Food: An Unrecognized Source of Loop Diuretic Resistance

Drug administration via feeding tubes-a procedure that carries risks: systematic identification of critical factors based on commonly administered drugs in a cohort of stroke patients

PURPOSE

Drug administration via feeding tubes is considered a process with many uncertainties. This review aimed to give a comprehensive overview of data available on feeding tube application and to carry out risk assessments for drug substances commonly administered to stroke patients.

METHODS

Drugs frequently administered via feeding tubes were identified through a retrospective analysis of discharge letters from a stroke unit. Physicochemical, pharmacokinetic, and stability properties of these drugs and data on drug-enteral nutrition interactions were systematically searched for in the European Pharmacopoeia, Hagers Handbook of Pharmaceutical Practice, Birchers clinical-pharmacological data compilation, and the Martindale Complete Drug Reference, as well as from databases including DrugBank, DrugDex, PubChem, Google Scholar, and PubMed.

RESULTS

Of the drugs most commonly administered via feeding tubes in the present stroke patient cohort, bisoprolol, candesartan, and ramipril could be considered the least critical due to their overall favourable properties. Acetylsalicylic acid, amlodipine, hydrochlorothiazide, omeprazole and esomeprazole, simvastatin, and torasemide pose risks based on pH or light-dependent instability or proposed food effects. The most critical drugs to be administered via feeding tubes are considered to be furosemide, levodopa, and levothyroxine as they show relevant instabilities under administration conditions and substantial food effects; the latter two even possess a narrow therapeutic index. However, little information is available on drug-tube and drug-formula interactions.

CONCLUSION

Feeding tube administration of medications turned out to be a highly complex process with several unmet risks. Therefore, investigations that systematically assess these risk factors using clinically relevant model systems are urgently needed.

Interplay of Breast Cancer Resistance Protein (Bcrp/Abcg2), Sex, and Fed State in Oral Pharmacokinetic Variability of Furosemide in Rats

Poor and variable oral bioavailability of furosemide (FUR) presents critical challenges in pharmacotherapy. We investigated the interplay of breast cancer resistance protein (Bcrp)-mediated transport, sex, and fed state on FUR pharmacokinetics (PK) in rats. A crossover PK study of FUR (5 mg/kg, oral) was performed in Sprague-Dawley rats (3 males and 3 females), alone or with a Bcrp inhibitor, novobiocin (NOV) (20 mg/kg, oral), in both fed and fasted states. Co-administration of NOV significantly increased FUR extent (AUC) and rate (C_max) of exposure by more than two-fold, which indicates efficient Bcrp inhibition in the intestine. The female rats showed two-fold higher AUC and C_max, and two-fold lower renal clearance of FUR compared to the male rats. The latter was correlated with higher renal abundance of Bcrp and organic anion transporters (Oats) in the male rats compared to age-matched female rats. These findings suggest that the PK of Bcrp and/or Oat substrates could be sex-dependent in rats. Moreover, allometric scaling of rat PK and toxicological data of Bcrp substrates should consider species and sex differences in Bcrp and Oat abundance in the kidney. Considering that Bcrp is abundant in the intestine of rats and humans, a prospective clinical study is warranted to evaluate the effect of Bcrp inhibition on FUR PK. The potential confounding effect of the Bcrp transporter should be considered when FUR is used as a clinical probe of renal organic anion transporter-mediated drug-drug interactions. Unlike human data, no food-effect was observed on FUR PK in rats.

