T topic of calculation skills this month is the use of transdermal opioid drugs in palliative care. The British National Formulary provides guidance on drug use in palliative care, including recently updated conversion tables from oral morphine to both buprenorphine and fentanyl transdermal patches. Elements of this section have been updated in the most recent edition available on-line (www.bnf.org) compared to BNF 64. Fentanyl is a potent opiate analgesic approximately 100 times more potent than morphine. Inappropriate conversion of dosage between these two drugs in the past has led to fatalities due to respiratory depression. Buprenorphine is a semi-synthetic opioid used via the transdermal route to control moderate chronic pain. Different formulations are available to treat drug addiction or to control moderate acute pain in non-opioidtolerant individuals. Buprenorphine has similar side effects to other opioids but differs in that it is thought to have a ceiling effect for respiratory depression. Nevertheless, respiratory depression may still be fatal in overdose. Neither drug is suitable via the transdermal route to treat acute pain or for patients with rapidly changing analgesic requirements because the long time to steady state prevents rapid dose titration. In the UK, two brands of buprenorphine patches are currently available: BuTrans (Napp) designed to release drug for 7 days, and Transtec (Napp) designed to release drug for 4 days. Two types of fentanyl patch are available (matrix patches and reservoir patches) but the same dosage advice applies to both formulations. In 2008, the Medicines and Healthcare Regulatory Agency/Commission on Human Medicines (MHRA/CHM) stated that fentanyl patches should only be used in patients who have previously tolerated opioids because of a risk of significant respiratory depression in Alison Eggleton