The influence of age on renal and extrarenal effects of frusemide

Tubuloglomerular Feedback in Renal Glucosuria: Mimicking Long-term SGLT-2 Inhibitor Therapy

A patient with renal glucosuria due to a congenital knock-out of the sodium-glucose cotransporter 2 (SGLT-2) protein because of a compound heterozygous mutation in the SLC5A2 gene may provide a natural model mimicking the effects of long-term SGLT-2 inhibitor therapy, which has been shown to exert kidney-protective effects beyond its antidiabetic properties. One possible mechanism for the protective effects of SGLT-2 inhibitor therapy might be the activation of tubuloglomerular feedback by increased outflow of sodium, chloride, and glucose to distal parts of the nephron, including the macula densa. Subsequently, afferent arteriolar vasoconstriction is induced and blood flow, intraglomerular filtration pressure, and glomerular filtration rate (GFR) all decline. However, prolonged tubuloglomerular feedback activation could change the sensitivity of tubuloglomerular feedback and hence decrease the beneficial effects of SGLT-2 inhibition on kidney function. Tubuloglomerular feedback is mediated by the Na⁺/K⁺/2Cl⁻ cotransporter. Hence furosemide, which blocks this cotransporter, is a medical option to test tubuloglomerular feedback because GFR should increase after administration of this loop diuretic. In our patient with long-term activated tubuloglomerular feedback due to SGLT-2 mutations, we show that the sensitivity of tubuloglomerular feedback is maintained, demonstrated by an increase in GFR measured using iohexol clearance following furosemide administration. This observation supports the idea that long-term SGLT-2 inhibitor therapy is kidney protective through a functional tubuloglomerular feedback.

Everything we always wanted to know about furosemide but were afraid to ask

Furosemide is a widely used, potent natriuretic drug, which inhibits the Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-2 in the ascending limb of the loop of Henle applied to reduce extracellular fluid volume expansion in heart and kidney disease. Undesirable consequences of furosemide, such as worsening of kidney function and unpredictable effects on sodium balance, led to this critical evaluation of how inhibition of NKCC affects renal and cardiovascular physiology. This evaluation reveals important knowledge gaps, involving furosemide as a drug, the function of NKCC2 (and NKCC1), and renal and systemic indirect effects of NKCC inhibition. Regarding renal effects, renal blood flow and glomerular filtration rate could become compromised by activation of tubuloglomerular feedback or by renin release, particularly if renal function is already compromised. Modulation of the intrarenal renin angiotensin system, however, is ill-defined. Regarding systemic effects, vasodilation followed by nonspecific NKCC inhibition and changes in venous compliance are not well understood. Repetitive administration of furosemide induces short-term (braking phenomenon, acute diuretic resistance) and long-term (chronic diuretic resistance) adaptations, of which the mechanisms are not well known. Modulation of NKCC2 expression and activity in kidney and heart failure is ill-defined. Lastly, furosemide's effects on cutaneous sodium stores and on uric acid levels could be beneficial or detrimental. Concluding, a considerable knowledge gap is identified regarding a potent drug with a relatively specific renal target, NKCC2, and renal and systemic actions. Resolving these questions would increase the understanding of NKCCs and their actions and improve rational use of furosemide in pathophysiology of fluid volume expansion.

Pharmacodynamics in older adults: a review

BACKGROUND

Older individuals experience physiologic changes in organ function related to aging or to specific disease processes. These changes can affect drug pharmacodynamics in older adults.

OBJECTIVE

The goal of this article was to review age-related changes in pharmacodynamics and their clinical relevance.

METHODS

PubMed and International Pharmaceutical Abstracts were searched (January 1980-June 2006) for the following combination of terms: pharmacodynamic and elderly, geriatric or aged. References cited in other reviews were also evaluated. The current review focused on age-related pharmacodynamic changes in agents affecting the central nervous system (CNS), cardiovascular, and endocrine functions.

