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Biomedical subjects

G Castañeda-Hernández

Publications and source records attributed to G Castañeda-Hernández.

At least 19 recordsLinked to original sources
PubMed2006

Acute spinal cord injury changes the disposition of some, but not all drugs given intravenously.

STUDY DESIGN: Experimental laboratory investigations in paraplegic rats. OBJECTIVE: In order to understand why acute spinal cord injury (SCI) changes the disposition of some, but not all drugs given intravenously (i.v.), pharmacokinetic parameters of drugs with different pharmacological properties were evaluated to determine the influence of SCI on physiological processes such as distribution, metabolism and excretion. SETTING: Mexico City, Mexico. METHODS: Rats were subjected to severe SCI (contusion) at T-9 level; pharmacokinetic studies of phenacetin, naproxen or gentamicin were performed 24 h after. These drugs were not chosen as markers because of their therapeutic properties, but because of their pharmacokinetic characteristics. Additional studies including plasma proteins, liver and renal function tests, and micro-vascular hepatic blood flow, were also performed at the same time after injury. RESULTS: Acute SCI significantly reduced distribution of drugs with intermediate and low binding to plasma proteins (phenacetin 30% and gentamicin 10%, respectively), but distribution did not change when naproxen - a drug highly bound to plasma proteins (99%) - was used, in absence of changes in plasma proteins. Metabolism was significantly altered only for a drug with liver blood flow - limited clearance (phenacetin) and not for a drug with liver capacity-limited clearance (naproxen). The liver function test did not change, whereas the hepatic micro-vascular blood flow significantly decreased after SCI. Renal excretion, evaluated by gentamicin clearance, was significantly reduced as a consequence of SCI, without significant changes in serum creatinine. CONCLUSIONS: Changes in drug disposition associated to acute SCI are complex and generalization is not possible. They are highly dependent on each drug properties as well as on the altered physiological processes. Results motivate the quest for strategies to improve disposition of selective i.v. drugs during spinal shock, in an effort to avoid therapeutic failure.

Acute Disease↗
PubMed2001

Mechanisms involved in the cardiovascular alterations immediately after spinal cord injury.

The early cardiovascular effects resulting from an acute spinal cord injury (SCI) produced by a contusion procedure at T5-T6 were evaluated in anaesthetized rats. The mean arterial pressure (MAP) and heart rate (HR) were measured during one hour after the injury. A marked decrease in MAP and HR was observed immediately after injury, followed by an abrupt increase in MAP. These changes were observed between 3 and 9 min and the basal values were recovered after 20 min. Fall in the MAP and HR and increase in MAP induced by SCI were abolished by atropine. The interruption of the parasympathetic outflow by vagotomy also significantly diminished the fall and increase in MAP and the fall in HR. Likewise, pre-treatment with nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) completely abolished the effects produced by SCI. These data suggest that after SCI the decrement in MAP and HR was probably due to acetylcholine release from parasympathetic fibers and NO from endothelial source probably by a cholinergic stimulation. Additionally, the MAP increase observed was probably due to a reflex compensatory vasoconstriction.

Acetylcholine↗
PubMed2001

Pharmacokinetic/pharmacodynamic modeling of antipyretic and anti-inflammatory effects of naproxen in the rat.

Pharmacokinetic/pharmacodynamic modeling was used to characterize the antipyretic and anti-inflammatory effects of naproxen in rats. An indirect response model was used to describe the antipyretic effects of naproxen after short intravenous infusions. The model assumes that basal temperature (T(a)) is maintained by the balance of fever mediators given by a constant (zero order) rate of synthesis (K(syn)), and a first order rate of degradation (K(out)). After an intraperitoneal injection of lipopolysaccharide, the change in T(a) was modeled assuming an increase in fever mediators described as an input rate function [IR(t)] estimated nonparametrically. An inhibitory E(max) model adequately described the inhibition of IR(t) by naproxen. A more complex model was used to describe the anti-inflammatory response of oral naproxen in the carrageenin-induced edema model. Before carrageenin injection, physiological conditions are maintained by a balance of inflammation mediators given by K(syn) and K(out) (see above). After carrageenin injection, the additional synthesis of mediators is described by IR(t) (see above). Such mediators induced an inflammatory process, which is governed by a first order rate constant (K(IN)) that can be inhibited by the presence of naproxen in plasma. The sigmoidal E(max) model also well described the inhibition of K(IN) by naproxen. Estimates for IC(50) [concentration of naproxen in plasma eliciting half of maximum inhibition of IR(t) or K(IN)] were 4.24 and 4.13 microg/ml, for the antipyretic and anti-inflammatory effects, respectively.

