Pentoxifylline in renal disease, a tour through the literature

Tomorrow is another exciting edition of #NephJC. We will be discussing pentoxifylline in diabetic nephropathy. There is a summary of the article at

In support of that article and to aid the discussion, Christos Argyropoulos has stepped up to the blogger plate to provide some color on pentoxifylline.



In wild anticipation of next week’s #NephJC on Pentoxifylline (PTX)  let’s go over some of the known facts about the drug:
  • It is a non-selective phosphodiesterase inhibitor.  PDEs are enzymes that inactivate cyclic nucleotides and have been organized in 11 families (Table 1 [1]) based on sequence, structural and pharmacological considerations. Inhibition of PDE4 by PTX (Figure 1) [1] increases cAMP & stimulates PKA activity. 
  • Activation of PKA leads to phosphorylation of the cAMP response element binding protein (CREB) which in turn leads to suppression of the TNF-a[2,3] synthesis at the transcriptional level
  • Inhibition of cAMP production by these phosphodiesterases has a broad range of immunomodulatory effects (Table 2[1])
  • The drug also affects red cell deformability and favorably affects microcirculatory blood flow
  • “Mainstream” indications: intermittent claudication, vascular dementia, sickling crises, acute alcoholic hepatitis
  • Figure 1: Pentoxifylline (white) complexed with PDE4 (ribbons). Also shown are the Mg2+ and Zn2+ cofactors of PDE4 (spheres)
  • Pharmacokinetics: bioavailability (10-30%), elimination (mostly renal as 50-80% of the drug is recovered in the urine), half life (24-48 mins)
Table 1 Human PDE isozymes

Table 2 Effects of PDE inhibition on human inflammatory cells
 Pharmacological considerations would lead one to anticipate that PTX  will exert a favorable effect on diabetic (or any other form) of kidney disease, since: 
  1. PTX alters RBC deformability and improves microcirculation
  2. Acts as adenosine antagonist (and thus counters vasoconstriction)
  3. Possible decline in intraglomerular pressure decreasing hyperfiltration and proteinuria
  4. Anti-cytokine effects on MCP1[4], TNF, GFs for fibroblasts (CTGF through smad 3/4) 
  5. Antifibrogenic in rat models of CKD (remnant kidney, pyelo, crescentic GN Figure 2[5])
  6. In the streptozocin model of diabetic nephropathy prolonged use of PTX  was found to reduce renal inflammation (urinary MCP1 and monocytic infiltration in biopsies) and also proteinuria (Figure 3 [6])
  7. PTX may even be useful in optimizing renal allograft function after transplantation since it has been experimentally shown to:
  8. Protects from the acute (and possibly chronic) toxicity of calcineurin inhibitors (reviewed in [7])
  9. Decrease cyclosporing-induced renal endothelin release and vasoconstriction [8]
  10. It reduces the urinary levels of TNF-alpha, IL-6 and IL-10 [3,9] which are involved in the inflammatory response of renal allograft rejection
Figure 2 Effect of PTX treatment on accumulation of a-SMA+ myofibroblasts and collagen III in a rat model of crescentic GN
Figure 3 Effects of PTX on urinary cytokines and proteinuria in the streptozocin model of diabetic nephropathy
The non-clinical, experimental data supporting the use of PTX in renal fibrosis involve both diabetic and non-diabetic forms of disease and are summarized in Table 3. In all these studies PTX exhibited a strong anti-proteinuric effect, while inhibiting renal fibrosis and renal cytokine use [10]
Table 3 Animal studies of the antiproteinuric effects of PTX
What is the current clinical evidence supporting the use of PTX in various forms of renal disease?
Due to the inferred potential of PTX to amelioriate renal inflammation and fibrosis, there have been numerous, small studies in various renal conditions. 

