A popular high blood pressure drug has been linked to an increase risk of skin cancer in older Australians, but experts have warned against suddenly stopping the medicine.
A new study by scientists at UNSW Sydney has found hypertension medication hydrochlorothiazide - one of the most prescribed high blood pressure drugs in Australia - increases older people's risk of developing malignant melanoma and lip cancer.
The drug contains photosensitising properties, which can make skin more sensitive to the sun.
The findings are based on a big data analysis of skin cancer rates in a case-control study among older Australians and support similar findings from previous international studies.
Researchers looked at data provided by the Department of Veterans' Affairs (DVA), for veterans aged 65 and over who lived in NSW between 2004 and 2015. It included de-identified information about GP visits and tests, medicine dispensing, hospitalisations, and cancer registrations.
They compared hydrochlorothiazide use in people who had been diagnosed with lip cancer (45 cases) or malignant melanoma (659 cases) with those who had neither diagnosis (13,300 controls).
Lead author and research fellow at UNSW Medicine's Centre for Big Data Research in Health, Dr Benjamin Daniels, said for lip cancer the risk also appears to be cumulative. "That is, the longer that hydrochlorothiazide is used, the higher the risk of developing lip cancer."
But he was keen to stress that anyone taking the medication should not suddenly stop taking it.
"Hypertension is a condition that needs to be carefully managed," says Dr Daniels. "We don't want anyone to suddenly stop taking hydrochlorothiazide out of fear of developing skin cancer."
High blood pressure - or hypertension - is a chronic illness affecting more than a third of Australian adults. If left untreated, hypertension can lead to serious health conditions, like stroke and heart disease.
Dr Daniels said the skin cancer risk is something for prescribers to be aware of.
"Doctors may want to consider conducting more skin checks for their patients or reinforcing advice around sun-smart behaviours that everyone should be aware of, like adequate protection when UV is higher than three and avoiding sun exposure during peak UV times," he said.
To reflect this newly understood risk, the product information - information that helps health professionals in prescribing medicine - has been updated for medicines containing hydrochlorothiazide.
"This [update] will help prescribers and patients to make informed choices about the benefits and risks of hydrochlorothiazide-containing medicines," a Therapeutic Goods Administration spokesperson said. The TGA encourages anyone who has concerns about this issue to speak with their healthcare professional.
"By informing physicians around the potential risk of skin cancer in Australia associated with this common treatment, we hope our findings can help improve the care of patients dealing with hypertension," said Dr Daniels.
In Australia roughly two in three people will be diagnosed with a skin cancer by the time they're 70 years old.
The results, published in Basic & Clinical Pharmacology & Toxicology, support similar findings from previous international studies.
