Choosing a maintenance dose

Most drugs are given at regular intervals to maintain therapeutic plasma concentrations ( Bennett..eia/ 1994). In the patient with renal failure, maintenance doses should be modified to avoid toxicity. The maintenance dose is normally adjusted by lowering the dose per dosing interval or by extending the dosing interval. For example, for an anticonvulsant to sustain plasma concentrations above a seizure threshold, a reduced dose given at a 'normal' dosing interval is more appropriate. Increasing the dosing interval is more appropriate for a drug with a long half-life. A combined method of lowering the dose and extending the dosing interval may be needed for the majority of drugs.

Maintenance doses, volume of distribution, percentage excreted unchanged, and plasma protein binding of the more common drugs used in intensive care are given in Table 1.

Table 1 Required dose intervals and maintenance doses for common intensive care drugs in renal failure

Drug

First dose

First interval

GFR>50

GFR 10-50

GFR<10

Aminoglycoside

Amikacin

Individualize

Individualize

Individualize

Individualize

Individualize

Gentamicin

Individualize

Individualize

Individualize

Individualize

Individualize

Tobramycin

Individualize

Individualize

Individualize

Individualize

Individualize

Cephalosporines

Cefamandole

0.5-1.0 g

Every 4-8 h

Every 6 h

Every 6-8 h

Every 12 h

Cefazolin

0.5-1.5 g

Every 6 h

Every 8 h

Every 12 h

Every 24-48 h

Cefmetazole

2.0 g

Every 6-12 h

Every 16 h

Every 24 h

Every 48 h

Cefoperazone

1-2 g

Every 12 h

100%

100%

100%

Cefotaxime

1.0 g

Every 6 h

Every 6 h

Every 8-12 h

Every 24 h

Cefotetan

1-2 g

Every 12 h

100%

50%

25%

Cefoxitin

1-2 g

Every 6-8 h

Every 8 h

Every 8-12 h

Every 24-48 h

Ceftazidime

1-2 g

Every 8 h

Every 8-12 h

Every 24-48 h

Every 48 h

Ceftriaxone

0.2-1.0 g

Every 12 h

100%

100%

100%

Cefuroxime sodium

0.75-1.5 g

Every 8 h

Every 8 h

Every 8-12 h

Every 12 h

Miscellaneous antibacterial

Aztreonam

12.5 mg/kg

Every 8-12 h

100%

50%-75%

25%

Clindamycin

150-300 mg

Every 6 h

100%

100%

100%

Erythromycin

150-300 mg

Every 6 h

100%

100%

50%-75%

Imipenem

0.25-1.0 g

Every 6 h

100%

50%

25%

Metronidazole

7.5 mg/kg

Every 6 h

100%

100%

50%

Teicoplanin

6.0 mg/kg

Daily

Every 24 h

Every 48 h

Every 72 h

Vancomycin

500 mg

Every 6 h

Individualize

Individualize

Individualize

Penicillins

Ampicillin

250 mg-2 g

Every 6 h

Every 6 h

Every 6-12 h

Every 12-24 h

Mezeiocillin

1.5-4.0 g

Every 4-6 h

Every 4-6 h

Every 6-8 h

Every 8 h

Nafcillin

1-2 g

Every 4-6 h

100%

100%

100%

Penicillin G(benzylpenicillin)

0.5-4 million IU

Every 6 h

100%

75%

20%-50%

Piperacillin

3-4 g

Every 4 h

Every 4-6 h

Every 6-8 h

Every 8 h

Ticarcillin Antifungal agents Amphotericin Fluconazole Antiviral agents Acyclovir

Foscarnet Ganciclovir

20-40 mg 200-400 mg

Every 4 h

Daily Daily

Every 8 h

Every 8 h induction doses Every 12 h

Every 24 h 100%

5 mg/kg every 8 h

28 mg/kg Every 12 h

Every 24 h 100%

5 mg/kg every 12-24 h

15 mg/kg

Every 24-48 h

Every 24-36 h 100%

2.5 mg/kg every 24 h

6 mg/kg

Every 48-96 h

Drug

First dose

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