- Choose the electrolyte to replete — potassium, magnesium, or phosphate. The relevant inputs appear automatically.
- Enter the current serum level (and, for phosphate, body weight in kg). For potassium you may also adjust the target.
- The tool returns an estimated repletion dose/amount and a route & monitoring note as soon as the inputs are valid.
- Treat every figure as an estimate: dosing rules are approximate and center-dependent. In CKD/AKI, reduce the dose, slow infusions, and recheck levels — impaired excretion makes over-correction easy.
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When to Use
Use this aid when you have a documented low electrolyte (hypokalemia, hypomagnesemia, or hypophosphatemia) and want a quick, defensible starting estimate for replacement. It converts the common bedside rules of thumb — "each 10 mEq of KCl raises serum K by ~0.1 mEq/L," severity-banded magnesium dosing, weight-based phosphate dosing — into a single tidy result with a route and monitoring reminder. It is a teaching/sanity-check tool, not a protocol generator: confirm the diagnosis, identify the cause, and reconcile every figure against your institution's standing orders.
Appropriate use
Adults with a confirmed low serum potassium, magnesium, or phosphate in whom you are planning replacement and want an order-of-magnitude estimate of dose and route. Useful at the bedside, on rounds, and for teaching the standard repletion heuristics.
When NOT to rely on it
These are population estimates with wide individual variability. Serum levels reflect only a fraction of total-body stores (especially for potassium and magnesium), and the "10 mEq → 0.1 mEq/L" potassium rule holds only with normal renal function and is very approximate. Do not use the unmodified estimates in CKD, AKI, or oliguria (impaired excretion → over-repletion and life-threatening hyper-K/hyper-Mg/hyperphosphatemia), nor as a substitute for cardiac monitoring during IV potassium or magnesium. Always defer to institutional protocols and individualized assessment.
Pearls & Pitfalls
Fix magnesium first
Hypomagnesemia drives refractory hypokalemia by promoting renal potassium wasting. If potassium will not come up despite repletion, check and correct the magnesium — replete magnesium before or alongside potassium. Always treat the underlying cause too (diuretics, GI losses, refeeding, alcohol use), not just the number.
Oral when you can, recheck after
Oral repletion is preferred whenever the patient can tolerate it and the deficit is not severe/symptomatic — it is safer and self-limiting. Reserve IV for severe or symptomatic deficits or when the gut is unavailable, give IV potassium and magnesium with monitoring, and recheck the level after a repletion course before giving more. Useful unit conversions: 1 g MgSO₄ = 8.12 mEq = 4.06 mmol Mg; 1 mmol phosphate ≈ 31 mg.
Pitfalls
(1) CKD/AKI/oliguria: impaired excretion means the standard doses can over-correct — reduce the dose, slow the infusion, and monitor closely (hyper-K, hyper-Mg, hyperphosphatemia are dangerous). (2) IV potassium has rate limits (peripheral ≤10 mEq/hr; central ≤20 mEq/hr with monitoring) — never push it. (3) IV phosphate carries calcium–phosphate precipitation risk and can drop calcium; infuse over 6–12 h and watch for hypocalcemia. (4) Serum levels underestimate total-body deficits, so estimates may under-dose chronic depletion — clinical correlation and rechecks are essential. (5) These figures are not a substitute for institutional protocols.
Why Use It
Potassium, magnesium, and phosphate are the electrolytes clinicians replete most often, and each has its own dosing logic — a potassium "raise-per-dose" rule of thumb, severity-banded magnesium dosing, and weight-based phosphate dosing. Holding all three in your head at the bedside is error-prone, so this tool collects the standard heuristics in one place and pairs each with the route and monitoring caveats that matter most. For nephrology and critical-care patients in particular, the dominant consideration is renal: reduced excretion turns a routine repletion into a real risk of over-correction, which is why the tool keeps the CKD/AKI caution front and centre. Treat it as a teaching aid and a sanity check — a fast way to get an order-of-magnitude estimate — and always confirm against your institution's protocols and the individual patient.
