Myobloc Drug Interactions: What to Avoid and What to Tell Your Doctor

Before your Myobloc injection, it's essential that your doctor knows about every medication, supplement, and herbal product you're taking. Certain drugs can significantly amplify Myobloc's effects — leading to excessive muscle weakness, dangerous breathing problems, or other serious complications. Here's what matters most.

Most Important: Other Botulinum Toxin Products

Combining Myobloc with another botulinum toxin product — or using them within several months of each other — can produce additive neuromuscular weakness that may be excessive and dangerous. This includes:

Botox (onabotulinumtoxinA)

Dysport (abobotulinumtoxinA)

Xeomin (incobotulinumtoxinA)

Daxxify (daxibotulinumtoxinA-lanm)

The effect of administering different botulinum toxin products at the same time or within several months of each other is not fully known, and excessive neuromuscular weakness can be exacerbated if one toxin is given before the effects of a prior toxin have fully resolved. Always tell your doctor when you last received any botulinum toxin injection, regardless of type.

Aminoglycosides and Neuromuscular Blockers

These drugs can potentiate Myobloc's neuromuscular blocking effects, resulting in excessive and dangerous weakness. Use with caution and only when necessary. Examples:

Aminoglycosides: amikacin, gentamicin, neomycin, tobramycin, streptomycin

Neuromuscular blocking agents: atracurium, vecuronium, pancuronium, and other curare-like compounds (usually used in surgical settings)

Anticholinergic Medications

Since Myobloc works by blocking acetylcholine (an anticholinergic effect), combining it with other anticholinergic drugs can produce additive systemic anticholinergic effects. This can worsen side effects like dry mouth, constipation, urinary retention, confusion, and blurred vision.

Commonly used anticholinergic drugs to discuss with your doctor include:

Bladder medications: oxybutynin (Ditropan), tolterodine (Detrol), solifenacin (VESIcare), darifenacin (Enablex)

Parkinson's medications: benztropine (Cogentin), trihexyphenidyl (Artane)

Antihistamines with anticholinergic properties: diphenhydramine (Benadryl), chlorpheniramine, cyproheptadine, brompheniramine

Tricyclic antidepressants: amitriptyline, nortriptyline, amoxapine

Motion sickness drugs: scopolamine, meclizine, cyclizine

Atropine (used in some cardiac and procedural settings)

Muscle Relaxants

Muscle relaxants can add to Myobloc's neuromuscular blocking effects, potentially producing excessive weakness. Common muscle relaxants to discuss with your doctor:

Baclofen (Lioresal) — used for spasticity, commonly co-prescribed with botulinum toxins

Cyclobenzaprine (Flexeril)

Carisoprodol (Soma)

Tizanidine (Zanaflex)

Methocarbamol (Robaxin)

Are There Food or Supplement Interactions?

There are no known significant food interactions with Myobloc. Alcohol is generally safe to consume in moderation before or after Myobloc injections, but there's no specific contraindication.

Blood-thinning supplements (fish oil, vitamin E, garlic) are not contraindicated but may increase bruising at the injection site. If you're prone to bruising, discuss stopping these supplements 7–10 days before your injection with your doctor.

Special Situations: Neuromuscular Disease

Patients with underlying neuromuscular diseases — ALS, myasthenia gravis, Lambert-Eaton syndrome, or motor neuropathies — are at significantly increased risk for severe adverse effects from Myobloc, including life-threatening respiratory failure and dysphagia. These conditions are not absolute contraindications, but they require extremely careful risk-benefit assessment and close monitoring.

What to Tell Your Doctor Before Your Injection

Bring a complete medication list (including OTC drugs, supplements, and herbals) to every Myobloc appointment. Specifically mention:

Any other botulinum toxin injections in the past 4–6 months

Any antibiotics you're taking or recently completed (especially aminoglycosides)

All muscle relaxants, sleep aids, anticholinergic drugs, and antihistamines

Any diagnosis of ALS, myasthenia gravis, Lambert-Eaton syndrome, or other neuromuscular disease

Pregnancy or breastfeeding status — safety is unknown

For a full review of Myobloc side effects, see: Myobloc Side Effects: What to Expect. And if you're still searching for a pharmacy that carries Myobloc, medfinder can do that work for you.