process conditions were optimized prior to evaluation of dissolution and biopharmaceutical performance. Soluplus^®, a low T_g amphiphilic polymer especially designed for solid dispersions enabled melt extrusion at 110 °C although some drug-polymer incompatibility was observed. Addition of 5% citric acid as a pH modifier was found to suppress the degradation. The area under plasma concentration time curve (AUC_0-24h) and peak plasma concentration (C_max) were four times higher for the modified solid dispersion compared to that of pure artemisinin.

Trench, lollipop, lift and chop technique for mild to moderate cataracts

No abstract available.DOI: http://dx.doi.org/10.3126/nepjoph.v4i2.6561 Nepal J Ophthalmol 2012; 4 (2): 344-345  

Valproate- and aminophylline-induced 'wet dog shakes'--a function of dose and time

The time course of appearance of 'wet dot shakes' (WDS) was examined following valproic acid (VPA, 100, 200, 300, 400 mg/kg i.p.) and aminophylline (AMP, 50, 100, 150 mg/kg i.p.) injections. VPA and AMP at various doses showed a qualitative difference in their ability to induce WDS with no difference in intensity, confirming 'all or none' nature of the phenomenon. There was a significant (p<0.001), dose-dependent increase in the number of whole body shakes following first three doses of VPA but not after the administration of its highest dose (400 mg/kg). In contrast, the numbers of WDS produced by AMP were inversely proportional to its increasing doses. The maximum numbers of WDS were observed at 300 mg/kg of VPA and 50 mg/kg of AMP, within 10 min and 20-30 min during 1 h and 1 h 30 min observation period, respectively. The present stereotyped behavior induced by acute, single dose administration of VPA and AMP in non-toxic doses, being a reproducible phenomenon, lasting for a brief period may be anticipated to serve as a tool to explore mechanisms underlying WDS.

Influence of caffeine on pharmacokinetic profile of sodium valproate and carbamazepine in normal human volunteers

The present study evaluates effect of pharmacokinetic interaction between caffeine (300 mg) in three divided doses with sodium valproate (400 mg) and carbamazepine (200 mg) given as single doses, in normal human volunteers, using a open cross over design. Both the serum concentration of sodium valproate and pharmacokinetic parameters remained unaltered, as against significant reduction in plasma concentration and area under the concentration curve of carbamazepine following the coadministration of caffeine. Also, the plasma t 1/2 (of carbamazepine was prolonged by two folds and bioavailability reduced by about 32% in presence of caffeine. The results are of clinical significance as xanthine consumption may have to be restricted in patients on carbamazepine therapy and this aspect may need further investigation.

Time course of action of three adenosine A1 receptor agonists with differing lipophilicity in rats: comparison of pharmacokinetic, haemodynamic and EEG effects

In this study we investigated the relationship between the pharmacokinetics and the cardiovascular and electroencephalogram (EEG) effects of three adenosine agonists with differing lipophilicity. Conscious normotensive rats received either 600 microg/kg N6-(p-sulphophenyl) adenosine (SPA), 200 microg/kg N6-cyclopentyladenosine (CPA) or 600 microg/kg 1-deaza-2-chloro-N6-cyclopentyladenosine (DCCA) in a 5-min intravenous infusion. Changes in haemodynamics and EEG were monitored in conjunction with arterial blood sampling to determine blood concentrations of the compounds. The three adenosine agonists showed large differences in pharmacokinetic properties, resulting in terminal half-lives of 66 +/- 10, 8.2 +/- 0.4 and 24 +/- 1 min (mean +/- SEM) for SPA, CPA, and DCCA respectively. SPA had a significantly lower blood clearance relative to CPA and DCCA, whereas DCCA had the largest volume of distribution and degree of plasma protein binding. The relationship between concentration and heart rate could be described adequately by the sigmoidal Emax model. For SPA, CPA, and DCCA the EC50 values based on free drug concentrations were 423 +/- 92, 1.8 +/- 0.4 and 9.5 +/- 1.1 nM respectively. These in vivo values correlated closely with the affinity of the compounds for the adenosine A1 receptor as determined in radioligand binding studies, with corresponding Ki values of 1410 +/- 220, 4.7 +/- 0.6 and 102 +/- 74 nM (mean +/- SEM) respectively. In the EEG, only CPA produced a small decrease in the amplitude of beta waves. This study demonstrates that the three adenosine analogues have large differences in pharmacokinetics, which complicates comparison of their cardiovascular and central responses simply on the basis of dose. The application of an integrated PK/PD approach permits estimates of potency and activity which are independent of underlying dose and pharmacokinetics.

