Morphine weakens antiplatelet response among patients with ST-elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI) to restore blood flow to the heart.This was the key finding from a study presented at the recent ACC 2016 Scientific Sessions.

Patients treated with morphine had worse measures of platelet activity within an hour of receiving a loading dose of aspirin plus ticagrelor (Brilinta, AstraZeneca) or clopidogrel. [ACC 2016, abstract 1105-113]

“Morphine has been widely used to alleviate chest pain and anxiety of patients suffering from an acute MI,” said study author Dr. Manivannan Srinivasan from the East and North Hertfordshire NHS Trust in the UK. “But the drug can also delay gastric emptying and reduce the absorption of other oral medications.”

Srinivisan and team examined 125 consecutive patients (mean age 66; 93 percent male) with acute STEMI who were scheduled to undergo emergency primary PCI. Of these, 101 patients (81 percent) had received morphine in ambulance enroute to the hospital. About half had hypertension, 42 were smokers, and 16 percent had type 2 diabetes (T2D).

Once in the catheterization laboratory, 102 patients were each given a loading dose of aspirin 300 mg and clopidogrel 600 mg while the rest received ticagrelor 180 mg. Within 30 to 60 minutes, blood tests were done to determine occlusion time and lysis time.

Compared with the patients who had not received opiates, those who had received morphine had a shorter mean occlusion time (358 s vs 670 s; p<0.001) and a longer median lysis time (1392 s vs 1184 s; p=0.006).

However, by day 2, the two groups had similar occlusion times (485 s vs 552 s) and lysis times (1322 s vs 1184 s).

The study was not powered to determine hard safety end points, but there was a nonsignificant trend to greater in-hospital adverse events in the 101 patients who had received morphine vs the other 24 patients (1 vs 0 death, 1 vs 0 MI, and 2 vs 0 stroke).

“Whether this [morphine] affects recurrent early thrombosis risk and whether nonopiate analgesia may proffer advantages in this setting require further assessment,” said the researchers.

Large clinical trials are warranted to confirm the finding and to determine how this effect on platelets translates into patient outcomes. “Until then, caution should be exercised in the use of IV morphine and consideration given to other intravenous medication if morphine treatment is to be used,” said Srinivasan.

“There are other alternatives that we can explore, such as nonopioid medication such as IV paracetamol,” he noted. “Once morphine is given, we may consider giving other IV agents that bypass the gastric emptying, such as GP IIb/IIIa inhibitors or bivalirudin.”