The perils of Gabapentin

One of the things that I always highlight when teaching fellows and residents is the importance of appropriate drug dosing for patients on dialysis and one of the drugs that is most often inappropriately dosed in my experience is gabapentin. Today, an article in JASN highlights again the importance of not overusing this drug in the dialysis population. 

Gabapentin and pregabalin are often used in patients with CKD primarily to treat neuropathic pain and restless leg syndrome and given the high prevalence of diabetes in this population, the proportion who receive these drugs is very high. In patients with normal renal function, the maximum dose of gabapentin is 3600mg daily in divided doses. However, gabapentin is renally cleared and so the dose needs to be adjusted according to the GFR. For patients on dialysis, the recommended dose is 100-300mg post dialysis on dialysis days only. However, this is routinely exceeded in clinical practice. 

The study in JASN looked at medicare prescriptions for gabapentin and pregabalin in dialysis patients examined the relationship between the doses used and a variety of outcomes including altered mental status, falls and fractures. 20% of the dialysis population received at least one prescription for these drugs in 2011. Even at the lowest doses (less than 300mg daily), there was an association between the use of these drugs and AMS and falls while doses greater than 300mg daily were associated with a 40% increase in the risk of fracture. Similar results were found for the higher doses of pregabalin. 

Of course, this was an observational study and there may have been unmeasured confounders that may have biased the results but the authors did account for other medications that can increase the risk of falls. 

Overall, this should serve as a reminder to the community that we need to more carefully police the dosing of medications in our dialysis population, particularly when they are admitted to hospital.

Azathioprine Toxicity

Azathioprine is one of the oldest immunosuppressant medications, which has been used in the field of solid organ transplantation over the past 5 decades. It is metabolized into its inactive forms by the enzyme thiopurine methyltransferease (TPMT). Genetic polymorphisms of the gene coding for this enzyme are common in the general population (~ 10% are heterozygotes causing low enzyme activity and ~ 0.3% cause complete lack enzyme activity). Testing for the enzyme activity is recommended prior to treatment with azathioprine or any thiopurines in children. However, it is not consistently tested for in adult patients who are immunosuppressed with azathioprine for inflammatory bowel disease, organ transplantation or rheumatologic conditions. Genotypic (testing for polymorphisms in the TPMT gene) and phenotypic (measuring levels of substrates and products of the enzyme in RBCs) testing for TPMT are commercially available but the concordance between them is not 100%.

The following are the metabolites that are tested for in the phenotypic testing:
6- Mercaptopurine – (Ref: 3.0- 6.6) nmol/ml/hr
6- Methylmercaptopurine riboside – (Ref: 5.04 – 9.57) nmol/ml/hr
6- Methylthioguanine riboside – (Ref: 2.7 – 5.8) nmol/ml/hr

Phenotypic testing performed within 30-90 days after a blood transfusion can result in inaccurate interpretation of the results because of donor RBCs influencing the test results. Moreover ethnicity, type of disease, concurrent drug treatment, red cell kinetics and transfusions should be taken into account while interpreting the results of TPMT enzyme activity. Single nucleotide polymorphisms (SNPs) account for the major TPMT low activity variant forms. Four TPMT alleles, TPMT*2, *3A, *3B, and *3C, account for over 90% of inactivating polymorphisms.

The approximate commercial cost is ~ $200 for phenotyping and ~$450 for genotyping. Clinical Pharmacogenetic Implementation Consortium (CPIC) has developed an evidence-based guideline on how to adjust thiopurine doses based on TPMT activity.

Posted by Karthikeyan Venkatachalam
Transplant Fellow
Washington University School of Medicine
St Louis

Cidofovir nephrotoxicity and Probenecid

I recently saw an interesting case. A woman was being treated with cidofovir for adenovirus which was presumed to be responsible for an acute cardiomyopathy. Concurrent with cidofovir, she was also receiving probenecid for renoprotection, which I was not familiar with.

