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Biomedical subjects

A Richens

Publications and source records attributed to A Richens.

At least 55 records · Page 3Linked to original sources
PubMed1993

Anticonvulsant effects of extracts of the west African black pepper, Piper guineense.

A water extract of the West African black pepper Piper guineense L. was tested for activity against audiogenic seizures in DBA/2 mice, and against seizures induced in T.O. mice by N-methyl-DL-aspartate (NMDLA), pentylenetetrazole (PTZ) and maximal electroschock. Single intraperitoneal doses of the extract produced significant protection of DBA/2 mice against audiogenic seizures. The highest of three doses tested produced 100% and 58% protection at 6 h and 18 h after treatment, respectively. The extract also protected T.O. mice against convulsions induced by NMDLA and maximal electroshock but it had no significant effect on PTZ-induced convulsions. The doses of the extract tested did not cause significant impairment of performance of T.O. mice on a rotarod test. The results indicate that the extract of P. guineense has prolonged anticonvulsant activity at doses which do not cause significant CNS depression.

Acoustic Stimulation↗
PubMed1993

Vigabatrin-induced decrease in serum phenytoin concentration does not involve a change in phenytoin bioavailability.

The possibility that vigabatrin (VGB) decreases serum phenytoin (PHT) concentration by lowering the oral bioavailability of PHT was investigated in 21 patients with epilepsy. Each patient was switched from oral to intravenous PHT for 5 days before and after combined treatment with VGB. After VGB (2-3.5 g day(-1) for at least 5 weeks), serum PHT concentrations decreased slightly from 87 +/- 25 to 76 +/- 31 micromol l(-1) (means +/- s.d., P < 0.05), but in a subgroup of seven patients the decrease was more prominent (from 72 +/- 22 to 49 +/- 17 micromol l(-1), P < 0.005). At baseline (before VGB), serum PHT remained unaffected (85 +/- 30 micromol l(-1)) after switching PHT dosage to the intravenous route, indicating that the oral availability of the drug was virtually complete. During VGB treatment, serum PHT was also unchanged (74 +/- 34 micromol l(-1)) after switching from oral to intravenous therapy, and this was also true for the subgroup of patients showing a prominent interaction (48 +/- 18 micromol l(-1)). The urinary recoveries of PHT and its metabolites pHPPH and mHPPH remained constant throughout the study. It is concluded that the oral availability of PHT is unaffected by VGB and that the VBG-induced decrease in serum PHT is mediated by alternative mechanisms.

Adolescent↗
PubMed1993

Effects of zolpidem on saccadic eye movements and psychomotor performance: a double-blind, placebo controlled study in healthy volunteers.

1. Peak saccade velocity provides a valuable means of assessing the sedative effect of drugs in humans. The present study investigated the effects of zolpidem, an imidazopyridine hypnotic, on saccade velocity in healthy volunteers after single and repeated administration. 2. Zolpidem 5 mg, 10 mg and 20 mg significantly and dose dependently depressed peak saccade velocity during the 1.5 h after a single administration. On the morning after zolpidem administration, peak saccade velocity had returned towards pretreatment levels. Nitrazepam 10 mg also significantly depressed peak saccade velocity but the effect was maintained the following morning. The saccade response to zolpidem (5 and 10 mg) was undiminished after the seven nightly doses. 3. Nightly administration of zolpidem improved subjective sleep quality and there was no evidence of rebound insomnia following cessation of drug treatment.

Adult↗
PubMed1992

Performance of techniques for measurement of therapeutic drugs in serum. A comparison based on external quality assessment data.

Ten assay techniques were compared using measurements of a range of 15 drugs spiked in freeze-dried samples of serum reported to the Heathcontrol External Quality Assessment Scheme between November 1988 and January 1991. Three measures of performance were studied: frequency of outliers greater than 3 standard deviations from the sample mean, the coefficient of variation (CV) of sample measurements, and the difference of the sample mean from the spike value. The most consistently precise technique was polarisation fluoroimmunoassay (PFIA). It was in the group of techniques producing significantly fewer outliers and lower CVs than other techniques for all its target analytes. However, a specific interaction with the animal serum used as sample matrix resulted in significant negative bias in PFIA measurements of carbamazepine. Other immunoassay techniques and high-performance liquid chromatography also performed well for a range of analytes, in most cases giving less than 6% of outliers with CVs of less than 13% and less than 5% bias. The least satisfactory techniques were nephelometry and gas-liquid chromatography with derivatisation, which for several analytes gave significantly more outliers and higher CV values than other techniques. In samples containing carbamazepine-10, 11-epoxide, immunoassay measurements of carbamazepine showed cross-reactivity with the epoxide metabolite of between 7 and 15%.

Carbamazepine↗
PubMed1992

Bioavailability and dissolution of proprietary and generic formulations of phenytoin.

A comparative study of the bioavailability of seven formulations of phenytoin was carried out on 17 patients with epilepsy who were taking phenytoin regularly as part of their drug therapy. Three patients withdrew for personal reasons. No significant differences were found between Epanutin capsules and other generic formulations. However significant differences were noted between the generic products. Phenytoin BP tablets manufactured by Regent Laboratories (now withdrawn) had a relative bioavailability of only 76% compared with tablets manufactured by A H Cox and Company. In vitro dissolution tests requirements were met by all formulations of generic 100 mg tablets, and it was concluded that in vitro dissolution tests are not reliable indicators of biological equivalence. Significantly higher plasma levels were found with Epanutin Infatabs, but this was accounted for by their higher content of phenytoin, which is present in the acid form rather than the sodium salt.

Adolescent↗
PubMed1992

Lamotrigine as an add-on drug in the management of Lennox-Gastaut syndrome.

