Why is latent tuberculosis usually treated with one antibiotic while active tuberculosis is treated with 2 or more drugs?

Conventional wisdom has been that in active tuberculosis (TB) patients harbor large numbers of replicating Mycobacterium tuberculosis (Mtb), requiring multiple antibiotics to prevent the emergence of resistant mutants. In contrast, Mtb under latent or “inactive” conditions is presumed to have little capacity for mutation due to reduced bacterial replication, thus generally requiring only one antibiotic for preventive therapy.1

However, the assumption that Mtb has a low capacity for mutation in latent TB due to slow bacterial replication has been challenged in recent years. An experimental study in macaque monkeys with latent Mtb infection using whole genome sequencing demonstrated that despite reduced replication, Mtb acquires a similar number of chromosomal mutations during latency as it does during active infection.1

This finding supports the more current and evolving concept of latent TB which assumes diverse mycobacterial growth states, ranging from complete absence of organisms to actively replicating bacterial populations.2 It also explains why, although effective, isoniazid monotherapy may be a risk factor for the emergence of INH resistance in latent TB. 1,3

 Bonus Pearl: Did you know that INH treatment of latent TB in adults is 60-80% protective when given for 6 months, and 90% protective when given for 9 months? 4


  1. Ford CB, Lin PL, Chase M, et al . Use of whole genome sequencing to estimate the mutation rate of Mycobacterium tuberculosis during latent infection. Nat Genet. 2011;43:482-86. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3101871/
  2. Gideon HP, Flynn JL. Latent tuberculosis: what the host “sees”? Immunol Res 2011;50:202-12. https://www.ncbi.nlm.nih.gov/pubmed/21717066
  3. Balcells ME, Thomas SL, Faussett PG, et al. Isoniazid preventive therapy and risk for resistant tuberculosis. Emerg Infect Dis 2006;12:744-51. https://www.ncbi.nlm.nih.gov/pubmed/16704830
  4. Piccini P, Chiappini E, Tortoli E, et al. Clinical peculiarities of tuberculosis. BMC Infect Dis 2014; 14 (Suppl 1):S4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4015485/


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Why is latent tuberculosis usually treated with one antibiotic while active tuberculosis is treated with 2 or more drugs?

How is prealbumin related to albumin?

Aside from being synthesized in the liver and serving as a transport protein in the blood, prealbumin (PA) doesn’t really have much in common with albumin. More specifically, PA is not derived from albumin and, in fact, the two proteins are structurally distinct from each other!

So where does PA get its name? PA is the original name for transthyretin (TTR), a transport protein that primarily carries thyroxine (T4) and a protein bound to retinol (vitamin A). The name arose because TTR migrated faster than albumin on gel electrophoresis of human serum.1

Because of its much shorter serum half-life compared to that of albumin ( ~2 days vs ~20 days),2 PA is more sensitive to recent changes in protein synthesis and more accurately reflects recent dietary intake (not necessarily overall nutritional status) than albumin. 3

But, just like albumin, PA may represent a negative acute phase reactant, as its synthesis drops during inflammatory states in favor of acute phase reactants such as C-reactive protein. 4 So be cautious about interpreting low PA levels in patients with active infection, inflammation or trauma.



  1. Socolow EL, Woeber KA, Purdy RH, et al. Preparation of I-131-labeled human serum prealbumin and its metabolism in normal and sick patients. J. Clin Invest 1965; 44: 1600-1609. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC292644/
  2. Oppenheimer JH, Surks MI, Bernstein G, and Smith JC. Metabolism of Iodine-131-labeled Thyroxine-Binding Prealbumin in Man. Science 1965; 149: 748-750. https://www.ncbi.nlm.nih.gov/pubmed/14330531
  3. Ingenbleek Y, Young VR. Significance of prealbumin in protein metabolism. Clin Chem Lab Med 2002; 40: 1281-1291. https://www.ncbi.nlm.nih.gov/pubmed/12553432
  4. Shenkin A. Serum prealbumin: is it a marker of nutritional status or of risk of malnutrition? Clin Chem 2006;52:2177 – 2179. http://clinchem.aaccjnls.org/content/52/12/2177


Contributed by Colin Fadzen, Medical Student, Harvard Medical School, Boston, MA.


