The advent of subcutaneously injectable glucagonlike peptide–1 (GLP-1) receptor agonists for the management of type 2 diabetes during 2005 was arguably one of the greatest therapeutic advances for the condition since metformin.
I was an early advocate of the class, given its potent glucose-lowering efficacy, secondary benefits of significant weight reduction, and a low risk for hypoglycemia (if not used alongside sulfonylureas or insulin).
During 2016, the first cardiovascular outcomes trial for a GLP-1 agonist, in the form of the LEADER study, was reported. These trials were mandated by the Food and Drug Administration in the aftermath of the rosiglitazone debacle in which the type 2 diabetes drug had its use restricted because of cardiovascular events attributed to it in a meta-analysis. These events weren’t seen in a subsequent trial, and the FDA’s restrictions were later lifted.
LEADER examined the once-daily GLP-1 agonist liraglutide and showed that, in addition to its glucose-lowering effects, liraglutide brought cardiovascular benefits to the table. Moreover, during 2019, the REWIND trial, the cardiovascular outcome trial for once-weekly subcutaneous dulaglutide, revealed the same cardiovascular benefits but also demonstrated a lower incidence of macroalbuminuria, albeit with no significant improvements in hard renal endpoints such as estimated glomerular filtration decline or rates of dialysis.
Despite these compelling benefits, the uptake of GLP-1 agonists has always been slower than that of other compelling agents such as the sodium-glucose cotransporter 2 inhibitors, mainly because the latter are oral drugs, while GLP-1 agonists were initially injectable medications. This difference has proven to be a barrier for patients and clinicians alike.
However, in 2019, oral semaglutide, in doses of 7 mg and 14 mg, was approved by the FDA as the first (and still only) commercially available oral GLP-1 agonist to improve glycemic control in adults with type 2 diabetes. This approval was hailed as a “game changer” at the time. The treatment had no proven cardiovascular benefits, only lack of cardiovascular harm in PIONEER 6. The SOUL cardiovascular outcome trial for oral semaglutide in doses of 7 mg and 14 mg is due to be completed during 2024. But semaglutide certainly had compelling glucose-lowering efficacy and secondary benefits of significant weight loss similar to those of its injectable counterparts.
Cardiovascular benefits of injectable semaglutide for type 2 diabetes were demonstrated in the SUSTAIN-6 trial in 2016, and the U.S. label for Ozempic was amended accordingly in 2020.
Again, I was an early adopter of oral semaglutide, and it has been great for my patients with type 2 diabetes to have the option of a noninjectable GLP-1 agonist. However, it is not without its drawbacks: Oral semaglutide must be taken on an empty stomach, at least 30 minutes before any other food, drink, or medication, and with no more than 120 mL water to maximize absorption and bioavailability.
I am of South Asian origin and have a strong family history of type 2 diabetes. If I develop type 2 diabetes in the future and require treatment escalation to a GLP-1 agonist, I will most likely opt for a weekly injectable, as it would best fit my lifestyle. But having choices of preparation has been a huge advantage in helping my patients best individualize their therapies.
I attended the recent American Diabetes Association congress in San Diego, which had two interesting oral GLP-1 agonist sessions on the program.
The first discussed the efficacy and safety of a new daily oral nonpeptide GLP-1 agonist, orforglipron, for weight reduction in adults with obesity. The phase 2 results were impressive, with clinically significant reductions in weight and cardiometabolic parameters, and a reassuring safety profile similar to that of the injectable GLP-1 agonists.
Notably, because orforglipron is a nonpeptide, it can be taken without any food, water, or medication restrictions. This indeed could turn out to be a real game changer by simplifying the complex administration of oral semaglutide, which no doubt has hampered compliance.
In fact, an Association of British Clinical Diabetologists real-world audit (also presented at the ADA Congress as a poster) of oral semaglutide use for type 2 diabetes found clinically significant hemoglobin A1c and weight reductions, but perhaps less than expected when compared with the clinical trial program, which could be a sign of poor adherence.
A phase 3 trial of orforglipron is underway (ATTAIN-2), exploring its efficacy and safety in adults with obesity or overweight and type 2 diabetes, but it is not due to be completed until 2027.
I also attended the session presenting the results of the OASIS 1 and PIONEER-PLUS trials of higher-dose oral semaglutide.
OASIS 1 explored the efficacy and safety of high-dose oral semaglutide, 50 mg once daily, for the treatment of adults with overweight or obesity without type 2 diabetes. The investigators found clinically significant reductions in body weight of around 15%-17% from baseline, compared with placebo. This result was similar to the weight loss observed in the STEP 1 trial of 2.4 mg weekly subcutaneous injectable semaglutide in adults with obesity (a much lower dose is needed when GLP-1 agonists are given as injectables because the oral forms are not very bioavailable). The side-effect profile was also similar.
PIONEER PLUS explored the efficacy and safety of high-dose oral semaglutide 25 mg and 50 mg in adults with inadequately controlled type 2 diabetes. Patients treated with 50 mg oral semaglutide had around a 2% reduction in A1c and an 8-kg (18-lb) reduction in weight from baseline. It is well known that people with obesity and type 2 diabetes lose less weight than those with obesity alone, so this result was impressive. Again, the safety profile was similar to that of the wider class, with predictably high levels of gastrointestinal side effects.
I hope that future developments bring the class to an even wider demographic and perhaps reduce some of the global inequities in managing type 2 diabetes and obesity. It should be easier (and cheaper) to mass-produce and distribute an oral medication, compared with an injectable one.
However, it should be noted that, in the United Kingdom, the National Health Service tariff cost of oral semaglutide (at usual doses for type 2 diabetes) remains similar to that of injectable semaglutide (at doses for type 2 diabetes rather than obesity). And notably, the U.K. National Institute for Health and Care Excellence, which decides whether new drugs will be funded on the NHS, has recently delayed its decision on approving tirzepatide, a dual GLP-1 and GIP agonist, for type 2 diabetes, citing the requirement for further evidence for its clinical and cost-effectiveness. This is not uncommon for NICE, and I fully expect tirzepatide to gain NICE approval on resubmission later in 2023.
One solution to contain costs might be a phased approach to the management of obesity, with initial stages using highly efficacious obesity drugs such as tirzepatide, injectable semaglutide, or high-dose oral semaglutide, and then transitioning to lower-efficacy and cheaper obesity drugs for weight maintenance.
On this note, a generic version of liraglutide (a once-daily injectable GLP-1 agonist) will be available during 2024. Moreover, it will be interesting to see the cost of orforglipron, assuming that it is approved, when it becomes commercially available in a few years, given that a nonpeptide agent should be cheaper to produce than a peptide-like semaglutide.
This phased approach is analogous to the treatment of rheumatoid arthritis, where potent targeted biologic therapy is often used early on to achieve remission of rheumatoid arthritis, followed by a switch to a conventional disease-modifying antirheumatic drug for maintenance therapy, for reasons of long-term safety and health economics.
Using this approach for obesity management might help the sustainability of health care systems.
Dr. Fernando is a general practitioner near Edinburgh. He reported receiving speaker fees from Eli Lilly and Novo Nordisk.
A version of this article first appeared on Medscape.com.