Diabetic Kidney Disease

The role of PTX in diabetic nephropathy was recently examined in a Cochrane group meta-analysis[11] of 17 randomized controlled trials of 991 participants with diabetic kidney disease. The methodological quality of these studies was poor: only 4/17 reported the method of randomization, no study reported the method of allocation and only 9/17 were at low risk of bias.  
  • Compared with placebo, PTX reduced albuminuria, proteinuria and SBP/DBP. The effects on BP were seen in Type 1 but not Type 2 patients (Figure 4)
  • Compared with routine care, PTX reduced albuminuria and proteinuria, but did not affect creatinine or BP. Adverse effects were not increased by PTX (Figure 5)
  • In head to head comparisons of PTX v.s. ACEi (two studies) and clonidine/methyldopa (1 study): 
    • There was no significant difference in SCr, albuminuria, proteinuria, or blood pressure between pentoxifylline and the active comparator (captopril or clonidine/methyldopa) for patients with type 1 and type 2 DKD
    • CrCl was significantly increased when pentoxifylline was compared to clonidine and methyldopa (MD 10.90 mL/min, 95% CI -1.40 to 20.40) but not captopril (MD 3.26 mL/min, 95% CI -1.05 to 7.59).
Figure 4 Meta-analysis of studies of PTX v.s. placebo
Figure 5 Meta-analysis of studies of PTX v.s. routine care
Though somewhat promising, the limitations in the primary data sources led the Cochrane group authors to conclude: “Evidence to support the use of pentoxifylline for DKD was insufficient to develop recommendations for its use in this patient population. Rigorously designed, randomised, multicentre, large scale studies of pentoxifylline for DKD are needed to further assess its therapeutic effects.”
In the PREDIAN[12] , prospective, randomized, open-label study of patients with diabetic kidney disease due to type 2 diabetes and CKD stages 3-4, the use of PTX (1200mg/day) on top of Renin Angiotensin System Inhbitors (RASi) for two years resulted in 
  • slower  eGFR decline (by 4.3 ml/min/1.73m2 95%CI: 3.1-5.5 p less than 0.001)
  • decreased proteinuria
  • decreased urinary concentration of TNF-alpha

Non-diabetic forms of CKD

A small number of small studies with small follow up have been reported in the literature. Though no quantitative evidence synthesis has been undertaken, a qualitative appraisal of these studies (Table 4 [10]) suggests that PTX may reduce proteinuria and possibly stabilize eGFR. Among these studies, the one by Perkins was unique in examining the effects of PTX on the eGFR slope before and after the initiation of PTX (Figure 6 and Table 5). For pentoxifylline-treated participants, the mean estimated GFR decrease during treatment was slower compared with the year before study enrollment (−9.6 ± 11.9 mL/min/1.73 m2/y; mean difference, −8.4 mL/min/1.73 m2/y; 95% confidence interval, −14.8 to −2.1; P = 0.01). In that particular study, PTX had no effect on proteinuria.
Table 4 Clinical Studies of PTX in non-diabetic kidney disease

Figure 6 Effects of PTX on eGFR slope decline
Table 5 Effects of PTX v.s. placebo on eGFR slope[13]

General CKD

A single center-retrospective analysis from Taiwan, reported renal outcomes of PTX combined with ACEi/ARB v.s. ACEi/ARB in CKD stages 3b-5. In that study roughly 2/3 of patients received PTX and 21.5% of the study population developed ESRD over a median follow-up of 2.25 years. Though observational, the two groups of patients were well matched with respect to a large number of characteristics (age, gender, BMI, eGFR, BP, hemoglobin, anemia, Ca,P, uric acid, cholesterol, triglyceride and proteinuria) but not diabetes (there were more diabetics in the PTX group: 54.2 v.s. 44.6% p=0.02). Even though PTX did not reduce proteinuria at 1 year of follow-up, pts who received PTX and ACEi/ARB had a ~30% lower (HR 0.694, 95% CI: 0.498-0.968, p=0.031) adjusted (for age, gender, baseline eGFR, diabetes status, hypertension and baseline proteinuria) risk of developing ESRD relative to patients who received ACEi/ARB but no PTX. Interestingly enough, the effects of PTX appear to be limited in the group with baseline proteinuria (UPCR over 1g/g), in unadjusted (Figure 6, p=0.33 v.s. p=0.005) or adjusted analyses (HR: 0.602, 95%CI: 0.413-0.877 p=0.008)
Figure 7 Probability of renal survival in patients treated with PTX+ACEi/ARB v.s. ARB stratified on the basis of baseline proteinuria

