Inclusion Criteria:

• All sexes and ethnic groups.
• Age at study entry 55 years and above.
• Clinical diagnosis of symptomatic probable AD (MMSE 26 to 15 or Short Test of Mental Status 31 to 15 inclusive and/or Clinical Dementia Rating Scale/CDR = 0.5 to 2, inclusive).
• Not on cholinesterase inhibitors or memantine; or if on cholinesterase inhibitors and/or memantine, on a stable dose for at least three months.
• Body Mass Index (BMI) within range of 19 – 50 kg/ m^2.
• Participants must be accompanied by a LAR designated to sign informed consent and to provide study partner reported outcomes at all visits.
• Participants must have no plans to travel over the ~3 months between Visits 3 and 14 that interfere with study visits.
• Tau positivity by brain PET imaging.
• Adequate blood counts; i.e., platelets > 50,000 per microliter; HB > 9/dL, and ANC > 1000 per microliter.
• Availability and consent from a LAR.

Exclusion Criteria:

• Unwilling or unable to give informed consent.
• Pregnancy.
• QTc > 450 msec on baseline ECG.
• MRI contraindications.
• Presence of uncontrolled psychiatric disorder (as per clinical judgement).
• Presence of uncontrolled systemic lupus erythematosus (as per clinical judgement).
• Substance or alcohol abuse (current alcohol use > 3 alcoholic beverage/day or > 21 per week and as per clinical judgement).
• Hearing, vision, or motor deficits despite corrective devices (as per clinical judgement).
• Myocardial infarction, angina, stroke, or transient ischemic attack in the past 6 months.
• Chronic heart failure (as per clinical judgement).
• Neurologic, musculoskeletal, or other condition that limits subject’s ability to complete study physical assessments (as per clinical judgement).
• AST/ALT > 2.5x upper limit normal.
• Presence of significant liver disease with total bilirubin > 2X upper limit or as per clinical judgement.
• Inability to tolerate oral medication (as per clinical judgement).
• Abnormality in any of the screening laboratory studies (see section 6.21.2) or as per clinical judgement.
• Malabsorption (as per clinical judgement).
• Known human immunodeficiency virus infection (as per clinical judgement).
• Known active hepatitis B or C infection.
• Invasive fungal or viral infection (as per clinical judgement).
• Known hypersensitivity or allergy to D or Q.
• Uncontrolled pleural/pericardial effusions or ascites (as per clinical judgement).
• New/active invasive cancer except non-melanoma skin cancers.
• Inability to tolerate oral medications (as per clinical judgement).
• Subjects taking medications that are sensitive to substrates or substrates with a narrow therapeutic range for CYP3A4, CYP2C8, CYP2C9, or CYP2D6 or strong inhibitors or inducers of CYP3A4 (e.g., Cyclosporine, Tacrolimus, or Sirolimus). If antifungals are absolutely necessary from an infectious disease perspective, then they will be allowed only if the levels are therapeutic.
• Strong inhibitors of CYP3A4.
• Subjects who are diabetic and on sulfonylureas (such as Glipizide, Glimepiride, Glyburide), SGLT2 inhibitors (such as Dapagliflozin and Empagliflozin), or insulin due to risk for hypoglycemia.
• Diabetes alone or Metformin use are not grounds for exclusion.
• Gastric bypass/reduction.
• Crohn’s disease.
• Myopathies (increased or low calcium, vitamin D deficiency, elevated creatine kinase or ESR) (as per clinical judgement).
• Subjects taking potentially senolytic agents within the last year: such as Fisetin, Quercetin, Luteolin, Dasatinib, Piperlongumine, or Navitoclax.
• Subjects currently taking drugs that induce cellular senescence: alkylating agents, anthracyclines, platins, other chemotherapy.
• eGFR < 10 ml/ min/ 1.73 m^2.
• Creatinine clearance < 60 mL/min/1.73 m^2.
• Subjects on therapeutic doses of anticoagulants (e.g., warfarin, heparin, low molecular weight heparin, factor Xa inhibitors, etc.).
• Subjects taking the following antimicrobial agents: aminoglycosides, azole antifungals (Fluconazole, Miconazole, Voriconazole, Itraconazole), macrolides (Clarithromycin, Erythromycin), antivirals (Nelfinavir, Indinavir, Saquinavir, Ritonavir, Elbasvir/Grazoprevir), Quinolones, Rifampin within 10 days.
• Subjects on antiplatelet agents (Clopidogrel (Plavix); Dipyridamole + Asprin (Aggrenox); Ticagrelor (Brilinta); Prasugrel (Effient); Ticlopidine (Ticlid) or Other) who are unable or unwilling to reduce or hold therapy prior to and during the 2-day drug dosing. Subjects may continue their previous regimen on day 3. Baby aspirin, if absolutely necessary from cardiac perspective, will be allowed.
• Subjects taking H2 antagonists or proton pump inhibitors who are unable or unwilling to reduce or hold therapy for at least 2 days prior to and during each of the 2-day courses of D+Q.
• Subjects may use antacids prior to and during each of the 2-day courses of D+Q.
• On antiplatelet agents (e.g., full dose Aspirin, Clopidogrel etc.). Baby aspirin, if absolutely necessary from cardiac perspective, will be allowed.
• Subjects taking the following other drugs if they cannot be held for at least 2 days before and during administration of D+Q: Digoxin, Lithium, all statins, Repaglidine, Bosentan, Gemfibrozil, Olmesartan, Enalapril, Valsartan, Methotrexate, corticosteroids, thyroid hormones, Eluxadoline, Eltrombopag, Nitroglycerin, Pioglitazone, Glyburide, Enzalutamide, Ezetimibe, Colchicine, imatinib, Cyclosporine, Tacolimus, Sirolimus, Carbamazepine, Flecainide, Phenytoin, Phenobarbital, Rifampicin, Theophylline, Warfarin, heparin, full dose ASA, clopidogrel, celecoxib, desipramine, thioridazine, venlafaxine, Tizanidine, Atomoxetine, Voriconazole, Citalopram, Diazepam, Escitalopram, Propranolol, Clozapine, Cyclobenzaprine, Mexiletine, Olanzapine, Ondansetron, Riluzole.
• Presence of any condition that the Investigator believes would put the subject at risk or would preclude the patient from successfully completing all aspects of the trial.

*Active immunosuppression therapy may include common systemic drugs such as Tacrolimus, Sirolimus, Cyclosporin, Rituximab (or other monoclonal antibodies), Mycophenolate Mofetil. Most potential subjects on these medication therapies will be identified through the exclusion criteria outlined above.

Special vulnerable populations will be excluded such as fetuses, neonates, pregnant women, children, prisoners, institutionalized individuals, or others who may be considered vulnerable populations except for patients with dementia.