Electrolyte Repletion — Potassium, Magnesium, Phosphate
Choose the electrolyte, enter the current level (and weight for phosphate), and get an estimated repletion dose with a route and monitoring note. Tick the CKD/AKI box for a stronger caution. Every figure is an estimate — defer to your institution's protocols.
⚕ Estimates based on commonly-used rules of thumb (Kraft MD et al. Am J Health Syst Pharm. 2005; Gennari FJ. N Engl J Med. 1998; ASPEN parenteral electrolyte guidance). Dosing is approximate and center-dependent; serum levels underestimate total-body stores. In CKD/AKI, reduce doses and monitor closely. For licensed clinicians; not a substitute for institutional protocols or individualized assessment.
Next Steps
Use the estimate as a starting point, then individualize, monitor, and recheck.
- Identify and treat the cause — diuretics, GI losses, refeeding syndrome, alcohol use, DKA recovery, and renal wasting all change the strategy, not just the dose.
- Prefer the oral route when the patient tolerates it and the deficit is mild; reserve IV for severe/symptomatic deficits or an unavailable gut, and give IV potassium and magnesium with cardiac monitoring.
- Correct magnesium first when potassium is refractory — hypomagnesemia perpetuates renal potassium wasting and blocks repletion.
- Recheck the level after a repletion course before giving more, and watch for over-correction — especially in CKD/AKI, where excretion is impaired.
- For potassium specifically, cross-check the dietary contribution with the potassium dietary load tool; for acid–base context use the bicarbonate deficit estimator.
Evidence & References
Estimation rules used
| Electrolyte | Rule of thumb (estimate) |
|---|---|
| Potassium (K⁺) | ~10 mEq KCl raises serum K⁺ by ~0.1 mEq/L (normal renal function). Replacement ≈ (target − current) ÷ 0.1 × 10 mEq. Oral preferred; IV ≤10 mEq/hr peripheral, ≤20 mEq/hr central with monitoring. |
| Magnesium (Mg²⁺) | Mild 1.6–1.9 mg/dL → oral Mg. Moderate 1.0–1.5 → IV MgSO₄ ~2–4 g. Severe <1.0 or symptomatic → IV MgSO₄ ~4–8 g over hours. (1 g MgSO₄ = 8.12 mEq = 4.06 mmol.) |
| Phosphate (PO₄) | Mild 2.3–3.0 mg/dL → oral. Moderate 1.5–2.2 → IV ~0.16–0.32 mmol/kg. Severe <1.5 → IV ~0.32–0.64 mmol/kg over 6–12 h. (1 mmol PO₄ ≈ 31 mg.) |
Cautions
| Situation | Implication |
|---|---|
| CKD / AKI / oliguria | Impaired excretion — reduce dose, slow infusion, monitor for hyper-K / hyper-Mg / hyperphosphatemia |
| Refractory hypokalemia | Correct magnesium first — it perpetuates renal K⁺ wasting |
| IV phosphate | Calcium–phosphate precipitation and hypocalcemia risk; infuse over 6–12 h with monitoring |
These figures are widely-taught heuristics, not validated formulas. Serum levels reflect only a fraction of total-body stores, so estimates may under-dose chronic depletion; always recheck levels and individualize. Replace institutional protocols, never substitute for them.
References
- Kraft MD, Btaiche IF, Sacks GS, Kudsk KA. Treatment of electrolyte disorders in adult patients in the intensive care unit. Am J Health Syst Pharm. 2005;62(16):1663–1682. doi:10.2146/ajhp040300.
- Gennari FJ. Hypokalemia. N Engl J Med. 1998;339(7):451–458. doi:10.1056/NEJM199808133390707.
- American Society for Parenteral and Enteral Nutrition (ASPEN). Clinical guidelines / position papers on parenteral electrolyte and phosphate repletion. JPEN / Nutr Clin Pract. (current edition).