Renal Transplantation

The utility of PTX in clinical renal transplantation was first reported more than 15 years ago [14]. In that study 140 consecutive patients who received a transplant between January 1993 and November 1994 were randomized in a double blinded fashion to receive PTX (starting with the induction of anesthesia) or placebo for at least 6 months after transplant. The immunosuppressive regimen used in that study involved induction with ALG/Steroids/Azathioprine and maintenance with Cyclosporine A either alone or in combination with azathioprine. Acute Rejection, Delayed Graft Function and patient survival rates did not differ in the two patient groups. The use of PTX appeared to be associated with improved renal outcomes in the patients who experienced an acute rejection episode (ACR) (Figure 8)
The actuarial, 1 year survival rates were: 
  • Control Group:  97% in the absence of rejection episode vs. 59% in patients with rejection, Log-Rank = 13.6 P less than 0.001). 
  • PTX Group:
    • 89.3% without vs. 
    • 72% with rejection; 
    • Log-Rank =2.3 (NS)
  • Between group comparisons stratified by ACR (positive or negative) and excluding pts who died or lost their graft in the first 3 months after transplantation: 
  • Pts with ACR: Log rank test : 6.66(P=0.01) 
  • Pts w/o  ACR: Log rank test : 1.8 (NS) 
Figure 8 Renal Outcomes in kidney transplant patients who received pentoxifylline v.s. placebo
More recently[15] the effects of PTX were reported in patients with biopsy proven CAN who had been on standard triple immune suppression (Steroid + calcineurin inhibitor + mycophenolate mofetil). In this single arm study the use of PTX was associated with a short lived (3 month) effect in reducing proteinuria. When individual data were examined 29.4% of patients responded with more than over 50% reduction in proteinuria, while 58.8% (10/17) of patients exhibited stable graft function.


Overall a number of studies have shown the potential utility of PTX in diabetic or non-diabetic kidney disease and renal transplantation. The majority of these studies were limited by number of participants, duration of follow-up and methodology, yet a consistent pattern of reduced proteinuria and possibly stabilization of the loss of renal function emerges. A number of studies have shown that TNF-alpha is implicated in renal fibrosis[16–18] so that the clinical effects of PTX appear a posteriori biologically plausible. Nevertheless a number of questions still remain:
  • Are the effects of PTX on proteinuria distinct from its effects on eGFR?
  • What are the predictors of response at the individual patient level?
  • How soon should PTX be started in order to achieve its maximal effect?
  • Can PTX be used to reduce proteinuria and stabilize eGFR in patients who are not proteinuric at baseline?
  • Will PTX have a beneficial effect in patients who are intolerant of ACEis or ARBs?

To answer these questions, a number of clinical projects will have to be designed. In particular, future studies should include a large number of patients with diabetic and non-diabetic kidney disease on maximal RASi therapy for a randomized assessment of PTX in a double blinded, placebo controlled fashion. Studies specific to immunologically mediated renal diseases e.g. SLE or crescentic GNs should be considered, given the existence of promising animal studies. For patients who are intolerant of RASi (e.g. development of hyperkalemia or reduction of eGFR), a large scale replication of the study by Perkins to assess the effects of PTX on eGFR slope before and after therapy should be contemplated. In all these studies, predictors of response should be sought among clinical, laboratory (e.g. proteinuria/albuminuria/baseline eGFR and its slope) and inflammatory biomarkers (e.g. cytokine levels in blood and urine) to obtain a better understanding of the effects of PTX in renal disease.