RESULTS

Older adults frequently demonstrate an exaggerated response to CNS-active drugs. This is in part due to an underlying age-related decline in CNS function and in part due to increased pharmacodynamic sensitivity for some benzodiazepines, anesthetics, and opioids. The most important pharmacodynamic differences with age for cardiovascular agents are the decrease in effect for beta-adrenergic agents. This decline in response in vascular, cardiac, and pulmonary tissue may be due to a decrease in Gs protein interactions. Most studies indicate there is no decrease in cx-receptor sensitivity with age. Angiotensin-converting enzyme inhibitors do not show age-related differences in elderly patients. With the dihydropyridine calcium channel blockers, there was a slight increase in effect for older adults, but this was only for treatment-naive patients and was transient. Nondihydropyridines did not show an age- associated change in pharmacodynamic effect; however, in the elderly, there appeared to be a decrease in the PR interval prolongation normally seen with these agents. Studies of diuretics indicated that the changes in diuretic and natriuretic effects seen in the elderly were associated with pharmacokinetic changes and were not pharmacodynamic in nature. There was a lack of consistent evidence regarding whether sulfonylureas show age-related changes in pharmacodynamic effect.

CONCLUSIONS

There is a general trend of greater pharmacodynamic sensitivity in the elderly; however, this is not universal, and these age-related changes must be investigated agent-by-agent until further research yields greater understanding of the molecular mechanisms underlying the aging process.

Hyponatremia and Arginine Vasopressin Dysregulation: Mechanisms, Clinical Consequences, and Management

Hyponatremia, the most common electrolyte disorder, occurs frequently in older people and in hospitalized patients. Physiological changes of aging that interact with diseases and drugs commonly present in older people put this population at greater risk for hyponatremia. It can accompany central nervous system disorders, pulmonary and renal disease, cancer, congestive heart failure, and liver cirrhosis, as well as many commonly used drugs. Delayed recognition can lead to symptomatic hyponatremia with consequent cerebral edema and possibly irreversible neurological damage. Symptoms and signs of hyponatremia may be subtle or not attributed to hyponatremia. Most cases are of the euvolemic type, in which extracellular fluid volume is normal and is often due to the syndrome of inappropriate secretion of antidiuretic hormone. Hyponatremia can also occur in association with hypervolemia or hypovolemia. Common to all of these circumstances is increased secretion of arginine vasopressin (AVP). Understanding of the pathophysiological basis of hyponatremia and of brain compensatory mechanisms is critical to safe treatment. Fluid restriction or infusion of hypertonic saline can improve symptoms and normalize serum sodium levels but does not address excess AVP, which in most cases is the underlying cause of the disorder. A major new approach to treatment of hyponatremia is the development of aquaretics: AVP-receptor antagonists that provide a targeted therapeutic approach to correcting the many kinds of hyponatremia caused by excess AVP levels.

Pharmacokinetics in older persons

BACKGROUND

Physiologic changes and disease-related alterations in organ function occur with aging. These changes can affect drug pharmacokinetics in older persons.

OBJECTIVE

This article reviews age-related changes in pharmacokinetics and their clinical relevance.

METHODS

A PubMed search was conducted using the terms elderly and pharmacokinetics. Other reviews were also included for literature searching. The review includes literature in particular from 1990 through April 2004. Some articles from before 1990 were included to help illustrate principles of age-related pharmacokinetics.

RESULTS

There are minor changes in drug absorption with aging. The effect of aging on small-bowel transporter systems is not yet fully established. Bioavailability of highly extracted drugs often is increased with age. Transdermal absorption may be delayed, especially in the case of water-soluble compounds. Fat-soluble drugs may distribute more widely and water-soluble drugs less extensively in older persons. Hepatic drug metabolism shows wide interindividual variation, and in many cases, there is an age-related decline in elimination of metabolized drugs, particularly those eliminated by the cytochrome enzyme system. Any decrement in cytochrome enzyme metabolism appears nonselective. Synthetic conjugation metabolism is less affected by age. Pseudocapillarization of the sinusoidal endothelium in the liver, restricting oxygen diffusion, and the decline in liver size and liver blood flow may influence age-related changes in rate of hepatic metabolism. Frailty, physiological stress, and illness are important predictors of drug metabolism in older individuals. Inhibition of drug metabolism is not altered with aging, but induction is reduced in a minority of studies. Renal drug elimination typically declines with age, commensurate with the fall in creatinine clearance. Renal tubular organic acid transport may decline with age, while the function of the organic base transporter is preserved but may be less responsive to stimulation.

