Absorption and disposition kinetics of chlorothiazide in protein-calorie malnutrition

Parameterization of small intestinal water volume using PBPK modeling

To facilitate accurate predictions of oral drug disposition, mechanistic absorption models require optimal parameterization. Furthermore, parameters should maintain a biological basis to establish confidence in model predictions. This study will serve to calculate an optimal parameter value for small intestinal water volume (SIWV) using a model-based approach. To evaluate physiologic fidelity, derived volume estimates will be compared to experimentally-based SIWV determinations. A compartmental absorption and transit (CAT) model, created in Matlab-Simulink®, was integrated with a whole-body PBPK model, developed in PK-SIM 5.2®, to provide predictions of systemic drug disposition. SIWV within the CAT model was varied between 52.5mL and 420mL. Simulations incorporating specific SIWV values were compared to pharmacokinetic data from compounds exhibiting solubility induced non-proportional changes in absorption using absolute average fold-error. Correspondingly, data pertaining to oral administration of acyclovir and chlorothiazide were utilized to derive estimates of SIWV. At 400mg, a SIWV of 116mL provided the best estimates of acyclovir plasma concentrations. A similar SIWV was found to best depict the urinary excretion pattern of chlorothiazide at a dose of 100mg. In comparison, experimentally-based estimates of SIWV within adults denote a central tendency between 86 and 167mL. The derived SIWV (116mL) represents the optimal parameter value within the context of the developed CAT model. This result demonstrates the biological basis of the widely utilized CAT model as in vivo SIWV determinations correspond with model-based estimates.

Pharmacokinetic changes in drugs during protein-calorie malnutrition: correlation between drug metabolism and hepatic microsomal cytochrome p450 isozymes

The rats with protein-calorie malnutrition (PCM, 5% casein diet for a period of 4-week) were reported to exhibit 60 and 80% suppression in the hepatic microsomal cytochrome P450 (CYP) 1A2 and CYP2C11 levels, respectively, and 40-50% decreases in CYP2E1 and CYP3A1/2 levels compared to control (23% casein diet for a period of 4-week) based on Western blot analysis. In addition, Northern blot analysis showed that CYP1A2, CYP2E1, CYP2C11, and CYP3A1/2 mRNAs decreased in the state of PCM as well. Hence, pharmacokinetic changes of the drugs in rats with PCM [especially the area under the plasma concentration-time curve from time zero to time infinity (AUC) changes of metabolite(s)] reported from literatures were tried to explain in terms of CYP isozyme changes in the rats. Otherwise, the time-averaged nonrenal clearance (CL NR) of parent drug was compared. Pharmacokinetic changes of the drugs in other types of malnutritional state, such as kwashiorkor and marasmus, in both human and animal models were also compared. The drugs reviewed are as follows: diuretics, antibiotics, anticancer agents, antiepileptics, antiarrythmics, analgesics, xanthines, antimalarials, and miscellaneous.

Effects of diet on sensitization to cocaine-induced stereotypy in female rats

The progressive increase in cocaine-induced stereotyped behavior that accompanies repeated cocaine injections (sensitization) was examined in rats consuming different diets. Adult female Sprague-Dawley rats were fed one of three diets: low protein (6% casein), adequate protein (25% casein), or a standard chow diet. Following 1 week of adaptation to the diets, the rats were injected every 3-4 days with either cocaine (30 mg/kg, IP) or saline, and the total amount of stereotypy was measured over a 90-min interval following each of four injections. Cocaine-induced stereotypy peaked at 40-50 min following each injection, after which it declined for all diet groups. With repeated injections, the total amount of stereotypy increased in all diet groups. By the fourth injection, the low protein diet group (6% casein) exhibited a slower onset and a possibly prolonged duration of cocaine-induced stereotypy when compared with the two adequate protein diet groups (25% casein and chow). Interestingly, the rats in the two purified diet groups (6% casein and 25% casein) exhibited significantly more stereotypy across injections than those in the chow diet group. Weight differences did not explain the differences in stereotypy present among the diet groups. This study concludes that diet significantly alters the pattern of cocaine-induced stereotypy in female rats, especially after repeated exposure.

Malnutrition and reactivity to drugs acting in the central nervous system

There is a well-established body of data demonstrating that protein or protein-calorie malnutrition experienced early in life is associated with neuroanatomical, neurochemical, as well as behavioral alterations in both animals and humans. A number of studies has focused on the following question: are the neuroanatomical and/or neurochemical changes produced by early malnutrition responsible for the altered behaviors reported in malnourished animals? A tool that has been used to help answer this question is the administration of drugs with specific actions in the various neurotransmitter systems in the central nervous system (CNS). This neuropharmacological approach has produced a considerable amount of data demonstrating that malnourished animals react to drugs differently from controls, suggesting that the altered behavioral expression of these animals could be partly explained by the alterations in the brain function following malnutrition. The present review will provide an overview of the literature investigating the reactivity of malnourished animals to psychoactive drugs acting through GABAergic, catecholaminergic, serotonergic, opioid and cholinergic neurotransmitter systems. Altered responsiveness to psychoactive drugs in malnourished animals may be especially relevant to understanding the consequences of malnutrition in human populations.