Cidofovir is a nucleotide analogue used primarily to treat CMV retinitis in patients with AIDS. However, cidofovir is also used to treat a number of DNA viruses including adenovirus. The main toxicity of cidofovir is nephrotoxicity, which can manifest as AKI, proteinuria, or a Fanconi-type syndrome with proximal tubular dysfunction. Nephrotoxicity can be reduced by co-administration with iv fluids and probenecid (the dosing regimen for the latter is 2g po 3 hours prior to the dose, then 1 g po 2 hours and 8 hours after.

How does probenecid reduce cidofovir nephrotoxicity? Over 80% of cidofovir is excreted unchanged in the urine in 24 hours. Most of this occurs via glomerular filtration, but cidofovir is also actively taken up from blood by the kidneys via the "organic anion transporter" located on the basolateral side of renal proximal tubular cells, and is then more slowly secreted into the tubular lumen. Renal clearance of cidofovir therefore exceeds the corresponding GFR.

The relatively slow secretion of cidofovir into the tubular lumen, in comparison to uptake from the blood, results in a long intracellular half-life of the drug in the proximal tubular cells which appears to underlie the nephrotoxicity. Probenecid, by inhibiting the organic anion transporter, prevents tubular uptake and protects the kidneys. This was demonstrated nicely in a pilot study in HIV patients. Interestingly, and somewhat paradoxically, this means that probenecid reduces nephrotoxicity while also DECREASING the renal clearance of the drug and thus INCREASING serum cidofovir concentrations as much as two-fold.

Probenecid is a banned drug for athletes for a related reason - because it blocks entry of certain drugs into the urine, it has been used as a masking agent for other banned performance-enhancing drugs including steroids. 

Posted by David Leaf

Nephrotoxicity of Dietary Supplements and Alternative Medicine

A few weeks ago, one of our pharmacists gave a comprehensive presentation about the potential nephrotoxicity of a variety of commonly used herbal, alternative and dietary supplements. He has a particular interest in this as he deals largely with our transplant patients. There are many potential interactions between these compounds and immunosuppressant medications. He agreed to allow me put it up in full here. It is a really useful guide that I know I'll be referring to often in the future.



Posted by Steven Gabardi

Biosimilars: does a rose by any other name smell as sweet?

A biopharmaceutical, or biologic, is any medicinal product manufactured in or extracted from a living system, such as a microorganism or plant or animal cells. Several biologic agents are produced using recombinant DNA technology, while others may be manipulated or humanized after their production. Most of these agents are very large and complex molecules compared to traditional small-molecule drugs. Given this fact, the manufacturing process of biologics is more challenging than traditional drugs, as even minor changes in the manufacturing process can impact efficacy or immunogenicity. 

 Use of biologic agents is now commonplace in many disease states, including oncology, rheumatology, renal transplant and nephrology. One of the major limitations of use of these agents is their associated costs. A small molecule drug costs, on average, $1/day, with generic drugs often costing just cents. In comparison, a biological drug costs, on average, $22/day. It is estimated that global biological sales are projected to reach $221 billion by 2017. One way to limit the healthcare expenditure on biologic agents is to allow for competition within the marketplace. However, given the complex manufacturing processes involved in making biologics, the Food and Drug Administration (FDA) has traditionally not allowed generic competition for these products, even after their patents have expired. This all changed on March 23, 2010 when the Patient Protection and Affordable Care Act was signed into law. This created an abbreviated licensure pathway for biological products that are demonstrated to be “biosimilar” to or “interchangeable” with approved, reference biological agents. 

 A biosimilar is simply defined as a biopharmaceutical protein designed to have active properties similar to an innovator biologic and approved through an abbreviated regulatory process. Due to the complexity of the manufacturing process, biosimilars should not be considered generic versions of biologics. The FDA requires animal studies to assess toxicities, as well as human pharmacokinetic (PK) and clinical studies prior to approval of a biosimilar product. The objective of the PK study is to demonstrate comparability of relevant parameters in a sufficiently sensitive and homogeneous population. This analysis is often done in concert with the clinical study. For the clinical study, the primary objective is to establish biosimilarity, not clinical benefit, as its efficacy is already known from the registration studies of the innovator product. Biosimilarity is often established through a randomized, parallel group, comparative clinical trial. 

