The
antibiotic imipenum (
thienamycin-
formamidine) is partially hydrolyzed during excretion by a renal brush border dehydropeptidase. The co-administration of imipenum with the renal dehydropeptidase inhibitor
cilastatin results in an increase of the urinary recovery of the
antibiotic, both in animals and humans. To study the pharmacokinetics of
imipenem and
cilastatin, subjects with normal renal function and patients with different degrees of
renal insufficiency received intravenously 250 mg imipenum alone and 250 mg
imipenem with 250 mg
cilastatin. The mean plasma half-life of
imipenem varied from 52 min in subjects with normal renal function to 173 min in subjects with
end-stage renal failure studied while off-dialysis. The plasma half-life of
imipenem was not affected by the co-administration of
cilastatin. The mean plasma half-life of
cilastatin varied from 54 min in normals to 798 min in patients with
end-stage renal failure. The co-administration of
cilastatin resulted in an increase of the urinary concentration and in the urinary recovery of
imipenem, the effect being more pronounced in the subjects with normal or only mildly impaired renal function. The plasma clearance of
imipenem was decreased when
cilastatin was co-administered, possibly due to inhibition of tubular secretion of
imipenem. Elimination studies performed during haemodialysis indicated efficient removal of both
imipenem and
cilastatin during a 4 h session. In view of the important increase in half-life of
cilastatin as a function of increasing
renal failure, a dosage reduction is proposed in patients with severe
renal failure. It is recommended that the maximum dose of
imipenem/cilastatin would be limited to either 1000/1000 mg twice daily or 500/500 mg four times daily in patients with a
creatinine clearance of less than 15 ml/min. Also, a supplementary dose of
imipenem and
cilastatin after dialysis is recommended.