Influence of the CYP2C9 AND CYP2C19 polymorphisms on phenytoin hydroxylation in healthy individuals from south India.

BACKGROUND AND OBJECTIVES: Phenytoin, a widely used anti-epileptic drug, is metabolized mainly by CYP2C9 (90%) and partly by CYP2C19 (10%) to its major metabolite 5-(para-hydroxyphenyl)-5- phenylhydantoin (p-HPPH). The CYP2C9 and CYP2C19 genes encoding these enzymes are polymorphically expressed and most of the variants result in decreased metabolism of the respective substrates. The present study was undertaken to investigate the influence of the CYP2C9*2 and *3 as well as CYP2C19*2 and *3 variant genotypes on phenytoin hydroxylation in healthy subjects from south India. METHODS: A total of 27 healthy, unrelated, subjects were administered a single oral dose of 300 mg phenytoin. Four hours later, 5 ml of blood was collected and genotyped for CYP2C9*1, *2, *3, CYP2C19*1, *2 and *3 by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Phenytoin and the major metabolite p-HPPH were estimated by reverse phase HPLC. The metabolic ratio was calculated as concentration of phenytoin/p-HPPH. RESULTS: A significant correlation was observed between the CYP2C9 genotype and metabolic ratio of phenytoin/p-HPPH (r = 0.472, 95% CI 0.100 to 0.728; P = 0.01). While no association was found with CYP2C19 alone, a significant correlation was observed between the combined CYP2C9 and CYP2C19 genotypes and phenytoin metabolic ratio (r = 0.507, 95% CI 0.146 to 0.749; P< 0.01). INTERPRETATION AND CONCLUSION: CYP2C9*2 and *3 mutant alleles caused decreased hydroxylation of phenytoin in vivo, whereas the mutant alleles of CYP2C19 played only a minor role in the metabolism of phenytoin in subjects of our study. The results of present preliminary study needs to be confirmed with a larger sample.

Formalin assay parameters differ in confirming the antinociceptive mechanism of domperidone in mice.

Domperidone, a prokinetic drug with minimal extrapyramidal side-effects was investigated for its antinociceptive response in mice using formalin assay procedure. Two parameters namely the pain score and the time spent by the animal in licking/biting the formalin injected paw were considered. Domperidone (1, 2.5 or 5 mg/kg; ip) injected 15 min prior to formalin effectively reduced the pain score bringing it to zero at the 15th minute and was also effective till 30 min but to a lesser degree. This effect of domperidone (2.5 mg/kg) was significantly attenuated in naloxone pretreated mice indicating a partial role for opioid pathways. In the other parameter i.e. time spent in licking/biting, domperidone in all the doses employed failed to modify significantly the same by the animal in the early phase. In contrast, a dose related inhibition of the time spent was recorded in the late phase. Besides, a trend towards the enhancement of the inhibitory effect of domperidone (2.5 mg/kg) in the late phase was noticed in naloxone pretreated mice. Possibly, the peripheral analgesic mechanisms may play a role in this response since the late phase was considered akin to inflammation. The results confirm the antinociceptive effect of domperidone and suggest that caution be exercised while selecting the parameters when formalin assay is employed.

Influence of honey on orally and intravenously administered diltiazem kinetics in rabbits.

Effect of honey on plasma concentration of diltiazem after oral and intravenous administration in rabbits, has been studied. For oral study, single dose of diltiazem (5 mg/kg, p.o.) along with saline was administered to New Zealand white rabbits (n=8). Blood samples were collected at 0, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6 and 8 hr after drug administration from marginal ear vein. After a washout period of one week, diltiazem was administered with honey (2.34 ml/kg; p.o.) and the blood samples were collected as above. To the same animals honey (2.34 ml/kg; p.o.) was continued once daily for 7 days. On 8th day, honey and diltiazem were administered simultaneously and blood samples were collected at similar time intervals as mentioned above. For intravenous study the pharmacokinetic was done in each animal on two occasions. The first study was done after single dose administration of diltiazem (5 mg/kg; i.v.) along with saline (2.34 ml/kg; p.o.). Blood samples were collected at 0, 0.083, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4 and 6 hr after i.v. diltiazem administration. The same animals were treated with honey (2.34 ml/kg; p.o.) for seven days. On day 8, the second study was carried out with single dose i.v. administration of diltiazem along with honey (2.34 ml/kg; p.o.) and blood samples were collected. In the oral study, single dose administration of honey decreased the AUC and Cmax of diltiazem associated with significant increase in clearance and volume of distribution when compared to saline treated group. After one week administration of honey, diltiazem kinetic data showed further reduction in AUC and Cmax and increase in clearance and volume of distribution. In the i.v. study also, multiple dose administration of honey significantly reduced the AUC and increased the clearance value of diltiazem. The results suggest that honey may decrease the plasma concentration of diltiazem after its oral or i.v. administration in rabbits.

Effect of honey on carbamazepine kinetics in rabbits.

The study was undertaken to determine the effect of honey on carbamazepine kinetics in rabbits. The study was done on three occasions in each animal. Study 1 was carried out after single dose administration of carbamazepine (80 mg/kg, po), along with saline (2.34 ml/kg, po). After a wash out period of one week, the second study was carried out by co-administration of carbamazepine with honey (2.34ml/kg, po). After this, the animals continued to receive honey (2.34ml/kg, po), once daily, for 7 days. On the eighth day of honey treatment, the carbamazepine kinetics was studied again. Pharmacokinetic analysis revealed that single as well as multiple dose honey treatment showed a significant decrease in area under the plasma time concentration curve (AUC) when compared with saline treated control. A significant increase in the clearance (CL/F) rate of carbamazepine was observed only after multiple dose honey treatment. Both single and multiple dose honey treatment did not show any significant effect on other pharmacokinetic parameters like t1/2, Cmax, Tmax and Vd when compared with saline treated group. Data thus obtained suggested that honey decreases the bioavailability of carbamazepine.

