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Half-life  ( t 1/2 ) is the time required for serum concentrations to decrease by one-half after absorption and distribution are complete. It takes the same amount of time for serum concentrations to drop from 200 to 100 mg/L as it does for concentrations to decline from 2 to 1 mg/L ( Fig. 8–3 ). Pharmacotherapy: A Pathophysiologic Approach, 8e > Section 1. Foundation Issues > Chapter 8. Clinical Pharmacokinetics and Pharmacodynamics > Clinical Pharmacokinetic Concepts > Half-Life > Figure 8-3. Calculation of the  half-life  of a drug following IV bolus dosing. Half-life  is important because it determines the time required to reach steady state and the dosage interval. It takes approximately three to five half-lives to reach steady-state concentrations during continuous dosing. In three half-lives, serum concentrations are at  90% of their ultimate steady-state values. Because mos...

Clearance (CL) is the most important pharmacokinetic  parameter  because it determines the steady-state concentration for a given dosage rate. When a drug is given at a continuous IV infusion rate equal to  k 0 , the steady-state concentration ( C ss ) is determined by the quotient of  k 0  and CL ( C ss  =  k 0 /CL). If the drug is administered as individual doses ( D ) at a given dosage interval ( ), the average steady-state concentration ( C ss ) over the dosage interval is given by the equation 4 where  F  is the fraction of dose absorbed into the systemic vascular system. The average steady-state concentration over the dosage interval is the steady-state concentration that would have occurred had the same dose been given as a continuous IV infusion (e.g., 300 mg every 6 hours would produce an average  C ss equivalent to the actual  C ss  produced by a continuous infusion administered at a rate of 50 mg/h). Physiolog...

                                        CLINICAL PHARMACOKINETICS Pharmacokinetic concepts have been used successfully by pharmacists to individualize patient  drug therapy  for about a quarter century. Pharmacokinetic consultant services and individual clinicians routinely provide patient-specific drug-dosing recommendations that increase the  efficacy  and decrease the toxicity of many medications. Laboratories routinely measure patient serum or plasma samples for many drugs, including antibiotics (e.g., aminoglycosides and  vancomycin ),  theophylline , antiepileptics (e.g.,  phenytoin , carbamazepine ,  valproic acid ,  phenobarbital , and  ethosuximide ),  methotrexate ,  lithium , antiarrhythmics (e.g., lidocaine  and  digoxin ), and immunosuppressants (e.g.,  cyclosporine  and  tacrolimus ). ...

»  What is Acne? Acne is a skin condition that causes whiteheads, blackheads, and inflamed red growths (papules, pustules, and cysts) to form. These growths are commonly called pimples or "zits." ALTERNATIVE NAMES Acne vulgaris; Cystic acne; Pimples; Zits How can one get rid of acne? Are homemade peels or facepacks helpful? Acne  or pimples are common,  particularly among adolescents and young adults. This is due to hormonal influences (testosterone) at that age. The sebaceous glands of the skin produce an oily secretion - sebum. These glands get blocked due to overgrowth of the superficial layers of the skin. Acne  is not just a skin problem but also has negative impact on the patient's self-esteem. This is particularly true of young girls and boys. Hence, it is important to treat acne at the earliest. The treatment of acne is best done by a dermatologist or skin specialist. He may advice topical treatment such as benzoyl peroxide...