This paper examines the pharmacokinetics of atenolol, a cardioselective beta-1 adrenoreceptor blocking agent used primarily to treat hypertension. The discussion covers atenolol's mechanism of action and its development as a successor to propranolol, its absorption profile (approximately 50% oral bioavailability), elimination half-life of six to seven hours, and predominant renal excretion. The paper also addresses contraindications across different populations, including the elderly, pregnant women, and children, and concludes with a brief review of the cost of the 50 mg tablet formulation.
Atenolol is a medication available in 25 mg, 50 mg, and 100 mg tablets. It is described as "a synthetic, beta1-selective (cardioselective) adrenoreceptor blocking agent" that "may be chemically described as a benzeneacetamide" (Drugs.com, 2011). It is also characterized as being "without intrinsic sympathomimetic and membrane stabilizing activity" (Ogbru, 2006). The drug was developed as a treatment for hypertension and was introduced as a replacement for propranolol (Healthline, 2011). The key advantage of atenolol over propranolol is that it does not cross the blood-brain barrier, and therefore it does not carry as many central nervous system complications.
Atenolol cannot be completely absorbed as it travels through the gastrointestinal (GI) tract. "Approximately 50% of an oral dose is absorbed from the gastrointestinal tract, the remainder being excreted unchanged in the feces. Peak blood levels are reached between two and four hours after ingestion" (Drugs.com, 2011). The drug is absorbed rapidly and consistently, but incompletely, leaving a bioavailability of approximately fifty percent. Because the drug is not easily metabolized by the liver, 85% of it is renally excreted when administered intravenously, compared with 50% for the oral tablet. Only approximately 6% to 16% of the drug is bound to proteins in the plasma (MIS, 2004).
According to Drugs.com (2011), "the elimination half-life of oral atenolol is approximately 6 to 7 hours, and there is no alteration of the kinetic profile of the drug by chronic administration. Following intravenous administration, peak plasma levels are reached within 5 minutes. Declines from peak levels are rapid (5- to 10-fold) during the first 7 hours; thereafter, plasma levels decay with a half-life similar to that of orally administered drug." The elimination of the drug occurs almost entirely through the kidneys and is not significantly affected by dialysis or by liver impairment.
Because atenolol is primarily a medication for hypertension, research on its use in certain specialized populations remains limited. The pharmacokinetic profile in children is not well established, as there have not been sufficient pediatric subjects to define these parameters clearly (MIS, 2004). No meaningful differences in drug effects have been observed between men and women. Studies have demonstrated the strong effectiveness of atenolol as "an effective antihypertensive agent providing 24-hour reduction of blood pressure" (Drugs.com, 2011).
The drug may be used in adults and elderly patients for hypertension, as well as in cases of angina pectoris and myocardial infarction. Contraindications in the adult population include a systolic blood pressure below 100 mmHg or a resting heart rate below 50 beats per minute. Special caution is required when prescribing atenolol to elderly patients. Although this group tends to have higher rates of hypertension and the other conditions for which atenolol is prescribed, monitoring of systolic blood pressure is particularly important in patients aged 60 years and older (Drugs.com, 2011).
As noted in the prescribing literature, "in general, elderly patients present higher atenolol plasma levels with total clearance values about 50% lower than younger subjects. The half-life is markedly longer in the elderly compared to younger subjects. The reduction in atenolol clearance follows the general trend that the elimination of renally excreted drugs is decreased with increasing age" (Drugs.com, 2011). This age-related decline in renal clearance is consistent with broader findings about renal drug elimination in aging populations.
"Price range for the 50 mg tablet formulation"
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