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How is prealbumin related to albumin?

Could constipation contribute to hyperkalemia in my patient with chronic kidney disease?

Yes! Constipation may be an important contributor to hyperkalemia in some patients with chronic kidney disease (CKD).

 Under normal conditions, 80-90% of excess dietary potassium (K+) is excreted by the kidneys, with the remainder excreted through the GI tract.1 However, in advanced CKD, particularly in the setting of end-stage kidney disease (ESKD), the GI tract assumes a much more important role in maintaining K+ balance. 

As early as 1960’s, the daily fecal excretion of K+ was found to be directly related to the wet stool weight, irrespective of creatinine clearance. Furthermore, K+ excretion in stool was as high as ~80% of dietary intake (average 37%) in some hemodialysis (HD) patients compared to normal controls (average 12%). 2

Such increase in K+ excretion in the GI tract of patients with CKD was later found to be primarily the result of K+ secretion into the colon/rectum rather than reduced dietary K+ absorption in the small intestine 1,3, was inversely related to residual kidney function, and as a consequence could serve as the main route of K+ excretion in patients with ESKD. 4

Collectively, these findings suggest that in addition to non-dietary factors such as medications, we may need to routinely consider constipation as a potential cause of hyperkalemia in patients with advanced CKD or ESKD. 1

Bonus Pearl: Did you know that secretion of K+ by the apical surface of colonic epithelial is mediated in part by aldosterone-dependent mechanisms? 5


  1. St-Jules DE, Goldfarb DS, Sevick MA. Nutrient non-equivalence: does restricting high-potassium plant foods help to prevent hyperkalemia in hemodialysis patients? J Ren. Nutr 2016;26: 282-87. https://www.ncbi.nlm.nih.gov/pubmed/26975777
  2. Hayes CP, McLeod ME, Robinson RR. An extrarenal mechanism for the maintenance of potassium balance in severe chronic renal failure. Trans Assoc Am Physicians 1967;80:207-16.
  3. Martin RS, Panese S, Virginillo M, et al. Increased secretion of potassium in the rectum of humans with chronic renal failure. Am J Kidney Dis 1986;8:105-10. https://www.ncbi.nlm.nih.gov/pubmed/3740056
  4. Cupisti A, Kovesdy CP, D’Alessandro C, et al. Dietary approach to recurrent or chronic hyperkalemia in patients with decreased kidney function. Nutrients 2018, 10, 261;doi:10.3390/nu10030261. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5872679/
  5. Battle D, Boobes K, Manjee KG. The colon as the potassium target: entering the colonic age of hyperkalemia treatment. EBioMedicine 2015;2: 1562-1563. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4740340/pdf/main.pdf


Contributed in part by Alex Blair, MD, Mass General Hospital, Boston, MA.

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Could constipation contribute to hyperkalemia in my patient with chronic kidney disease?

Should I routinely screen my patients with heart failure for iron deficiency?

Even in the absence of anemia, screening for iron deficiency (ID) has been recommended in patients with heart failure (HF) with reduced ejection fraction (HFrEF) by some European and Australia-New Zealand cardiology societies. 1

In contrast, the 2017 American College of Cardiology/American Heart Association/Heart Failure Society of America guidelines do not mention routine screening for ID in such patients but instead state (under “Anemia”) that in patients with NYHA class II and III HF and ID (ferritin < 100 ng/mL or 100 to 300 ng/mL plus transferrin saturation <20%), IV iron replacement “might be reasonable” to improve functional status and quality of life (IIb-weak recommendation).2

