10)Factors of human body that affect drug action

Question 1

Age

Answer 1

Newborns have immature body systems + elderly people have diminishing functions ⇢ Drugs metabolise differently as we age

In infants/children

• GI enzyme activity ⇣ + Gastric secretion Slower
• Pancreatic + duodenal enzyme activity almost non existent upto age of 4 months
• Best to avoid oral drugs until 6 months of age

In neonates

• Decreased plasma proteins ⇢ ⇡Bioavailability of drugs

Question 2

Metabolism + Excretion

Answer 2

For infants ⇢ undeveloped

Glomerular filtration rate for newborns ⇣ + doesn’t reach adult levels until 6-12 months

Drugs that rely on urinary excretion can build up to toxic levels

Elderly

⇣Metabolic rate w/most significant change happening in phase 1 xenobiotic reactions of liver

Renal clearance ⇣ = Prolonging half life of drugs

Question 3

Body weight

Answer 3

• Adult meds ⇢ calculated on basis of avg adult weight of 150 pounds
• Paediatric meds ⇢ Calculated based on body S/A or child’s weight
• Heaver patients = higher doses

Question 4

Sex

Answer 4

• Females ⇢ Require smaller doses than men ⇢ different fat ratios + presence of certain hormones
• Female sex hormones ⇢ Affect binding of drugs (analgesics, hypnotics, alcohol) to plasma proteins ⇢ more sensitive to their action
• Androgenic hormones ⇢ ⇡ speed of metabolism of drugs eg propranolol + salicylates
• Some drugs make menstrual bleeding worse ⇢ anticoagulants + salicylates

Question 5

Chronic diseases

Answer 5

Nephrotic syndrome

• Changes in drug absorption
• Disposition
• Insensitivity to diuretics

Chronic liver disease

• Impairs metabolism
• ⇡ toxic effects of: propranolol, pethidine, lidocaine
• Hypothyroidism

Question 6

Pregnancy

Answer 6

Pregnant women must be cautious when taking med to avoid damage to the developing foetus

• ⇡ progesterone = accelerated drug metabolism due to ⇡ enzyme activity
• ⇣ paternal plasma proteins
• ⇡ cardiac output = ⇡ renal flow = ⇡ G.F + Renal elimination of drug

Question 7

Safety makers of drugs for pregnancy

Answer 7

A = No risk in human studies

B = No risk in animal studies

C= Risk not ruled out

D = Positive evidence of risk

X = Contraindicated in pregnancy

N = No classification

Question 8

Breast feeding classifications

Answer 8

L1 = safest

L2 = safer

L3 = moderately safe

L4 = hazardous

L5 = contraindicated

Question 9

Ethnicity

Answer 9

Different ethnic groups have different reactions to drugs

• Eg: Beta-blockers are more effective on Chinese subjects compared to Caucasians + Afro-Caribbean’s