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Biomedical subjects

Richard I Shader

Publications and source records attributed to Richard I Shader.

At least 19 recordsLinked to original sources
PubMed2006

The effect of chronic lorazepam administration in aging mice.

To assess benzodiazepine tolerance in aged animals, lorazepam or vehicle was administered chronically to male Crl: CD-1(ICR)BR mice. Pharmacodynamic and neurochemical endpoints were examined on days 1 and 14 of drug administration. There was no age-related significant difference in plasma lorazepam levels. Young and middle-aged animals demonstrated behavioral tolerance to lorazepam, while the aged animals showed a similar trend which failed to reach significance. In addition, aged animals also showed a trend toward tolerance to the anticonvulsant effects of lorazepam. There were no changes in alpha1 mRNA levels in cortex or hippocampus following administration of lorazepam when compared to vehicle-treated animals in any age group. Aged animals, however, had an initial increase in alpha1 mRNA expression in cortex and hippocampus on day 1 of vehicle treatment followed by decreased expression on day 14. These age-related changes were abolished by lorazepam administration. In summary, age-related sensitivity to the effects of lorazepam was not demonstrated in the present study. However, comparison of these data to other studies indicates that the effect of chronic benzodiazepine treatment may be specific to the benzodiazepine administered, the technique used to quantify mRNA expression changes, the subunits of the GABA(A) receptor investigated and the brain region analyzed. The phenomenon of benzodiazepine sensitivity in the elderly is an area of research which remains controversial and may well be compound specific. Determining benzodiazepines that do not produce pharmacodynamic sensitivity, such as lorazepam, may allow more careful prescribing and dosing of these drugs, and perhaps even the development of specific agents which could avoid this sensitivity.

Aging↗
PubMed2005

Hyperforin plasma level as a marker of treatment adherence in the National Institutes of Health Hypericum Depression Trial.

BACKGROUND: A previously reported clinical trial of Hypericum perforatum (St John's wort) in depression did not demonstrate efficacy. We assessed treatment adherence by measuring plasma hyperforin and evaluated the possible impact of adherence on study results. METHODS: Outpatients with major depression (N = 340) were randomized to an 8-week trial of H. perforatum (900-1500 mg/d), sertraline (50-100 mg/d) as active comparator, or placebo. Plasma was available from 292 patients (86% of randomized). Samples from the placebo and H. perforatum groups were assayed for hyperforin, and samples from the sertraline group for sertraline/N-desmethyl-sertraline. RESULTS: Of the 104 patients randomized to placebo, 18 (17%) had detectable plasma hyperforin. Of the 97 patients randomized to H. perforatum, 17 (17%) had no detectable plasma hyperforin. All the assayed sertraline patients (N = 91) had plasma sertraline/N-desmethyl-sertraline. The clinical trial conclusions remained unchanged when only patients with plasma assay consistent with random assignment were included in the analyses. CONCLUSIONS: One of every 6 patients assigned to placebo had plasma hyperforin, and 1 of every 6 patients assigned to H. perforatum had no detectable plasma hyperforin. The finding underscores the difficulty of enforcing treatment adherence in clinical trials of preparations that are readily available in the community.

Adult↗
PubMed2005

Pharmocokinetics and pharmacodynamics of single-dose triazolam: electroencephalography compared with the Digit-Symbol Substitution Test.

AIMS: To investigate whether the electroencephalogram (EEG) directly reflects the CNS effects of benzodiazepines by evaluating the relation of the EEG to plasma drug concentrations and to Digit-Symbol Substitution Test (DSST) scores after a single dose of triazolam, a representative benzodiazepine agonist. METHODS: Thirteen healthy male subjects were given 0.375 mg triazolam or placebo in a double-blind crossover study. Plasma samples were collected during 8 h after dosage. Pharmacodynamic effects were measured by DSST and EEG at corresponding times. RESULTS: Pharmacokinetic parameters for triazolam were consistent with established values. Compared with placebo, triazolam significantly impaired psychomotor performance on the DSST (P < 0.001) and increased beta amplitude on the EEG (P < 0.002). DSST and EEG changes both closely tracked changes in plasma concentrations over time. The changes for the two measures were highly correlated with each other (r =-0.94, P < 0.001) based on aggregate values at individual time points. However, the variations in area under the curve of pharmacodynamic effect vs. time (AUCeffect) measured by either method did not reflect the variations in plasma AUC across individuals. The individual variability in AUCeffect from the EEG was similar to that measured by the DSST. CONCLUSIONS: Both the EEG and the DSST reflect the central benzodiazepine agonist effects of triazolam. Intrinsic variability in both measures is similar.

Adult↗
PubMed2004

Age and gender effects on the pharmacokinetics and pharmacodynamics of triazolam, a cytochrome P450 3A substrate.

