Posts Tagged ‘drug interactions with methadone’

Medication Interactions with Methadone and Buprenorphine

 

 

 

 

 

Patients being treated for opioid use disorder with methadone or buprenorphine often need other medications to treat chronic and acute medical conditions. When our opioid treatment program patients fill other prescriptions at retail pharmacies, the pharmacist might not know that the patient is on methadone or buprenorphine. Due to privacy laws, OTPs don’t report patient data to state prescription monitoring programs. That puts the burden on opioid treatment providers to watch for potential drug interactions.

I take that burden seriously.

Methadone, for various reasons, is more likely to have drug interactions than buprenorphine. Buprenorphine’s various pharmacologic properties reduce the risk of drug interactions. It has a high affinity for the opioid receptor, which means it’s not easily displaced off the receptor. Also, buprenorphine has a ceiling effect, so fluctuations in blood levels are less likely to cause sedation than methadone. Drug interactions can still occur, but not with the frequency or severity as with methadone.

Many medications interact with methadone, too many for me to reliably remember. I use a smart phone app to supplement my aging memory with up-to-date data. And if I can use these smart phone apps, believe me…anyone can. I prefer the Medscape app, though it’s only one of many. Other providers like Epocrates or others. If you work at an opioid treatment program and make dose decisions, I strongly recommend you get one of these apps, because there’s no way to remember or keep up with all new data.

Here are some of the main ways methadone interacts with other medications.

Sedatives

Any sedative medication can have an increased sedative effect when it is administered to a patient on methadone, or any other opioid, for that matter. Sedatives affect that ancient part of our brain that tells us to breath while we sleep. Opioids also affect that brain center, so when opioids and other sedatives are mixed, patients can fall asleep and stop breathing, which is how overdose deaths occur.

By far, the most commonly consumed sedative that my patients use, by prescription or illicitly, are benzodiazepines. However, other sedatives are just as deadly, and alcohol is a sedative drug too. Recently we’ve had more patients prescribe gabapentin (Neurontin) or its mirror-image molecule, pregabalin (Lyrica). These medications are commonly prescribed by primary care providers for just about any complaint of pain, anxiety, or anything else. When misused, or when taken with methadone, it can lead to impairment and even overdose.

I’ve railed against the inappropriate use of benzodiazepines so many times that even I get tired of hearing myself, so I’ll refer to reader to past blog entries. But let me just say that many patients being treated for opioid use disorder with methadone have been harmed by also taking benzos, prescribed or not prescribed. It’s a hazard that should be avoided if possible.

Cardiac Effects: prolonged QT interval

Methadone can prolong the QT interval in the heart. In the interest of not getting overly technical, let’s just say that the QT interval has to do with how the beats are conducted through the electrical system of the heart. If the QT interval lengthens past a critical point, it puts the patient at risk for a potentially fatal heart rhythm.

Many opioids can cause this, but methadone is probably the most well-known. Other opioids, like tramadol and oxycodone, carry some risk of QT prolongation, but usually not to a clinically significant degree. Some sources say buprenorphine can theoretically cause QT prolongation, but most experts don’t feel it’s clinically significant. In fact, if a patient on methadone develops QT prolongation issues, that patient is often recommended to switch to buprenorphine.

While methadone alone infrequently causes clinically significant QT interval prolongation, other factors can increase patient risk. For example, some patients with certain types of underlying heart problems may already be prone to QT prolongation and starting methadone could make this situation worse.

Many other medications also can cause QT prolongation. When these medications are started in a patient on methadone, the combination can cause significant QT interval prolongation.

For a recent list, go here: https://crediblemeds.org/pdftemp/pdf/CombinedList.pdf

As you will see, many common medications are listed. Common antibiotics, like cipro and erythromycin, cause prolonged QT interval and these are often prescribed to our patients. Many commonly prescribed mental health medications can prolong the QT interval.

What should opioid treatment providers do when a patient on methadone gets a new prescription for a medication which could critically prolong the QT interval? I’ve searched the internet and can’t find exact evidence-based solutions. But that’s not uncommon. Physicians often need to weigh decisions of risks and benefits of medications and act based on this.

