Half-life, drug

The effect of hemofiltration on drug elimination can be estimated from serum creatinine (SCr), age, and the MDRD-2 formula to predict the combined effect of filtration rate (eGFR = GFRresidual + HFR) on drug clearance and drug half-life during hemofiltration. 

Pharmacokinetics refers to activities within the body after a dmg is administered. These activities include absoqrtion, distribution, metabolism, and excretion (ADME). Another pharmacokinetic component is the half-life of the drug. Half-life is a measure of the rate at which drains are removed from the body. 

The plasma levels of triprolidine hydrochloride were determined in 16 normal male subjects.12 When administered orally at a concentration of 3.75 mg triprolidine hydrochloride in 15 ml of syrup, peak plasma levels of 8.2 ng/ml were achieved in 2 hours with a drug half-life of 5 hours. The low plasma levels found indicate a large volume of tissue distribution which was consistent with data obtained from rat studies. 

True steady state is usually only achieved for a prolonged period with intravenous infusion. If we assume that we wish for a similar steady value after oral administration, then we need to balance our dosing frequency with the rate of decline of drug concentration and the rule of thumb referred to earlier (dosing interval equal to drug half-life) can be applied. Unbound clearance and free drug are particularly applicable to drugs delivered by the oral route. For a well-absorbed compound the free plasma concentrations directly relate to Cli (intrinsic unbound clearance). 

For a small drug molecule, penetration into the target may often be easier to achieve than duration of action. Assuming duration of action is linked to drug half-life, then distribution as outlined below can be an important factor. 

Pharmacokinetics It is well absorbed from the Gl tract after oral administration (40% to 70%) peak plasma levels occur in 1 to 3 hours. Most (80%) of the plasma penicillamine is protein bound, primarily to albumin. Penicillamine is rapidly excreted in the urine 50% is excreted in the feces. Metabolites may be detected in the urine for up to 3 months after stopping the drug. Half-life ranges are 1.7 to 3.2 hours. 

Methamphetamine - Methamphetamine is rapidly absorbed from the Gl tract. The primary site of metabolism is in the liver. The biological half-life is in the range of 4 to 5 hours. Excretion occurs in the urine and is dependent on urine pH. Alkaline urine increases the drug half-life. 

Lactation Most of these agents are excreted in breast milk in small quantities. Children When using cephalosporins in infants, consider the relative benefit to risk. In neonates, accumulation of cephalosporin antibiotics (with resulting prolongation of drug half-life) has occurred. 

Drug Half-life (hr) Therapeutic Serum Level ( jLg/ml) Toxic Serum Level ( jLg/ml)... 

Drug Half-Life (hr) Duration of Action (hr) Activity of Metabolites... 

Rapidly and almost completely absorbed from the GI tract (absorption not affected by food). Protein binding 93%. Undergoes low first-pass metabolism not extensively metabolized. Primarily excreted in urine (more than 80% as unchanged drug). Half-life 6.5-10 hr. 

Pharmacokinetics Immediafe-release capsules are rapidly and well-absorbed following PO administration extended-release capsules are also well-absorbed. Protein binding 99%. Metabolized in liver. Excreted in urine less than 10% excreted as unchanged (unconjugated) drug. Half-life 2.4 hr. 

Pharmacokinetics Well absorbed. Metabolized in the liver to the active metabolite, carboxyprimaquine. Excreted in the urine in small amounts as unchanged drug. Half-life 4 6 hr. 

Pharmacokinetics Rapidly absorbed. Extensive metabolism in liver and kidneys. Minimal excretion in urine as unchanged drug. Half-life 36 min,... 

Elimination from the body is described quantitatively in terms of drug half-life and clearance. As a first approximation, the fall in drug concentrations in plasma... 

Drug Half-Life (hours) Urinary Excretion of Unchanged Drug Recommended Anti-inflammatory Dosage... 

Drug Half-Life (h) Oral Bioavailability (°/o) Peak Serum Concentration (mcg/mL) Oral Dose (mg) Primary Route of Excretion... 

Drug Half- life (h) Bioavailability (percent) Suggested Initial Dose Usual Maintenance Dose Range Reduction of Dosage Required in Moderate Renal Insufficiency1... 

Quinones, C., Caceres, J., Stud, M., and Martinez, A., Prediction of drug half-life values of anti-histamines based on the CODES/neural network model, Quant. Struct.-Act. Relat., 19, 448 -54, 2000. 

E. Clinical situations resulting in increased drug half-life... 

Drug attributes Mechanism of action, species cross-reactivity, availability of pharmacodynamic markers for evidence of activity, long drug half-life, potential for drug accumulation, and immunogenic potential. 

Drug Half-life [h] Bioavailability [%] Volume of distribution [L kg-1] Renal/hepatic clearance [%]... 

Half-Life The drug half-life (VA) is defined as the time required for the drug to decline by half (Figure 1-2). 

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