 The FDA has published “The Purple Book” that contains a list of licensed biologic products to help clinicians see whether a particular product has been determined by the FDA to be biosimilar to, or interchangeable with, a reference biologic product. Despite the approval pathway for biosimilars being signed into law over five years ago, it was not until March 2015 that the FDA approved the first biosimilar product, Zarxio® (filgrastim-sndz). Biosimilars are a relatively new in the US; however, the European Medicines Agency (EMA) has had a regulatory process for approval of biosimilars for nearly 10 years. Their approvals for biosimilars cover five classes: recombinant erythropoietins (i.e., epoetin alfa, epoetin zeta); recombinant granulocyte-colony stimulating factors (i.e., filgrastim); recombinant human growth hormone (i.e., somatropin); recombinant follicle stimulating hormone (i.e., follitropin alfa) and monoclonal antibodies (i.e., infliximab). To date, the EMA has approved 19 biosimilars. 

 Biosimilars in Nephrology 

After 6 years of successful use in Europe, data has demonstrated that biosimilar erythropoiesis-stimulating agents (ESAs) are safe and effective alternatives to brand-name epoetin alfa for treating anemia in patients with kidney disease. In United States, the patent for Procrit® (epotein alfa) expired in August 2013; however, the patent for Epogen® (epoetin alfa) remains active until May 2015. On the other hand, the patency for Aranesp® (darbapoetin alfa) will expire in 2024. Since the U.S. key patents on epoetin alfa have begun to expire, Hospira has submitted Biologics License Application to U.S FDA to get Retacrit® (epoetin zeta) approved as a proposed biosimilar for epoetin alfa.

  Biosimilars in Transplantation 

Monoclonal antibodies are very complex biologics that have shown to be effective for different indications. In renal transplantation, a series of monoclonal antibodies have been used as induction therapy or to treat steroid-resistant acute rejections, such as Simulect® (basiliximab) or Campath® (alemtuzumab). It appears that alemtuzumab will lose patent protection at the end of 2015, while basiliximab patent protection will expire in 2018. These could be among the first transplant-related immunosuppressive biosimilars approved in the US within the next five years.

-      Razan M. Alsheikh, PharmD, BCPS, PGY-2 Organ Transplant Pharmacology Resident, Brigham and Women’s Hospital, Boston, MA

-      Steven Gabardi, PharmD, FCCP, BCPS, Department of Transplant Surgery and Renal Division, Brigham and Women’s Hospital, Boston, MA

Spironolactone Revisited

As a renal fellow, I have found myself reaching for spironolactone more and more. It is very helpful when treating the patient with resistant hypertension, but it continues to be under-utilized. Aside from the renal-centric effects of aldosterone, there is evidence that mineralocorticoid receptor activation is responsible for pathogenic remodeling (both structural and electrical) after myocardial infarction. In fact, aldosterone is also produced by the heart, and cardiac expression of the mineralocorticoid receptor is increased in the setting of heart failure and MI. Perhaps aldosterone antagonists can reverse the cardiac remodeling, predisposition to arrhythmia, and risk of cardiovascular death we see in our kidney disease patients?

Remember, patients with ESRD do not die from kidney failure per se, but most die from cardiovascular and cerebrovascular disease. We know that spironolactone reduces mortality and hospitalization due to heart failure in patients with reduced LVEF (RALES trial), but we don’t know if these effects carry over to the ESRD population. However, two recent papers caught my eye.

