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Question 0

Clinical Relevance of Bioavailability

Answer 0

• Explains why the normal IV dose is the same as the normal oral dose for some drugs, but not other drugs.
• Explains why some drugs are not effective if given by different routes. Some drugs are not effective given orally, or rectally, or topically.
• Explains the importance of taking some drugs with food, but others on an empty stomach.

Question 1

what are the chemical factors that affect absorption

Answer 1

• lipid solubility: a drug must be lipid soluble for adequate GI absorption
• Rate of dissolution: Liquid>chewable>tablet/capsule>enteric coated>sustained release
• surface area: larger surface area> faster absorption
• blood flow: greater blood flow at the absorption site=Faster rate of absorption

Question 2

Patient variables that affect Absorption

Answer 2

• Infant skin is much more absorbent than adult.
• Broken or rashy skin or hot/sweaty/moist skin is more absorbent.
• Patients with bowel resections
• Diarrhea or Constipation - anything affecting GI motility might be expected to affect the extent & rate of absorption, especially sustained release (SR) products.
• Stomach acidity
• Presence or absence of food

Question 3

Variables affects Vd & Distribution

Answer 3

• The body composition of infants has a larger % of water & lesser % of muscle mass than adults do.
• Obese patients may have a larger than expected volume of distribution (Vd) for drugs that are highly distributed into adipose tissue
• Significant changes in body weight or body composition can alter Vd.
• Malnourished patients may have less serum proteins ( i.e. albumin) available for drug binding.
• Neonates and elderly have more permeable blood brain barriers.

Question 4

Drug Distribution

Answer 4

• blood-Brain Barrier: only lipid soluble drugs can cross the BBB & reach the CNS.
• Placental Barrier: lipid soluble drugs can cross & reach the developing fetus
• Breast milk: most drugs can enter a nursing mother’s milk supply
• Fluid areas & lipid tissues.

Question 5

what are some variables that affect clearance (Metabolism/ Excretion)

Answer 5

• Neonates have immature/ underdeveloped metabolic pathways & renal function.
• Infants & children have high liver metabolism and excretion rates.
• There is a natural decline in some liver enzyme activity and in renal excretion with age.
• Hepatitis or alcohol abuse may reduce liver metabolism

Question 6

Variables that affect clearance ( Metabolism/ Excretion) cont.

Answer 6

• Interacting medications may affect metabolism
• Genetics can play an important role in metabolism (ex> warfarin, codeine)
• Renal disease may reduce excretion of renally cleared medications. For patients receiving dialysis, adequate drug clearance may or may not be occurring.
• Congestive heart failure may reduce blood flow to the liver, kidney, and other organs that may cause a reduction in clearance.

Question 7

what are some causes of medication errors.

Answer 7

*wrong patient, wrong drug, wrong route, wrong dose.

Question 8

what are some ways to reduce errors?

Answer 8

• Computerized Physician Order Entry (CPOE)
• Pharmacists on rounds
• Bar code technology

Question 9

what are some adverse drug reactions?

Answer 9

• MILD: drowsiness, nausea
• SEVERE: depression, anaphylaxis, hemorrhage
• Most common in elderly and very young
• Identify and report ADRs

Question 10

what are some drug-food interactions?

Answer 10

• The absorption of some drugs will be enhanced if taken with food.
• The absorption of other drugs may be hindered if taken with food & should be taken on an empty stomach.
• Grapefruit Juice can cause significant cytochrome p450 interactions
• Caffeine can increase theophylline toxicity. Broccoli & Brussels sprouts can decrease efficacy of warfarin. Alcohol increased Tylenol toxicity.

Question 11

What is an empty stomach defined as?

Answer 11

An empty stomach is defined as at least 1 hr before food or 2 hrs after food.

Question 12

what are some strategies to prevent drug interactions?

Answer 12

• Perform a complete medication history including prescription, over the counter, and herbal drugs.
• Be familiar with the most common drug interactions & adverse effects of your patient’s medications; and look it up if you don’t know.
• Avoid the use of unnecessary drugs.
• Select a non-interacting medication
• Separate chelating or pH interacting drugs (antacids) by at least 2 hrs.
• Monitor more closely when adding or deleting possible interacting medications.
• -plasma levels
• -efficacy, adverse effects, or toxicity