1. Introduction
Canagliflozin is a sodium glucose co-transporter 2 (SGLT2)
inhibitor approved in over 30 countries, including the United
States and the European Union, as an adjunct to diet and exercise
for the treatment of adults with type 2 diabetes [1–8]. Clinical
studies in patients with inadequately controlled type 2 diabetes
have shown that canagliflozin lowers fasting and post-meal
glucose, reduces HbA1c, and is also associated with reductions in
body weight and blood pressure [1–8]. The decreases from
baseline in the total glucose area under the time-concentration
curve (AUC) after a standard meal reflect decreases in the premeal
glucose concentration as well as a decrease in the glucose
excursion above the pre-meal glucose level. The primary
mechanism by which canagliflozin treatment provides glucose
lowering in patients with type 2 diabetes is by reducing renal
tubular reabsorption of glucose, leading to increased urinary
glucose excretion (UGE), and thereby directly reducing elevated
plasma glucose (PG) concentrations. A previous single-dose study
of this agent, conducted in healthy volunteers, showed that
higher doses of canagliflozin (>200 mg) administered prior to a
standard meal challenge reduced the post-meal glucose excursion
to a greater extent than did lower doses, despite similar UGE
[9]. Although it is a selective SGLT2 inhibitor, canagliflozin is a
low-potency inhibitor of sodium glucose co-transporter 1
(SGLT1); it has ~160-fold greater potency against SGLT2 relative
to SGLT1 [10]. SGLT1 is an important glucose transporter in the
small intestine [11]. The observation that higher doses of
canagliflozin further reduced the increase in glucose level after
a meal raises the possibility that higher concentrations of
canagliflozin in the intestinal lumen after dose administration,
but prior to systemic drug absorption, might transiently inhibit
SGLT1-mediated glucose absorption in the gut, and thereby delay
the rate of glucose rise after a meal. Further evidence for this
hypothesis was provided by a dual-tracer study in healthy
participants demonstrating that a single dose of canagliflozin
300 mg delayed intestinal glucose absorption [12].
The present study was designed to assess the renal and nonrenal
(ie, gut glucose absorption) effects of canagliflozin on PG
excursion after a meal in patients with type 2 diabetes with
inadequate glycemic control on metformin. To examine this,
the effect of canagliflozin in lowering post-meal glucose
through SGLT2 inhibition of renal glucose reabsorption was
separated from the potential gastrointestinal effect of this
agent. Prior studies have shown that maximal effects on UGE are
sustained for 24 hours after treatment with canagliflozin doses
of ≥300 mg [4,9,13]. Based upon this, administration of canagliflozin
300 mg 24 hours prior to a meal would be expected to
provide the full renal tubular (SGLT2 inhibition) effect on glucose