Is methylene blue beneficial in treating calcium-channel-blocker overdose
November 29, 2011, 12:41 am
This interesting but far from conclusive case report suggests that methylene blue may be beneficial in treating overdose of the calcium channel blocker amlodipine (Norvasc). The theory is that some calcium channel blockers — including amlodipine — increase release of nitric oxide, causing vasodilatation and refractory hypotension. This is mediated through activation of cyclic guanosine monophosphate (cGMP).
Methylene blue has several potentially beneficial effects in these cases. It decreases cGMP formation, scavenges nitric oxide, and inhibits nitric oxide synthesis. However, previous data on whether the benefits of decreasing nitric oxide activity outweighs the risks have been contradictory.
This case report describes a 25-year-old woman who ingested forty 10-mg tablets of amlodipine. When she presented to hospital 1 hours later, her mental status was normal and vital signs relatively stable except for a pulse rate of 110/min.
Two to three hours after ingestion, she became hypotensive (75/40 mm Hg) and increasingly tachycardic. Over the next 5 to 6 hours, she remained hypotensive and her mental status deteriorated, despite treatment with fluids, calcium gluconate, glucagon, dopamine, norepinephrine, and high-dose insulin-eugylcemic therapy.
At the suggestion of the poison center, she was given methylene blue 16 hours after ingestion. One hour after this was started, her blood pressure increased to 90/75 mm Hg, and she was “eventually” weaned off pressors and insulin.
Was the improved hemodynamic status caused by methylene blue? As Jake Barnes says to Lady Brett Ashley at the end of The Sun Also Rises: “Isn’t it pretty to think so.” However, as the authors admit in their discussion of the report’s limitations, there is absolutely no evidence that this is the case. I also find it hard to believe — given the rapidity with which methylene blue works in treating methemoglobinemia — that it would not take effect in this case sooner than 1 hour after administration.
Nevertheless, the theory is interesting, and I was impressed with the fact that the clinicians obtained an echocardiogram while the patient was hypotensive. It showed a hyperdynamic left ventricle and normal inferior vena cava.