From the investigation made on the pharmacokinetics of amoxicillin in 12 cases with impaired renal function (including 7 cases of renal failure) and in 2 normal subjects, following results were obtained.
(1) Mean half-life of amoxicillin was 1 hour in normal subjects and 13 hours in renal failure. Urinary recovery of the drug within 6 hours in normal subjects was about 60 per cent on the mean. Serum level of the drug was lowered by 6-hour-hemodialysis by 80 per cent on the mean.
(2) If the values of half-life or elimination rate constant of an antibiotic in normal subjects and renal failure are given, the following equation is useful for assuming the half-life for the patient with any value of creatinine clearance.
{1-
p (1-
Ccr/100)}
KT=0.693Here,
T is half-life,
K is normal elimination rate constant, and
p is a constant denoting the ratio of renal elimination rate to overall elimination rate in the normal.
The value of
K is obtained on substituting 100 (ml/min.) for
Ccr. and the value of normal half-life (hours) for
T. With this value of
K and on substituting 0 for
Ccr and the value (hours) of half-life in renal failure for
T, the value of
p is obtained.
Then, patient's T is to be calculated on putting patient's
Ccr in the equation.
(3) The value of
p of amoxicillin calculated by above equation is 0.923, which means that normally about 90 per cent of the elimination is renal.
(4) The schedule of amoxicillin administration in the cases with impaired renal function was discussed.
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