Imipenem + Cilastatin (Primaxin)

Imipenem is given in combination with cilastatin, a specific inhibitor of the renal enzyme dehydropeptidase-1 that inactivates imipenem. Imipenem has an extremely wide spectrum of activity, including most aerobic and anaerobic Gram _ve, including those expressing extended spectrum beta-lactamases, and Gram +ve bacteria (but not MRSA). It has no activity against Stenotrophomonas maltophilia which emerges in some patients treated with imipenem.Acquired resistance is relatively common in P. aeruginosa and is starting to emerge in some of the Enterobacteriaceae including Enterobacter spp., Citrobacter spp. and the Proteus group.

Uses
• Mixed aerobic/anaerobic infections
• Presumptive therapy prior to availability of sensitivities for a wide range of severe infections
• Febrile neutropenia

Contraindications
CNS infections (neurotoxicity)
Meningitis (neurotoxicity)

Administration
• IV infusion: 0.5–1 g 6–8 hourly depending on severity of infection
Dilute with sodium chloride 0.9% or glucose 5% to a concentration of 5 mg/ml
500 mg: add 100 ml diluent, infuse over 30 min
1 g: add 200 ml diluent, infuse over 60 min
Unstable at room temperature following reconstitution – use immediately

In renal impairment:

CC (ml/min)	Dose (g)	Interval (h)
31–70	0.5–1	8
21–30	0.5–1	12
<20	0.25*	12

*or 3.5 mg/kg, whichever is lower

How not to use imipenem
Not compatible with diluents containing lactate
Adverse effects
Hypersensitivity reactions
Blood disorders
Positive Coombs’ test
↑ Liver function tests, serum creatinine and blood urea
Myoclonic activity
Convulsions (high doses or renal impairment)

Cautions
Hypersensitivity to penicillins and cephalosporins
Renal impairment
Elderly

Organ failure
Renal: reduce dose

Renal replacement therapy
0.5–1 g 12 hourly