where t1/2 is the half-life and ke is the elimination rate constant calculated from the slope of the declining portion of the concentration-time profile (Fig. 5.3). By definition, half-life denotes that 50% of the drug in the body at a given time will be eliminated over the calculated period. However, this does not mean that the same amount of drug is eliminated each half-life. For example, Figure 5.3 shows that during the first half-life period (0-5 hours) the drug concentration is reduced from 100 ^g/mL to 50 ^g/mL. However, during the second half-life period (5-10 hours), even though the amount in the body is reduced by 50%, the concentration falls only from 50 ^g/mL to 25 ^g/mL (a reduction in concentration of 25 ^g/mL). This concept is also illustrated in Table 5.1. It takes approximately five half-lives for 97% of the drug to be eliminated from the body (regardless of the duration of the half-life). Thus, if one wished to switch a patient from one drug to another but not have both drugs present in substantial quantities,

The Prevention and Treatment of Headaches

The Prevention and Treatment of Headaches

Are Constant Headaches Making Your Life Stressful? Discover Proven Methods For Eliminating Even The Most Powerful Of Headaches, It’s Easier Than You Think… Stop Chronic Migraine Pain and Tension Headaches From Destroying Your Life… Proven steps anyone can take to overcome even the worst chronic head pain…

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