Halfprin® is the only 162 mg. enteric coated aspirin available for the indicated use to reduce the risk of vascular mortality in people with a suspected acute myocardial infarction (MI). The Halfprin® 162 mg. aspirin has been determined to be the indicated dose to reduce the risk of fatal and nonfatal cardiovascular and cerebrovascular events in subjects with a suspected acute MI.


Suspected Acute MI

The use of aspirin in patients with a suspected acute MI is supported by the results of a large, multicenter 2 × 2 factorial study of 17,187 subjects with suspected acute MI.(1). Subjects were randomized within 24 hours of the onset of symptoms so that 8,587 subjects received oral aspirin (162.5 milligrams, enteric-coated) daily for 1 month (the first dose crushed, sucked, or chewed) and 8,600 received oral placebo. Of the subjects 8,592 were also randomized to receive a single dose of streptokinase (1.5 million units) infused intravenously for about 1 hour, and 8,595 received a placebo infusion. Thus, 4,295 subject received aspirin plus placebo, 4,300 received streptokinase plus placebo, 4,292 received aspirin plus streptokinase, and 4,300 received double placebo.

Vascular mortality (attributed to cardiac, cerebral, hemorrhagic, other vascular, or unknown causes) occurred in 9.4 percent of subjects in the aspirin group and in 11.8 percent of subjects in the oral placebo group in the 35-day follow up. This represents an absolute reduction of 2.4 percent in the mean 35-day vascular mortality attributable to aspirin and a 23 percent reduction in odds of vascular death.

Significant absolute reductions in mortality and corresponding reductions in specific clinical events favoring aspirin were found for reinfarction (1.5 percent absolute reduction, 45 percent odds reduction, 2p<0.00001), cardiac arrest (1.2 percent absolute reduction, 14.2 percent odds reduction, 2p <0.01), and total stroke (0.4 percent absolute reduction, 41.5 percent odds reduction, 2p<0.01). The effect of aspirin over and above its effect on mortality was evidenced by small, but significant, reductions in vascular morbidity in those subjects who were discharged.

The beneficial effects of aspirin on mortality were present with or without streptokinase infusion. Aspirin reduced vascular mortality from 10.4 to 8.0 percent for days 0 to 35 in subjects given streptokinase and reduced vascular mortality from 13.2 to 10.7 percent in the effects of aspirin and thrombolytic therapy with streptokinase in this study were approximately additive. Subjects who received the combination of streptokinase infusion and daily aspirin had significantly lower vascular mortality at 35 days than those who received either active treatment alone (combination 8.0 percent, aspirin 10.7 percent, streptokinase 10.4 percent, and no treatment 13.2 percent. While this study demonstrated that aspirin has an additive benefit in patients given streptokinase, there is no reason to restrict its use to that specific thrombolytic.


Gastrointestinal Reactions

Doses of 1,000 milligrams per day of aspirin caused gastrointestinal symptoms and bleeding that in some cases were clinically significant. In the Aspirin Myocardial Infarction Study (AMIS) (4) with 4,500 post infarction subjects, the percentage incidences of gastrointestinal symptoms for the aspirin (1,000 milligrams of a standard, solid--tablet formulation) and placebo-treated subjects, respectively, were: Stomach pain (14.5 percent, 4.4 percent); heartburn (11.9 percent, 4.8 percent); nausea and/or vomiting (7.6 percent; 2.1 percent); hospitalization for gastrointestinal disorder (4.8 percent, 3.5 percent). Symptoms and signs of gastrointestinal irritation were not significantly increased in subjects treated for instable angina with 325 milligrams buffered aspirin in solution.


In the AMIS and other trails, aspirin treated subjects had increased rates of gross gastrointestinal bleeding. In the ISIS--2 study (1), there was no significant difference in the incidence of major bleeding (bleeds requiring transfusion) between 8,587 subjects taking 162.5 milligrams aspirin daily and 8,600 subjects taking placebo (31 versus 33 subjects). There were five confirmed cerebral hemorrhage in the aspirin group compared with two in the placebo group, but the incidence of stroke of all causes was significantly reduced from 81 to 47 for the placebo versus aspirin group (0.4 percent absolute change). There was a small and statistically significant excess (0.6 percent) of minor bleeding in people taking aspirin (2.5 percent for aspirin, 1.9 percent for placebo). No other significant adverse effects were reported.

Cardiovascular and Biochemical

In the AMIS trail(4), the dosage of 1,000 milligrams per day of aspirin was associated with small increases in systolic blood pressure (BP) (average 1.5 to 2.1 millimeters Hg) and diastolic BP (0.5 to 0.6 millimeters Hg), depending upon whether maximal or last available readings were used. Blood urea nitrogen and uric acid levels were also increased, but by less than 1.0 milligram percent.

Subjects with marked hypertension or renal insufficiency had been excluded from the trail so that clinical importance of these observations for such subjects or for any subjects treated over more prolonged periods is not known. It is recommended that patients placed on long-term aspirin treatment, even at doses of 160 milligrams per day, be seen at regular intervals to assess changes in these measurements.


The recommended dose of aspirin to treat suspected acute MI is 160 to 162.5 milligrams taken as soon as the first infarct is suspected and then daily for at least 30 days. (One-half of a conventional 325-milligram aspirin tablet or two 80-81 milligram aspirin tablets may be taken.) This use of aspirin applies to both solid, oral dosage forms (buffered, plain, and enteric-coated aspirin) and buffered aspirin in solution. If using a solid dosage form, the first dose should be crushed, sucked, or chewed. After the 30-day treatment, physicians should consider further therapy based on the labeling for dosage and administration of aspirin for prevention of recurrent MI (reinfarction).


(1) ISIS-2 (Second International Study of Infarct Survival) Collaborative Group. "Randomized Trail of Intravenous Streptokinase, Oral Aspirin, Both, or Neither Among 17,187 Cases of Suspected Acute Myocardial Infarction: ISIS-2," lancet, 2:349-360, August 13, 1988.


Halfprin Tablets

162 mg. in bottle of 60* and 200

81 mg. in bottle of 90

*Easy to open bottle/ Not child-resistant caps.

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