Contraindications to the use of metformin

Jones et al conclude that metformin is now considered as the initial
therapy of choice in overweight patients with Type II diabetes(1).
However, it is important to note that over 80% of patients treated with
metformin alone will not maintain target glycaemic control over a long
period as defined by an HbA1C level below 7% (2). Use of additional agents
in combination with metformin will be necessary to achieve recommended
target levels. Jones et al are however right to urge the adoption of
'simplified and pragmatic set of guidelines' to facilitate the expanded
use of metformin,either alone or in combination.

Based on my experience of managing lactic acidosis in Sri Lanka, an
area that needs greater focus is the provision of sound medical advice to
metformin users travelling on holiday to the tropics. Care should be taken
to avoid or limit activities that lead to excessive dehydration,which
predisposes to intravascular volume loss resulting in tissue hypoxia and
reduced renal clearance. The 'holiday pastime' of excessive consumption of
alcohol should be moderated as its diuretic properties further exaggerate
the dehydration. Ethanol is also well documented to increase serum lactate
production via its oxidative metabolism to acetate and NADH resulting in a
shift in favour of the conversion of pyruvate to lactate(3). Dehydration
and excessive alcoholic consumption remain a potentially lethal
pathophysiological combination for the development of lactic acidosis in
metformin users travelling to the tropics.

(1) Jones GC,Macklin JP,Alexander WD. Contraindications to the use of
metformin. BMJ,2003;326;4-5.

(2)Turner RC,Cull CA,Frighi V,Holman RR. Glycaemic control with
diet,sulfonylurea,metformin or insulin in patients with type 2 diabetes
mellitus:progressive requirements for multiple therapies(UKPDS 49).
JAMA,1999;281(21);2005-12.

(3)Lieu D,Mader TJ.Survival from profound alcoholic related lactic
acidosis. J of Emergency Medicine,1999;17(5);841-6

Competing interests:  
GlaxoSmithkline markets Avandia for the treatment of Type II diabetes