CONCLUSION

Changes in pharmacokinetics occur due to age-related physiologic perturbations. These changes contribute to altered dose requirements in older persons, particularly in the case of drugs eliminated by the kidney. Interindividual variation, disease, frailty, and stress may overshadow age-related changes.

Cardiovascular Drug Therapy in Elderly Patients

An increasing number of elderly patients are exposed to cardiovascular drugs for the treatment of acute and/or chronic conditions. This is a result of the progressive aging of the population, a common feature in most industrialised countries, and an improvement in primary and secondary cardiovascular prevention strategies with increased survival rates. Traditionally, most elderly patients receiving cardiovascular drugs had advanced cardiac, liver and kidney disease that significantly influenced drug pharmacokinetic and pharmacodynamic parameters. Currently, however, many patients without significant organ impairment receive cardiovascular therapy for primary or early secondary prevention (i.e. increased vascular risk, asymptomatic left ventricular dysfunction, poststroke phase, type 2 diabetes mellitus), highlighting the need for a better understanding of specific age-related pharmacokinetic and pharmacodynamic effects. A systematic review has been conducted on the specific effects of aging, in the absence of major co-morbidities, on the pharmacokinetic and pharmacodynamic properties of traditional and newer cardiovascular drugs. Currently, the evidence available is poor or nonexisting for several drugs and mainly derived from very small and underpowered studies, thus limiting data interpretation. In particular, there is very little information on patients >80 years of age, thus raising important concerns about the correct use of these drugs in this constantly growing population.

Age-related changes in pharmacokinetics and pharmacodynamics: basic principles and practical applications

Advancing age is characterized by impairment in the function of the many regulatory processes that provide functional integration between cells and organs. Therefore, there may be a failure to maintain homeostasis under conditions of physiological stress. The reduced homeostatic ability affects different regulatory systems in different subjects, thus explaining at least partly the increased interindividual variability occurring as people get older. Important pharmacokinetic and pharmacodynamic changes occur with advancing age. Pharmacokinetic changes include a reduction in renal and hepatic clearance and an increase in volume of distribution of lipid soluble drugs (hence prolongation of elimination half-life) whereas pharmacodynamic changes involve altered (usually increased) sensitivity to several classes of drugs such as anticoagulants, cardiovascular and psychotropic drugs. This review focuses on the main age-related physiological changes affecting different organ systems and their implications for pharmacokinetics and pharmacodynamics of drugs.

Drug dosage in the elderly. Is it rational?

