InfusionFox
Cardiology

Diltiazem CRI

Atrial fibrillation rate control (most common CRI indication in vet ICU), supraventricular tachycardia refractory to vagal maneuvers, and rapid rate control in hyperthyroid cats or HCM cats without LVOT obstruction. CRI delivery preferred when sustained rate control is needed beyond the duration of bolus therapy. Continuous ECG and BP monitoring required throughout the infusion.

Stock: 5 mg/mL (5 000 µg/mL), 5 mL vial (25 mg per vial)
How this calculator works

Enter the patient's weight and the desired CRI dose. The calculator picks a concentration (1, 0.5, or 0.2 mg/mL) that keeps the pump in its accurate range.

Loading dose (0.05–0.25 mg/kg IV slowly over 2–3 min) is shown above the CRI maintenance rate. Most of the acute hypotension and AV-block risk lives in the loading bolus itself; give slowly and reassess before starting the CRI.

NEVER concurrent with IV beta-blockers; the additive AV-block effect can precipitate complete heart block. If the patient is on an oral beta-blocker, hold the next dose and consult cardiology before starting.

Typical range: 2.0–10.0 ug/kg/min (dogs and cats)
500 µg/mL
5 mL of 5 mg/mL stock (25 mg, 1 vial) into 45 mL of 0.9% NaCl or 5% dextrose in a 50 mL syringe
Use a different concentration

All preparations are pharmacologically equivalent. The default (500 µg/mL) fits the most common clinical use case. The alternatives below cover situational needs.

Awaiting input

Enter a patient weight to see the result.

Reference

How the calculation works

Diltiazem CRI is dosed in µg/kg/min. To convert a per-minute dose into a per-hour CRI rate, multiply by 60. The full formula:

$$\text{mL/hr} = \frac{\text{weight}_{\text{kg}} \times \text{dose}_{\mu g/kg/min} \times 60}{\text{concentration}_{\mu g/mL}}$$

Why the 60? The patient's weight (kg) times the dose (µg per kg per minute) gives micrograms per minute. Multiplying by 60 converts to micrograms per hour. Dividing by the concentration (µg per mL of the prepared CRI) yields mL per hour.

In target-pump-rate mode the pump rate is fixed by the clinician and the bag concentration is the unknown. The preparation runs in three steps.

Step 1: bag concentration

Same numerator as standard-bag mode (the total drug delivered per hour for this patient), but divided by the chosen pump rate instead of by a chosen bag concentration:

$$\text{bag concentration}_{\mu g/mL} = \frac{\text{weight}_{\text{kg}} \times \text{dose}_{\mu g/kg/min} \times 60}{\text{pump rate}_{\text{mL/hr}}}$$

Step 2: total drug in the bag

The bag concentration times the chosen bag volume gives the total micrograms of drug to add. Convert to milligrams (divide by 1,000) for the size of stock you'll actually be drawing:

$$\text{total drug}_{\mu g} = \text{bag concentration}_{\mu g/mL} \times \text{bag volume}_{\text{mL}}$$
$$\text{total drug}_{mg} = \frac{\text{total drug}_{\mu g}}{1{,}000}$$

Step 3: volume of stock to draw

Total drug divided by the stock vial concentration gives the volume of stock to draw and add to the bag:

$$\text{stock volume}_{\text{mL}} = \frac{\text{total drug}_{mg}}{\text{stock}_{mg/mL}}$$

Worked through together: divide the total drug in the bag by the stock vial's mg/mL to get the mL of stock that contains that much drug. That is the volume to pull into the syringe and add to the bag.

Worked example with current inputs

Enter a patient weight to see the worked example.

Reference

Recommended dilutions

Target concentration Dilution When useful
1000 µg/mL 10 mL of 5 mg/mL stock (50 mg, 2 vials) into 40 mL of 0.9% NaCl or 5% dextrose in a 50 mL syringe Concentrated preparation for patients ≥15 kg. Minimizes carrier-fluid load.
500 µg/mL 5 mL of 5 mg/mL stock (25 mg, 1 vial) into 45 mL of 0.9% NaCl or 5% dextrose in a 50 mL syringe Standard preparation for patients 3–15 kg. Uses one full vial of stock, convenient for the typical A-fib rate-control workflow.
200 µg/mL 2 mL of 5 mg/mL stock (10 mg) into 48 mL of 0.9% NaCl or 5% dextrose in a 50 mL syringe Dilute preparation for cats and small dogs (<3 kg). Essential when more concentrated preps would drop pump rate below 2 mL/hr at typical doses.

Stock: 5 mg/mL injectable, 5 mL vial = 25 mg per vial. Dilute in 0.9% NaCl or 5% dextrose; both compatible. The 5 mL vial size means a typical syringe-pump preparation uses one full vial (for the 0.5 mg/mL prep) or two vials (for the 1 mg/mL concentrated prep). Compatibility: avoid co-administration in the same line with furosemide (precipitation at higher concentrations) and with sodium bicarbonate. Y-site administration with other vasoactive drugs is generally compatible but verify for any specific drug combination. Storage: refrigerate the prepared syringe if not used immediately. Stability is 24 hours at room temperature, longer refrigerated. Discard if any precipitate appears.

Dilution helper — Diltiazem CRI

Work out how many mL of stock drug and diluent to combine for any target concentration. Stock is pre-filled for Diltiazem CRI; change it if you're using a different vial.

Suggestions from the reference table above
Draw up

Enter stock, target concentration, and final volume.