Personal Notes on Medications and Supplements for Kidney Patients: Kremezin, Probiotics, Magnesium, Fish Oil, Creatine and What to Avoid Before a Blood Test

Please read this first: this article is a summary of the site author's personal experience. Everyone's constitution, kidney stage and medications differ. Any drug or supplement mentioned here must be approved by your nephrologist or taken as prescribed — do not buy and use on your own.

1. Kremezin: Patented Spherical Activated Carbon

What it is

Kremezin® (AST-120) is an oral spherical carbon adsorbent developed by Kureha in Japan, 2 g per sachet. In the gut it adsorbs precursors of uremic toxins (especially those of indoxyl sulfate and p-cresyl sulfate), preventing their absorption into the blood so they leave in the stool.

The evidence

• Multiple Japanese studies show regular use lowers blood uremic toxin levels and slows CKD progression; some suggest it delays dialysis initiation
• The large international EPPIC trials (2015) missed their primary endpoint overall, but subanalysis showed benefit in adherent patients
• Several Taiwan medical centers list it as a self-paid option in pre-ESRD care, with shared decision-making (SDM) leaflets

My personal experience

• My creatinine fell after starting it, and it has continued to work after transplant
• Side effects: constipation, black stools (normal)
• Important caution: while on Kremezin, my potassium ran high at times — monitor your labs closely and discuss with your doctor. The carbon itself contains no potassium, but it may alter gut environment or bowel habits; individual variation is large
• Must be taken 1–2 hours apart from other medications, or it will adsorb them too

Key reminder

Kremezin is a patented, pharmaceutical-grade spherical carbon with specially engineered pore sizes that adsorb only uremic toxins of specific molecular weight. Ordinary activated charcoal bought off the shelf (food-grade, water-filter grade) does not have the same effect and may adsorb nutrients and medications instead. Do not substitute.

2. Renal Probiotics

The theory

CKD patients have gut dysbiosis — more bacteria that produce uremic toxins. Specific strains (certain Lactobacillus, Bifidobacterium, Streptococcus thermophilus) may theoretically reduce toxin precursor production.

The evidence

• Several small randomized trials show lower blood urea nitrogen and indoxyl sulfate, but long-term effects on eGFR are insufficiently proven
• A 2023 systematic review concluded "promising, but larger and longer studies are needed"
• Not all probiotics are equal — effects are strain-specific; ordinary yogurt or generic probiotics are not "renal probiotics"

My personal experience

• Used alongside Kremezin, my creatinine trended down, and it remains effective after transplant
• Check the potassium, phosphorus and sodium content when choosing (some excipients add up)
• Transplant patients are immunosuppressed; while probiotics are generally safe, there are case reports of probiotic bacteremia in immunocompromised people — always ask your transplant team first

3. Magnesium Supplements for Sleep

My experience

When I have trouble falling asleep, magnesium glycinate or magnesium citrate helps with sleep onset and muscle relaxation.

Forms of magnesium

The magnesium oxide most pharmacies stock is poorly absorbed and is used mainly as an antacid or for constipation — not an effective way to raise magnesium.

Critical warning for kidney patients

Magnesium is excreted mainly by the kidneys. In people with reduced function (especially eGFR < 30 and dialysis patients), supplementation can cause hypermagnesemia — nausea, muscle weakness, low blood pressure, diminished reflexes, and in severe cases arrhythmia and respiratory depression.

• Must be approved by your doctor and taken as prescribed
• Dialysate already contains magnesium; dialysis patients usually need no extra
• Check blood magnesium regularly

4. Fitness and Creatinine: Two Things That Distort Your Numbers

1. Heavy exercise the day before

Creatinine is a by-product of muscle metabolism. Intense exercise the previous day (especially weight training or long runs) releases creatinine from muscle breakdown, making the next day's creatinine noticeably higher and eGFR look worse.

My experience: I once played a full basketball game the day before a blood draw, and my creatinine jumped enough that my doctor nearly suspected a decline in kidney function.

Advice: avoid intense exercise for 24–48 hours before labs so results reflect true kidney function. If unavoidable, tell your doctor.

2. Gym supplements: creatine

Creatine monohydrate, popular among gym-goers, is metabolized into creatinine, raising blood creatinine during use — this does not mean kidney function has actually declined, but it confuses interpretation.

