Exam 5 Flashcards
Routes for administering a drug
Oral, Rectal, transcutaneous, subcutaneous, intramuscular, intravenous
Absorption is affected by
The formulation of the drug (tablet, capsule etc.) and the chemical natures of the drug (weak acid vs weak base, ionized vs nonionized) May be subjected to first-pass metabolism
Transportation of drugs
Transported as a free drug which can interact with its receptor and correlates with both the therapeutic and toxic effects or as a drug-protein complex
Distribution
Depends on the lipid solubility of the drug, with volume distribution characteristics of a drug and expressed mathematically
Volume distribution equation
Vd = D / Ct
Vd = volume of distribution
D = an injected dose
Ct = concentration of the drug in plasma
Metabolism of drugs
Undergo oxidation, reduction, hydroxylation and conjugation in liver, facilitated by microsomal cytochrome P-450 which can be influenced by drugs such as barbiturates, alcohol, smoking and diet, generation of the metabolite or metabolites of the parent drug, which may have significant or comparable therapeutic effects
Excretion
With the kidneys as the primary route of excretion which is affected by water solubility and pH of urine, the biliary tract, lungs and sweat glands in the event of severe renal failure
Pharmacokinetics
The quantitative study of drug disposition in the body, describe mathematically the fate of a drug after administration of a given dosage form by a given route of admission
The therapeutic window
Range between minimum toxic concentration and minimum effective concentration
Decay of serum drug concentration equation
Ct = C0e-^kdt for many drugs
Ct = the serum concentration of a drug at time t
C0 = the initial dose divided by the volume of distribution
Kd = a disposition or elimination constant
First order of kinetics of drug elimination
A constant fraction is eliminated per unit of time, This causes an exponential decrease in the concentration as a function of time
Decline of plasma concentration versus time for a drug obeying zero-order kinetics
Elimination rate is constant, independent of concentration, capacity limited
Zero-order kinetics equation
Ct = Co - kt
Half-life of the drug
The period of time during which the concentration of a drug decays in half, may be determined for phase II of the dose response curve
Half-life equation
Ct = C0e -kdt, T1/2 = 0.693/Kd
T1/2 doesn’t vary with plasma concentration of a drug which follows 1st order
T1/2 changes with plasma concentration of a drug which follows zero order kinetics
Multiple oral dose-response curve
The dose interval is T1/2, steady state after 5 half lives
Antiepileptic drugs
High protein binding and interindividual variation for the protein binding, liver enzyme induction, active metabolite, various toxic effect with different drugs, use therapeutic ranges, interpret plasma concentration, determined by immunoassays
Valproic acid
Used for petite mal, administered orally, GI absorption rapid, highly protein bound, eliminated by hepatic metabolism, toxic >120 ug/ml
Carbamazepine
Used for variety of seizures, less common, 70-80% protein bound, eliminated by hepatic metabolism, toxic >120 ug/ml
Phenytoin
Used for variety of seizures, orally, highly protein bound, zero-order kinetics
Phenobarbital
active form of primidone, used in several types, 50% bound to protein, eliminated by liver metabolism and kidney excretion, dosage adjustment required
Tricyclic antidepressants
imipramine, amitriptyline, doxepin and fluoxetine. first-pass effect, high protein binding, half-life varies
Therapeutic drug monitoring of antidepressants
No improvement after 4 weeks of therapy, question on noncompliance, measured by HPLC
Immunosuppressants
Used to prevent rejection of transplants, require establishment of individual dosage regimens to optimize therapeutic outcomes and minimize toxicity
Cyclosporine
Antirejection therapy in organ transplants, 5-50% absorption, distributed through RBCs and plasma, 98% protein bound, toxic >400 ng/mL, measured by FPIA or EMIT
Toxic effects of cyclosporine
Renal dysfunction, hypertension, hirsutism, tremors
Tacrolimus (FK-506)
Immunosuppressive drug, orally, more potent than cyclo, eliminated by hepatic metabolism, whole blood correlation, measured by immunoassays or HPLC/MS
Toxic effects of tacrolimus
Similar to cyclo in renal toxicity, thrombus formation
Aminoglycosides
Gentamicin, tobramycin, amikacin, streptomycin, neomycin and kanamycin, used in combination with beta-lactam antibiotics, require IV, IM, or intrathecal administration
Toxic effects of aminoglycosides
Nephrotoxicity and ototocixity
Therapeutic monitoring of aminoglycosides
Serum drug level upon initiation, serum drug level and serum creatinine level during therapy, measured by FPIA or EMIT
Vancomycin
Used for infection with staph epi and staph aureus, IV administration, eliminated by renal filtration and excretion, no established relationship between serum level and toxic effect
Toxic effects of vancomycin
Phlebitis, neutropenia, nephrotoxicity, nephritis and ototoxicity, measured by FPIA or EMIT
Cardioactive drugs
Significant toxic side effects, narrow therapeutic windows, active metabolites
Digoxin
improve cardiac contraction in CHF and correct supraventricular tachycardia, orally administered, highly bound to skeletal muscle and myocardial muscle, long half-time, eliminated through kidney
Toxic effects of cardioactive drugs
Cardiac dysfunction, CNS toxicity, GI toxicity, measured by FPLA or EMIT
Procainamide
Used to correct atrial and ventricular arrhythmias, orally, liver metabolized, kidney eliminated, active metabolite NAPA generated
Toxic effects of procainamide
Hypotension, bradycardia, prolongation of ECG intervals, SLE
Lidocaine
Used for ventricular arrhythmias and prevention of ventricular fibrillation, considerable overlap of therapeutic and toxic ranges, IV and IM administration, eliminated by hepatic metabolism
Toxic effects of lidocaine
CNS toxicity, atrioventricular node blockage
Lidocaine drug monitoring
Initial serum drug concentration, every 12 hours in patient with CHF, every 24 hours on prophylaxis after MI, measured by FPIA or EMIT
Salicylates
Used as analgesic, antipyretic and anti-inflammatory drug, function by decreasing thromboxane and prostaglandin formation through inhibiting cyclooxygenase