  1. Essayan DM (2001) Cyclic nucleotide phosphodiesterases. J Allergy Clin Immunol 108: 671–680. doi:10.1067/mai.2001.119555.
  2. Marques LJ, Zheng L, Poulakis N, Guzman J, Costabel U (1999) Pentoxifylline inhibits TNF-alpha production from human alveolar macrophages. Am J Respir Crit Care Med 159: 508–511. doi:10.1164/ajrccm.159.2.9804085.
  3. Duman DG, Ozdemir F, Birben E, Keskin O, Ekşioğlu-Demiralp E, et al. (2007) Effects of pentoxifylline on TNF-alpha production by peripheral blood mononuclear cells in patients with nonalcoholic steatohepatitis. Dig Dis Sci 52: 2520–2524. doi:10.1007/s10620-006-9723-y.
  4. Chen Y-M, Lin S-L, Chiang W-C, Wu K-D, Tsai T-J (2006) Pentoxifylline ameliorates proteinuria through suppression of renal monocyte chemoattractant protein-1 in patients with proteinuric primary glomerular diseases. Kidney Int 69: 1410–1415. doi:10.1038/
  5. Ng Y-Y, Chen Y-M, Tsai T-J, Lan X-R, Yang W-C, et al. (2009) Pentoxifylline Inhibits Transforming Growth Factor-Beta Signaling and Renal Fibrosis in Experimental Crescentic Glomerulonephritis in Rats. Am J Nephrol 29: 43–53. doi:10.1159/000150600.
  6. Han KH, Han SY, Kim HS, Kang YS, Cha DR (2010) Prolonged administration enhances the renoprotective effect of pentoxifylline via anti-inflammatory activity in streptozotocin-induced diabetic nephropathy. Inflammation 33: 137–143. doi:10.1007/s10753-009-9167-6.
  7. Nasiri-Toosi Z, Dashti-Khavidaki S, Khalili H, Lessan-Pezeshki M (2013) A review of the potential protective effects of pentoxifylline against drug-induced nephrotoxicity. Eur J Clin Pharmacol 69: 1057–1073. doi:10.1007/s00228-012-1452-x.
  8. Carrier M, Perrault LP, Tronc F, Stewart DJ, Pelletier CL (1993) Pentoxifylline decreases cyclosporine-induced renal endothelin release and vasoconstriction. Ann Thorac Surg 55: 490–492.
  9. Demir E, Paydas S, Balal M, Kurt C, Sertdemir Y, et al. (2006) Effects of pentoxifylline on the cytokines that may play a role in rejection and resistive index in renal transplant recipients. Transplant Proc 38: 2883–2886. doi:10.1016/j.transproceed.2006.08.160.
  10. Badri S, Dashti-Khavidaki S, Lessan-Pezeshki M, Abdollahi M (2011) A review of the potential benefits of pentoxifylline in diabetic and non-diabetic proteinuria. J Pharm Pharm Sci Publ Can Soc Pharm Sci Société Can Sci Pharm 14: 128–137.
  11. Shan D, Wu HM, Yuan QY, Li J, Zhou RL, et al. (2012) Pentoxifylline for diabetic kidney disease. Cochrane Database Syst Rev Online 2: CD006800. doi:10.1002/14651858.CD006800.pub2.
  12. Navarro-González JF, Mora-Fernández C, Muros de Fuentes M, Chahin J, Méndez ML, et al. (2014) Effect of Pentoxifylline on Renal Function and Urinary Albumin Excretion in Patients with Diabetic Kidney Disease: The PREDIAN Trial. J Am Soc Nephrol JASN. doi:10.1681/ASN.2014010012.
  13. Perkins RM, Aboudara MC, Uy AL, Olson SW, Cushner HM, et al. (2009) Effect of Pentoxifylline on GFR Decline in CKD: A Pilot, Double-Blind, Randomized, Placebo-Controlled Trial. Am J Kidney Dis 53: 606–616. doi:10.1053/j.ajkd.2008.11.026.
  14. Noel C, Hazzan M, Labalette M, Coppin MC, Jude B, et al. (1998) Improvement in the outcome of rejection with pentoxifylline in renal transplantation: a randomized controlled trial. Transplantation 65: 385–389.
  15. Shu KH, Wu MJ, Chen CH, Cheng CH, Lian JD, et al. (2007) Effect of pentoxifylline on graft function of renal transplant recipients complicated with chronic allograft nephropathy. Clin Nephrol 67: 157–163.
  16. Meldrum KK, Misseri R, Metcalfe P, Dinarello CA, Hile KL, et al. (2007) TNF-alpha neutralization ameliorates obstruction-induced renal fibrosis and dysfunction. Am J Physiol Regul Integr Comp Physiol 292: R1456–R1464. doi:10.1152/ajpregu.00620.2005.
  17. Therrien FJ, Agharazii M, Lebel M, Larivière R (2012) Neutralization of tumor necrosis factor-alpha reduces renal fibrosis and hypertension in rats with renal failure. Am J Nephrol 36: 151–161. doi:10.1159/000340033.
  18. Omote K, Gohda T, Murakoshi M, Sasaki Y, Kazuno S, et al. (2014) Role of the TNF pathway in the progression of diabetic nephropathy in KK-A(y) mice. Am J Physiol Renal Physiol 306: F1335–F1347. doi:10.1152/ajprenal.00509.2013.

