Lack of absorption of didanosine after rectal administration in human immunodeficiency virus-infected patients

The feasibility of rectal administration of didanosine (DDI) was studied in six human immunodeficiency virus-infected patients. After oral intake of a DDI solution (100 mg/m(2) of body surface area) combined with an antacid ( Maalox), pharmacokinetic parametric values were in accordance with previous ly published data; the mean a standard deviation for terminal half-life was 59.5 +/- 15.0 min, that for peak concentration was 5.2 +/- 3.9 mu mol/lite r, and that for the area under the time-concentration curve (AUC) was 494 /- 412 min . mu mol/liter. After rectal administration of a similarly prepa red DDI solution (100 mg/m2 of body surface area), plasma DDI levels were b elow the detection limit (0.1 mu mol/liter) at all time points in five of t he six patients, and in the remaining patient the AUC after rectal applicat ion was only 5% of that after oral administration. We conclude that oral ad ministration of DDI cannot be easily replaced by rectal application.