Explanation
Omeprazole is CYP2C19 inhibitor which can prolong the elimination of warfarin, particularly R-warfarin. R- warfarin is partially metabolized by CYP2C19. The combined use of omeprazole and warfarin has been associated with reports of increased INR and prothrombin time (PT).

Explanation
DPP4 Inhibitors, (D)Glucagon-like peptide-1 receptor agonists, (E)Thiazolidinediones (F)Biguanide Sulfonylureas work in beta cells in the pancreas that are still functioning to enhance insulin secretion. Alpha- Glucosidase Inhibitors stop -glucosidase enzymes in the small intestine and delay digestion and absorption of starch and disaccharides which lowers the levels of glucose after meals. DPP4 blocks the degradation ofGLP-1, GIP, and a variety of other peptides, including brain natriuretic peptide. Glucagon-like peptide-1 receptor agonists work in various organs of the body. Glucagon-like peptide-1 receptor agonists enhance glucose homeostasis through: (i) stimulation of insulin secretion; (ii) inhibition of glucagon secretion; (iii) direct and indirect suppression of endogenous glucose production; (iv) suppression of appetite; (v) enhanced insulin sensitivity secondary to weight loss; (vi) delayed gastric emptying, resulting in decreased postprandial hyperglycaemia. Thiazolidinediones are the only true insulin-sensitising agents, exerting their effects in skeletal and cardiac muscle, liver, and adipose tissue. It ameliorates insulin resistance, decreases visceral fat.
Biguanides work in liver, muscle, adipose tissue via activation of AMP-activated protein kinase (AMPK) reduce hepatic glucose production. SGLT2 inhibitors work in the kidneys to inhibit sodium-glucose transport proteins to reabsorb glucose into the blood from muscle cells; overall this helps to improve insulin release from the beta cells of the pancreas.

As the patient is over the age of 60 and he does not have CKD or diabetes, his goal BP should be SBP < 150 mmHg or DBP < 90 mmHg, and he is not currently at this goal with his medication regimen. Options are to maximize the current medication dosage (option A), or to add a second agent. Since calcium channel blockers like Norvasc are recommended as initial treatment options in African Americans, choosing Norvasc over lisinopril would probably be the more effective option.
Reference:
http://jamanetwork.com/journals/jama/fullarticle/1791497

Nadolol is not proven to reduce mortality in patients with systolic CHF. The efficacy of nadolol in HF has not been determined. For patients taking nadolol, it should be used with caution in those with compensated heart failure and patients should be monitored for a worsening of the condition. Bisoprolol, carvedilol, and sustained- release metoprolol succinate are the beta-blockers that have been proven to reduce mortality in patients with systolic CHF. These 3 beta-blockers have been effective in reducing the risk of death in patients with chronic HFrEF. Other beta-blockers were found to be less effective. Bucindolol did not exhibit uniform effectiveness across different populations. Metoprolol tartrate was found to be less effective in HF clinical trials.
Reference:
http://circ.ahajournals.org/content/128/16/e240

Explanation
It is not necessary that all the drugs get completely absorbed after oral administration. Most of them are incompletely absorbed. The extent of absorption varies from 5 to less than 100 % with oral ingestion of drugs.
Drugs which are too hydrophilic like atenolol are incompletely absorbed because the drug cannot cross the lipid membrane due to high hydrophilic nature of the drug. Similarly, drugs which are too lipophilic like acyclovir are not soluble enough to cross the water layer adjacent to the cell. P-glycoprotein is an efflux transporter which is present in the enterocytes and it inhibits absorption of drug. It is also known as export transporter or reverse transporter. It has many drugs as its substrate. Grape juice in fact inhibits P-glycoprotein in the intestine thereby decreasing the efflux of drug from the cells by P-glycoprotein. Thus ingestion of grape juice may lead to significantly increased absorption of the drug.