Step 1 — Calculate Loading Dose

Age years

Sex

Serum Creatinine μmol/L

Weight for dosing

Use actual weight (BMI <30). Switch to ideal for oedema or adjusted for BMI ≥30.

Dosing protocol

Hartford OD Dosing — Contraindications

CrCl <20 mL/min (use single dose + levels)
Pregnancy (use standard dosing with PK monitoring)
Burns >20% body surface area
Infective endocarditis (use synergy dosing 1mg/kg TDS)
Cystic fibrosis (augmented clearance — specialist dosing)
Ascites / third spacing (altered Vd)

Step 2 — Enter 6–14h Level

Timing: Take a single serum gentamicin level between 6 and 14 hours after the start of the first infusion. Plot on the Hartford nomogram to determine dosing interval.

Time since infusion start hours

Serum gentamicin level mg/L

Step 3 — Pre-Dose Level Monitoring

Pre-dose (trough) level mg/L

Pre-dose target: <1 mg/L before every dose (drug-free window). Check before 3rd/4th dose then twice weekly if stable. Daily if AKI or unstable renal function.

Hartford Nomogram — Interactive

Click to plot level

Click anywhere on the nomogram to plot your level · Or enter values in Step 2 above

▬ q24h zone ▬ q36h zone ▬ q48h zone ▬ Individualise / seek PK advice

Ongoing Monitoring Schedule

Situation	What to monitor	Frequency
Stable renal function	Pre-dose level	Twice weekly
Stable renal function	U&Es + creatinine	Twice weekly
AKI / unstable renal fn	Pre-dose level + U&Es	Daily
Duration >5 days	Audiometry assessment	Once (then PRN)
Each level	Confirm pre-dose <1 mg/L	Before every dose
If pre-dose >1 mg/L	Withhold dose, recheck	—

Step 1 — Patient Parameters & Empiric Dose

ASHP/IDSA 2020: Target AUC/MIC 400–600 mg·h/L (assuming MIC = 1 mg/L). Trough-only targets of 15–20 mg/L are no longer recommended — associated with increased nephrotoxicity without clear efficacy benefit.

Age years

Sex

Serum Creatinine μmol/L

Actual Body Weight kg

Infection severity / indication

Step 2 — AUC Calculation (Two-Level Method)

Sawchuk-Zaske two-level method: Collect a peak level 1–2h after infusion ends AND a trough level 30–60 min before next dose. Best drawn at steady state (3rd–4th dose for most patients, or earlier if unstable).

Dose administered mg

Infusion duration hours

Dosing interval hours

Peak level mg/L

Time of peak (from infusion end) h

Trough level mg/L

Time of trough (before next dose) h

AUC/MIC Result & Dose Recommendation

Enter patient parameters and levels above to calculate AUC/MIC.

How the AUC is Calculated

Empiric Initial Dosing Reference

For patients where serum levels are not yet available. Based on ASHP/IDSA 2020 population PK data (assuming MIC = 1 mg/L).

CrCl (mL/min)	Initial dose (ABW)	Interval	Expected AUC₂₄
>90	15–20 mg/kg	q8–12h	~400–500
50–90	15 mg/kg	q12h	~400–500
30–50	15 mg/kg	q24h	~400–500
15–30	15 mg/kg	q48h	Variable — level early
<15 / ESRD	Loading 25 mg/kg then LEVELS	After HD or levels	Highly variable

Loading dose: For critically ill patients, infective endocarditis, or serious MRSA — always give a loading dose of 25–30 mg/kg actual body weight (max 3g) over 60–90 min to achieve rapid therapeutic levels, regardless of renal function. Do not wait for levels before giving loading dose.