First, I inform patients if there might be a problem. Next, I decide if the risk presented by the medication is so high that I need to ask the prescriber to change it. Or, if the patient is young and healthy, I might decide to check an EKG to monitor the QT interval. Lowering the dose of methadone can help reduce the QT interval, but at the risk of de-stabilizing the patient, so that’s rarely the best course of action.

Opioid treatment programs vary widely in their abilities to get and interpret ECGs. Thankfully, I’m trained in Internal Medicine and feel comfortable getting my ECG calipers to calculate the QT interval and yes, of course I correct for heart rate too.

Here are two examples of how I handled potential QT situations.

The first patient was young and healthy, and dosing with methadone at 95mg per day. He was started on ciprofloxacin for two weeks for an infection. The other prescriber had done a culture of the infectious situation and cipro was one of few antibiotics that the bacteria was sensitive to, so antibiotic choices were limited. I decided to check an ECG after my patient had been taking cipro for a few days, and the QT was fine. He was able to remain on the cipro until the infection cleared, with no problems

The second patient was older, nearly 50, with several chronic medical conditions including severe mental health diagnoses. A new psychiatrist changed his medication and started him on ziprasidone (Geodon), a medication infamous for causing QT prolongation. My patient was dosing at 115mg per day, and extremely fearful about any dose change. I did an ECG as soon as I knew he was on Geodon, and his QT interval was significantly lengthened. I called his new psychiatrist and explained the problem and she immediately switched him to a lower-risk medication. A repeat ECG done a few days after the switch showed his QT was back to normal, and he did well on this second medication, with good resolution of his mental health symptoms.

Drug affected methadone metabolism by the Cytochrome P450 System

Other drugs and substances affect methadone blood concentrations by influencing the rate of methadone metabolism. Methadone is an active opioid, while its first metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (called EDDP for short), is not pharmacologically active. That metabolic process is done in the liver via the cytochrome P450 (CYP450 for short) system. Many other medications affect this system.

Some medications that affect the CYP 450 system slow methadone metabolism and are called inhibitors. They can increase methadone blood levels and the opioid effect it has. Conversely, medications called inducers speed metabolism of methadone into its inactive metabolite, and thus can reduce methadone’s blood level and effect.

Of course, rising or falling methadone blood levels affects patient stability.

To add to the complexity, there are different types of cytochrome P450 enzymes. Several are involved with methadone metabolism, named CYP 3A4, CYP 2D6, CYP2B6, and CYP 2C29. And each enzyme’s activity is further determined by what genes we’ve inherited. Other medications that are metabolized by CYP3A4 are thought to be particularly prone to affect methadone metabolism and regarded with more caution.

So…it’s complicated. But as if that complication weren’tt enough, some scientists now say that though in the past we thought methadone was mainly metabolized by CYP 3A4, that’s old data, and now, we should be looking at drugs metabolized by CYP 2B6. In fact, in a recent article I read, “It has now been unequivocally established that CYP2B6, not CYP3A4, is the principle determinant of methadone metabolism, clearance, elimination, and plasma concentrations in humans.”  [1]

Also, some medications act as inhibitors of inducers of methadone in a test tube but not in real life.

What’s a doctor to do?

Again, I’ve searched the internet for evidence-based recommendations. Should we increase the patient’s methadone dose if he’s started on a medication that induces methadone’s metabolism? Or should we wait to see if the patient has symptoms before we change the dose? Conversely, should we decrease a patient’s methadone dose if she is started on a medication that inhibits methadone’s metabolism, in case her blood levels are going to rise? Or should we just prohibit the use of any medication that can affect methadone blood levels?

That last option, though it would make my life easier, isn’t possible. For example, nearly all mental health medications interact with methadone in some way or another. There’s no way for a patient to get treatment without using medications with the potential to affect methadone metabolism.