Pharmacotherapy in the elderly requires an understanding of the age-dependent changes in function and composition of the body. Aging is characterised by a progressive loss of functional capacities of most if not all organs, a reduction in response to receptor stimulation and homeostatic mechanisms, and a loss of water content and an increase of fat content in the body. The most important pharmacokinetic change in old age is a decrease in the excretory capacity of the kidney; in this regard, the elderly should be considered as renally insufficient patients. The decline in the rate of drug metabolism with advancing age is less marked. In addition, the volume of distribution and the oral bioavailability of drugs may be changed in the elderly compared with younger individuals. Average dosage adjustments for the aged can be derived from simple equations and mean pharmacokinetic parameters from older and younger adults. However, these average dose adjustment factors neglect the large variation in the decline in organ functions among the elderly. Individual dose adjustment factors can be obtained from the drug clearance in a particular patient, where clearance/fractional bioavailability (CL/f) may be calculated from the area under the plasma concentration-time curve (AUC) of the drug in question. Using pharmacokinetic guidelines for dose adjustments, the same plasma drug concentrations result in elderly as in younger adults. However, we are frequently confronted with pharmacodynamic changes in old age which alter the sensitivity to drugs, irrespective of changes in drug disposition. For instance, the sensitivity of the cardiovascular system to beta-adrenergic agonists and antagonists decreases in old age and the incidence of orthostatic episodes in response to drugs that lower blood pressure is increased. The CNS is especially vulnerable in the elderly; agents that affect brain function (anaesthetics, opioids, anticonvulsants, psychotropic drugs) must be used very cautiously in this age group. The increased responsiveness to drugs in the elderly renders the measurement of drug plasma concentrations an attractive method to monitor pharmacotherapy in this age group. Sensitive technology to quantitatively determine plasma drug concentrations is available. However, optimal therapeutic plasma concentrations have not been established for most drugs in the elderly. Investigations concerning drug pharmacokinetic-pharmacodynamic relationships in the aged are an important area of future work in clinical pharmacology.

Drug-induced orthostatic hypotension in older patients

Orthostatic hypotension occurs in 10 to 30% of the elderly. In several studies it has been linked to recurrent falls and syncope. Generally, it has multiple causes, of which autonomic dysfunction plays an important role in elderly people. Very often orthostatic hypotension is induced by the use of drugs. In other cases, it is already present subclinically, and is worsened by the use of drugs to become symptomatic. For most drugs, changing pharmacokinetics result in a delayed elimination and/or in a greater bioavailability in the elderly. This results in a more pronounced effect for drugs with a desired hypotensive action [e.g. diuretics, calcium channel blockers, beta-blockers, angiotensin converting enzyme (ACE) inhibitors]. For those drugs in which hypotension is a known but unwanted adverse effect (e.g. nitrates, anti-Parkinsonian drugs, antidepressants, antipsychotics), responses will be greater in the elderly and orthostatic hypotension will occur more frequently. For elderly people, doses have to be reduced and/or the dose intervals prolonged in order to avoid such adverse reactions.

Pharmacokinetics and pharmacodynamics of the diuretic bumetanide in the elderly

In a cross-sectional study of the pharmacokinetics and pharmacodynamics of peroral and intravenous bumetanide (0.5 mg, single dose), total and renal clearance of the diuretic was significantly lower in elderly persons than in young adults, resulting in higher bumetanide plasma levels in the aged. Nonrenal clearance, bioavailability, and the volume of distribution were not significantly changed. Together with the decreased delivery into the urine the diuretic and natriuretic effect of bumetanide was reduced in the elderly. Renal clearance of bumetanide was linearly related with creatinine clearance, hence the decreases in bumetanide clearance and diuretic efficacy in the elderly are attributed to the age-dependent decline in renal function. The bumetanide concentration in urine and the fractional sodium excretion were not different in the two age groups, suggesting that the decrease in diuretic response in the elderly is a result of a reduction in the number of functioning nephrons, whereas the response of the remaining nephrons to bumetanide is unaltered.

A comparison of three diuretic regimens in heart failure

Eight patients with mild heart failure were treated in random order for 1 week with 2 mg bumethanide at 0800 and 1200 (treatment 1) h, 1 mg bumethanide at 0800, 1200, 1800, 2200 (treatment 2) and 5 mg bendroflumethiazide at 0800 and 1800 (treatment 3) h. The 'quality of life' did not differ significantly between the three treatment periods. At the presumed trough of the diuretic effect the circulating blood volume was largest during treatment 1; it was 6.3% smaller during treatment 2 (P < 0.02) and 6.7% lower during treatment 3 (P < 0.05). In comparison with treatment 1, the maximal increase in rate-pressure product during physical exercise was 24.6% higher in treatment 3. Compared with treatment 1 the area under the curve (AUC) for plasma lactate during physical exercise was 14% lower during treatment 2 (P < 0.05) and 18% lower during treatment 3 (P < 0.01). These findings suggest that the type of program for diuretic therapy influences the magnitude of inevitable diurnal fluctuations in body fluids, the ability of the heart to work and the ability of the body to adjust to the oxygen demand.