One was recently published in JACC, where 309 patients with ESRD were randomized to spironolactone 25mg once daily or a control group. The primary outcome was a composite of death or hospitalization from cardiovascular and cerebrovascular events, and the secondary outcome was death from any cause. At three years, the treatment group had significantly fewer cardiovascular and cerebrovascular events: 9 patients (5.7%) vs 19 (12.5%) in the control group (Adjusted HR 0.379, p = 0.016). There were also fewer deaths: 10 (6.4%) with spironolactone vs 30 (19.7%) in control group (Adjusted HR 0.335, p=0.003). Out of the 157 patients in the spironolactone group who stopped the drug, 7 developed gynecomastia, 9 had breast pain, and 3 patients had significant hyperkalemia (>6.5 meq/L). Of course, this was a small RCT and not blinded or placebo controlled. If these effects are true, this would yield a NNT of 14 to prevent one cardiovascular or cerebrovascular event and a NNH of 52 to cause one episode of hyperkalemia. 

A similar study published in JASN randomized 158 patients on PD and already on ACE/ARB therapy to 25mg of spironolactone or a control group.  After two years of follow up, the rate of change of LVMI was significantly lower at 6, 18, and 24 months in the spironolactone group. In a subgroup analysis of males who started the trial with LVMI ≤ 50 g/m2, the control group had a significant increase in LVMI over time while the spironolactone treated group was unchanged. Likewise, in males who started with LVMI > 50 g/m2, those treated with spironolactone had a significant reduction in LVMI over time compared to the controls. In this trial, serious hyperkalemia (>6.0) occurred infrequently: 2 in spironolactone group and 1 in control. Gynecomastia was more frequent in the spironolactone group (14.1% vs 2.5%), but some of these patients had their doses reduced or were switched to eplerenone. 

So what does this all mean? It’s exciting to think that mineralocorticoid antagonists may reduce LVH and cardiovascular events in our ESRD population. A larger, placebo controlled trial is needed to confirm these findings since these were small open-label trials. Fortunately this is underway with the ALCHEMIST trial (NCT01848639), which plans to randomize 825 hemodialysis patients to either spironolactone or placebo. In the meantime, it may be best to use spironolactone as an anti-hypertensive agent in a dialysis patient who is low risk for hyperkalemia. For instance, PD patients tend to have have low serum potassium thanks to high clearance. In the PD patients I’ve seen with hypertension and hypokalemia, I have been backing off pure anti-hypertensive agents (like hydralazine) and starting 25mg of spironolactone. These trials suggest that this dose is safe to use in dialysis patients and possibly has some effect in preventing LVH and improving long-term cardiovascular outcomes.

Posted by John Roberts

Baclofen in dialysis patients: Just say no!

At our hospital, we started noticing a pattern of admissions among some of our maintenance dialysis patients. In one case, an elderly woman with DM, peripheral arterial disease, and ESRD on thrice weekly hemodialysis was sent to the emergency department from her nursing facility for altered mental status. She was normal three days prior to admission, but when her nurse found her confused and difficult to arouse, they sent her to our ED. We got consulted to continue maintenance dialysis, but we noticed that she had a fluent aphasia and marked perseveration. The rest of her exam and workup was unremarkable.  I immediately called the nursing facility and had them fax over her medication administration record. Lo and behold, three days prior she was started on baclofen 5mg three times daily for complaints of lower extremity leg pain (which was probably her claudication anyway). We diagnosed her with acute baclofen neurotoxicity.

Baclofen is an oral antispasmodic that is used to treat muscle spasticity. Chemically, it is very similar to the CNS neurotransmitter GABA and it acts as an agonist at GABAB receptors, resulting in an inhibitory effect on neurons.  Baclofen is rapidly absorbed after ingestion and 90% of the drug is excreted unchanged by glomerular filtration. Therefore, patients with CKD and ESRD are at significant risk from baclofen accumulation and toxicity. The most common complaints are non-specific: drowsiness, headache, lethargy, nausea or vomiting. However, with a severe overdose, profound CNS depression occurs with respiratory depression, bradycardia, hypotonia, areflexia, myoclonus, or seizure activity.

The importance of baclofen toxicity in patients with renal failure has only recently been described and remains unappreciated by many physicians. El-Husseini et al. compiled a nice series of 41 cases of baclofen toxicity in patients with renal insufficiency. The majority of the patients had ESRD (62.9%) and the remaining either had advanced CKD or AKI. Despite being a small, heterogeneous case series, a few trends were seen. The onset of symptoms typically came two to four days after initiating the drug, and the mean daily dose was 20mg per day.