• For healthy people, current evidence considers creatine at recommended doses safe for the kidneys
• For people with reduced kidney function, long-term safety data are lacking, and it makes creatinine monitoring unreliable
• Must be approved by your doctor or taken as prescribed; if you use it, always tell your doctor at blood-test time

Other factors that affect creatinine

• Large meat intake (especially cooked red meat)
• Dehydration
• Certain drugs (cimetidine, trimethoprim, some antibiotics block creatinine secretion and raise readings)
• Muscle mass: muscular people have higher baselines — which is why KDIGO 2024 recommends adding cystatin C for athletes and bodybuilders

5. Fish Oil: Fine in Moderation, but Choose EPA > DHA

What I do

Fish oil is one of the few supplements I take in moderation. When choosing a product I look at a single criterion: EPA content higher than DHA. Many products on the market are DHA-dominant (for example algae or fish oils marketed for "children's brain development"), which is not the ideal ratio for adult kidney patients.

What EPA and DHA each do

Potential risks of too much DHA

More fish oil is not better. When the DHA proportion or total dose is high, risks reported in the literature include:

• Rise in LDL cholesterol (LDL-C): DHA-dominant formulas slightly raise LDL-C in several trials, whereas EPA alone generally does not
• Prolonged bleeding time: omega-3s inhibit platelet aggregation; at high doses bleeding time lengthens — especially important if you take anticoagulants or antiplatelets, or have surgery coming up (including fistula surgery)
• Gastrointestinal upset: fishy burps, diarrhea, nausea
• Arrhythmia (e.g. atrial fibrillation): recent large trials and meta-analyses link high-dose omega-3 (≥ 1 g/day) to a higher risk of atrial fibrillation, with risk increasing with dose

Reminders for kidney patients

• Choose EPA > DHA at a moderate dose (a typical maintenance dose is about 1 g/day EPA+DHA combined or less); don't chase mega-doses
• Dialysis patients: check that the product is not blended with cod liver oil (high vitamin A and D, which kidney patients clear poorly)
• Always ask your doctor first, especially if you are on anticoagulants, have a heart rhythm problem, or take immunosuppressants after transplant

Summary: My Principles

1. Any supplement — ask your doctor first. This is not a formality; kidney patients metabolize differently
2. Look at trends, not single points. One high reading? Think about what you did the day before
3. Patented drug ≠ generic product with a similar name. Kremezin is not ordinary charcoal; renal probiotics are not yogurt
4. Magnesium, potassium, phosphorus, sodium — the four words every kidney patient must check on a supplement label
5. Transplant patients, double the caution: immunosuppression and drug interactions mean everything new goes through the transplant team first

References

• Asai M, et al. Review of the efficacy of AST-120 (KREMEZIN®) on renal function in chronic kidney disease patients. Ren Fail. 2019.
• Schulman G, et al. Randomized Placebo-Controlled EPPIC Trials of AST-120 in CKD. J Am Soc Nephrol. 2015.
• Taipei Medical University Hospital. SDM leaflet: Self-paid Kremezin for pre-ESRD patients. 2022.
• Zheng HJ, et al. Probiotics, prebiotics, and synbiotics for the improvement of metabolic profiles in patients with CKD: systematic review and meta-analysis. Crit Rev Food Sci Nutr. 2021.
• KDIGO. 2024 Clinical Practice Guideline for the Evaluation and Management of CKD (cystatin C recommendation). 2024.
• Kreider RB, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation. J Int Soc Sports Nutr. 2017.
• National Kidney Foundation. Magnesium and Kidney Disease.
• Bhatt DL, et al. Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia (REDUCE-IT). N Engl J Med. 2019.
• Gencer B, et al. Effect of Long-Term Marine ω-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes: A Systematic Review and Meta-Analysis. Circulation. 2021.
• Allaire J, et al. A randomized, crossover, head-to-head comparison of EPA and DHA supplementation on inflammation markers and lipids (ComparED Study). Am J Clin Nutr. 2016.
• Liao Y, et al. Efficacy of omega-3 PUFAs in depression: A meta-analysis. Transl Psychiatry. 2019.

The content of this article is personal reflection and experience sharing only, and is not medical advice. For any questions about your health, illness or physical care, please seek help through professional medical channels and consult your physician.