Sixty-one healthy men and women, aged 20 to 75 years, received single 0.25-mg doses of triazolam, a cytochrome P450 (CYP) 3A substrate benzodiazepine, and placebo in a double-blind crossover study. Among women, age had no significant effect on area under the triazolam plasma concentration curve (AUC) (Spearman r=0.14, P=.44) or clearance (r =-0.09, P=.62). Among men, AUC increased (r=0.43, P <.02) and clearance declined (r=-0.42, P <.02) with increasing age. Gender differences in triazolam kinetics were not apparent. Compared with placebo, triazolam impaired digit-symbol substitution test performance, increased observer-rated sedation, impaired delayed recall of information learned at 1.5 hours after dosing, and increased electroencephalographic beta amplitude. Among men, mean values of relative digit-symbol substitution test decrement (P <.002) and observer-rated sedation (P <.05) were significantly greater in elderly subjects compared with young subjects. Age-dependent differences among women reached significance for observer-rated sedation (P <.02). A combination of higher plasma levels and increased intrinsic sensitivity explained the greater pharmacodynamic effects of triazolam in elderly subjects. Although the findings are consistent with reduced clearance of triazolam in elderly men, individual variability was large and was not explained by identifiable demographic or environmental factors.

Adult↗
PubMed2004

Kinetics and EEG effects of midazolam during and after 1-minute, 1-hour, and 3-hour intravenous infusions.

The objective of this study was to evaluate the kinetics and dynamics of midazolam when administered by three different infusion schemes, using electroencephalography to measure pharmacodynamic effects. In a three-way crossover study, 8 volunteers received midazolam (0.1 mg/kg) by constant-rate intravenous infusion. The durations of midazolam infusions for the three trials were 1 minute, 1 hour, and 3 hours. Plasma midazolam concentrations and electroencephalographic (EEG) activity in the 13- to 30-Hz range were monitored for 24 hours. Based on separate analysis of each subject-trial, mean values for volume of distribution and distribution or elimination half-life did not significantly vary. Central compartment volume and clearance differed among the three midazolam infusion trials; however, the magnitude of change was small. EEG activity in the 13- to 30-Hz range significantly increased for all three midazolam infusion trials. Plots of midazolam plasma concentration versus pharmacodynamic EEG effect for the 1-hour and 3-hour infusion trials did not reveal evidence of either counterclockwise or clockwise hysteresis. Plots from the 1-minute infusion trial demonstrated counterclockwise hysteresis, consistent with an equilibration effect-site delay. This was incorporated into a kinetic-dynamic model in which hypothetical effect-site concentration was related to pharmacodynamic EEG effect via the sigmoid E(max) model. Analysis of all three infusion trials together yielded the following mean estimates: maximum EEG effect, 16.3% over baseline; 50% maximum effective concentration, 31 ng/mL; and an apparent rate constant for drug disappearance from the effect compartment which approached infinity. Despite the delay in effect onset during the 1-minute midazolam infusion, midazolam infusions in duration of up to 3 hours produce CNS sedation without evidence of tolerance.

Adult↗
PubMed2004

A controlled study of the effects of state surveillance on indicators of problematic and non-problematic benzodiazepine use in a Medicaid population.

OBJECTIVE: Benzodiazepines (BZs) are safe, effective drugs for treating anxiety, sleep, bipolar, and convulsive disorders, but concern is often expressed about their overuse and potential for abuse. We evaluated the effects of physician surveillance through a Triplicate Prescription Program (TPP) on problematic and non-problematic BZ use. METHOD: This study uses interrupted time series analyses of BZ use in the New York (intervention) and New Jersey (control) Medicaid programs for 12 months before and 24 months after the New York BZ TPP. The regulation required NY physicians to order BZs on triplicate prescription forms with one copy forwarded by pharmacies to a state surveillance unit. Study participants were community-dwelling persons over age 18 continuously enrolled between January 1988 and December 1990 in New York (n = 125,837) or New Jersey Medicaid (n = 139,405). RESULTS: During the baseline year, 20.2% of New York and 19.3% of New Jersey cohort members received at least one BZ prescription. After the TPP, there was a sudden, sustained reduction in BZ use of 54.8% (95% CI = [51.4%, 58.3%]) in New York with no changes in New Jersey. Significantly greater reductions were experienced by young women, and persons living in zip codes that were urban, predominantly Black, or with a high density of poor households. Increases in potential substitute medications were modest. At baseline, nearly 60% of BZ recipients had no evidence of potentially problematic use. Despite a somewhat greater likelihood of discontinuation of BZ therapy among those with potentially problematic use, the largest impact of the TPP was a substantially greater relative reduction in access to BZs among non-problematic users. CONCLUSIONS: State-mandated physician surveillance dramatically reduces BZ use with limited substitution of alternative drugs, lowers rates of possible abuse, but may severely limit non-problematic BZ use.

Adult↗
PubMed2003

Pharmacokinetic properties of zolpidem in elderly and young adults: possible modulation by testosterone in men.