Since baclofen is small molecule (213 Daltons) and it has a relatively low volume of distribution and low degree of protein binding, it is readily removed by hemodialysis. There are only a few of clearance studies out there, but one report found that 4 hours of HD with a high-flux membrane resulted in a clearance of 120 ml/min, equivalent to a normal GFR! Since we have been more aware of baclofen, we have discovered more cases of neurotoxicity in our ESRD patients. We treat with daily sessions of high-flux HD for at least 4 hours until symptoms disappear. Our patient returned to her baseline after 3 consecutive days of HD. The authors of the case series highlight the lack of official dosing guidelines for baclofen in patients with renal insufficiency. Thus, many providers are unaware that this drug is contraindicated in those with advanced CKD and ESRD. Renal fellows are already primed to check for excessive gabapentin doses and NSAIDS, but I would add Baclofen to the list of drugs that should not be given to any patient with advanced CKD or ESRD.

Posted by John Roberts

Lithium and the Kidney: Old Observations & New Insights

Lithium is indispensable as an effective treatment for bipolar affective disorder. However, it has a narrow therapeutic index with desired therapeutic levels between 0.6 and 1.2 mEq/L. Lithium is handled by the kidney (responsible for almost all its excretion) in a manner very similar to sodium. It has a molecular weight of 7 daltons, has a moderate volume of distribution, is <10% protein bound and is therefore readily dialyzable. Lithium may cause of myriad of renal related toxicities, some of which are classic descriptions and some which are less well known. Much of this has been discussed on RFN before (here, here) but I felt a refresher with some additions was due.

Nephrogenic Diabetes Insipidus (NDI)

This is perhaps the best know and most common complication of lithium therapy, with an estimated prevalence of 20-70%. Patients present with polyuria and polydipsia due to a urinary concentrating defect that can lead to volume depletion, especially if access to free water is restricted. Lithium downregulates aquaporin-2, vasopressin-activated water channels expressed on the collecting duct principal cells. It is worth noting that ongoing volume depletion from NDI may aggravate the risk of supra-therapeutic levels and therefore chronic nephrotoxicity. Amiloride may help as it inhibits lithium reabsorption via ENaC in the collecting duct.    

Renal tubular Acidosis (RTA)

Lithium may induce a hyperchloremic non-anion gap metabolic acidosis, analogous to a distal RTA. It is likely due to decreased distal proton secretion. Unlike acidosis associated with amiloride, it is not associated with hyperkalemia probably because of their different effects on distal H⁺/K⁺-ATPase function.

Acute Lithium Nephrotoxicity

This may occur as an overdose in newly treated patients or those on long-term lithium therapy. Acute lithium intoxication may cause altered mental status and acute kidney injury. Drugs which decrease GFR (NSAIDs/RAAS inhibitors) may exacerbate intoxication as can thiazides, which cause a natriuresis and a subsequent reabsorption of Na (and lithium). With preserved renal function and mild intoxication, increasing urine output/forced diuresis may be all that is needed. Care should be taken using 0.9%NaCl if hypernatremia from NDI is present. As mentioned above, lithium is readily dialyzable and hemodialysis (ideally using a high flux membrane to aid clearance) is the primary management for severe cases. A lithium level >4mEq/L is considered an absolute indication for dialysis in most cases. A level >2.5mEq/L with severe symptoms, or renal impairment which will slow native clearance, is also an indication. If in doubt, most nephrologists would have a low threshold for dialysis, although it is usually not needed with a level <2.5mEq/L. Drug levels drop rapidly during dialysis but they do rebound so extended and repeated sessions are usually necessary. Continuous therapies are less efficient so are not desirable if severe intoxication is present but may be used if conventional dialysis is not immediately available.