Analgesics, Non-Narcotic↗
PubMed2000

Bayesian approach to control of amikacin serum concentrations in critically ill patients with sepsis.

OBJECTIVE: To compare the predictive performance of a Bayesian program incorporating a population model with and without severity of illness covariates in intensive care unit (ICU) patients with sepsis. DESIGN: The clinical, physiologic, and pharmacokinetic data of 62 patients with sepsis admitted to a tertiary-care center were analyzed retrospectively. The patients were randomly assigned to a active group and a validation group. The model was developed using a three-step approach involving Bayesian estimation of pharmacokinetic parameters, selection of covariates by principal component analysis, and final selection of covariates by stepwise multiple linear regression. The predictive performance of this model was tested in patients from the validation group and compared with that of a general population model without covariates. RESULTS: Regression analysis revealed that the Acute Physiologic and Chronic Health Evaluation (APACHE II) score was the most important determinant for amikacin volume of distribution (1.5 L/kg, APACHE II; r2 = 0.77). For amikacin clearance (CIamik), creatinine clearance (CIcr), positive end-expiratory pressure (PEEP), and use of catecholamines (CAT) were the most important predictors (CIamik = 44.5 + 0.67 CIcr - 1.29 PEEP - 8.34 CAT; r2 = 0.72). The relative mean error (deltaME) and root mean-square error (deltaRMSE) (95% CI) were -0.62 (-1.2 to 0.01) and 3.78 (2.3 to 4.8) mg/L, respectively. Since the 95% CI for deltaRMSE did not include zero, it appears that the model with covariates is significantly improved in terms of precision. CONCLUSIONS: Our results show that, in ICU patients treated with amikacin, it is relevant to consider covariates related to pathophysiologic status and therapeutic measures. Application of a Bayesian program allows improved control of the pharmacokinetic parameters in patients who exhibit rapidly changing physiologic conditions.

Amikacin↗
PubMed2000

Input rate as a major determinant of furosemide pharmacodynamics: influence of fluid replacement and hypoalbuminemia.

To investigate how the response to a bolus and an infusion of furosemide is modulated by the rate of fluid replacement and by hypoalbuminemia, rabbits received 5 mg/kg of furosemide as a bolus or infused over 60 min, whereas diuresis was replaced with 13, 121, or 238 ml/h NaCl 0.9%/glucose 5% (50:50). Natriuretic and diuretic efficiencies were greater with the infusion than with the bolus of furosemide. Fluid replacement increased natriuretic and diuretic efficiency of furosemide bolus but only diuretic efficiency of furosemide infusion. Furosemide net fluid depletion reached a plateau when fluid replacement increased beyond 121 ml/h. Repeated plasmapheresis decreased plasma albumin by 30% (P <.05) and increased furosemide unbound fraction (P <.05). Compared with control rabbits, hypoalbuminemia decreased the natriuresis of the bolus (22.7 +/- 1.5-16.6 +/- 1.3 mmol, P <.05) but not that elicited by furosemide infusion (26.2 +/- 1.8 mmol). Given as a bolus, furosemide natriuretic and diuretic response as a function of its urinary rate of excretion exhibited an hyperbolic relationship, and after its infusion a clockwise hysteresis, denoting tolerance. Plasma renin activity was increased by the bolus and the infusion of furosemide, even in the presence of 121 ml/h of fluid replacement. It is concluded that: 1) the increase in natriuretic/diuretic efficiency of the bolus induced by fluid replacement is greater than when furosemide is infused, 2) furosemide net effect does not increase proportionally to fluid replacement, and 3) the infusion of furosemide prevents the hypoalbuminemia-induced decrease in response of furosemide given as a bolus.

Animals↗
PubMed2000

Considerations on pharmacodynamics and pharmacokinetics: can everything be explained by the extent of drug binding to its receptor?

It is frequently assumed that pharmacological responses depend solely on the extent of drug binding to its receptor according to the occupational theory. It is therefore presumed that the intensity of the effect is determined by drug concentration at its receptor site, yielding a unique concentration-effect relationship. However, when dependence, abstinence, and tolerance phenomena occur, as well as for pharmacological responses in vivo that are modulated by homeostatic mechanisms, the rate of drug input shifts the concentration-effect relationship. Hence, such responses cannot be explained on the sole basis of the extent of drug binding to its receptor. Information on the cellular and molecular processes involved in the generation of abstinence, dependence, and tolerance will undoubtedly result in the development of pharmacodynamic models allowing a satisfactory explanation of drug effects modulated by these phenomena. Notwithstanding, integrative physiology concepts are required to develop pharmacokinetic-pharmacodynamic models allowing the description of drug effects in an intact organism. It is therefore important to emphasize that integrative physiology cannot be neglected in pharmacology teaching and research, but should be considered as an equally valuable tool as molecular biology and other biomedical disciplines for the understanding of pharmacological effects.