As these guidelines are primarily based on data derived from patients with HFrEF, whether patients with HF with preserved (eg, >45%) ejection fraction (HFpEF) should undergo routine screening for ID is even less clear due to conflicting data based on limited small studies 3,4

What is known is that up to 50% or more of patients with HF with or without anemia may have ID. 5 Although most studies involving ID and HF have involved patients with HFrEF, similarly high prevalence of ID in HFpEF has been reported. 6,7

A 2016 meta-analysis involving patients with HFrEF and ID found that IV iron therapy alleviates HF symptoms and improves outcomes, exercise capacity and quality of life irrespective of concomitant anemia; all-cause and cardiovascular mortality rates were not significantly impacted, however.8  

Fortunately, larger trials in the setting of acute and chronic systolic HF are underway (Affirm-AHF, 9 IRONMAN 10).  Stay tuned!

Bonus Pearl: Did you know that iron deficiency directly affects human cardiomyocyte function by impairing mitochondrial respiration  and reducing its contractility and relaxation?11


  1. Silverberg DS, Wexler D, Schwartz D. Is correction of iron deficiency a new addition to the treatment of the heart failure? Int J Mol Sci 2015;16:14056-74. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4490538/
  2. Yancy CW, Jessup M, Bozkurt B, et al. 2017 ACC/AHA/HFSA focused update of the 2013 ACCF/AHA guideline for the management of heart failure. Circulation 2017;136:e137-e161. https://www.ahajournals.org/doi/pdf/10.1161/CIR.0000000000000509
  3. Kasner M, Aleksandrov AS, Westermann D, et al. Functional iron deficiency and diastolic function in heart failure with preserved ejection fraction. International J of Cardiol 2013;168:12:4652-57. https://www.ncbi.nlm.nih.gov/pubmed/23968714
  4. Enjuanes C, Klip IT, Bruguera J, et al. Iron deficiency and health-related quality of life in chronic heart failure: results from a multicenter European study. Int J Cardiol 2014;174:268-275. https://www.ncbi.nlm.nih.gov/pubmed/24768464
  5. Drodz M, Jankowska EA, Banasiak W, et al. Iron therapy in patients with heart failure and iron deficiency: review of iron preparations for practitioners. Am J Cardiovasc Drugs 2017;17:183-201. https://www.ncbi.nlm.nih.gov/pubmed/28039585
  6. Bekfani T, Pellicori P, Morris D, et al. Iron deficiency in patients with heart failure with preserved ejection fraction and its association with reduced exercise capacity, muscle strength and quality of life. Clin Res Cardiol 2018, July 26. Doi: 10. 1007/s00392-018-1344-x. https://www.ncbi.nlm.nih.gov/pubmed/30051186
  7. Nunez J, Dominguez E, Ramon JM, et al. Iron deficiency and functional capacity in patients with advanced heart failure with preserved ejection fraction. International J Cardiol 2016;207:365-67. https://www.internationaljournalofcardiology.com/article/S0167-5273(16)30185-1/abstract
  8. Jankowska EA, Tkaczynszyn M, Suchocki T, et al. Effects of intravenous iron therapy in iron-deficient patients with systolic heart failure: a meta-analysis of randomized controlled trials. Eur J Heart Failure 2016;18:786-95. https://www.ncbi.nlm.nih.gov/pubmed/26821594
  9. https://clinicaltrials.gov/ct2/show/NCT02937454
  10. https://clinicaltrials.gov/ct2/show/NCT02642562
  11. Hoes MF, Beverborg NG, Kijlstra JD, et al. Iron deficiency impairs contractility of human cardiomyoctyes through decreased mitochondrial function. Eur J Heart Failure 2018;20:910-19. https://www.ncbi.nlm.nih.gov/pubmed/29484788  


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Should I routinely screen my patients with heart failure for iron deficiency?