Chronic Tubulointerstitial Nephritis (TIN)

A chronic TIN with interstitial fibrosis and tubular dropout is the commonest pathology seen when patients with lithium and renal impairment are biopsied. Consistent with this is a bland urine sediment with little/no proteinuria being common (although not exclusive-see next section). As nephrologists, our view of the prevalence of lithium induced CKD is skewed. The exact prevalence is difficult to determine but many patients have preserved renal function. The tricky decision is whether (and if so when) to stop therapy? This is rarely a decision the nephrologist can make alone and should be balanced with efficacy of treatment/alternatives available and usually led by the psychiatrist in my opinion.

Nephrotic Syndrome

It is less well known that lithium may be associated with a glomerulopathy. Minimal change disease is most often described but membranous nephropathy and FSGS has also been reported. Cases were considered lithium induced as proteinuria disappeared upon cessation of the drug, and when re-challenged (for psychiatric reasons), the nephrotic syndrome recurred. A series of 24 patients with lithium-induced nephrotoxicity from New York included one quarter with nephrotic-range proteinuria. My initial thoughts were that the FSGS lesions were likely secondary to nephron loss and resulting hyperfiltration injury. However, arguing against this is that presence of FSGS lesions did not correlate with severity of tubulointerstitial lesions. Moreover, there was a high incidence of extensive podocyte foot process effacement, to a degree uncommon in secondary FSGS. The mechanism of glomerular toxicity is unclear.

Renal Cell Tumors

It has recently been reported in Kidney International that chronic lithium use is associated with an increased risk of kidney tumours.  After a mean duration of lithium exposure of >21 years, patients had a significantly higher risk of solid renal tumours compared with gender, age and eGFR matched controls [Standardized Incidence Ratio i.e. ratio of observed-to-expected numbers of renal cancers was 7.51 and 13.69 in men and women respectively]. The tumours were a mixed bag of benign (oncocytomas, angiomyolipomas etc.) and malignant (clear cell, stromal, papillary) lesions. While these results are thought provoking, this was a retrospective study and the design seems open to detection bias in my opinion (were patients on lithium screened more than regular individuals?).

Hyperparathyroidism

As previously posted, lithium may cause hypercalcemia and stimulate PTH via a variety of postulated mechanisms (see previous post).

An atypical form of renal failure: granulomatous interstitial nephritis

A 42-year-old man developed AKI during his recent hospitalization due to presumed sepsis. He was started on vancomycin and levofloxacin as empirical therapy. When renal was consulted 7 days after admission, creatinine level had peaked at 4.39 mg/dl and WBC 33K with eosinophilia. Urinalysis was associated with 2+ proteinuria and 2+ leukocyte esterase with some granular casts, though no cellular casts were visualized. On examination, he had generalized erythematous rash associated with diffuse body edema.

The initial diagnosis by the team was thought to be ATN associated with sepsis, though the presence of rash and eosinophilia raised the concern for superimposed drug-induced acute interstitial nephritis (AIN).

A renal biopsy was performed and the histopathologic findings revealed an AIN with granulomatous features (figure on the top left - Courtesy of Dr Rennke/Dr Bijol).

AIN is a common finding in kidney biopsies of patients with acute renal failure in the hospital. However, granulomatous interstitial nephritis (GIN) occurs in only about 1% of biopsies. GIN is a histologic form of interstitial nephritis characterized by the presence of necrotizing or non-necrotizing granulomas in renal biopsy. Its pathogenesis is not well defined. Some immunologic mechanisms were proposed as culprits such as T-cell-mediated delayed hypersensitivity, anti-tubular basement membrane antibodies and autoimmune antibody response.

Potential etiologies include:

 - Drug-induced processes [[most common]] (Antibiotics, NSAIDs, Diuretics (thiazide), Allopurinol, Anticonvulsant (lamotrigine), Omeprazole, Bisphosphonate, All-trans retinoic acid, Heroin abuse)
- Infections (xanthogranulomatous pyelonephritis, tuberculosis and other mycobacterial infections; Histoplasmosis and other fungal infections; adenovirus)
- Systemic inflammatory conditions (Sarcoidosis, Wegener granulomatosis, TINU, Crohn’s disease)

In about 15% of cases, an exact etiology for GIN is not found.

