How Long Should You Wait Between Metaxalone and Oxycodone?

Thanks for bringing this one to HelloPharmacist! We get timing questions a lot, and we're always happy to provide guidance, although we do always fall back on making sure you talk to your prescriber about what is best for your specific medical situation.

There isn't an official or required waiting period between metaxalone and oxycodone. If your doctor prescribed both together, the safest approach is to take each one exactly as directed on its label. If your prescriber didn't spell out a schedule, it's worth making a quick call before assuming how they should be spaced.

Why Spacing the Doses Apart Doesn't Eliminate Side Effect Risk

Metaxalone, the generic for Skelaxin, is a skeletal muscle relaxant, while oxycodone is an opioid.

Both slow activity in the central nervous system, so when they are active at the same time, their sedating effects can add together.

Oxycodone's prescribing information specifically warns that combining it with other central nervous system depressants, a category that includes muscle relaxants, increases the risk of excessive sedation and potentially dangerous respiratory depression.

Research backs up why this combination deserves respect, as concomitant use of prescription opioids and skeletal muscle relaxants has been associated with an increased risk of opioid overdose.

The somewhat reassuring nuance is that, in this research, metaxalone generally appeared to carry less risk than several other muscle relaxants, such as baclofen and carisoprodol, when combined with opioids.

That doesn't make the pairing risk-free, but it may be one reason a prescriber chooses metaxalone when a muscle relaxant is needed alongside an opioid.

How Long Each Medication Stays Active in Your Body

The noticeable effects of both metaxalone and immediate-release oxycodone generally last for several hours, often roughly four to six hours, although the exact duration varies from person to person.

Because of that, separating the doses by around four to six hours may help reduce the period when the strongest sedating effects of both medications occur at the same time. In other words, spacing them may help you avoid the worst of the additive drowsiness, dizziness, and impairment.

However, spacing the doses does not completely separate the medications in your body.

Immediate-release oxycodone commonly provides pain relief for about four to six hours, but some of the medication remains in your system after the noticeable pain-relieving effect begins to wear off.

Metaxalone may also have noticeable effects for only several hours, but its elimination half-life is considerably longer, generally around eight to nine hours (a half-life is the time it takes the body to eliminate approximately half of a dose, so metaxalone remains in the body well beyond the point when its most noticeable effects have faded).

Therefore, even if you take oxycodone four to six hours after metaxalone, there will still be a meaningful amount of metaxalone in your system. The same is true in reverse.

So, yes, spacing the doses can reduce the peak overlap and may make additive side effects less intense, but it cannot completely prevent the medications from overlapping because their half-lives are longer than their most noticeable effects.

When both medications are prescribed on a regular schedule, some overlap is essentially unavoidable.

That is why the focus should be on using the lowest effective doses, avoiding alcohol and other sedating substances, and knowing which warning signs to watch for rather than trying to eliminate all overlap based on the clock.

Laboratory work has also explored whether muscle relaxants might slow the breakdown of opioids such as oxycodone. While metaxalone's effect in this area appears weak, it is another reason the combination may be flagged for pharmacist review.

A Serotonin Consideration Worth Knowing About

One lesser-known point is that oxycodone's labeling lists metaxalone among medications with serotonergic effects. Combining serotonergic medications with opioids has rarely been associated with serotonin syndrome.

This is uncommon, but new symptoms such as agitation, a fast heartbeat, heavy sweating, muscle twitching, unusual muscle stiffness, or fever should be reported to a medical professional promptly.

Day to day, the bigger practical concerns are excessive drowsiness, dizziness, confusion, poor coordination, or slowed or shallow breathing.

Very slow breathing, difficulty waking up, or an inability to stay awake warrants emergency care. If you take an opioid regularly, it is also reasonable to ask your pharmacist or prescriber about keeping naloxone on hand.

Final Words

There is no specific number of hours that completely prevents metaxalone and oxycodone from interacting. Both may have noticeable effects for roughly four to six hours, so separating the doses by that amount may reduce the strongest overlap and help limit additive drowsiness.

However, both medications remain in the body longer than their noticeable effects last, especially metaxalone because of its longer half-life. Therefore, spacing the doses cannot completely eliminate the risk of additive sedation or slowed breathing.

The best approach is to follow the schedule your prescriber provided, use only the prescribed doses, and avoid alcohol and other sedating medications unless your prescriber has specifically approved them.

If your prescriptions don't clearly explain how to time the doses, call your pharmacist, who can review your exact doses and help set up an appropriate schedule.

Feel free to reach back out if anything else comes up!