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Pharmacology > Prescribing in special populations > Flashcards

Prescribing in special populations Flashcards

1
Q

Approach to rational prescribing

A

Step 1: Define the patient’s problem

Step 2: Specify the therapeutic objective

Step 3: Verify whether your P-treatment is suitable for this patient

Step 4: Start the treatment

Step 5: Give information, instructions and warnings

Step 6: Monitor (stop) the treatment

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2
Q

Special risk groups

A
  • Kidney disease
  • Liver disease
  • Elderly
  • Pregnancy
  • Lactation
  • Very young
  • Obesity
  • Porphyria
  • Palliative care
  • Competitive sports
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3
Q

Prescribing in renal failure

A

•Drug/active metabolite may accumulate in renal failure, causing toxicity

–e.g. aminoglycosides largely excreted unchanged in urine

•Reduced dose and/or increased dosage interval often necessary

Exception ® need higher doses of loop diuretics

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4
Q

Prescribing in liver disease

A
  • Drugs metabolised by the liver may have prolongation of half-lives/elimination times resulting in toxicity
  • If possible, select drug with no hepatic metabolism, or metabolised by conjugation rather than cytochrome P450 (conjugation is less affected by liver disease)
  • Reduce the dose of drugs that undergo extensive first pass elimination (e.g. propranolol) as portal hypertension reduces pre-systemic elimination by bypassing the liver with vascular shunting
  • Higher risk of drug-induced hepatotoxic reactions
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5
Q

How is absorption changed in elderly

A

Relatively unchanged

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6
Q

How distribution changes in elderly

A

•decrease in total body water and lean body mass, with increase in fat mass

–Water soluble drugs, e.g. aminoglycosides, can cause toxicity

–Lipid soluble drugs e.g. benzodiazepines, can have a prolonged elimination half life

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7
Q

How metabolsim changes in elderly

A

•oxidative metabolism reduced, conjugation unchanged

–Administer drugs with high hepatic extraction, e.g. morphine, with caution

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8
Q

How excretion changes in elderly

A

•decline in glomerular filtration rate with advance age

–Always determine eGFR, even if the serum creatinine is within normal range

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9
Q

Effects of drug on pregnancy

A

Teratogenicity

Low birth weight

preterm labour

postnatal effects

miscarriage

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10
Q

How absorption changes in pregnancy

A

Change in rate and extent

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11
Q

How distribution changes in pregnancy

A

–Increase plasma volume in later stage leading to increased Vd of some drugs

•E.g. Sub-therapeutic concentrations of antiepilectic drugs

–

–Changes in protein and free fatty acids affecting drug binding

–

–Increase in fat

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12
Q

How metabolism changes in pregnancy

A

–Variable hepatic metabolism/elimination

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13
Q

Excretion in pregnancy

A

–increase in glomerular filtration rate

•Renally eliminated drugs may be reduced

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14
Q

PK changes in children: aboprtion

A

•Oral Absorption

–Neutral -> acidic pH (2 years)

–Gastric Emptying delayed in infants under 6-8 months and shorter in older infants.

–Intestinal mucosa immature

–Frequent feeding

  • Intramuscular: Variable blood flow to muscles in neonates
  • Percutaneous absorption faster and more extensive
  • Rectal absorption not changed much by maturation (but alters with position of suppository)
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15
Q

PK chnges in childrren and adults:

A

–Increased body water : fat ratio highest in neonates (80-90% vs 55-60% in adults)

•infants have higher Vd for water soluble drugs (e.g aminoglycosides) than adults -> so need a higher loading dose

–Plasma protein binding lower in neonates

–Membrane permeability:

  • BBB immature, larger CNS volume
  • Apparent Volume of distribution increases approximately linearly with weight

Young children (aged 1-2 years) have a shorter half-life than adults and infants

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16
Q

PK changes in metabolsm between adults and children

A

–Phase 1 (oxidation / reduction / hydrolysis)-> active / inactive metabolites

–Phase 2 (glucoronidation / sulphation / methylation) -> more readily excretable polar metabolites