Further work-up on the case above did not reveal any systemic inflammatory process or infections, though a high suspicion for antibiotic-induced GIN was raised. In particular, there has been case reports of levofloxacin-associated GIN.

The treatment of GIN depend on the underlying associated factor. For example, in drug-induced processes, the removal the offending agent will play a central role in the treatment; while in infection-related cases, the underlying infection must be controlled.

In the case presented, antibiotics were changed and an empirical trial of steroids was administered. Patient’s creatinine slowly trended down in the subsequent weeks but plateau at 1.5 mg/dl. Though there has been no randomized trials, most GIN cases deserve a trial of steroids once infectious etiologies are excluded, in particular based on the intense inflammation observed on the biopsies.

Anthony Gueratto Klepp

Eduardo Kaiser Ururahy Nunes Fonseca

Leonardo V. Riella

Aristolochic Acid Nephropathy

Aristolochic acids (AA) are found in products derived from the aristolochia genus of plants which are used extensively in herbal medicines, particularly in Asia. Nephrotoxicity resulting from AA exposure was originally described in a case series of women taking diet supplements in Belgium but has subsequently been identified in the US, Europe and Asia. Consumption of products containing AA remains endemic in some areas with an estimated exposure in up to 40% of the Taiwanese population. The disease known as Balkan endemic nephropathy – described the population living around tributaries of the Danube river- is now thought to result from contamination of wheat flour with seeds of plants containing AA.

Patients with AA nephropathy typically present with renal insufficiency and anemia. Urinalysis reveals a few red cells and mild proteinuria. The rate of decline of renal function varies but may depend on the cumulative dose of AA. Renal histology is characterized by extensive interstitial fibrosis with tubular atrophy and low numbers of inflammatory cells. There is a very high incidence of urothelial atypia and carcinoma. Exposure to AA can be confirmed by the presence of AA-DNA in biopsy tissue. 

Therapy consists of routine management of CKD alongside regular screening for urothelial malignancy. A trial of steroids can be considered in selected patients. The risk of urothelial malignancy is so high that some consider patients for bilateral nephrouretecomy once RRT as been established.

Despite being banned in many countries, products containing AA remain available. The true incidence of CKD and urothelial malignancy resulting from AA exposure remains unknown. It is possible that a lack of awareness means that a significant proportion of AA resulted morbidity remains undiagnosed.  For a comprehensive review of the subject see here.

Image from Wikipedia.

Posted by Jonathan Dick

What are you smoking?

I recently saw an interesting case series published in CJASN where they reported four cases of oliguric AKI  associated with synthetic cannabinoids use. Renal biopsy revealed acute tubular injury in three of them and calcium oxalate crystals  in two.

Interestingly, around the same period of time I was rotating in nephrology consult service and had an elderly patient with history of paraplegia and neurogenic bladder (on intermittent self-catheterization), who was brought to the ER with altered mental status for which he was intubated for airway protection. On presentation, he was found to have acute kidney injury (Cr 6.0). His renal function continued to deteriorate with no specific etiology for his renal failure, so he had a renal biopsy which showed evidence of an active tubulointerstitial nephritis with marked tubular injury and calcium oxalate crystals present within the tubular lumina. Remarkable findings in his history included the recent use of cannabinoids. He never had history of renal stones. His home medication includes: methadone, oxycodone, nortriptyline and pregabalin. Admission labs showed normal osmolar gap and negative toxicology analysis. Urine microscopy showed muddy brown casts with no identifiable crystals.  Abdominal ultrasound did not reveal any renal calculi. Renal replacement therapy was started for uremic symptoms and he continued to require replacement therapy after his discharge.

