IVIG Calculator — Dose, Infusion Rate and Step-Up Time
An immunoglobulin pump rate is (ordered mg/kg/min x weight in kg x 60) ÷ concentration in mg/mL. For a 70 kg patient on a 10% product at 0.5 mg/kg/min that is 21 mL/hr. The reason it needs a calculator of its own is that IVIG is not run at one rate: it is started low and stepped up at intervals, so the sum has to be repeated at every step, and the total time only falls out once you know how much volume is left when the last rate is reached. Enter the weight, the dose and the product strength below and the whole schedule is worked out at once.
Escalation steps, as written on the order. The last step runs until the bag is empty.
Why the Rate Climbs Instead of Holding
Most infusions have one rate because the thing being delivered has one target. Immunoglobulin has two, and they pull in opposite directions: the dose has to go in, and the speed at which it goes in is itself the main driver of how badly the patient tolerates it.
The reactions clinicians watch for during an immunoglobulin infusion — headache, chills, flushing, rigors, myalgia, and less commonly thrombotic and renal events — are associated with the rate of delivery far more than with the total amount given. That makes the first ninety minutes a tolerance test rather than a dosing exercise. Starting at a low rate and holding it gives a reaction room to declare itself while the drug is still going in slowly enough that stopping or halving the rate is a real option. By the time the maintenance rate is reached, the patient has already demonstrated they can take it.
This is why a single mL/hr figure is the wrong answer to an immunoglobulin order, and why a generic infusion rate calculator cannot help. There is no one rate. There is a sequence, and the useful output is the whole sequence plus the time it adds up to.
The Thing Concentration Does Not Change
Ask around an infusion unit why a patient was switched to a concentrated product and someone will tell you it shortens the appointment. It does not. At a given ordered rate, the strength of the product makes no difference whatsoever to how long the infusion takes, and the arithmetic is worth seeing because it is so counterintuitive.
Grams are grams: a 70 kg patient prescribed 0.4 g/kg needs 28 g whichever bottle it comes from. A weaker product means more volume: 28 g is 280 mL at 10% and 560 mL at 5%. But the ordered rate is in mg/kg/min, and converting it to a pump setting divides by the concentration, so the weaker product also runs at half the mL/hr. Double the volume at half the speed takes exactly the same time.
| Product | Volume for 28 g | Pump rate at 4 mg/kg/min | Time at that rate |
|---|---|---|---|
| 5% (50 mg/mL) | 560 mL | 336 mL/hr | 1 hr 40 min |
| 10% (100 mg/mL) | 280 mL | 168 mL/hr | 1 hr 40 min |
| 20% (200 mg/mL) | 140 mL | 84 mL/hr | 1 hr 40 min |
The concentration cancels. Write the time out in full and it reduces to a formula with no concentration term in it at all:
Time (hours) = (Grams x 1000) ÷ (mg/kg/min x Weight in kg x 60)
So chair time is set by the dose per kilogram and the rate the order finishes at, and by nothing else. Including the escalation, the 28 g example above comes to 2 hr 44 min on a four-step ramp to 4 mg/kg/min. That figure is identical for the 5%, the 10% and the 20% product.
What concentration genuinely changes is the fluid load: 560 mL against 140 mL of the same drug at the same dose. That is a quarter of the volume into a patient whose heart or kidneys cannot take the extra half litre, and it is the actual reason for the switch. The appointment is just as long. It is the litre that was the problem.
The Ceiling Is a Property of the Product, Not the Patient
The step schedule this page starts with is a commonly described shape, not a recommendation. Licensed starting rates and maximum rates differ between immunoglobulin products, sometimes substantially, and they differ again by indication and by whether the patient is immunoglobulin-naive. A rate that is routine for one brand can be above the licensed ceiling for another at the same concentration.
So the order and the product label are the source for every rate in the schedule, and the fields above are editable for exactly that reason. What a calculator can legitimately do is the arithmetic and the timekeeping: convert each ordered rate into a pump setting, work out how much volume each held step consumes, and tell you when the bag will be empty. Deciding what the rates should be is not arithmetic.
SCIg Is the Same Drug and a Different Calculation
Subcutaneous immunoglobulin shares the dose arithmetic and almost nothing else. The grams still come from body weight and the volume still comes from the concentration, which for SCIg is usually a 20% product, so the volumes are small. But the rate is not weight-based. It is ordered in mL per hour per infusion site, and the real constraint is how much fluid a single site will take before it becomes uncomfortable.
That turns the problem from a sequence of rates into a division: the total volume split across however many sites are needed to stay under the per-site ceiling, infused in parallel. Weekly or twice-weekly dosing also means the per-infusion grams are a fraction of an IVIG course, which is why SCIg volumes look so unalarming next to the figures above.
Where an Immunoglobulin Order Goes Wrong
The error that reaches the pump most often is a unit slip between mg/kg/min and mL/hr. They are both "the rate", they are quoted in the same conversation, and they differ by a factor of the weight and the concentration together, which is a large number and a different one for every patient. For the 70 kg example on a 10% product, 0.5 mg/kg/min is 21 mL/hr, so typing 0.5 into the pump runs it forty-two times too slowly. The slip in the other direction is the dangerous one: treating an ordered 21 mL/hr as though it were 21 mg/kg/min gives 882 mL/hr, the same factor of forty-two in the direction that cannot be undone by waiting.
The second is dosing weight. Immunoglobulin dosed on actual body weight in a markedly obese patient produces a large total, and whether that is intended is a prescribing decision, not something to resolve at the chairside by picking a different number. If the weight on the order is not the weight you would have used, that is a question for the prescriber rather than an input to adjust.
The third is quieter: assuming the step schedule completes. On a small dose or a concentrated product the fixed steps can deliver the entire volume before the maintenance rate is ever reached, and a schedule written out in advance will then overstate both the rate the patient actually received and the time it took. The calculator above stops at the step the infusion genuinely finishes in.
For the parts of an infusion order that are not immunoglobulin — a plain mL/hr, drops per minute on a gravity set, or the volume to draw from a vial — the IV calculator handles those, and the dose calculator covers weight-based dosing in mg/kg where no infusion is involved.
IVIG Questions, Answered
How do you calculate an IVIG infusion rate in mL per hour?
Why is IVIG given at a rate that keeps increasing?
How long does an IVIG infusion take?
Does the product concentration change the dose or just the volume?
Can I use the same calculation for subcutaneous immunoglobulin?
What happens if the bag empties before the last step?
Educational reference only. Confirm any clinical calculation independently before acting on it. How this page is reviewed
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