Required section · Section 4 of 6

Guided case: a timed vancomycin pair

A serious-MRSA bloodstream-infection case uses vancomycin 1,250 mg IV every 12 hours infused over 1 hour. Doses start 08/13 05:00, 08/13 17:00, 08/14 05:00, and 08/14 17:00. Dose 5 runs 08/15 05:00–06:00 after about 4.7 half-lives; dose 6 starts 08/15 17:00. The model is one-compartment, first-order, steady-state intermittent infusion.

The 07:30 post-distribution specimen is 22.1 µg/mL = 22.1 mg/L; the 16:45 trough is 11.8 µg/mL = 11.8 mg/L. k = ln(22.1 / 11.8) / 9.25 = 0.0678 h⁻¹; half-life = ln(2) / k ≈ 10.2 h; end-infusion Cmax ≈ 22.1 × e^(0.0678 × 1.5) = 24.47 mg/L.

For intermittent infusion at steady state, Cmax,ss = (R0 / (V × k)) × ((1 − e^(−k × Tinf)) / (1 − e^(−k × τ))). With R0 = 1,250 mg/h, Tinf = 1 h, and τ = 12 h, V ≈ 88.69 L, CL = k × V ≈ 6.016 L/h, and AUC24 = 2 × 1,250 / 6.016 ≈ 416 mg·h/L. The 400–600 mg·h/L target applies only to the stated serious-MRSA/MIC context.

Concentration-time chart: post-distribution 22.1 µg/mL at 07:30 and trough 11.8 µg/mL at 16:45; AUC24 approximately 416 mg·h/L is a separate calculated annotation. — Figure 1Timed vancomycin concentrations at 07:30 and 16:45, with AUC24 ≈416 mg·h/L shown separately.

Proportional timeline from 08/13 through 08/15 showing q12h doses, dose 5 05:00–06:00, 07:30 post-distribution collection, 16:45 trough collection, and dose 6 at 17:00. — Figure 2Dose and peripheral collection events.

Vancomycin case data in collection order.
Event	Date and time	Source or result	Interpretive role
Dose 1	08/13 05:00–06:00	1,250 mg IV over 1 h	q12h steady-state lead-in
Dose 2	08/13 17:00–18:00	1,250 mg IV over 1 h	q12h steady-state lead-in
Dose 3	08/14 05:00–06:00	1,250 mg IV over 1 h	q12h steady-state lead-in
Dose 4	08/14 17:00–18:00	1,250 mg IV over 1 h	q12h steady-state lead-in
Dose 5	08/15 05:00–06:00	1,250 mg IV over 1 h	after about 4.7 half-lives
Post-distribution specimen	08/15 07:30	Peripheral, 22.1 µg/mL	1.5 h after infusion end
Trough specimen	08/15 16:45	Peripheral, 11.8 µg/mL	15 min before dose 6
Dose 6	08/15 17:00	1,250 mg IV starts	next q12h dose
Calculated result	—	AUC24 ≈416 mg·h/L	serious MRSA, MIC 1 mg/L context

Knowledge checks

Reading and checks are open. Sign in only to save.

Knowledge check 1

What is the preferred interpretation of the case trough of 11.8 µg/mL?

Choose one option.

About 416 mg·h/L from the stated one-compartment steady-state model.

Increase the dose because it is below the former 15-20 mg/L trough target.

Discard it because all troughs below 15 mg/L are invalid.

Knowledge check 2

Which documented fact supports using the 07:30 vancomycin result as a post-distribution level?

Choose one option.

It was drawn 1.5 hours after infusion end.

Creatinine was stable.

Section status

Finish this section

Reading and checks are open. Sign in only to save.

The module finishes after every required section is marked done and every check in those sections is correct.