Same as with the QT interval problem, the degree of risk must be assessed for each patient. The degree of risk varies with patient medical history,  and the known risk of the inducers or inhibitors. For example, patients newly started on phenytoin nearly always have a clinically significant drop in methadone blood level. For those patients, I’ll make sure I have an order in place to increase their methadone dose with any symptoms of opioid withdrawal.

Most other cases aren’t so clear-cut. I’ll inform patients of potential risks and ask that they communicate with us regularly.

Almost all medications that treat HIV influence methadone metabolism, making it essential for the opioid treatment provider to communicate directly with the provider prescribing HIV medications.

In fact, good communication is essential with other prescribers and I try to cultivate a cooperative attitude with them, so far as it is possible with me.

Our opioid treatment program patients, particularly as they age, will be prescribed medication with possible interactions with their methadone. For their safety, each OTP must have a system in place that: 1. Gets patients to report new prescriptions as soon as possible 2. Gets that information to the program medical provider in order to make decisions about safety and monitoring 3. Informs patients of potential risks 4.  Arranges follow up meeting with medical providers when appropriate 5. Opioid treatment providers must collaborate with other prescribers when necessary

Each OTP needs a system that works for their facility, and methods can differ widely between OTPs. It doesn’t matter how we get the job done, just that it gets done.

Our patients’ safety depends upon this.

  1. Kharasch, “Current Concepts in methadone metabolism and Transport,” Clinical Pharmacology in Drug Devopment, 2019

 

 

Drug Interactions with Methadone

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Recently, medical directors of opioid treatment programs in my state pondered how to handle the risk of medication interactions with methadone. In my area of the country, chart reviews of patients who died while taking methadone revealed many decedents were taking other medications with known interactions with methadone. Obviously, we want to prevent these deaths, and need to protect against drug interactions.

To predict a possible drug interaction, the OTP doctor must know all of the other medications that the patient is taking, both prescription and non-prescription. I assume all doctors at opioid treatment programs ask the patients what medications they are prescribed on the first day, along with what they take over the counter. That’s a good start, but often it’s not sufficient.

On that first day, patients aren’t feeling well. They are in opioid withdrawal and they yearn to feel better. They may forget about some medication or assume it’s not important to mention. They may forget about over-the-counter medications. Sometimes patients deliberately keep silent about medications if they’re worried they won’t be allowed to continue them. Most commonly this happens with benzodiazepines, but doctors can detect prescriptions for these controlled substances, since they are listed on our state’s prescription monitoring program.

Benzodiazepines are the most common drug found in patients who have died while prescribed methadone.

At my opioid treatment programs, we keep lists of our patients’ medications in their charts.
We tell patients to please tell us right away if they are prescribed any medications after they enter our program, so we are alerted to possible drug interactions. Patients are instructed to tell the nurses, since they see nurses most often, and the nurses then tell me. It’s OK for patients to tell counselors, but counselors aren’t medically trained so they must pass the information on the nurses and doctors.

Keeping an up to date list of each patient’s medications is challenging, but do-able with a good system in place. However, the list isn’t worth much unless the doctor is made aware of all prescribed medications, so each opioid treatment program’s system must include a way to provide the doctor with all this information.

At my programs, I sign a form giving my approval (or disapproval) of all medications that are prescribed for the patient, and I write orders if any further action needs to be taken, like asking the patient about any withdrawal symptoms or sedation. But this might happen a few days after the medication is started, so nurses also send me texts with notice of any new medication. This is the best method for me, since I can quickly text back with any orders for enhanced patient monitoring. One program sends emails which I can receive on my smart phone, read immediately, and send my response.

Opioid treatment program physicians need to know which medications can interact with methadone. This list can be long, and varies somewhat depending on the source of information.

Methadone interacts with other drugs in several ways; since it’s metabolized by specific enzymes in the liver, called the cytochrome P450 system, other drugs affect this system can affect the patient’s blood level of methadone. Sometimes other medications can induce, or speed up, methadone’s metabolism, which can drop the patient’s methadone blood level. Other medications inhibit methadone’s metabolism, causing the methadone blood level to rise. In the first situation, a previously stable patient may start to feel withdrawal. In the second situation, the patient may become sedated from methadone and even be at risk for a fatal overdose.

