Metabolic basis of drug interactions in the intensive care unit

Acute kidney injury induced by antimicrobial agents in the elderly: awareness and mitigation strategies

The use of antimicrobial agents has increased in recent years as treatments have diversified and resistant bacteria have appeared. With increased use of antimicrobial agents, elderly patients are prone to adverse drug reactions (ADRs) as a result of factors such as drug-drug interactions, polypharmacy, long-term use, and over- or under-dosage. In particular, elderly patients using antimicrobials are at increased risk to develop drug-induced acute kidney injury (AKI), which is the most common severe ADR in such patients. AKI is a serious problem that is associated with mortality amongst hospitalized patients. Antimicrobial-induced AKI can be classified into three different types: acute tubular necrosis (ATN), acute interstitial nephritis (AIN), and renal tubule lumen obstruction. AKI can generally be prevented by proper maintenance of fluid balance. To design dosage regimens that ensure efficient drug excretion via the kidney, it is necessary to accurately estimate renal function; however, the kidney undergoes age-dependent structural and functional alterations over time. Therefore, proper management of antimicrobial agents by an antimicrobial stewardship team may lead to decreased incidence of AKI. This article reviews antimicrobial-induced AKI and discusses potential strategies for increasing awareness of AKI and mitigating its clinical effects.

Pharmacology of morphine in obese patients: clinical implications

Morphine is an analgesic drug used to treat acute and chronic pain. Obesity is frequently associated with pain of various origins (e.g. arthritis, fibromyalgia, cancer), which increases the need for analgesic drugs. Obesity changes drug pharmacokinetics, and for certain drugs, specific modalities of prescription have been proposed for obese patients. However, scant data are available regarding the pharmacokinetics and pharmacodynamics of morphine in obesity. Prescription of morphine depends on pain relief but the occurrence of respiratory adverse effects correlates with obesity, and is not currently taken into account. Variations in the volume of distribution, elimination half-life and oral clearance of morphine, as well as recent advances in the respective roles of drug-metabolizing enzymes, catechol-O-methyltransferase and the mu opioid receptor in morphine pharmacokinetics and pharmacodynamics, may contribute to differences between obese and non-obese patients. In addition, drug-drug interactions may alter the disposition of morphine and its glucuronide metabolites, which may either increase the risk of adverse effects or reduce drug efficacy.

Mini-series: I. Basic science. Uncertainty and inaccuracy of predicting CYP-mediated in vivo drug interactions in the ICU from in vitro models: focus on CYP3A4

Drug-drug interactions (DDIs) contribute significantly to the incidence of adverse drug reactions. Important advances in the knowledge of human drug-metabolizing enzymes have fueled the integration of in vitro drug metabolism and clinical DDIs studies for use in drug development programs and in the clinical setting. The activity of cytochrome P450 (CYP) 3A4 and P-glycoprotein are critical determinant of drug clearance, interindividual variability in drug disposition and clinical efficacy, and appears to be involved in the mechanism of numerous clinically relevant DDIs. Cell-based in vitro models are being increasingly applied in elucidating the pharmacokinetic profile of drug candidates during the preclinical steps of drug development. Human liver, intestinal samples and recombinant human CYP3A4 are now readily available as in vitro screening tools to predict the potential for in vivo DDIs. Although it is easy to determine in vitro metabolic DDIs, the interpretation and extrapolation of in vitro interaction data to in vivo situations requires a good understanding of pharmacokinetic principles. Clinicians and pharmacokineticists should recognize that in vitro models may not be clinically relevant in all situations. In the current article, research will be presented on drug metabolism and DDIs along with examples illustrating the utility of specific in vitro or in vivo approaches. In addition, the impact and clinical relevance of complexities such as dosing-route dependent effects, multi-site kinetics of drug-metabolizing enzymes and non-CYP determinants of metabolic clearance will be addressed.

Assessing & preventing medication interactions

The use of multiple drugs to treat medical conditions has become a common practice that significantly increases the risk of drug interactions.This article describes three types of drug interactions by clarifying how these occurrences transpire within the body. Practical strategies for preventing drug interactions are provided.