The use of these synthetic cannabinoid preparations has increased significantly in the United States over the past few years, and the incidence of acute kidney injury (AKI) from use of these agents  is underestimated. CDC investigators have identified 16 patients (15 males; median age, 18.5 years) from 6 states who presented to emergency departments in 2012 with acute kidney injury after smoking a synthetic cannabinoid product.  Six patients had acute tubular injury and three had acute interstitial nephritis. Even though we can relate tubular injury and interstitial nephritis to the use of cannabinoids  , presence of calcium oxalate crystals was perplexing. In the case series reported in CJASN, they mentioned the presence of calcium oxalate crystals in two patients, but the mechanism of development of these crystals was not fully elucidated . We are hypothesizing that synthetic cannabinoids could be the potential cause for calcium oxalate deposition in this patient (after all causes of secondary hyperoxaluria were excluded). One possible explanation is that synthetic cannabinoids contain additional compounds which are plant in origin and these may be oxalogenic

Synthetic cannabinoids use should be in our differential diagnosis for unexplained AKI in young adult population as it can cause either ATN or AIN or both. A high index of suspicion is required as they may not be detected on routine urine drug screens.

Posted by Mahmoud Kamel

Renal Grand Rounds - Case of the month

A young woman with h/o polysubstance abuse and seizures was admitted to hospital with status epilepticus. She was treated with a propofol infusion at 5mg/kg/hr which was maintained due to perceived continuing seizure activity. On hospital day 5, she developed an acute metabolic deterioration – rhabdomyolysis : CPK 100,000, AG metabolic acidosis (HCO3 18) and non-oliguric AKI. Her EKG also became abnormal (RBBB). The diagnosis was propofol infusion syndrome.

What is propofol Infusion Syndrome (PRIS)? 

Like many syndromes, PRIS is a conglomeration of clinical and biochemical manifestations.  Based on  83 case reports from 1992-2007, PRIS is characterized by:

1) Metabolic acidosis, (pH less than 7.30 or HCO3 less than 19)

2) Rhabdomyolysis (CPK more than 10K)

3) Renal failure

4) Cardiac dysfunction (Brugada-like EKG pattern, asystole, PEA, sustained VTs, heart failure, or bradycardia) 

5) Hypertriglyceridemia (TG more than 400)

6) Hyperkalemia

7) Hypotension (or use of vasopressor agent)

8) Hepatic transaminitis

9) Hypoxia (PO2 less than 60mmHg). 

The first 5 manifestations are the most common. While there is no requirement for the number of clinical manifestations a patient must exhibit to meet diagnosis for PRIS, a prospective study showed that most patients exhibit at least 3 defining manifestations within 3 days of propofol use.  In the same study, the incidence of PRIS was found to be a low 1% --similar to other estimates.  However, PRIS is associated with high mortality, up to 30% in some studies. Moreover, because many of these manifestations are common, the presence of any of them could be attributed to another etiology, thus delaying diagnosis of PRIS.  For instance, in the case vignette, the initial rise of CK was attributed to seizure rather than PRIS.

Pathophysiology of PRIS

Inhibition of electron flow along the mitochondrial electron transport chain/ impairs oxygen utilization. Propofol or its metabolites inhibits fatty-acid oxidation leading to buildup of toxic fatty acid intermediates. As described in this nice review.

Risks of PRIS?

Critical illness (especially, CNS illness); Use of propofol dosage more than 4 mg/kg/hr —the usual adult maintenance dose is 0.3 to 3mg/kg/hr; duration of Propofol use greater than 24hr; exogenous cathecholamines and corticosteroids; poor intake of carbohydrate, see this reference.

Management of PRIS

Early recognition/diagnosis; Cessation of propofol infusion; Cardiopulmonary support; Hemodialysis (strongly advocated by expert opinion and outcome of case series).  However, there are no known RCT of use of renal replacement therapy in the treatment of PRIS.  Nonetheless, in case series, survivors of PRIS are more likely to have received HD/CVVH.  Therefore, prolonged use of HD/CVVH is worth considering by renal consult service.  Because propofol is lipophilic and has volume of distribution of 20-40L, it is poorly cleared by HD/CVVH, prolonged RRT is likely needed for PRIS management.

The patient in the case was treated with CVVH overnight, and then transitioned to intermittent HD.  At the time of her discharge, she was off HD with her Cr back to baseline.

See this previous post by Nate on PRIS.

Posted by Opeyemi Olabisi