Prescribing During Intermittent Haemodialysis

Intermittent haemodialysis usually runs 3 to 4 hours, three times weekly, and removes small, water-soluble drugs with a low protein binding and a small volume of distribution. Residual kidney function still contributes to clearance and should be counted.

Predictors of removal. Molecular weight under about 500 daltons (high-flux membranes remove much larger molecules), protein binding under 80 to 90 percent, a volume of distribution under about 1 L/kg, and low endogenous clearance.

Dose principle. Give the dose of a dialysable drug after the session on dialysis days, and so replace what was removed. A loading dose is unchanged. Maintenance doses use the band for a GFR under 10 mL/min.

Dialysed examples. Aminoglycosides, vancomycin (high-flux), most penicillins and cephalosporins, aciclovir, lithium, metformin, gabapentin, pregabalin, levetiracetam, atenolol, metoprolol and the ACE inhibitors.

Not significantly dialysed. Ceftriaxone, digoxin, amiodarone, warfarin, phenytoin, doxycycline, clindamycin, carvedilol, amlodipine and statins.

Preferences. Choose agents that are not dialysed and need no adjustment when possible, such as ceftriaxone, for convenience. Prefer unfractionated heparin to enoxaparin, which accumulates.

Avoid. Metformin, NSAIDs, morphine, codeine, pethidine, nitrofurantoin, magnesium and aluminium containing products and gadolinium agents of high risk.

Special groups.

• Children: dose by mg/kg after dialysis and check levels where available.

• Older adults: expect intradialytic hypotension, so avoid giving antihypertensives before the session.

• Pregnancy: more intensive dialysis is used, so involve a nephrologist.

• East Africa: dialysis may be less frequent or interrupted, so avoid regimens that rely on thrice-weekly clearance unless sessions are secure.

• Vancomycin: loading 25 mg/kg intravenously (maximum 3 g), then 500 to 1000 mg after each session, directed by a pre-dialysis level of 15 to 20 mg/L.

• Gentamicin: 1.5 to 2 mg/kg after the session, with the next dose given only when the pre-dialysis level is under 2 mg/L.

• Cefazolin: 2 g intravenously after each session (3 g after the long interdialytic interval).

• Meropenem: 500 mg intravenously every 24 hours, given after dialysis.

• Aciclovir intravenous: 5 mg/kg every 24 hours for the 10 mg/kg regimen, given after dialysis.

• Gabapentin: a supplemental 125 to 350 mg after each session on top of 100 to 300 mg once daily.

• Anticoagulation of the circuit: unfractionated heparin by a bolus and infusion directed by local practice.

Monitoring. Take drug levels before the session, check the potassium and bicarbonate before and after, and record the dry weight and intradialytic blood pressure.

Stop rules. Stop or hold any drug that causes intradialytic hypotension, recurrent hyperkalaemia or bleeding at the circuit.

Referral and escalation. Contact the dialysis unit when a session is missed, when potassium is 6.0 mmol/L or over, when a dialysable poison such as lithium is taken, or when a drug level stays out of range.

Common errors. Giving dialysable drugs before the session, giving enoxaparin, continuing metformin, and giving full antihypertensive doses before dialysis.