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CSP 2 > Prescribing in Liver and Renal Disease > Flashcards

Prescribing in Liver and Renal Disease Flashcards

1
Q

What does pharmacokinetics involve?

A

ADME - absorption, distribution, metabolism, elimination

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2
Q

How can liver function be assessed through the history?

A

Known CLD
Chronic viral hepatitis; NASH cirrhosis
Hx of hepatic toxins
Alcohol

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3
Q

How can liver function be assessed through examination?

A

Spider naevi; gynaecomastia; jaundice; loss of

seconary sexual hair; ascites

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4
Q

How can liver function be assessed through investigations?

A 
Liver function tests (LFTs)
Prothrombin time (INR)
Albumin
Bilirubin
Ultrasound
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5
Q

What is the Child Pugh scoring system?

A 
A way of assessing liver function.
The score employs five clinical measures of liver disease. Each measure is scored 1–3, with 3 indicating most severe derangement.
Chronic liver disease is classified into Child–Pugh class A to C, employing the added score from above.
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6
Q

What are the five measures used in the Child Pugh scoring system?

A

Ascites, albumin, bilirubin, encephalopathy, prothrombin time

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7
Q

Class A CLD - how many points on the Child Pugh score and what is their 2 year survival?

A

<6; 85%

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8
Q

Class B CLD - how many points on the Child Pugh score and what is their 2 year survival?

A

7-9; 60%

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9
Q

Class C CLD - how many points on the Child Pugh score and what is their 2 year survival?

A

> 10; 35%

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10
Q

What is the MELD score?

A

It is an objective score that predicts death in cirrhotic patients. It requires calculator; not able to done at bedside. The elements are age, creatinine, bilirubin, INR etc…

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11
Q

Describe the metabolism of a drug (via first pass metabolism) in a healthy patient vs in CLD.

A

In a healthy patient, drugs goes via portal vein (high concentration of drug here) to liver then undergoes first pass metabolism and then a limited amount of drug enters the systemic circulation.

In CLD, there are collaterals present/portosystemic shunts. This means there is a high concentration of drug in portal vein AND collaterals so less first pass metabolism occurs overall and so an increased amount of drug enters the systemic circulation.

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12
Q

Describe the metabolism of a prodrug in a healthy patient vs in CLD.

A

In a healthy patient, there is a high concentration of prodrug in portal vein. In the liver, prodrug conversion to active metabolite occurs and then the active drug enters systemic circulation.

In CLD, there is reduced prodrug conversion to active metabolite so less active drug enters systemic circulation.

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13
Q

Drugs that cause enzyme inhibition lead to a lower or higher drug concentration?
What dose change needs to be made to target drugs?

A

This causes decreased metabolism so leads to higher drug concentration and potential toxicity.

Need to reduce dose of target drug

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14
Q

Give some examples of enzyme inhibitors.

A 
Antibiotics (erythromycin, ciprofloxacin, metronidazole, sulphonamides, chloramphenicol, isoniazid)
Allopurinol
Amiodarone
Cimetidine
Ethanol (acute)
Ketoconazole
Diltiazem, verapamil
Omeprazole
Sodium valproate
Quinidine
5HT reuptake blockers
Protease inhibitors
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15
Q

Enzyme inhibition vs enzyme induction - when is maximum effect seen?

A

Within few hours

2-3 weeks

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16
Q

Drugs that cause enzyme induction lead to a lower or higher drug concentration?
What dose change needs to be made to target drugs?

A

Increased metabolism leads to lower drug concentration and lower efficacy.
Need to increase dose of target drug

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17
Q

What is there a risk of when enzyme inducers are stopped?

A

When enzyme inducer stopped, there is a risk of toxicity
from the target drug and therefore need to monitor and
reduce dose

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18
Q

Give some examples of enzyme inducers.

A 
– Rifampicin
– Phenytoin
– Phenobarbitone, other barbiturates
– Carbamazepine
– Ethanol (chronic)
– Sulphonylureas
– Nevirapine
– St John’s wort
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19
Q

Drug-induced hepatotoxicity - what drugs can cause hepatitis?
How is this diagnosed?

A

Dose–dependent - paracetamol, alcohol, azathioprine
Dose–independent - isoniazid, pyrazinamide, amiodarone, nifedipine

Raised ALT/AST

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20
Q

Drug-induced hepatotoxicity - what drugs can cause fatty change in liver?
How is this diagnosed?

A

Alcohol, tetracyclines

Ultrasound

21
Q

Drug-induced hepatotoxicity - what drugs can cause cholestasis?
How is this diagnosed?

A

Chlorpromazine, chlorpropamide, erythromycin,
nitrofurantoin, nifedipine, statins, co-amoxiclav

Raised Bil/ALP

22
Q

Common drugs to dose-adjust in CLD - how much is the SSRIs dose reduced by?

A

~50%

23
Q

Common drugs to dose-adjust in CLD - how are neuroleptics dose changed?

A

Smallest initiation dose and escalations doses

24
Q

Common drugs to dose-adjust in CLD - how are benzodiazepines prescribed differently?