  • Reduced hepatic metabolism in neonates, reaching adult levels by 6-12 months, then exceed adult levels for 1-4 years, returning to adult levels by adolescence
  • Liver volume, blood flow and biliary function correlate well with Body Surface Area (BSA)
17
Q

PK changes in children: excretion

A
  • Clearance increases non-linearly with weight so the maintenance dose per kg is highest around 2 years of age
  • Renal function reaches maturity ~ age 1-2 years, when the GFR correlates well with the BSA
18
Q

PK/PD of antihistamines in children

A

paradoxical excitation even at low doses

19
Q

Chloramphenicol- PK/PD in children

A

grey baby syndrome

20
Q

Phenothiazine anti-emetics PK/PD in children

A

•extrapyramidal side effects even at low doses

21
Q

Aspirin PK/PD problems in children

A

associated with Reyes syndrome (rash, vomiting, and liver damage

22
Q

Sulphonmide PK/PD problems in children

A

risk of kernicterus if under 2 months

23
Q

Tetracyclines PK/PD problems in children

A

teeth discoloration, impaired bone growth if under 8 years

24
Q

Why is it important to calculate correct dose in children

Challenges

A

PK chnage in children affects ADME

–Variability in weight for age

–Variability in lean body mass

–Underweight

–Overweight / obese

•By Body surface area

25
Q

Advantages and disadvantages of oral drug adminstration

A

usually preferred : syrup and dispersable tablet, tablet depends on age

usuallycontains sucrose

26
Q

advantages and disadvantages of topical admin

A

Easy to open and if open burns/wounds increased absoprtion

27
Q

advantages and disadvantages of of rectal admin

A

potenttially quick, easy access

cannot use adult suppositories

absorption depends on position

28
Q

advantages and disadvantages of parenteral admin

A

Only if essential

prepare away from child, do not make splint too tight

outer thigh

29
Q

The challenges of adherence for paediatric patients and their caregivers

A

•Formulation, taste, appearance and ease of administration

•

•Accommodate child’s routine

•

•Role of parents, caregivers

•

•Adolescents

30
Q

The legal requirements and recommendations for a prescription in South Africa

A

Name, qualification, registration number and address of prescriber; (Note that the prescriber’s ‘practice number’ being the BHF number has been replaced with their registration number with the relevant statutory health council);

The name, identification number and address of the patient; in the case of a neonate, the details of the parent/guardian, and in the case of a veterinarian prescription, the person to whom the medicine/scheduled substance is to be sold; (Identity number is a new requirement);

The date of issue of the prescription;

The approved name or proprietary name of the medicine;

Dosage form;

Strength of the dosage form and the quantity of the medicine – Schedule 6 must have the quantity in figures and words;

Instructions for the administration of the dosage, frequency of administration and withdrawal period in the case of medicines for food producing animals;

The age and gender of patient, or species of animal; and

Number of times the prescription may be repeated

31
Q

Prescribing in lactation

A
  • Essential drugs only
  • Avoided or monitored drugs
  • Careful timing of drugs ingestion and breastfeeding
  • Think about ADRs in the nursing infant
  • Drugs that affect milk production
32
Q

Prescribing in obesity

A

•Lipophilicity of the drug

–Increased Vd for some

  • Loading dose needed might be higher
  • TBW vs IBW vs Adjusted body weight
  • If applicable think TDM
33
Q

Prescribing in porphyria

A

•Check drug classification list

–Not Porphyrinogenic

–Probably Not Porphyrinogenic

–Possibly Porphyrinogenic

–Probably Porphyrinogenic

–Porphyrinogenic

–Not yet classified

34
Q

Prescribing in competitive sports

A

Check what is banned during competitions and in general for sportsmen/women

Pharmacology (13 decks)

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