AIMS: The influence of ageing on the pharmacokinetics of zolpidem, an extensively prescribed hypnotic medication, was evaluated in healthy human volunteers. METHODS: A series of 16 elderly (age: 61-85 years) and 24 young (age: 22-42 years) volunteers received single 5 mg oral doses of zolpidem tartrate. Serum zolpidem concentrations were determined by HPLC with fluorescence detection in samples drawn during 8 h after dosage. The effect of testosterone on zolpidem biotransformation was evaluated in vitro using human liver microsomes. Possible induction of CYP3A protein expression and function was studied in cultured human hepatocytes. RESULTS: Among men, apparent oral clearance of zolpidem was decreased in elderly compared to young subjects (3.8 vs 11.0 ml min-1 kg-1, P < 0.01), Cmax was increased (93 vs 40 ng ml-1, P < 0.01), and half-life increased (2.7 vs 1.5 h, P < 0.03). Among women, zolpidem oral clearance was decreased in the elderly (3.0 vs 5.8 ml min-1 kg-1, P < 0.02), Cmax increased (108 vs 60 ng ml-1, P < 0.001), with no difference in t1/2 (2.3 vs 2.4 h). Among male subjects, free serum testosterone concentrations were lower in the elderly (10.5 vs 19.0 pg ml-1, P < 0.01), and were significantly correlated with zolpidem clearance (r2 = 0.46, P < 0.001). Multiple regression analysis indicated a greater relative contribution of serum testosterone than age to the oral clearance of zolpidem among men. In human liver microsomes, co-incubation of zolpidem (10 micro m) with varying concentrations of testosterone produced activation of biotransformation of zolpidem to its principal hydroxylated metabolite. Maximum activation was achieved at equimolar concentrations of testosterone (10 micro m). However, testosterone did not induce immunoactive CYP3A4 expression or catalytic function in cultured human hepatocytes. CONCLUSIONS: The increased Cmax and lower oral clearance of zolpidem in the elderly are consistent with recommendations of lower clinical doses of zolpidem in the elderly. Our clinical and in vitro data both suggest that reduced free serum testosterone may have a modulatory role in age-dependent changes in zolpidem pharmacokinetics in men.

Administration, Oral↗
PubMed2003

The effect of age on sildenafil biotransformation in rat and mouse liver microsomes.

Sildenafil [SIL (Viagra); Pfizer, New York, NY] is a widely prescribed agent for erectile dysfunction in men older than 65 years. The present study evaluated experimental models to assess age-dependent changes in SIL biotransformation using hepatic microsomes from male rats and mice ranging from 6 weeks to 26 months of age. The role of specific isoforms in the conversion of SIL to its primary circulating metabolite, UK-103,320 (piperazine N-desmethyl sildenafil) in the mouse was also investigated using immunoinhibitory antibodies. Although CYP2C11 largely mediated UK-103,320 formation in the rat, UK-103,320 formation was principally inhibited by a CYP3A antibody in the mouse. An age-related decrement in metabolite formation rate was observed for both species, although this effect was more pronounced in the old rats (reduced to 7% of young) than in the old mice (reduced to 51% of young). CYP2C expression was assessed by Western blot analysis in rat and mouse livers. Age-related differences in hepatic CYP3A expression in the mouse were also compared with metabolite formation rates in the mouse model. Decrements with age in CYP2C and -3A expression in the aging rodents paralleled the decrements in SIL biotransformation, suggesting that age-related differences in SIL metabolic rate may, in part, reflect differences in expression. Although the role of specific CYP enzymes and the clearance values for this reaction may differ among species, age-related changes in these rodent models are consistent with the reduced clearance of SIL observed in human studies.

Aging↗
PubMed2003

Short-term exposure to low-dose ritonavir impairs clearance and enhances adverse effects of trazodone.

Antiretroviral agents may participate in drug interactions that influence the efficacy and toxicity of other antiretrovirals, as well as pharmacologic treatments of coincident or complicating diseases. The viral protease inhibitor, ritonavir, may cause drug interactions by inhibiting the activity of cytochrome P450-3A (CYP3A) isoforms. In a single-dose, blinded, four-way crossover study, 10 healthy volunteer subjects received 50 mg of trazodone hydrochloride or matching placebo concurrent with low-dose ritonavir (four doses of 200 mg each) or with placebo. Compared to the control condition, ritonavir significantly reduced apparent oral clearance of trazodone (155 +/- 23 vs. 75 +/- 12 ml/min, p < 0.001), prolonged elimination half-life (6.7 +/- 0.7 vs. 14.9 +/- 3.9 h, p < 0.05), and increased peak plasma concentrations (842 +/- 64 vs. 1125 +/- 111 ng/ml, p < 0.05) (mean +/- SE). Coadministration of trazodone with ritonavir increased sedation, fatigue, and performance impairment compared to trazodone plus placebo; differences reached significance only for the digitsymbol substitution test. Three subjects experienced nausea, dizziness, or hypotension when trazodone was given with ritonavir; 1 of these subjects also experienced syncope. Thus short-term low-dose administration of ritonavir impairs oral clearance of trazodone and increases the occurrence of adverse reactions. The findings are consistent with impairment of CYP3A-mediated trazodone metabolism by ritonavir.

Administration, Oral↗