Physiological changes due to age. Implications for cardiovascular drug therapy

Cardiovascular disease is the single largest cause of death in the elderly. Many of the published studies concerning the physiology and pharmacology of the aging cardiovascular system are seriously flawed. Problems include failure to measure the drug bioavailability and the selection of subjects with overt or subclinical disease. With exercise, the rise in heart rate is inversely proportional to age and maximum heart rate is reduced. Baroreceptor reflex activity appears to decline with age. Cardiac output is maintained in the elderly, with a slower heart rate and a greater stroke volume than in the young. Plasma noradrenaline (norepinephrine) levels increase in the elderly but there is no change in the sensitivity of the vasoconstrictor alpha 1-adrenoceptor. There is evidence for a decline in the activity of the vasodilator beta 2-adrenoceptor with age. It is difficult to make general rules about the effect of aging on the disposition and elimination of drugs. Each drug must be tested separately.

Furosemide kinetics and dynamics in rats and humans

1. Increasing doses of furosemide (F) were given intravenously to rats and humans and initial pharmacokinetics and pharmacodynamics were compared. 2. Weight-related initial renal excretion rate of F was twice as high in rats and serum concentration at 30 min was twice as high in humans (P less than 0.01). 3. Volume of distribution for F was 44% larger in rats (P less than 0.01). 4. Maximal weight-related diuretic and natriuretic responses were, like the theoretical maximal efficiency, 5-6 times higher in the rat. The potency was 230 times lower in the rats. 5. On a molecular basis species differences in kinetics disappeared when standardization was based on ERPF and species differences in dynamics disappeared when standardization was based on GFR.

Effects of aging on responses to furosemide

Furosemide causes both diuretic and non-diuretic changes in renal function. We compared responses to intravenous furosemide 0.5 mg.kg-1 in 38 subjects (30 males, 8 females) aged 18 to 30 with those in 14 subjects (9 males, 5 females) aged 50 and over. There were no consistent differences attributable to gender. Older persons showed greater natriuresis (47 percent in males and 26 percent in females) but their increment in plasma renin activity was markedly reduced. The urinary excretion of thromboxane B2 was elevated in older subjects (58 +/- 10 vs. 30 +/- 4 ng/4 h, p less than 0.05 for males; 48 +/- 7 vs. 29 +/- 4 ng/4 hr, p less than 0.05 for females) while that of 6-keto prostaglandin F1 alpha was not different. While differences in the diuretic response to furosemide may be due to pharmacokinetic differences, the non-diuretic response differences may reflect age related changes in renal prostaglandin synthesis.

Furosemide pharmacokinetics and pharmacodynamics in health and disease--an update

The literature on furosemide pharmacokinetics and pharmacodynamics is critically reviewed, concentrating on those papers published subsequent to the 1979 reviews of this topic. Intravenous and oral data are presented for healthy volunteers and for patients with various disease states. It is the latter populations about which the majority of the studies have been published since 1979. Inter- and intraindividual variations in bioavailability are discussed, as are data on the metabolism of furosemide to its glucuronide conjugate. Published studies examining the relationship between furosemide pharmacodynamics and pharmacokinetics are also evaluated. The literature is reviewed through June 1988.

Plasma protein binding of furosemide in the elderly

The protein binding of furosemide was investigated in plasma from 22 old and 11 young subjects by equilibrium dialysis. The unbound fraction of furosemide was 3.16% in plasma from the elderly and 1.7% in plasma from the young. A significant correlation was found between the unbound fraction of furosemide and the plasma concentration of albumin. The average number of binding sites was 3.8 (elderly) and 2.7 (young) 10(-6) mol/g albumin. The average association constant (K) was 4.3 (elderly) and 4.2 (young) 10(5) M-1. By increasing the concentration of furosemide up to 200 micrograms/ml buffer the unbound fraction of the drug rose to 5.2% (elderly) and 3.5% (young).