Is this the best review on treating hypertension in pregnancy? Updated

Note: this is a living post that is growing as I brush up on preeclampsia

From Hypertension:

Update on the Use of Antihypertensive Drugs in Pregnancy


Another great article:

New aspects of pre-eclampsia: lessons for the nephrologist

Also with a free PDF. Thanks NDT.


Although these renal changes in general are believed to resolve completely after delivery, recent evidence suggests that pre-eclampsia may leave a permanent renal damage.

CKD is a risk factor for pre-eclampsia in advanced CKD 3-5, weak evidence

the risk for pre-eclampsia and other pregnancy complications is sub-stantially increased in women with chronic kidney disease (CKD) stages 3–5 

 CKD 1-3 is not a risk factor unless the woman also has hypertension, higher quality evidence.

but these women were not at increased risk for pre-eclampsia. However, there was a significant biological interaction between eGFR and hypertension making eGFR 60–89 ml/min per 1.73 m2 a risk factor for pre-eclampsia if the women were also hypertensive.

Pre-eclampsia increases the risk for subsequent kidney biopsy and subsequent ESRD:

In the first study, women with pre-eclampsia in their first pregnancy had a considerably increased risk of developing kidney disease that needed investigation with a kidney biopsy [Adverse Perinatal Outcome and Later Kidney Biopsy in the Mother in JASN]. 

women who previously had pre-eclampsia had a four to five times increased risk of later end-stage renal disease, independent of primary renal disease [Preeclampsia and the Risk of End-Stage Renal Disease in NEJM]. Women with recurrent pre-eclamptic preg- nancies and women who gave birth to offspring with low birth weight had an even higher risk. The increased risk remained significant throughout the follow-up period of nearly 40 years. 

 In regards to the natural history of pre-eclampsia:

It should also be kept in mind that although the extensive glomerular changes during pre-eclampsia are believed to completely resolve after pregnancy [The Glomerular Injury of Preeclampsia in JASN], no studies have routinely performed a kidney biopsy months after the pre-eclamptic pregnancy. The fact that as many as 20–40% have microalbuminuria after a pre-eclamptic pregnancy may argue for a permanent glomerular damage in a great proportion of these women [Microalbuminuria after pregnancy complicated by pre-eclampsia in NDT, Blood pressure and renal function seven years after pregnancy complicated by hypertension].

Warning about these conclusions regarding pre-eclampsia causing CKD:

When interpreting the studies of pre-eclampsia and later kidney disease, it should be remembered that pre-eclampsia might unmask asymptomatic or undiagnosed CKD, a disease that might have been present also before pregnancy. A pre-pregnancy eGFR >60 ml/min per 1.73 m2 measured at screening was in a population-based sample associated with future pre-eclampsia risk in hypertensive women [Kidney function and future risk for adverse pregnancy outcomes in NDT]

This article by Eiland, Nzerue, and Faulkner in PubMed Central does a nice job reviewing the pathogenesis of the preeclampsia.

ACEi talk.

A pharmacist from Blue Cross, Kim Moon, sent me an e-mail and told me she was a fan of the PBFluids and my and twitter. That, of course, instantly made her my newest bestie. She then asked me to do a webinar addressing common issues that prevent primary care doctors from prescribing ACEi/ARB to patients with diabetes. I agreed, anything for a fan of the blog.