Why is my hospitalized patient with alcohol withdrawal syndrome so thrombocytopenic?

Although thrombocytopenia associated with chronic alcoholism may be related to complications of cirrhosis (eg, platelet sequestration in spleen due to portal hypertension, poor platelet production, and increased platelet destruction) (1), it may also occur in the absence of cirrhosis due to the direct toxic effect of alcohol on platelet production and survival (2).

In a prospective study of patients ingesting the equivalent of a fifth or more daily of 86 proof whiskey admitted for treatment of alcohol withdrawal—without evidence of severe liver disease, infection or sepsis— 81% had initial platelet counts below 150,000/µl, with about one-third having platelet counts below 100,000 µl (as low as 24,000/ul) (3).

In most patients, 2-3 days elapsed before the platelet count began to rise significantly, peaking 5-18 days after admission. Others have also reported that platelet counts rise within 5-7 days and normalize in a few weeks after alcohol withdrawal (1); bleeding complications have been uncommon in this setting.

Perhaps even more intriguing is the report of the association between thrombocytopenia in early alcohol withdrawal and the development of delirium tremens or seizures (sensitivity and specificity ~ 70%, positive predictive value less than 10% but with a negative predictive value of 99%) (4)! In fact, the authors suggested that, if their findings are corroborated, a normal platelet count could potentially be used to identify patients at low risk of alcohol withdrawal syndrome and therefore outpatient therapy. 

1. Mitchell O, Feldman D, Diakow M, et al. The pathophysiology of thrombocytopenia in chronic liver disease. Hepatic Medicine: Evidence and Research 2016;8 39-50. https://www.dovepress.com/the-pathophysiology-of-thrombocytopenia-in-chronic-liver-disease-peer-reviewed-article-HMER
2. Cowan DH. Effect of alcoholism on hemostasis. Semin Hematol 1980;17:137-47. https://www.ncbi.nlm.nih.gov/pubmed/6990498
3. Cowan DH, Hines JD. Thrombocytopenia of severe alcoholism. Ann Intern Med 1971;74:37-43. http://annals.org/aim/article-abstract/685069/thrombocytopenia-severe-alcoholism.

4. Berggren U, Falke C, Berglund KJ, et al. Thrombocytopenia in early alcohol withdrawal is associated with development of delirium tremens or seizures. Alcohol & Alcoholism 2009;44:382-86. https://www.ncbi.nlm.nih.gov/pubmed/19293148

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Why is my hospitalized patient with alcohol withdrawal syndrome so thrombocytopenic?

Is neurotoxicity caused by cefepime common?

The incidence of cefepime-induced neurotoxicity (CIN) has varied from 1% to 15%.1 Potential clinical manifestations of CIN include delirium, impaired level of consciousness, disorientation/agitation, myoclonus, non-convulsive status epilepticus, seizures, and aphasia.1  Many of these signs and symptoms (eg, delirium) are common among hospitalized patients.

Although renal dysfunction and inadequately adjusted dosages are often cited as risk factors, one-half of patients develop suspected CIN despite apparently proper adjustment for renal function.In addition,  several case reports of CIN have involved patients with normal renal function. 2  A study of 1120 patients receiving cefepime found epileptiform discharges in 14 cases, most having normal renal function.3 Of interest, in the same study, the prevalence of epileptiform discharges was 6-fold higher than that of meropenem!

