PPM Launches Online Opioid Calculator
PPM: What are the challenges facing physicians when prescribing [dosing] opioids, or switching from one opioid to another? In other words, why is there a need for an opioid conversion calculator?
Dr. Brennan: In the 21st century, we’ve come to recognize that people respond differently to different medications. This tool has taken the most current data collected on individual drugs, and provided an easy-to-use, readily available tool for clinicians—whether pharmacists, physicians, or nurses—at the point of care so we can safely and effectively switch patients from one drug to another, with a significant emphasis on safety. Safety is trumping all other efforts with this.
So, why is this necessary? There are a variety of reasons a patient may need to switch opioids: from loss of insurance, change of insurance, or an insurance plan changing its prescription formulary to side effects, etc. Very often patients are sitting in the examination room when a clinician finds out their patient can no longer take a certain medicine. So, by having this Website and this tool, clinicians will be able to—with the patient in the room—do a safe calculation based on the best published and available data. As such, physicians will have the ability to switch their patient from one medication to another that might better benefit the patient in an easy, scientifically based, state-of-the-art approach.
Dr. Perkins: One benefit of the PPM opioid calculator is that it makes calculating equivalent doses very easy. One problem with conversions is knowing the equivalent doses. The conversions can involve complex mathematical equations. The calculator can easily and accurately make these calculations quickly. Another reason for developing an opioid calculator is to address the complexity of converting from a long-acting agent to a shorter-acting agent. For example, morphine is the gold standard—it is what every other opioid is compared to. Some of the opioids have much longer half-lives than morphine, and people don’t realize that. If you’re transitioning from an opioid with a long half-life to something like morphine with a short half-life, there are risks involved, and you need to be aware of those risks to avoid respiratory depression. We have outlined these risks under the “Tips and Warnings” sections when conversions to or from a specific opioid are performed.
PPM: What are some of the safety issues surrounding opioid dosing?
Dr. Fudin: There are a number of issues. One issue is inter-patient variability, not only among populations—for example, an Asian versus Caucasian population—but also physiological differences between those populations (polymorphism). But besides that, there are genetic differences even within populations. So, for instance, if you convert from one opioid to another, even if it was an exact science, when you convert to the desired opioid, the patient may actually need a far, far lower dose. So, even if we could create a perfect calculator, there are still going to be inter- and intra-patient variables the prescriber needs to consider. That’s a huge challenge.
Dr. Brennan: I agree. One of the things we’ve learned in the last 25 years is different people have different sensitivities not only to side effects, but to potencies of drugs. And that’s based on a number of genetic and experiential factors. So, we recognize that, and have incorporated a number of warnings and provisos into the new tool. We have given some flexibility to the clinician that will allow for a safe switch or rotation from one drug to another. What’s been done is that, based on size of the patient, and based on best published data on the relative strengths of drugs, a safety level has been built in to err on the side of caution for converting from drug A to drug B.
On top of that, we’ve given clinicians added wiggle room to make it an even more conservative conversion. This is vital, because most clinicians have had inadequate training on how to switch drug doses. The tools that have been in doctors’ offices mostly are tools developed by pharmaceutical companies to allow one brand of narcotic to be switched to another brand of narcotic. Well, those are one-way conversions. So, by giving clinicians an unbiased, non-branded kind of format [which includes all opioids], we think we’re enabling them to make safer and easier switches with this algorithm and formula.
Dr. Perkins: We tried to be conservative with dosing, especially when switching to a long-acting agent like fentanyl transdermal patches. Patches can be a convenient method of drug delivery because they don’t require IV access and patients don’t have to swallow a pill. If you start at a conservative dose, you can always supplement with as-needed medication, but if you start with too high of a dose, you can’t get it back. So, we tried to provide conservative, yet reasonable, dosing—not too conservative, so patients won’t get pain control, but conservative enough to take side effect profiles into account.
PPM: Is the calculator then useful for physicians who might be initiating pain medications in an opioid-naïve patient?
Dr. Fudin: Absolutely. In fact, as Dr. Brennan noted, many of the current guidelines for opioid dosing have starting doses that are not very conservative at all. The one prime example is methadone. Therefore, methadone should only be prescribed by a physician who is thoroughly trained in its use. In many guidelines—which can be found on the Internet, in textbooks, and in journals—the starting dose of methadone is listed as 10 to 20 mg every eight hours in an opioid-naïve patient. The reason for that is because that’s what appeared in the PDR [Physicians’ Desk Reference] many years ago and the companies that first manufactured methadone used that dose.
Well, we now recognize that if you start an opioid-naïve patient on that dose, it could be fatal. With our calculator, instead of 10 to 20 mg every eight hours, if you want to get the correct dose of methadone for an adult patient weighing 50 kg or greater, it’s going to tell you 10 to 20 mg in 3-4 divided doses over 24 hours. So, in other words, instead of giving an answer of 20 mg three times a day, you’re going to get an answer that’s about 25% of that.
A far as I can tell, and I’ve looked at seven different calculators, the other calculators are basing their doses on old information that has been accumulated through the years and has become habit. What we did for the initial dosing is base it on the most conservative starting point.