The most commonly used clot buster in the world is an agent called Streptokinase. This particular medicine is obtained from a group of bacteria called Streptococcus and hence the name. Currently, synthetic form of this drug is produced in the labs, in India, using recombinant DNA technology. The synthetic preparation attempts to reduce some of the side effects that are seen with the natural preparation, and could be available commercially in the near future.

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Some of the other commonly used thrombolytics around the world are called tPA (tissue plasminogen activator), alteplase and, recently, tenecteplase among others. These agents are several times more expensive than streptokinase and the overall efficacy of dissolving the clot and restoring blood flow to the heart muscle during a heart attack is slightly superior when compared to streptokinase. The side effect profile of the other agents is somewhat better than that of streptokinase. In a developing country like India, the economical streptokinase is more appropriate in a general sense, although tPA may be an option for many patients.

How do clot busters work?:

These clot busting medications act by activating a naturally occurring clot dissolving agent in our bodies called plasmin. Unfortunately, streptokinase activates the clot dissolving substance throughout the body’s circulation and hence opens the possibility of bleeding complications. The most feared complication is bleeding in the brain which happens in a very small number of patients. It is important to note that while risk of major bleeding from different body systems is greater with streptokinase, there are some studies that have shown a slightly higher risk for bleeding in the brain with the use of tPA. Since the clot busters save many lives from the deathly grip of a heart attack, the risks are worth taking, in many patients.

Who should not receive the clot busters?

• With pain that has lasted for longer than 24 hours

• Who only have ST segment depression on ECG. This ECG finding is suggestive of a Non ST elevation MI, which often only affects the 

innermost layer of the heart muscle. This will be checked by your doctor prior to making the decision to administer the clot buster.

People at risk for bleeding should not receive clot busters. These include people:

• Recovering from recent surgery

• With active bleeding from stomach ulcers 

• With very high blood pressure

• With a history of a recent stroke, head injury or a bleeding disorder.

Streptokinase may not be very effective in those who received the medication within the last one year and alternative clot busters should be considered in those who have history of allergic reaction to an earlier use of streptokinase.

Who should receive clot busters?

• Within 24 hours of chest pain considered to be suggestive of heart attack and associated ECG changes as determined to be indicative of heart attack, by your doctor (ST elevation MI changes on the ECG or other appropriate ECG criteria)

It is crucial to recognise that by administering the clot busters to eligible patients at the earliest opportunity the damage to heart muscle and the death rate is reduced. The most dramatic benefits are seen when the clot busters are given in the first hour after beginning of heart attack (Golden Hour) and with every passing hour the benefit reduces, but continues to be useful for up to 12 – 24 hours. Early administration not only saves lives, but by reducing the damage to the heart, long-term complications like heart failure are reduced. 

Hence, it is imperative to administer the clot busters to eligible patients at the earliest possible time. In the context of heart attack – TIME IS LIFE!

Dr G Balachander
Cardiologist
Illinois, USA