Influence of adenosine, dipyridamole, adenosine antagonists and antiepileptic drugs on EEG after discharge following cortical stimulation

The effects of adenosine (100 nM, icv), dipyridamole (DPM, 5 mg/kg, i.p.), adenosine A1 receptor antagonist 8-cyclopentyl-theophylline (8-CPT, 10 mg/kg, i.p.), and aminophylline (AMP) and caffeine (CAF) (at equivalent doses of 35 mg/kg, i.p.), were examined in rats. Anti-epileptic drugs (AEDs) were also administered i.p., viz, carbamazepine (CBZ, 10 mg/kg); phenobarbitone (PB, 10 mg/kg); phenytoin (PHT, 20 mg/kg); valproic acid (VPA, 300 mg/kg); and diazepam (DZP, 10 mg/kg), to study their effects on EEG after discharge (AD) and postictal depression (PID) induced by cortical stimulation. The AD parameters: (1) duration of EEG-AD (sec) and (2) number of spikes was noted both during pre and post drug treatment sessions. Adenosine and DPM had no special effects on AD parameters but showed significant prolongation of PID. All the adenosine antagonists, 8-CPT, AMP and CAF produced significant prolongation of AD duration, increase in number of spikes and reduced the duration of PID to a significant extent. Interestingly, some of the AEDs, viz. CBZ, VPA and DZP showed abolition of all the EEG-AD parameters whereas PB and PHT failed to show any significant effect. The results confirm previous findings on involvement of adenosine in postictal events.

Aminophylline alters pharmacokinetics of carbamazepine but not that of sodium valproate--a single dose pharmacokinetic study in human volunteers

Pharmacokinetic interaction of aminophylline with single dose sodium valproate (400 mg) and carbamazepine (200 mg) was evaluated in normal healthy volunteers using a cross over design. Neither the serum concentrations nor the pharmacokinetic parameters of sodium valproate (SV) were altered by the coadministration of aminophylline (AMP). In contrast AMP significantly decreased the plasma concentrations of carbamazepine (CBZ). The Cmax of CBZ was significantly lowered from 1.73 +/- 0.18 to 0.94 +/- 0.08 microgram/ml and the AUC o-t was significantly decreased from 76.19 +/- 6.20 to 52.66 +/- 1.84 micrograms/h/ml (P < 0.05). The pharmacokinetic parameters of CBZ that were altered in the presence of AMP were: the Tmax and t1/2 which was prolonged about threefold from 5.60 +/- 1.60 to 16.80 +/- 7.94 h and 44.88 +/- 4.50 to 125.07 +/- 29.09 h, respectively. The Vd was marginally increased from 2.19 +/- 0.13 to 3.85 +/- 0.57 L/kg and the Cl was decreased from 34.07 +/- 3.78 to 25.26 +/- 5.15 mL/min. None of these alterations are statistically significant. Bioavailability of CBZ was reduced by 29% in the presence of AMP, while that of SV was increased by about 8%. Results are of clinical significance because simultaneous administration of CBZ and AMP may reduce the efficacy of CBZ in epileptic patients.

An inexpensive method for fabrication of intracerebroventricular cannulae for rats

An inexpensive and simple method to fabricate intracerebroventricular (i.c.v.) cannulae for rats with readily available material is described here. The procedure is cost effective and quick. The cannulae thus designed are suitable for injecting minute quantities (microliters) of drugs/chemicals interacerebroventricularly for acute or chronic experiments in rats.

Involvement of adenosine in postictal events in rats given electroshock

The effect of a selective adenosine antagonist, 8-cyclopentyl 1,3-dimethylxanthine (8-CPT) was used to examine involvement of adenosine in ictal and postictal events in rats subjected to maximal electroshock (MES). MES induces the ictal event of hindlimb tonic extension (HLTE) followed by postictal depression (PID). 8-CPT 10 mg/kg, ip produced maximal significant reduction of PID without affecting HLTE, further confirming involvement of adenosine in PID. Carbamazepine and sodium valproate were studied independently and were coadministered with 8-CPT to determine if their anticonvulsant activity was modulated by adenosine and if they altered PID. 8-CPT did not antagonize the seizure protection afforded by CBZ or SV. CBZ significantly reduced postictal events whereas SV had no significant effect. These observations further confirm a role for adenosine in postictal phenomena.