Current Clinical and Pharmacological Approaches to the Prescription of Loop Diuretics in Patients with Chronic Heart Failure

Heart failure (HF) is a growing public health problem with an estimated prevalence of 38 million patients worldwide. Congestion and formation of edema – are typical symptoms of heart failure. Diuretics are the mainstay of therapy in heart failure and are used to relieve congestion and improve exercise tolerance. Also, the administration of diuretics should be considered to reduce the risk of HF hospitalization. Loop diuretics are used by nearly 80% of all chronic HF patients and remain the drugs of choice. Although diuretics are one of the most prescribed classes of drugs, recommendations for their titration scheme for long-term use have not yet been finalized, nor have there been major prospective randomized controlled studies on the effect of diuretics on morbidity and mortality. A Cochrane meta-analysis has shown that in patients with chronic HF, loop and thiazide diuretics might reduce the risk of death and worsening of HF in comparison to placebo and could lead to improved exercise capacity. Guideline recommends the use lowest possible dose of diuretics due to probable electrolyte disturbances, further neurohormonal activation, accelerated kidney function decline, and symptomatic hypotension. Diuretic resistance is associated with an unfavorable prognosis and an increased risk of readmission. There are significant pharmacokinetic differences between the loop diuretics. Compared with furosemide, torasemide has a high bioavailability irrespective of food intake, and carries a longer half‐life and duration of effect; also, the benefits of torasemide are its additional anti-fibrotic and neurohormonal effects. Optimization of diuretic therapy in patients with HF remains a challenge and requires further research, as well as an individual approach to patients, since there is no convincing evidence base.

Relieving the tension in hypertension: Food-drug interactions and anti-hypertensive mechanisms of food bioactive compounds

Hypertension is a global health problem. Statistics report from the World Health Organization reveals its prevalence in about a quarter of the world global population. Due to the complications associated with hypertension, it is required to be well managed or prevented pharmacologically or non-pharmacologically. Pharmacologically, the major antihypertensive drugs used are centrally acting sympatholytic drugs, diuretics, vasodilators, angiotensin converting enzyme inhibitors, and angiotensin II receptor blockers while non-pharmacological means of management include lifestyle changes, intake of diet or supplements with antihypertensive effects. Interestingly, the use of diet as a complement with drug intake has become very popular due to occurring side effects over time. Recent research efforts have revealed that foods such as fruits and vegetables contain bioactive substances that modulate the activities of macromolecules involved in the development, complications, and management of hypertension. PRACTICAL APPLICATIONS: Recent research efforts have suggested the efficacy of diets rich in fruits and vegetables in the management of hypertension. This review examines some of the mechanisms involved in the dietary management or prevention of hypertension by bioactive compounds found in foods. This review promotes the use of diet in the management of the condition and also suggests that precautions to be taken in the combined use of food and drugs.

Cardiorenal Syndrome: Classification, Pathophysiology, Diagnosis, and Treatment Strategies: A Scientific Statement From the American Heart Association

Cardiorenal syndrome encompasses a spectrum of disorders involving both the heart and kidneys in which acute or chronic dysfunction in 1 organ may induce acute or chronic dysfunction in the other organ. It represents the confluence of heart-kidney interactions across several interfaces. These include the hemodynamic cross-talk between the failing heart and the response of the kidneys and vice versa, as well as alterations in neurohormonal markers and inflammatory molecular signatures characteristic of its clinical phenotypes. The mission of this scientific statement is to describe the epidemiology and pathogenesis of cardiorenal syndrome in the context of the continuously evolving nature of its clinicopathological description over the past decade. It also describes diagnostic and therapeutic strategies applicable to cardiorenal syndrome, summarizes cardiac-kidney interactions in special populations such as patients with diabetes mellitus and kidney transplant recipients, and emphasizes the role of palliative care in patients with cardiorenal syndrome. Finally, it outlines the need for a cardiorenal education track that will guide future cardiorenal trials and integrate the clinical and research needs of this important field in the future.

Dilemmas in the Dosing of Heart Failure Drugs: Titrating Diuretics in Chronic Heart Failure

Despite advances in medical therapy over the past few decades, the incidence of heart failure hospitalisation continues to rise. Diuretics are the most common therapy used to treat heart failure as they relieve congestion. However, there is a lack of guidance on how to best use these medications. Guidelines support the use of diuretics at the lowest clinically effective dose but do not specify a diuretic strategy beyond that. Here we review the diuretics available for treatment, potential mechanisms of diuretic resistance and ways to address this in the ambulatory setting, and review tools that have been developed to help guide diuretic use in the treatment of chronic heart failure.

