- Zidovudine (AZT), either initiated or continued, by patients randomized to both treatment arms. AZT given concurrently with foscarnet may be administered at a dose of 100 or 200 mg every 4 hours (q4h) at the investigator's discretion. Patients randomized to the delayed treatment arm may initiate or continue AZT administration at a dose of 100 or 200 mg q4h at the investigator's discretion. AZT may not be administered during the first 3 weeks of foscarnet therapy. Patients randomized to immediate therapy may begin or resume AZT when they enter the 2nd week of maintenance therapy (week 4 of the 10-week study period), if their hemoglobin is = or > 8 g/dl and absolute neutrophil count is = or > 1000 cells/mm3 at that time. Caution should be used in the concurrent use of foscarnet and ciprofloxacin, as such use has appeared to exacerbate renal failure in one patient.