The elderly patient. A special case for diuretic therapy

Diuretics are among the most widely prescribed drugs, especially for the elderly with cardiac failure or hypertension. Progressive structural and functional changes occur in the kidneys after the fourth decade, leading to impairment of the ability of the kidneys to handle sodium, water and solutes. The renal reserves of the elderly are about half those of the young. In addition, the renin-aldosterone system shows reduced activity in old age. The pharmacokinetics and pharmacodynamics of diuretics in the elderly are reviewed, and the influence of congestive cardiac failure is emphasised with regard to the kinetics of diuretics and the deleterious effect of diuretic-induced hypokalaemia and hypomagnesaemia on the pharmacology of digoxin. Guidelines are suggested for the use of diuretics in the elderly, including the avoidance of unnecessary use, the careful choice of diuretic used, the need for small initial doses, and the prevention of hypokalaemia. The place of potassium-sparing agents for the elderly and adverse effects of diuretics, either mechanical, metabolic or toxic are discussed. Mechanical problems are related to the rate and volume of urine produced, and the resulting effects on bladder function and on blood volume. Although toxic effects are relatively rare, metabolic effects include electrolyte changes, impairment of glucose tolerance, and increased serum uric acid and lipids. Most of these adverse effects are preventable by careful management; the consensus is that they are not of sufficient clinical significance to outweigh the long record of efficacy and safety of diuretic therapy in the elderly. Diuretics will, and should, continue to be used extensively in elderly patients with hypertension and/or cardiac failure.

Resistance to loop diuretics. Why it happens and what to do about it

Resistance to loop diuretics is often encountered clinically. Studies in healthy subjects have shown that overall response to loop diuretics depends upon the interplay between the total amount of drug reaching the urine, the time course of its entry into urine and the pharmacodynamics of response to diuretic in the urine. The mechanism by which diuretic resistance occurs has been elucidated in several clinical conditions. Treatment with inhibitors of prostaglandin synthesis has no effect on diuretic appearance in urine but blunts response by blocking the increase in renal blood flow produced by loop diuretics. In the elderly and in patients with moderate renal insufficiency, the mechanism of resistance appears to be purely pharmacokinetic, involving altered access of diuretic into the urine. In contrast, patients with nephrotic syndrome and hepatic cirrhosis manifest a purely pharmacodynamic form of resistance: in nephrosis, diuretic may bind to protein in the urine; in cirrhosis the mechanism of resistance is unclear. Lastly, in patients with congestive heart failure, with intravenous administration, resistance represents a pharmacodynamic phenomenon. With oral administration, however, the time course but not the extent of absorption is altered; consequently, in this setting, both pharmacokinetic and pharmacodynamic changes may contribute to the subnormal response. Strategies for overcoming resistance to loop diuretics in patients receiving NSAIDs or those with renal disease, hepatic cirrhosis or congestive heart failure include one or more of: increasing the dose size; administering frequent 'small' (but effective) doses; continuous intravenous infusion of the diuretic; or concomitant administration of another diuretic such as metolazone or hydrochlorothiazide.

Renal, haemodynamic, and hormonal effects of human alpha atrial natriuretic peptide in healthy volunteers

The effects of atrial natriuretic peptide (ANP) were investigated in six healthy male volunteers taking a constant diet (120 mmol sodium and 60 mmol potassium daily). They were given an intravenous bolus of 100 micrograms human alpha-ANP on one day or placebo on another day 1-3 weeks apart in a double-blind randomised study. After ANP, urinary sodium excretion increased four-fold, and urine volume, calcium, magnesium, and phosphorus excretion doubled within 30 min of the injection. ANP induced an immediate fall in arterial pressure, followed by a longer vasodepressor phase which exceeded the duration of the effect on electrolyte excretion. There were no significant changes in plasma renin activity, aldosterone, antidiuretic hormone, or noradrenaline when compared with placebo.