Reverse single radial immunodiffusion for estimation of titre of anti IgG antibody

Reverse Single Radial Immunodiffusion (SRID) for estimating titre of anti IgG antisera is reported. Unlike the conventional radial immunodiffusion, the antigen (IgG) is held immobile in the gel while the antibody (Anti IgG) diffuses radially from the well (7 microliters) and the diameter of the resulting immuneprecipitates after immunodiffusion at 4 degrees C for 24 hr, represents a linear correlation with the antibody titre. The procedure was standardised by an extensive trial and error employing different concentrations of human IgG in the gel (60-240 micrograms) against varying dilutions of the standard antibody (titre: 3.8 mg/ml). The best results were obtained at 80 micrograms of IgG in the gel. The locally raised rabbit anti IgG antisera displayed a distinctive titre pattern under optimised conditions. Technical reproducibility, high-sensitivity threshold (0.25 mg/ml), simultaneous visual scrutiny of several antibody batches at a glance and ability to assess the shelf life of the stored antisera are its distinct assets.

Antiepileptic drugs delay the onset of seizures induced by aminophylline in conscious rats

Aminophylline, 285.7 +/- 2.19 mg/kg infused intravenously in unanaesthetized rats produced onset of seizures within 3.2 +/- 0.99 minutes. Seizures were repetitive and death occurred in 10.5 +/- 1.75 minutes. Pretreatment of rats with carbamazepine, sodium valproate and diazepam at doses that prevented electroshock induced seizures were effective in significantly postponing seizures and death, but did not reduce mortality. Concomitant EEG studies in aminophylline infused rats showed that cortical excitability evidenced by initial cortical spiking occurred at 42 secs and polyspiking at 165 seconds. Following diazepam, the initial cortical spike was delayed 50 fold, appearing after 36 minutes. Antiepileptic drugs and EEG monitoring may prove useful in patients with status asthmaticus receiving intravenous aminophylline.

Influence of adenosine receptor antagonists, aminophylline and caffeine, on seizure protective ability of antiepileptic drugs in rats

Interaction of methylxanthines, aminophylline (AMP) and caffeine (CAF) on seizure protective ability of various antiepileptic drugs (AEDs), diphenylhydantoin (DPH), phenobarbitone (PB), diazepam (DZP), sodium valproate (SV) and ethosuximide (ESM) was investigated in rats. In the maximal electroshock seizure (MES) test, ED100 doses (mg/kg, ip), against hind limb tonic extension (HLTE) were DPH, 20; PB, 10; DZP, 10 and SV, 300. The interaction of AEDs with AMP (100 mg/kg, ip) reduced the seizure protection afforded by DPH, PB and DZP to 20%, while the efficacy of SV remained unimpaired. Interaction with CAF (200 mg/kg, ip) abolished the seizure protection by DPH and DZP, reduced that by PB to 20%, while the protective effect of SV was unchanged. In pentylenetetrazole (PTZ, 70 mg/kg, sc) induced seizure test, ED100 doses (mg/kg, ip) against clonic convulsions were PB, 10; DZP, 1; SV, 300 and ESM, 200. Complete seizure protection against clonic convulsions following SV or ESM was not significantly influenced by either AMP or CAF, whereas the protective effect of PB and DZP was reversed. SV and ESM showed a qualitative departure in their anti-seizure activity profiles following interaction with either AMP or CAF when compared with the other AEDs.

End stage renal disease serum contains a specific renal cell growth factor

End stage renal disease (ESRD) kidneys display abnormal growth characterized by a continuum of cystic disease, adenoma and carcinoma. This study evaluates the hypothesis that serum of patients with ESRD contains increased amounts of a growth factor which specifically induces proliferation of renal cells. ESRD sera compared to sera from normal controls induced a two to three-fold increase in the proliferative rate of renal cell carcinoma cell lines and normal kidney explants compared to cell lines from other sites. The increased proliferative activity of ESRD sera on renal cells was paralleled by an increase in cytosolic free calcium. The growth factor activity was encoded by a polypeptide of between 15 and 30 kd. The activity of ESRD sera on renal cells was not mimicked or inhibited by epidermal growth factor, basic fibroblast growth factor and platelet derived growth factor indicating that the renal cell specific growth factor activity in ESRD is different from these factors.

Inhibition of anticonvulsant action of carbamazepine by aminophylline and caffeine in rats

Interaction of two well known methyl xanthines, aminophylline--an antiasthmatic agent--and caffeine--commonly present in beverages, on the seizure protective ability of carbamazepine (CBZ) against electrically and chemically induced seizures in rats was investigated. Aminophylline (75 mg/kg, ip) did not alter the activity of CBZ (10 mg/kg, ip; ED100) on maximal electroshock seizures while dose dependent antagonism of CBZ efficacy was seen at 100 and 150 mg/kg, ip. Similar effects were observed with caffeine (200 and 250 mg/kg, ip). At the highest tolerated doses, aminophylline (150 mg/kg, ip) and caffeine (250 mg/kg, ip) produced antagonism of CBZ protection against pentylenetetrazole seizures. These observations support the possibility that the antagonism due to the interaction of these drugs could be related to their action at adenosine receptor sites in the brain.