Proposed mechanisms for CIN include its avidity for central nervous system GABA-A receptors (higher than that of many beta-lactam antibiotics) combined with its high concentration in brain tissue.1 Renal impairment, decreased protein binding, increased organic acid accumulation can increase transfer of cefepime across the blood brain barrier from an expected 10% to up to 45% of its serum concentration, further contributing to its neurotoxicity.4



  1. Appa AA, Jain R, Rakita RM, et al. Characterizing cefepime neurotoxicity: a systematic review. Open Forum Infectious Diseases 2017 Oct 10;4(4):ofx170. doi: 10.1093/ofid/ofx170. eCollection 2017 Fall. https://www.ncbi.nlm.nih.gov/pubmed/29071284
  2. Meillier A, Rahimian D. Cefepime-induced encephalopathy with normal renal function. Oxford Medical Case Reports, 2016;6, 118-120. https://academic.oup.com/omcr/article/2016/6/118/2362353
  3. Naeije G, Lorent S, Vincent JL, et al. Continuous epileptiform discharges in patients treated with cefpime or meropenem Arch Neurol 2011;68:1303-7. https://www.ncbi.nlm.nih.gov/pubmed/21987544
  4. Payne LE, Gaganon DJ, Riker RR, et al. Cefepime-induced neurotoxicity: a systematic review. Critical Care 017;21:276. https://www.ncbi.nlm.nih.gov/pubmed/29137682


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Is neurotoxicity caused by cefepime common?

Should my patient with compensated heart failure be placed on a sodium-restricted diet?

Although sodium restriction is routinely recommended for patients with heart failure (HF), the data is often conflicting with a number of studies even suggesting that it may be harmful in some patients.

Two randomized trials (by the same group) involving patients with compensated HF recently discharged from the hospital reported that “less restricted” sodium diet (2.8 gm/d) along with fluid restriction (1 L/day) and high dose furosemide (at least 125-250 mg furosemide twice daily) was associated with less rates of readmissions and improved levels of brain natriuretic peptide, aldosterone and plasma renin activity compared to patients on more restricted sodium diet (1.8 gm/d). 1,2

Analysis of data from the multihospital HF Adherence and Retention Trial enrolling New York Heart Association functional class II/III HF patients found that sodium restriction (<2.5 gm/d) was associated with significantly higher risk of death or HF hospitalization but only in patients not on an angiotensin converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB). 3

In normal subjects who are not sodium deprived, excess sodium intake has been shown to cause expansion of intravascular volume without increasing total body water. 4 Thus, sodium restriction combined with diuretics may reduce intravascular volume and renal perfusion, further stimulating the renin-angiotensin-aldosterone system and fluid retention. 5

Bonus Pearl: Did you know that the 2013 American College of Cardiology Foundation/American Heart Association guidelines downgraded the recommendation for sodium restriction to Class IIa (reasonable) with Level of Evidence:C? 6


  1. Paterna S, Gaspare P, Fasullo S, et al. Normal-sodium diet compared with low-sodium diet in compensated congestive heart failure: is sodium an old enemy or a new friend? Clin Sci 2008;114:221-230. https://www.ncbi.nlm.nih.gov/pubmed/17688420
  2. Paterna S, Parrinello G, Cannizzaro S, et al. Medium term effects of different dosage of diuretic, sodium, and fluid administration on neurohormonal and clinical outcome in patients with recently compensated heart failure. Am J Cardiol 2009;103:93-102. https://www.ncbi.nlm.nih.gov/pubmed/19101237
  3. Doukky R, Avery E, Mangla A, et al.Impact of dietary sodium restriction on heart failure outcomes. J Am Coll Cariol HF 2016;4:24-35. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4705447/
  4. Heer M, Baisch F, Kropp J et al. High dietary sodium chloride consumption may not induce body fluid retention in humans. Am J Physiol Renal Physiol 2000;278:F585-F595. https://www.ncbi.nlm.nih.gov/pubmed/10751219
  5. Rothberg MB, Sivalingam SK. The new heart failure diet: less salt restriction, more micronutrients. J Gen Intern Med 25;1136-7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2955483/
  6. Yancy CW, Jessup M, Bozkurt B, et al. 2013 CCF/AHA guideline for the management of heart failure: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 2013;62:e147-239. https://www.ncbi.nlm.nih.gov/pubmed/23741058

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Should my patient with compensated heart failure be placed on a sodium-restricted diet?