Gentamicin TDM Reference

Level Targets

Regimen	Pre-dose (trough)	Post-dose (peak)	Timing
OD dosing (Hartford)	<1 mg/L	Not routinely measured	6–14h post-dose (nomogram)
Synergy (endocarditis)	<1 mg/L	3–5 mg/L	Trough: before dose; Peak: 1h post
Traditional TDD	<2 mg/L	5–10 mg/L	Peak 1h post; trough pre-dose

Toxicity Thresholds

Level	Action
Pre-dose <1 mg/L	Safe to give next dose
Pre-dose 1–2 mg/L	Withhold dose — recheck in 4–6h. Review interval.
Pre-dose >2 mg/L	WITHHOLD. Contact pharmacy/microbiology. Check U&Es urgently.
Any level in AKI	Withhold further doses. Levels guided only. Consider alternative.

Nephrotoxicity Risk Factors

High risk combinations — extra vigilance:
Gentamicin + vancomycin (synergistic nephrotoxicity) · Gentamicin + NSAIDs · Gentamicin + ciclosporin/tacrolimus · Pre-existing CKD · Volume depletion · Age >65 · ICU / septic shock · Pre-existing hearing loss (↑ ototoxicity risk)

Ototoxicity & Nephrotoxicity

Nephrotoxicity (proximal tubular cell death): Typically reversible if drug stopped early. Manifests as rising creatinine, oliguria, granular casts. Risk: cumulative dose, pre-existing CKD, volume depletion, concomitant nephrotoxins.

Ototoxicity (cochlear and vestibular): Often irreversible. Cochlear damage → high-frequency sensorineural hearing loss (often bilateral). Vestibular damage → oscillopsia, ataxia, nausea. Risk: total cumulative dose, pre-existing hearing loss, renal impairment. Audiometry before and during therapy if >5 days.

Vancomycin TDM Reference — ASHP/IDSA 2020

AUC/MIC Targets

AUC₂₄ (mg·h/L)	MIC assumed	Interpretation
<400	1 mg/L	Sub-therapeutic — treatment failure risk. Increase dose/frequency.
400–600	1 mg/L	✓ Therapeutic target — maintain current regimen
600–700	1 mg/L	Supra-therapeutic — consider reducing dose. Monitor renal function.
>700	1 mg/L	Toxic — high AKI risk. Reduce dose urgently. Hold dose if trough >25 mg/L.

Trough Levels (when AUC not available)

Trough (mg/L)	Interpretation
<10	Sub-therapeutic. Increase dose or frequency.
10–15	Low-therapeutic. Consider increasing if serious infection.
15–20	Traditional target for serious MRSA (trough-based method)
20–25	High. Monitor renal function. Consider dose reduction.
>25	Toxic. Withhold dose. Urgent renal review. High AKI risk.

ASHP 2020 note on trough-only monitoring: Targeting trough 15–20 mg/L is no longer recommended for serious MRSA. It is associated with increased nephrotoxicity because of inter-patient AUC variability — the same trough can correspond to AUC of 350–900 mg·h/L. AUC-guided monitoring is preferred.

When to Use AUC vs Trough Monitoring

Scenario	Recommended approach
Serious MRSA (bacteraemia, IE, osteomyelitis, meningitis)	AUC/MIC-guided (target 400–600)
Non-serious infection (SSTI, colonisation)	Trough-only acceptable (target 10–15)
Surgical prophylaxis (single dose)	No TDM required
ICU / rapidly changing renal function	AUC-guided + daily levels
Dialysis (HD/CRRT)	Levels after each session; target AUC 400–600

Vancomycin Infusion Reactions

Red Man Syndrome (rate-related reaction, NOT allergy): Flushing, erythema, pruritus of face/neck/trunk ± hypotension during infusion. Not IgE-mediated. Managed by slowing infusion rate (minimum 60 min per gram — so 1.5g over 90 min, 2g over 120 min).

True vancomycin allergy (rare): Anaphylaxis (urticaria, bronchospasm, angioedema, hypotension) — manage as anaphylaxis. Alternative glycopeptide: teicoplanin (cross-reactivity ~15%). Daptomycin if severe allergy.

Maximum infusion rate: No faster than 10 mg/min for any dose. For large loading doses (e.g. 3g), infuse over minimum 3 hours.

Gentamicin & VancomycinDose Calculators

Gentamicin & Vancomycin
Dose Calculators