A Clinical Trial of Alternating and Intermittent Regimens of 2',3'-Dideoxycytidine and 3'-Azido-3'-Deoxythymidine in the Treatment of Patients With AIDS and Advanced ARC

Inclusion Criteria Concurrent Medication: Encouraged though not required: * Inhaled pentamidine as prophylaxis for Pneumocystis carinii pneumonia (PCP). * Allowed: * AL-721 use is discouraged but not prohibited. * Use of aspirin, acetaminophen, and nonsteroidal anti-inflammatory agents should be minimized, with continuous use for \> 72 hours discouraged. * Acute therapy (7 days) with oral acyclovir. * Acute therapy with ketoconazole. Concurrent Treatment: Allowed: * Up to 4 units of packed red blood cells for hemoglobin toxicity. All patients must have the following: * A consistently positive serum HIV p24 antigen = or \> 70 pg/ml, defined by the Abbott HIV antigen test, on two occasions. The tests must be within 1 month of study entry, separated by at least 72 hours, and the last must be within 2 weeks of starting therapy. Any negative antigen test during the period will exclude the patient from the study. * A positive antibody to HIV confirmed by any federally licensed ELISA test kit. * Patients in group A must have AIDS related complex (ARC) as defined by the documented presence of at least one of the following: * Recurrent oral candidiasis. * Hairy leukoplakia. * History of herpes zoster. * Temperature \> 38.5 degrees C with or without night sweats, persisting for \> 14 consecutive days or \> 15 days in a 30-day interval prior to study entry. * Weight loss of \> 15 lbs. or 10 percent of body weight noted in a 120-day period prior to study entry. * Diarrhea defined as = or \> 3 liquid stools per day, persisting for \> 30 days prior to study entry without definable cause. * Patients in group B must have CDC-defined AIDS not requiring systemic maintenance chemotherapy. Exclusion Criteria Co-existing Condition: Patients with the following conditions or symptoms are excluded: * Transfusion dependence requiring 2 units of blood more than once per month. * Significant malabsorption (\> 10 percent weight loss within the past 3 months with serum carotene \< 75 IU/ml or vitamin A \< 74 IU/ml). * Significant cardiac or liver disease. * Significant neurologic abnormalities defined by any one of the following: * A significant abnormality on the ddC Neuropathy Targeted Symptom Questionnaire defined as a symptom score \> 4 (moderate severity) in any one of six categories or a score \> 2 (mild severity) in any two of six categories. * Moderate abnormalities on standardized neurologic exam. * Any severe abnormality (a value = or \> 4.0) on standardized 4-arm quantitative sensory testing of vibration threshold. * Diabetes, renal failure, or alcoholism. * Dose-limiting or transfusion-requiring toxicity during a previous course of zidovudine therapy. * History of idiopathic thrombocytopenic purpura. * Requirement for prolonged acyclovir therapy. Patients in group A must not have the following: * Opportunistic infection or malignancy fulfilling the CDC definition of AIDS. * Neoplasms other than basal cell carcinoma of the skin or in situ carcinoma of the cervix. Patients in group B must not have the following: * Active opportunistic infection or AIDS-defining opportunistic infection requiring ongoing systemic therapy and/or prophylaxis other than inhaled pentamidine for Pneumocystis carinii pneumonia prophylaxis. * Symptomatic visceral Kaposi's sarcoma (KS), progression of KS within the month prior to study entry. * Concurrent neoplasms other than KS, basal cell carcinoma of the skin or in situ carcinoma of the cervix. Concurrent Medication: Excluded: * Neurotoxic drugs. * Prolonged acyclovir therapy. * Antineoplastic therapy. * Systemic therapy and/or prophylaxis for an AIDS-defining opportunistic infection, other than inhaled pentamidine for Pneumocystis carinii pneumonia (PCP) prophylaxis. * Other antiretroviral agents, immunomodulators, or systemic corticosteroids. * Other experimental medication. Concurrent Treatment: Excluded: * Transfusion dependency (requiring 2 units of blood more than once per month). Prior Medication: Excluded: * Antiretroviral agents within 60 days of study entry. * Biologic modifiers or corticosteroids within 30 days prior to study entry. * Dideoxycytidine (ddC). Prior Treatment: Excluded: * Blood transfusion within 2 weeks of entry. Any negative HIV p24 antigen test during the month prior to entry will exclude the patient from the study. Active drug or alcohol abuse.