Management of Cardio-Renal Syndrome and Diuretic Resistance

OPINION STATEMENT

Diuretic resistance in acute heart failure has emerged as a powerful predictor of adverse outcome, which is often independent of underlying glomerular filtration rate (GFR). Metrics of diuretic efficacy differ in their accuracy, convenience, and biological plausibility, which should be taken into account when interpreting their results. Loop diuretic efficacy depends on adequate delivery of both the pharmacological agent itself and its substrate (i.e., sodium chloride) to the loop diuretic site of action at the luminal side of the thick ascending limb of Henle's loop. This requires an adequate dosing strategy, with higher doses needed when GFR is low. Importantly, the kidneys are able only to regulate the effective circulatory volume. Thus, specific problems of intravascular volume depletion and poor cardiac output with impaired renal perfusion should be addressed. Addition of thiazide-type diuretics should be considered when a progressive decrease in loop diuretic efficacy is observed with prolonged use (i.e., the braking phenomenon). Furthermore, thiazide-type diuretics are a useful addition in patients with low GFR to maximally boost fractional sodium excretion when nephron perfusion is poor. However, thiazide-type diuretics limit free water excretion and should be withheld in cases of hypotonic hyponatremia. Mineralocorticoid receptor antagonists (MRA) and acetazolamide are interesting options to increase loop diuretic efficacy, but further study is needed to assess whether improved diuretic efficacy also translates into clinical outcome benefits. Finally, ultrafiltration should be considered in patients with refractory diuretic resistance as persistent volume overload after decongestive treatment is associated with worse outcomes. Whether more upfront use of individually tailored ultrafiltration is superior to pharmacological therapy remains to be shown by adequately powered randomized clinical trials.

Effect of hypouricaemic and hyperuricaemic drugs on the renal urate efflux transporter, multidrug resistance protein 4

BACKGROUND AND PURPOSE

The xanthine oxidase inhibitors allopurinol and oxypurinol are used to treat hyperuricaemia, whereas loop and thiazide diuretics can cause iatrogenic hyperuricaemia. Some uricosuric drugs and salicylate have a bimodal action on urate renal excretion. The mechanisms of action of these hypo- and hyperuricaemic drugs on the handling of urate in renal tubules have not been fully elucidated. Recently, we identified the multidrug resistance protein (MRP) 4 as a luminal efflux transporter for urate in the proximal tubule.

EXPERIMENTAL APPROACH

Here, we studied the effect of these drugs on [(14)C]urate transport using human embryonic kidney 293 cells overexpressing human MRP4 and in membrane vesicles isolated from these cells.

KEY RESULTS

Allopurinol stimulated MRP4-mediated cellular urate efflux and allopurinol and oxypurinol both markedly stimulated urate transport by MRP4 in membrane vesicles. Bumetanide and torasemide had no effect, whereas furosemide, chlorothiazide, hydrochlorothiazide, salicylate, benzbromarone and sulfinpyrazone inhibited urate transport, at concentrations ranging from nanomolar up to millimolar. Probenecid stimulated urate transport at 0.1 microM and inhibited transport at higher concentrations.

CONCLUSIONS AND IMPLICATIONS

These data suggest that inhibition of MRP4-mediated urate efflux by furosemide and thiazide diuretics could have an important function in their hyperuricaemic mechanisms. Furthermore, stimulation of MRP4-mediated renal urate efflux could be a new mechanism in the hypouricaemic action of allopurinol and oxypurinol. In conclusion, MRP4 may provide a potential target for drugs affecting urate homoeostasis, which needs to be further evaluated in vivo.