Animals↗
PubMed1999

Effect of coadministration of caffeine and either adenosine agonists or cyclic nucleotides on ketorolac analgesia.

Caffeine potentiation of ketorolac-induced antinociception in the pain-induced functional impairment model in rats was assessed. Caffeine alone was ineffective, but increased the effect of ketorolac without affecting its pharmacokinetics. Intra-articular administration of adenosine and N6-cyclohexyladenosine (CHA, an adenosine A1 receptor agonist), but not 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS-21680, an adenosine A2A receptor agonist), significantly increased ketorolac antinociception. This effect was not local, as contralateral administration was also effective. Ipsilateral and contralateral administration of adenosine and CHA also increased antinociception by ketorolac-caffeine. Intra-articular 8-Bromo-adenosine cyclic 3',5'-hydrogen phosphate sodium or 8-Bromo-guanosine-3',5'-cyclophosphate sodium (cGMP) given ipsilaterally or contralaterally did not affect ketorolac-induced antinociception. Nevertheless, ipsilateral, but not contralateral, administration of 8-Br-cGMP significantly increased antinociception by ketorolac-caffeine, suggesting a local effect. The results suggest that caffeine potentiation of ketorolac antinociception is mediated, at least partially, by a local increase in cGMP and rule out the participation of adenosine receptor blockade.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1999

A review of the pharmacokinetic and pharmacodynamic factors in the potentiation of the antinociceptive effect of nonsteroidal anti-inflammatory drugs by caffeine.

Caffeine is an effective analgesic adjuvant because it increases the antinociceptive effect of NSAIDs while reducing the probability of side effects. The mechanism by which caffeine increases the antinociceptive action of NSAIDs does not appear to include a pharmacokinetic interaction. The potentiation appears to be due to a pharmacokinetic mechanism including actions at the central and the peripheral levels. Because caffeine shifts the effect-compartment concentration-effect relation of NSAIDs to the left and this relationship is sigmoidal, there is no potentiation if the NSAID concentrations are too high or too low with respect to EC(50). The best potentiation can be observed if the NSAID doses used yield effect-compartment concentrations in the vicinity of EC(50). Therefore further investigation of the PK/PD relations of caffeine-NSAID combinations for different pain states and intensities is needed to optimize the therapeutic use of these mixtures.

Animals↗
PubMed1999

Limited sampling model for area-under-the-curve monitoring in pediatric patients receiving either Sandimmune or Neoral cyclosporin A oral formulations.

Several limited sampling equations were tested to predict the area under the curve (AUC) of cyclosporin A (CsA) at steady state in 10 children with end-stage renal disease receiving oral CsA 2.5 mg/kg b.i.d. as two different formulations, namely Sandimmune and Neoral, according to a randomized crossover design with a one-month washout period. AUC was significantly correlated with CsA concentration at 5 h. The equation derived from this single concentration time point was able to adequately predict the AUC for Sandimmune but not for Neoral. The equation derived from CsA concentration data, measured at 2 and 12 h, significantly improved predictive performance in terms of bias and precision, allowing adequate AUC predictions in both formulations. CsA concentration at 2 h was also able to predict Cmax, while the concentration at 12 h corresponded to the trough value in a b.i.d. dosing scheme. Therefore, it is concluded that a limited sampling model including concentration data at 2 and 12 h allows the estimation of AUC, Cmax and trough levels, yielding a complete profile in patients exposed to CsA as Sandimmune or Neoral. Hence, this model can be used for therapeutic monitoring of CsA levels in pediatric patients being switched from one formulation to another.

Administration, Oral↗
PubMed1999

Ingestion of chilli pepper (Capsicum annuum) reduces salicylate bioavailability after oral asprin administration in the rat.

The bioavailabilities of aspirin (acetylsalicylic acid) and of salicylic acid were studied in male Wistar rats after acute and chronic administration of a Capsicum annuum extract, containing 100 mg of capsaicin per gram. With a single administration of 100 mg/kg of the extract, aspirin blood levels remained unchanged, but salicylic acid bioavailability was reduced in 44% compared with control animals. With a single administration of 300 mg/kg of the extract, aspirin blood levels were undetectable while salicylic acid bioavailability was reduced in 59%. Chronic administration once daily for 4 weeks of 100 and 300 mg/kg of the extract resulted in undetectable aspirin blood levels, while salicylic acid bioavailability was reduced in 63 and 76%, respectively, compared with controls. Results show that Capsicum ingestion reduces oral drug bioavailability, likely as a result of the gastrointestinal effects of capsaicin.

Administration, Oral↗