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Correspondence: Capsaicin; Metformin; Aspirin
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Has capsaicin been proven to provide symptomatic relief for osteoarthritis? Or is the evidence still insubstantial?
GP, Te Aroha
There is good evidence for the use of topical capsaicin in many chronic pain conditions but only limited data showing
symptomatic relief in osteoarthritis.
There are four small randomised controlled trials comparing capsaicin with placebo in patients with osteoarthritis.
The mean reduction in pain was 33% with a number needed to treat (NNT) of four (95% CI). However the follow up period
was generally short (maximum nine weeks) and the distribution of joints studied varied between hip, knee, shoulder and
Despite the paucity of evidence eight out of nine international guidelines recommend the use of capsaicin as an adjunct
in the treatment of osteoarthritis. Treatment is safe but 40% of patients are troubled by local burning, stinging or
Zhang W, Li Wan Po A. The effectiveness of topically applied capsaicin. A meta-analysis. Eur J Clin Pharmacol
In the correspondence section of BPJ 16, the editors
response to the query about metformin and folate states that chronic therapy with metformin is associated with decreased
absorption of vitamin B12. I thought that just low B12 levels had been associated with metformin therapy, and didn’t
know that the mechanism of reduced B12 levels associated with metformin had been elucidated. Can you provide a reference
that shows reduced absorption to be the mechanism of the metformin-associated low B12 levels?
Pharmacist, Palmerston North
Although the precise mechanism by which metformin reduces serum B12 concentrations remains unknown, an effect on gastrointestinal
absorption seems most likely. Although, as the correspondent states, this remains an association rather than an established
causal mechanism. Initially B12 malabsorption was attributed to metformin induced changes in GI motility and gut bacterial
flora, but these theories have recently been discounted. Alternatively, metformin may reduce the absorption of vitamin
B12 by reducing the availability of calcium ions which are required to facilitate the absorption of the B12-intrinsic
References cited in:
Ting RZ et al. Risk factors of vitamin B12 deficiency in patients receiving metformin. Arch Int Med;
2006 (166): 1975-9.
Aspirin in children
In your correspondence item about gargling with aspirin
in BPJ 16, I note that it says that aspirin is not recommended in children under 16 years. I thought that aspirin
was not recommended in children under 12 years old. Is there new evidence to show that 13-16 year olds are also at significantly
increased risk of Reye’s Syndrome from aspirin, compared with those older than 16 years?
Pharmacist, Palmerston North
Aspirin is not recommended for children due to an association with Reye’s syndrome. In the UK, prior to 1986
an average of nine cases of Reye’s syndrome per year were associated with aspirin used in children aged under
12. Aspirin was subsequently banned in children aged under 12 and the condition virtually disappeared in this age group.
However, from 1986 - 2002 occasional reports continued to appear in children aged over 12 including a fatal reaction
in a 13 year old girl. As a result, the UK Medicines Control Agency recommended that children under 16 should not be
given aspirin because of its links to the syndrome.
These recommendations have been adopted by other countries and it is also the current recommendation in the BNF for
It would appear that the recommendations were not changed in some countries including New Zealand where the current
datasheets for aspirin preparations still carry the under 12 warning. These differences are probably based on the variable
opinions of national drug regulatory authorities in the context of a very rare and unlikely event. Our research identified
the under 16 recommendation which although precautionary seems prudent given the availability of alternatives to treat
fever in children.
McDonald S. Aspirin use to be banned in under 16 year olds. BMJ 2002;325:988
Available from: www.bmj.com/cgi/content/full/325/7371/988/c (Accessed
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