A new drug has been added to the
array of blood glucose-lowering oral agents available
to type II diabetics in Canada. Sitagliptin, the first
in a family of drugs called dipeptidyl peptidase-4 (DPP-4)
inhibitors, was approved by Health Canada on January
3 — but only in combination use with metformin,
the most commonly prescribed diabetes oral med. The
combo therapy has been shown in several studies to be
over twice as effective as metformin alone at controlling
blood glucose levels.
The approval is welcome news to
physicians who treat the nearly 50% of type II diabetics
unable to get their A1c levels below the 7% target.
"When diet and exercise don't lower blood sugar levels,
aggressive measures are recommended to achieve rapid
glycemic control, so we often start patients on two
drugs together — that's where sitagliptin comes
in," explains Dr J Robin Conway, director of the Diabetes
Clinic in Smiths Falls, ON.
Sitagliptin attacks a different
pathway from the other diabetes drugs available. "It
inhibits an enzyme that breaks down incretins," says
epidemiologist Jean-Mare Ékoé, president
of the Diabetes Quebec Professional council. Incretins
are hormones that boost the release of insulin from
the pancreas and slash the production of the body's
natural glucose in the liver.
LONG-TERM
EFFECTS
But this doesn't make sitagliptin a panacea for diabetes.
The disease's progressive nature means that, ultimately,
most diabetics end up on insulin once they've exhausted
all oral options available and can no longer achieve
target A1c levels, says Dr Conway.
Longterm side effects are also
unknown. The drug has only been on the market in the
US for a year. The most common reported side effects
were upper respiratory tract infections and diarrhea
but, as Dr Ékoé points out, the heart-damaging
effects of rosiglitazone were only found after post-marketing
studies.
ON
THE UP SIDE
Sitagliptin compares favourably with rosiglitazone in
another area: preservation of pancreatic function. Until
now, rosiglitazone and drugs in its family were the
only ones to slow down the dysfunction of insulin-producing
cells in the pancreas, says Dr Conway. Sitagliptin shows
promise in doing the same.
It also shows a lower risk of hypoglycemia
than other meds, adds Dr Ékoé. A couple
of other features make it an attractive second-line
option for both patients and doctors, according to Dr
Ékoé. Sitagliptin doesn't lead to weight
gain and it comes in a fixed dose (100mg) — no
titration required.
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