A couple of months ago and long before the lecture was written she needed a title, so I threw out, “ACE inhibitors, the good, the bad, and the ugly”

Then I saw this tweet:

‘The good, the bad and the ugly’ appears in the title of over 450 scientific papers. Just sayin’
— Dr John Weiner (@AllergyNet) June 9, 2014

How embarrassing. Well, here’s the show:

Link to video (740MB)
PDF (52.4MB) 
Keynote (132MB)

Streaming the video from google drive seems to be broken. Here is a forum describing the problem, and Google’s lack of response to the issue. My work around has been to pony up the $60 and join Vimeo plus.

Imagine if the wards were really like the boards

1. You have a new patient with a drug you’ve never heard of before. Your next step is to:

  1. Look it up on your phone.
  2. Ask a colleague what the drug is.
  3. Take a careful look at the patients medical history and try to figure out the purpose of the drug from the context. Hopefully it won’t be relevant to the question you are asked.

2. The patient develops an infection and ID suggests adding clarithromycin. The patient is on a number of cardiac drugs and you are worried about QT prolongation. You should:

  1. Look up the possible interactions on your phone.
  2. Depend on your memory of potential drug-drug interactions. Because, though you hate to brag, you did pretty good in medical school and have a keen mind.
  3. Give the clarithromycin, but also order telemetry for the patient, because you are a careful doctor.

3. A patient presents for confusion and is found to have hyponatremia. She has the following labs:

  • Urine Na 80
  • Urine K 40
  • Serum Na 105
  • Urine output 600 mL over the last 18 hours
Calculate the electrolyte free water clearance.
  1. Don’t worry that you are bad at math, this is probably SIADH so just prescribe tolvaptan.
  2. I can’t remember the equation, but this just smells like an experimental question. I’m sure I can take care of the patient without this calculation. Let’s look at the possible choices and I’ll take a logical guess.
  3. Fire up MedCalc, put in the values. Out comes the answer.

4. The biopsy comes back for a patient with proteinruia. The Pathologist calls it dense deposit disease. You have never seen a patient with this before but you did do presentation on MPGN type two 11 years ago in fellowship.

  1. Perfect, you’ve got this. This is nephrology, there’s no way the standard of care has changed in the last decade.
  2. Hit the computer and look it up on UpToDate and do a quick lit search focusing on the top nephrology journals. Consider eculizumab.
  3. Review KDIGO GN clinical practice guidelines. Scream out loud when you find that it is not covered. Fall back on answer 2.

New neph blog: UC Kidney Stone Program

Fred Coe and the crew from University of Chicago have started a kidney stone blog. This is the most prominent nephrology scientist to stick his toe in the blogging world. Dr. Coe was one of my teachers when I was at the University of Chicago (I blogged about him here and here). Dr. Coe has been instrumental in establishing the foundations of kidney stone science and continues to move field forward. He was a category in 2014’s NephMadness:

(5) Dr. Charlie Pak versus (4) Dr. Fred Coe 

Charlie Pak and Fred Coe are the Bob Knight and Dean Smith of kidney stones. Not only did they dominate the field and do the pioneering work establishing the fundamental discoveries of the field, but they also trained the next generation of stone scientists that are currently leading the field. 

To this day the centers where Pak and Coe worked are world leaders in the field. In a plot twist, that would most likely happen in a comic book origin story, they were classmates at the University of Chicago Medical School, class of ‘61, and then were residents together at U of C. 

Dr. Coe remained at University of Chicago but Pak went elsewhere to established the Clinical Research Center and a new Division in Mineral Metabolism at University of Texas Southwestern Medical Center at Dallas. 

They even jointly won the Belding Scribner Award from the ASN in 2000.  

Intellectually they have staked out differing areas of excellence, Dr. Coe has focused on the the importance of the earliest stones to be anchored to the kidney. The location for these tiny early stones is Randall’s Plaques. The theory is that these tiny crystals form in the interstitium adjacent to the thin limb of the loop of Henle, they grow and eventually erode into the renal papilla. There, they are in contact with  supersaturated urine which can deposit calcium oxalate (or other other types of stones?). The plaques can be seen on cystoscopy and their presence predicts stone formers. Stone formation correlates with the degree of plaque coverage.