We report our experience with lamotrigine add-on therapy in the treatment of 11 patients with Lennox-Gastaut syndrome. Lamotrigine is a novel antiepileptic drug, chemically unrelated to the major anticonvulsants in current use. Ten patients experienced a > 50% reduction in seizure frequency, 1 patient experienced no change in seizure frequency. All patients tolerated lamotrigine satisfactorily and no side-effects were reported.

Anticonvulsants↗
PubMed1991

The influence of age on the pharmacokinetics of the antiepileptic agent oxcarbazepine.

The disposition of oxcarbazepine was studied in 12 young and 12 elderly healthy male and 12 young and 12 elderly healthy female volunteers, with emphasis on the influence of age. Oxcarbazepine was administered as a single dose of either 300 mg (men) or 600 mg (women), followed by multiple-dose (300 mg) administration twice a day for 7 days (men) or 6 days (women). Semilogarithmic plasma concentration-time curves showed an increasing decline at decreasing concentrations. Accumulation of the pharmacologically active metabolite monohydroxycarbamazepine was found to be more than one would anticipate on the basis of linear and unchanged pharmacokinetics. Saturation did not seem to occur at the level of renal excretion. No apparent differences between male and female volunteers were observed. A significant higher maximum concentration, higher area under the curve parameters, and a lower elimination rate constant were observed in the elderly. These observations are in line with a smaller renal clearance of monohydroxycarbamazepine in the elderly group. In a clinical situation, these age-related differences are not likely to have important implications. In general, treatment with oxcarbazepine was well tolerated.

Adolescent↗
PubMed1991

Determination of vigabatrin in plasma by reversed-phase high-performance liquid chromatography.

A method is described for the determination of vigabatrin in 50 microliters of plasma by isocratic high-performance liquid chromatography using fluorescence detection. The procedure involves protein precipitation with methanol followed by precolumn derivatisation with o-phthaldialdehyde reagent. Separation of the derivatised vigabatrin was achieved on a Microsorb C18 column using a mobile phase of 10 mM orthophosphoric acid:acetonitrile:methanol (6:3:1) at a flow rate of 2.0 ml/min. Assay time is 15 min and chromatograms show no interference from commonly coadministered anticonvulsant drugs. The total analytical error within the range of 0.85-85 micrograms/ml was found to be 7.6% with the within-replicates error of 2.76%. The minimum detection limit was 0.08 micrograms/ml and the minimum quantitation limit was 0.54 micrograms/ml.

Aminocaproates↗
PubMed1991

Overview of the clinical efficacy of lamotrigine.

Testing the efficacy of lamotrigine (LTG) in epileptic patients has been approached in several ways. The first pilot study examined the effect of a single dose of LTG in patients with frequent interictal spikes, and a reduction in spike frequency was observed. Subsequently, single doses reduced photosensitivity in appropriate patients. Single-blind administration of LTG for 1 week in addition to the patients' regular antiepileptic drugs (AEDs), in patients with refractory seizures, reduced seizures despite the short duration of therapy. This regimen was continued using a placebo-controlled crossover study with 1-week duration of treatment. Efficacy in partial and tonic-clonic seizures was subsequently confirmed in four double-blind crossover studies; a meta-analysis of these four studies showed a 30% reduction in partial seizures despite the intractable nature of the seizures in the patients included. Current studies aim at evaluating the drug as monotherapy and in different seizure types.

Anticonvulsants↗
PubMed1991

Pharmacology and clinical pharmacology of vigabatrin.

Vigabatrin is an enzyme-activated, irreversible inhibitor of gamma-aminobutyric acid (GABA) aminotransferase, which causes a marked increase in cerebral GABA concentration and a resulting anticonvulsant action. Recovery from its effects requires the synthesis of new enzyme, and this may take several days following a single dose. The pharmacokinetics of vigabatrin are not a good guide to its duration of action. It is cleared rapidly by renal elimination (giving a plasma half-life of approximately 7 to 9 hours), and therefore the effect of the drug long outlasts its presence in the body. Plasma drug level monitoring is therefore of little value in regulating vigabatrin therapy. The drug is not bound to plasma proteins. Interactions with other drugs would not be expected because of its predominant renal elimination and its lack of protein binding. Also, vigabatrin does not induce liver enzymes, as do many of the standard antiepileptic drugs. In several trials, however, a small but significant reduction in phenytoin levels has been seen following the addition of vigabatrin to the antiepileptic medication. The mechanism for this reduction in phenytoin levels has not yet been elucidated, though it does not appear to be of clinical significance.

4-Aminobutyrate Transaminase↗
PubMed1991

Performance of techniques used to detect drugs of abuse in urine: study based on external quality assessment.

Twenty-five samples of lyophilized urine from the U.K. External Quality Assessment Scheme for Drugs of Abuse were analyzed by an average of 95 laboratories between April 1987 and December 1989. Samples contained mixtures of analytes and included replicated concentrations of morphine, methadone, amphetamine, and cocaine at 0, 1, 2, and 5 mg/L and of benzoylecgonine at 0, 0.4, 1, 2, and 4 mg/L. Some chromatographic techniques were inadequate for detecting morphine, amphetamine, cocaine, and benzoylecgonine at the lower concentrations of analytes studied: gas-liquid chromatography was least sensitive for morphine; in-house thin-layer chromatography (TLC) was least sensitive for the other analytes. Few significant differences in specificity were detected between techniques, although significant interference from structurally related compounds was demonstrated in assays of morphine, methadone, and amphetamine. Exceptions were the Boehringer (BCL) test for opiates and TLC applied to amphetamine and benzoylecgonine, which demonstrated considerable lack of specificity.

Amphetamine↗