The Pharmacodynamics And Pharmacokinetics Of Sotalol Biology Essay

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Sotalol, also known by the trade names as Betapace, Betapace AF and Sotacor, is used to help regulate the heartbeat of people with different forms or arrhythmias. Sotalol's active ingredient is Sotalol hydrochloride, which is a white crystalline solid with a molecular weight of 308.8 (drugs.com 2010). Diagram 1 shows the structural formula of Sotalol hydrochloride.

Diagram 1: structural formula of Sotalol hydrochloride (drugs.com 2010)

Therapeutic uses

Sotalol is approved for the treatment of life-threatening ventricular arrhythmias and the maintenance of sinus rhythm in patients with atrial fibrillation (B.G.Katzung et al 2009). The drug is able to do this as it is able to block the beta receptors in the heart (netdoctor 2004). With the beta receptors being blocked the heart rate is reduced and also pumps blood with less force, which means the power of the ventricles is reduced. In addition to this sotalol can regulate the electrical impulses in the heart which cause it to beat (netdoctor 2004), resulting in a steady regular heart beat, therefore controlling arrhythmias.

Pharmacodynamics and Mechanism of action

Sotalol has 2 different types of properties to it; class 2 (beta-adrenoreceptor blocking) and class 3 (cardiac action potential duration prolongation) (drugs.com 2010). The drug is formulated as a racemic mixture of D- and L-sotalol (B.G.Katzung et al 2009). Both of the isomers help prolong potential action but the L isomer is responsible for the beta blocking activity. The beta-blocking effect of Sotalol is non-cardioselective, half maximal at about 80 mg/day and maximal at doses between 320 and 640 mg/day (drugs.com 2010). Unlike other class 2 antiarrhythmic drugs, sotalol doesn't have membrane stabilizing effects (Minneman et al 2005).

Unlike the L isomer, the D-isomer doesn't have the beta blocking effect. The D-isomer provides the drug with the class 3 property which prolongs action potentials. However there have been some issues with the D isomer in sotalol as it was found to be associated with increased mortality (Minneman et al 2005).

Pharmacokinetics

Diagram 2: the principal display panel (drugs.com 2010)Sotalol is mainly administered orally in the form of a tablet or capsule with doses of 40, 80,120,160 and 240mg of the active ingredient sotalol hydrochloride. The inactive ingredients include calcium hydrogen phosphate dehydrate, maize starch, povidone K30, sodium starch glycollate, talc and magnesium stearate (sotalol information leaflet).

The drug can also come in the form of an injection when taking the tablets which would be given in the case of emergencies to control abnormal heart beats (netdoctor 2004). The drug can be given as an injection on its own during tests to investigate abnormal heartbeats, or as a temporary substitution for tablets (netdoctor 2004).

The oral bioavailability of sotalol is 90-100% (drugs.com). After being administered it is absorbed into the bloodstream and peak levels are reached in 2.5 to 4 hours (eMC 2010). Sotalol does not bind to plasma proteins (drugs.com 2010) and is not metabolized in the liver (B.G.Katzung et al 2009) resulting in sotalol remaining unchanged when it is eliminated from the body. The amount of sotalol can be affected when it is administered with a meal. The absorption is reduced by approximately 20% when administered with a standard meal, in comparison to fasting conditions (eMC 2010). Furthermore sotalol crosses the blood brain barrier poorly, with cerebrospinal fluid concentrations only 10% of those in plasma (eMC 2010).

The elimination half life of Sotalol is between 10 and 20 hours and it is mainly eliminated by renal excretion. When the drug is excreted, between 80 and 90% of Sotalol is expelled from the body in the urine where Sotalol remains unchanged. The other 10 to 20% is excreted in the faecal matter. However geriatric patients who are taking Sotalol must be careful of Sotalol accumulating in the body. Due to them having impaired renal function they are often on a lower dosage to avoid the drug accumulation.

Cautions and side effects

When taking Sotalol it is possible that side effects may occur. These can include irregular or slow heart beat, chest pains, feeling dizzy, tired, light headed and may have headaches. Other effects may include breathing difficulties, swelling, fever and nausea, stomach pains, muscle cramps and blurred vision. If any of these symptoms are noticed then the doctors' attention is required but the Sotalol tablets must still be taken.

There are some individuals who must refrain from using sotalol due to their medical conditions. These may include asthma, kidney failure and circulatory problems including low blood pressure, a slow heart beat or having a heart attack or heart disease.

With geriatrics especially, it is possible to overdose on sotalol. If this was to happen the individual is likely to suffer from bradycardia, congestive heart failure, hypotension, bronchospasm and hypoglycaemia (drugs.com 2010). If an overdose was to occur the individual will discontinue taking the drug and will be monitored closely. Fortunately as sotalol does not bind to plasma proteins, the level of sotalol is simple enough to reduce by haemodialysis.

Conclusion

To conclude, sotalol is a very effective at helping regulate the heart beat in people who suffer with arrhythmias. As the drug usually comes in the form of tablets, administration is easy (compared to an injection which can be fiddly). However if used to treat the wrong type of patient, the drug can be lethal. These patients can include geriatrics, they must be careful of drug accumulation due to renal failure, or people with previous heart problems, such as heart disease or heart attacks.

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