The blog is full of scientific and practical advice about kidney stones. His first post about why a blog is particularly insightful. 

A blog post is not a book chapter, a review article, a scientific article, or even a newsletter but something else entirely. It is the exact right size to convey one point and no more. It has no room for ornament or circumlocution, for fuzziness or indirection or even for two different points. You cannot avoid that moment when the main point must ring out clearly.

And this paragraph is just so Coe:

Being a singular, real, and immediate focus of attention, a point is something to work with. We can debate it, dissect it, even dismiss it if evidence permits or its logic is flawed. If a point appears to be sound, people can accept it as true for the moment, as an element that can be put together with like elements to make a picture of reality for this one disease. It is a picture that is true for the moment, arising as it does from science, just as the moment caught up in the pointillist net of Georges Seurat’s exquisite Sunday Afternoon on the Island of La Grande Jatte, being great art, will be true forever.

Welcome to the blogosphere Dr. Coe, we look forward to your posts. Your blog has earned a spot on my list of Notable Nephrology and Medical Blogs.

Lecture on modern strategies to keep up to date in the medical literature. #FOAMed at Work.

I love it when fellows turn the tables on their attendings and school them on how the kids do it today.

Kamran Boka is currently a critical care fellow at Henry Ford Hospital but when he was a wee resident he worked with me at St John Hospital. This is an excellent lecture, make sure you check it out. Boka is fully engaged in the 21st century medical infosphere:

Check it out. He has important lessons for everyone.

Urine specific gravity, not that great at estimating osmolality

I have a clinic patient with SIDAH and until the FDA regains some sanity and Otsuka provides a more rational price this will continue to be a frustrating battle. This patient had some pretty typical labs for a patient with SIADH, except for the specific gravity. I don’t remember seeing such a discrepancy between the Sp Grav and osmolality before.

I thought a Specific Gravity of 1.010 was essentially isosmotic. But check out this urine Spec Grav 1.012 osm 587.
— Joel Topf (@kidney_boy) September 4, 2014

One of the sharpest nephrologists on twitter, Christos Argyropoulos, replied with this reference:

@kidney_boy I got over this myth 4 years ago
— ChristosArgyropoulos (@ChristosArgyrop) September 4, 2014

The conclusions from the abstract:

RESULTS: This study demonstrated that USG obtained by both reagent strip and refractometry had a correlation of approximately 0.75 with urine osmolality. The variables affecting the correlation included pH, ketones, bilirubin, urobilinogen, glucose, and protein for the reagent strip and ketones, bilirubin, and hemoglobin for the refractometry method. At a pH of 7 and with an USG of 1.010 predicted osmolality is approximately 300  mosm/kg/H(2)O for either method. For an increase in SG of 0.010, predicted osmolality increases by 182  mosm/kg/H(2) O for the reagent strip and 203  mosm/kg/H(2)O for refractometry. Pathological urines had significantly poorer correlation between USG and osmolality than “clean” urines.

Here is a table I made from the conclusions:

Sodium, in the spotlight for next week’s #NephJC

In August, the NEJM pushed out three articles examining the role of sodium in human disease. These are the subject of September 9’s #NephJC.

The first article is the Association of Urinary Sodium and Potassium Excretion with Blood Pressure. This question used the large epidemiologic study, Prospective Urban Rural Epidemiology (PURE) to answer the question.

PURE enrolled 157,543 adults age 35 to 70 from 18 low-, middle-, and high-income countries on 5 continents.

The study collected 102,216 fasting first morning urines. The authors used the Kawasaki formula to extrapolate 24 hour urine sodium and potassium from the samples. They collected 24-hour samples on 1,000 patients and found that they over estimated sodium intake by about 7%:

The mean sodium excretion was 4.9g and the mean potassium excretion was 2.1 grams.