A

Reduce maintenance by 50%

25
Q

Common drugs to dose-adjust in CLD - which group of drug is a risk factor for spontaneous bacterial peritonitis?

A

PPIs

26
Q

Common drugs to dose-adjust in CLD - how is metronidazole used?

A

Use twice daily only

27
Q

Common drugs to dose-adjust in CLD - when should statins be avoided? Otherwise what is the dose?

A

Avoid if cholestasis; otherwise smallest initiation dose

28
Q

Analgesic drugs to dose-adjust in CLD - what are the risks of paracetamol and how is it dose-adjusted?

A

– Max 2g day regularly
– 3g daily can be used occasionally as required
– Avoid in advanced CLD

RISK OF HEPATOTOXICITY

29
Q

Analgesic drugs to dose-adjust in CLD - risk of NSAIDs and how are they dose-adjusted?

A

– Avoid in advanced CLD

RISK OF GASTRIC BLEEDING AND HEPATOTOXICITY

30
Q

Analgesic drugs to dose-adjust in CLD - how are opiates, particularly morphine and fentanyl, dose adjusted?

A

– Reduce morphine dose and frequency by 50% for regular dosing
– Fentanyl seems to be better tolerated in CLD, reduce dose/frequency by 25-50% for regular dosing

31
Q

How do we measure and monitor renal function?

A

Serum creatinine (μmol/L)
Estimates of Glomerular Filtration Rate (GFR) (ml/min)
Creatinine clearance

32
Q

What is serum creatinine dependent on?

When does it become elevated?

A

Muscle mass

Only elevated once ~50% of renal function lost

33
Q

What is taken into consideration with the eGFR MDRD formula?

A

Creatinine, age, race, gender

34
Q

Disadvantage of using serum creatinine to measure renal function?

A

poor predictor of GFR

35
Q

Disadvantage of using eGFR to measure renal function?

A

Does not take into account weight therefore inaccurate at extremes of weight

36
Q

What is taken into consideration with the eGFR Cockcroft-Gault formula for estimated creatinine clearance?

A

Age, weight, gender, serum creatinine

37
Q

How is creatinine clearance calculated?

A

The concentration of Cr in urine timees by volume of urine, divided by conc of Cr in plasma.

38
Q

Explain elimination of drugs in a healthy kidney vs CKD.

A

In a healthy kidney, the drug is eliminated.
There is a high concentration of drug renal artery and in CKD, there is reduced elimination by kidney. This means increased half life and potential for drug accumulation.

39
Q 
The use of drugs in patients with reduced renal
function can give rise to problems for several reasons. What are they? (4)
A
  • Reduced renal excretion of a drug or its metabolites may cause toxicity
  • Sensitivity to some drugs is increased even if elimination is unimpaired
  • Many side–effects are tolerated poorly by patients with
    renal impairment
  • Some drugs are not effective when renal function is
    reduced
40
Q

The level of renal function below which the dose of a drug must be reduced depends on…?

A

the proportion of the drug eliminated by renal

excretion and its toxicity

41
Q

Many elderly patients have renal impairment - why might this not be indicated by a raised serum Cr?

A

Because of reduced muscle mass

42
Q

Why might it be important to give a loading dose in CKD if an immediate effect is required (even though the size of the maintenance dose is reduced)?

A

This is because it takes about 4-5 t½ of the drug to achieve steady-state plasma concentrations
Because the plasma half-life of drugs excreted by the
kidney is prolonged in renal impairment it can take many doses for the reduced dosage to achieve a therapeutic plasma concentration.

43
Q

What drugs should be avoided in CKD?

A

Nephrotoxic drugs

44
Q

Give some examples of drugs that are mostly renally cleared?

A
  • Antibiotics - aminoglycosides, vancomycin
  • Anticoagulants - low-molecular weight heparins
  • Cardiac drugs - atenolol, digoxin
  • Opioids - morphine
  • Hypoglycaemics - metformin, insulin
  • Others - methotrexate
45
Q

Pre-renal causes of drug-induced nephropathy. (3)

A

Anti-hypertensive medications –> hypotension
Furosemide and other diuretics –> dehydration
ACE-inhibitors –> reduced renal perfusion

46
Q

Intrinsic renal causes of drug-induced nephropathy. (3)

A

Gold, NSAIDs –> glomerular injury
NSAIDs, β-lactam antibiotics, PPIs –> interstitial nephritis
Lithium –> diabetes insipidus

47
Q

Presentation of immune mediated interstitial nephritis?

A

Can be up to several months after 1st exposure
Allergic-like symptoms e.g. fever, rash etc
Eosinophilia/uria

48
Q

Post-renal causes and mechanism of drug-induced nephropathy (obstructive nephropathy).

A

Same mechanism as uric acid nephropathy - crystals collect and obstruct in collecting ducts and can occasionally precipitate in renal parenchyma.
Drugs themselves can precipitate - aciclovir, HIV protease inhibitors, methotrexate - or drugs can predispose to other crystals - orlistat, allopurinol.

CSP 2 (12 decks)

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