Other medications, mostly sedatives, act on the same centers in the central nervous system as methadone to produce even more sedation. These actions can be synergistic. Synergy between two medications means that the effect of two drugs is greater than you would expect. To put it another way, instead of one plus one equals two, suddenly one plus one equals three or even four. You get more effect than you bargain for.

Then there’s the whole QT interval prolongation that can be caused by methadone. Many other commonly used medications also prolong the QT interval, so that when they are prescribed with methadone, patients are theoretically placed at increased risk of a potentially fatal heart arrhythmia. Relatively common drugs like citalopram (Celexa), erythromycin, and cipro can cause QT interval prolongation.

How can a doctor know about the ways drugs interact with methadone? Most of the main drugs, like sedatives, methadone inducers and inhibitors, we know off the top of our heads, but technology gives us many ways to augment our brain power. Doctors can reference one of the three or four free smart phone apps. These are particularly helpful with the QT interval prolongers, since that list is very long and frequently changing.

Now for the hardest part: what should a doctor to do when a patient gets a medication that can interact with methadone? I’ve scoured the internet, and there are no easy answers. The Addiction Treatment Forum, has published some general guidelines that seem prudent: http://www.atforum.com/pdf/Drug_Interactions.pdf

As the AT Forum points out, just because an interaction may occur doesn’t mean it will occur. Certainly we should notify the patient of possible drug interactions and ask them to report any sedation or withdrawal while they are taking the new medication so that we can adjust the methadone dose accordingly. If the new medication is only prescribed for a week or two, the patient may not need a dose adjustment.

We may recommend getting an EKG if the new medication is known to prolong the QT interval. It’s nice if that can be done at the opioid treatment program, but OTPs may not be doing regular screening, especially after the Cochrane report of 2013 called routine EKG screening of methadone patients into question. (See my blog post of 9/19/13)

Should an EKG be done? Who should do it? What should we do if the QT interval is prolonged? If the second medication is essential to treat a serious ailment, should the patient’s methadone dose be reduced? Should that patient switch to buprenorphine? Is the risk of partially treated opioid addiction potentially more harmful to the patient than the other serious ailment for which the patient is being treated?

I don’t know the answers and I can’t find anyone else who can give me solid answers about what to do in cases where my patients are prescribed other medications that interact with methadone. For now, I am taking what I feel are prudent precautions, and trying hard not to over-react and pull a patient off methadone, since I know for sure methadone is live-saving. It’s important to remember that just because an interaction is possible doesn’t mean it will happen.

If another doctor prescribes a medication short-term that may interact with methadone, I want the patient to be informed of a possible reaction. I may, with the patient’s permission, call the doctor to ask them if it can be changed to a safer medication, or I may ask the nurses to check with the patient about sedation or withdrawal each day when they come in to dose. Sometimes I’ve asked patients on higher take home levels to come to the OTP more often for closer monitoring until we see the full effects of a new medication, then return them to their usual take home status.

Patients need to tell us when they stop medications, too. I had one patient who was on phenytoin (Dilantin) for the treatment of seizures. Since this medication induces methadone metabolism and drops the serum methadone level, I had increased the patient’s dose of methadone to keep him out of withdrawal. But then, deciding he no longer needed to take phenytoin, he suddenly stopped it and became sedated. Thankfully he reported his sedation to the nurses and we quickly figured out what had happened. His dose had to be lowered quite a bit to prevent overdose, since off phenytoin, his blood level of methadone apparently rose abruptly.

At one of the OTPs where I work, I can easily get an EKG to monitor the QT interval. At the other, I have to ask the other doctor to check and EKG. Particularly with psychiatric medications, this creates difficulties, since psychiatrists usually don’t do EKGs in their offices. The patient has to be referred to a third facility if I feel an EKG is essential. This can become expensive to a patient without insurance, so it’s better if the doctor prescribes a medication that doesn’t affect the QT interval, if possible.

As time goes on, I think we’ll get more information about medication interactions with methadone, and I’d like to see more specific guidelines about how to handle potential