Simple sensitive microbioassay for adenine arabinoside and hypoxanthine arabinoside in human plasma

High-pressure liquid chromatographic methods for determining arabinosyladenine-5'-monophosphate, arabinosyladenine, and arabinosylhypoxanthine in plasma and urine

New high-pressure liquid chromatographic methods for determining concentrations of arabinosyladenine (Ara-A), its 5'-monophosphate (Ara-AMP), and arabinosylhypoxanthine (Ara-H) in plasma and urine are presented. A fluorescence detector is used for Ara-A and Ara-AMP, which are first converted to highly fluorescent derivatives with chloroacetaldehyde. This increases sensitivity greatly over previous methods. The sensitivities of the methods (in micrograms per milliliter) are as follows: in plasma, Ara-AMP, 0.002; Ara-A, 0.0015; and Ara-H, 0.35; and in urine, 9 times these values, respectively. Drug concentration data are also presented, which were obtained after doses of Ara-AMP were given intramuscularly to two patients treated with this drug for severe herpes zoster. One patient was given 13 mg of Ara-AMP per kg of body weight once daily, and the other was given 6.5 mg/kg twice daily. Peak Ara-AMP and Ara-A levels in plasma occurred within 1 h after the doses, and neither exceeded 2 micrograms/ml. Ara-AMP and Ara-A concentrations in plasma fell to less than 0.01 micrograms/ml in both patients by 4 to 6 h after the doses. Peak Ara-H concentrations in plasma occurred within 1 to 2 h after doses and were 21 micrograms/ml in patient 1 and 2. The highest concentration of Ara-AMP in urine was 0.09 micrograms/ml. The highest Ara-A concentration in urine was 62 micrograms/ml, and the highest Ara-H concentration in urine was 1,080 micrograms/ml. An interfering substance of unknown nature, cochromatographing with Ara-H, was encountered sporadically in urine samples. An algorithm based on differential spectrophotometry to identify and correct for this problem is described. Estimates of the renal clearances of Ara-AMP, Ara-A, and Ara-H are also given.

Inhibition of human cytomegalovirus by combined acyclovir and vidarabine

The inhibition of human cytomegalovirus (HCMV) isolates by acyclovir (ACV) and vidarabine (ara-A) was assessed by using an infectious-center plaque-reduction assay. When fixed concentrations of 4.5 micrograms of ACV and 250 ng of ara-A per ml were compared singly and in combination, the viral inhibition resulting from the ACV-ara-A combination was synergistic for three of four HCMV clinical isolates studied and additive for one HCMV isolate. An additional four HCMV strains obtained at postmortem examination from the lungs of bone marrow transplant patients were assessed for sensitivity to ACV-ara-A by using the dose required for 50% viral inhibition (ID50) as the endpoint. The mean ID50 of ACV for the four HCMV isolates was 12.3 micrograms/ml, whereas the mean ID50 of ara-A was 3.4 micrograms/ml. When 1 microgram of ara-A per ml (which yielded a mean plaque reduction of 23.6%) was combined with ACV, a mean of 5.2 micrograms of ACV per ml was required for 50% viral inhibition. The sum of the fractional inhibitory concentrations for each of the four HCMV isolates was less than 1, indicating synergy by the ACV-ara-A combination. Although DNA synthesis in growing human embryonic lung fibroblast (HEL) cells, as determined by [3H]thymidine incorporation, was diminished to 61% of that in untreated control cells when 22.5 micrograms of ACV and 1 microgram of ara-A per ml were used, there was no additive inhibition of DNA synthesis when the two-drug combination was used. HEL cell growth remained at 97% of control cell growth at 72 h when concentrations as high as 45 micrograms of ACV combined with 1 microgram of ara-A per ml were used.

Virus inhibition assay for measurement of acyclovir levels in human plasma and urine

A simple microplate virus inhibition assay which measures the levels of acyclovir in plasma and urine samples from patients was developed. The assay is based upon the inhibition of the cytopathic effect of herpes simplex virus type 1 on human fibroblast cells. The extent of inhibition of virus cytopathic effect, caused by dilutions of samples from patients, allowed determination of acyclovir concentrations to be made. The assay, which measured biological activity, could detect acyclovir levels of greater than or equal to 1.0 microM. Peak and valley levels measured in plasma samples from two patients were comparable to values obtained by radioimmunoassay. The assay is simple, rapid, and quantitative, and it can be adapted to routine use for a large number of specimens.