It was difficult for me to understand the difference between the Observed excretion and Usual excretion but the authors seemed to reference the Usual excretion as the definitive curve.
Sodium excretion was higher in rural areas and in lower income countries. The reverse was true for potassium, higher in cities and higher in higher income countries.
The meat of the paper was the positive association between sodium intake and blood pressure. For every additional gram of sodium excretion the systolic blood pressure went up 1.46 mm Hg and the diastolic rose 0.54 mm Hg (P less than 0.001). Statistical mumbo jumbo increased those numbers to 2.11 systolic and 0.78 mm Hg diastolic. This relationship was non-linear with increased blood pressure effect as the sodium excretion rose over 5 grams.
Potassium had the opposite effect with systolic blood pressure falling 0.75 systolic (1.08 after statistical adjustment) and diastolic dropping 0.06 (0.09 adjusted) mm Hg for every gram increase in potassium excretion. 
Older people showed larger changes in blood pressure with increased sodium excretion.
The sodium effect on blood pressure was a lot larger that the 0.94 mmHg systolic and 0.03 mmHg diastolic found in the landmark INTERSALT study but still seems like a pretty small effect given the difficulty in getting to a low a salt diet. Look at the bell curve showing only 0.2% of samples hitting the WHO goal of less than 2.3 g a day.

Sodium, in the spotlight for next week’s #NephJC, part 2

The second article in the NEJM package was Urinary Sodium and Potassium Excretion, Mortality, and Cardiovascular Events.

This is an interesting study because so much of the arguments based on salt focus on the intermediate end-point of blood pressure, one can lose sight on the big daddy, total mortality. Previous studies have shown that low sodium diets have paradoxically been associated with higher rates of cardiovascular disease and death. These studies have often been dismissed by sodium puritans by pointing out that including patients with pre-existing cardiovascular disease will pollute the results because these, obviously, high risk patients are told to maintain a low sodium diet.

This study was performed using the same international cohort as the previous trial, The PURE study. This study enrolled 101,945 patients and analyzed early-morning fasting urine samples. They used the same Kawasaki formula that over estimated sodium excretion as in the other PURE study.

They used multiple models to analyze the data.

Patients with pre-existing cardiovascular disease, cancer or events in the first two years of follow-up were excluded from the analysis. They also did an additional analysis using propensity scoring to further reduce imbalanced confounders.

The most important letter in the PURE acronym is P for prospective. In this case it allowed them to match the cross sectional sodium excretion data with long-term follow data. Mean follow-up was 3.7 years. The primary outcome was death or a major cardiovascular event. Over the period covered by the study they recorded 3,317 outcomes. The risk from changes of sodium intake was seen at the edges of intake:

Increased mortality at sodium excretion over 7 grams and below 3 grams
Green indicates an association with sodium excretion. Red indicates no significant association.
The U-Shaped curve seen with sodium was not seen with potassium. The more potassium excretion the lower the risk of the primary outcome.
The results were essentially the same in the propensity-score-matched analysis.
I found this paragraph from the discussion to be particularly salient:

Current guidelines, which recommend a maximum sodium intake of 1.5 to 2.4 g per day, are based on evidence from largely short-term clinical trials showing that reducing sodium intake from a moderate to a low level results in modest reductions in blood pressure. The projected benefits of low sodium intake with respect to cardiovascular disease are derived from models of data from these blood-pressure trials that assume a linear relationship between sodium intake and blood pressure and between blood pressure and cardiovascular events. Implicit in these guidelines is the assumption that there is no unsafe lower limit of sodium intake. However, sodium is known to play a critical role in normal human physiology, and activation of the renin–angiotensin–aldosterone system occurs when sodium intake falls below approximately 3.0 g per day.

The authors make it clear that an epidemiologic association between mortality and sodium excretion is not the same as finding increased mortality or lack of benefit from patients lowering their sodium intake. Advice that the authors of the third study should have taken the time to internalize.

Finally, our study provides an epidemiologic comparison of groups that consume different levels of sodium, and it does not provide information on the effect on clinical outcomes of reducing sodium intake. Therefore, our findings should not be interpreted as evidence that the intentional reduction of sodium intake would alter the risk of death or cardiovascular disease.