Effect of two types of Indian breakfast on bioavailability of cefuroxime axetil.

BACKGROUND & OBJECTIVES: The oral bioavailability of cefuroxime axetil is enhanced by food. This study was done to compare the effect of two types of Indian breakfast on the bioavailability of cefuroxime axetil in healthy volunteers. METHODS: Eight healthy male volunteers participated in the crossover study. Subjects were randomized to receive either one of the two types of breakfast, Diet-A or Diet-B, 10 min before single dose of 500 mg cefuroxime axetil. After a washout period of one week the study was repeated with the other type of diet. Diet-A included idly with chutney. Diet-B included poori and dal-fry. Blood samples for pharmacokinetic analysis were obtained prior to dosing and at 0.25, 0.50, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0 and 8.0 h following dosing and urine collections were done for 8 h. The serum and urine samples were assayed by using HPLC. RESULTS: The AUC and Cmax were significantly increased after oral administration of cefuroxime axetil with Diet-B, when compared to Diet-A (P < 0.01 and P < 0.02 respectively). The values of apparent absorption rate constant, lag-time, Tmax and t1/2 beta for the two regimens were not significantly different. The volume of distribution and plasma clearance for cefuroxime were significantly lower (P < 0.02, P < 0.001 respectively) in the regimen with Diet-B. The 8 h urinary recovery of cefuroxime was 16.59 and 28.44 per cent (P < 0.005) with Diet-A and Diet-B respectively. INTERPRETATION & CONCLUSIONS: The administration of cefuroxime axetil with poori and dal-fry may enhance the bioavailability when compared with idly and chutney.

Objective structured practical examination in pharmacology for medical laboratory technicians.

The objective structured practical examination (OSPE) is a useful evaluation method for testing psychomotor skills. Students for the degree in medical laboratory technology require to learn certain skills which will make them useful in any research or teaching laboratory in experimental pharmacology. We outline an OSPE which can be used for evaluating students in experimental pharmacology.

Effect of hyoscine butylbromide and atropine on heart rate during nocturnal sleep.

This is a single blind crossover study designed to test the effects of hyoscine butylbromide (HBB), an anticholinergic which does not cross the blood brain barrier (BBB), on the temporal changes in heart rate during nocturnal sleep. The effects were compared with atropine sulphate which is known to cross the BBB. Ten healthy male volunteers slept in the JIPMER sleep disorders laboratory for three nights and received either saline, atropine sulphate (0.4 mg, i.v.) or HBB (10 mg, i.v.) just prior to sleep onset. All night polysomnography recording was done to monitor heart rate during the specific stages of sleep. The normal physiological fall in heart rate is blunted by both drugs during slow wave sleep whereas only HBB prevented the fall in rapid eye movement sleep. Therefore, HBB may be a better choice as pre-anaesthetic medication for patients with cardiac abnormalities since it does not alter heart rate during both slow wave sleep and rapid eye movement sleep.

Comparative effects of hyoscine butylbromide and atropine sulphate on sleep architecture in healthy human volunteers.

The changes in sleep architecture, heart rate and respiratory rate to hyoscine butylbromide (HBB), a peripherally acting anticholinergic was studied. These effects were compared with that of atropine sulphate, a drug known to cross the blood brain barrier. The study followed a single blind cross over design with a one week washout period. Atropine sulphate (0.4 mg) and HBB (10 mg) were given intravenously to ten adult healthy male volunteers before sleep onset. Normal saline was used as control. All night sleep polysomnography was done with the standard montage for sleep staging. Respiration and airflow were also monitored. Rapid eye movement (REM) latency was significantly increased with both the drugs whereas the duration of REM sleep was decreased only with atropine. Slow wave sleep (SWS) was also increased significantly by atropine. There was no change in heart rate, or respiratory rate during any of the sleep stages. HBB affects the initiation of REM sleep whereas atropine affects both its initiation and maintenance.

Ascorbic acid delays the development of tolerance to amphetamine induced anorexia but does not affect the reverse tolerance which develops to the locomotor activity.

Ascorbic acid (1 g/kg) accentuated anorectic and locomotor effects of amphetamine (5 mg/kg) and delayed development of tolerance to anorectic effect. On the contrary, it did not alter the pattern of reverse tolerance to increased locomotor activity. The results suggest that modulation of dopamine receptor sensitivity by ascorbic acid may be the reason for the delay in development of tolerance to amphetamine induced anorexia.

A comparative study of creatinine clearance rate in type I (IDDM) and II (NIDDM) diabetic patients.

The endogenous creatinine clearance test was done in 14 Type I and 15 Type II poorly controlled diabetic patients and compared with respective age matched healthy volunteers. Type I diabetics had significantly lower creatinine clearance rate, body mass index and serum albumin levels when compared to their control group. In Type II diabetics these values remained unaltered. Both Type I and Type II diabetics had significantly higher blood sugar and glycosylated haemoglobin levels. The creatinine clearance rate had significant positive correlation with patients' body mass index and serum albumin levels. This suggests that the undernutrition of Type I diabetics may be responsible for the decreased creatinine clearance.