Transcript Ischaemic Heart Disease

Ischaemic Heart Disease
Group D
Scenario
Mr Pex (55 yrs) has taken these medications for 2 years:
 Perhexiline 100mg bd- anti-angina
 Gliclazide 80mg bd- hypoglycaemic agent
 Fluoxetine 20mg d- antidepressant
It is suspected that Mr. Pex has perhexiline toxicity because he
has signs and symptoms of hepatotoxicity and peripheral
neuropathy
 How it should be managed
 Place of Monitoring levels of Perhexiline
 Explanation of any medications that could be responsible for
the abnormalities in the clinical chemistry profile
 Whether the abnormalities are likely to be ongoing
 Recommended management for this patient with respect to his
medication regimen
Clinical chemistry profile
Parameter
Reading
Reference
Status
AST
75
10- 45 u/L
Elevated
ALT
67
5- 40 u/L
Elevated
Alk Phos
220
25-100 u/L
Elevated
LDH
400
110-230 u/L
Elevated
Total Bilirubin
34
2- 20 umol/L
Elevated
Fasting BSL
2.8
3- 8 mmol/L
Elevated
Perhexiline
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indicated for angina
plasma/blood perhexiline concentrations must be maintained
within the range 0.15-0.6mg/L (0.5- 2umol/L)
Perhexiline is metabolised via CYP450 2D6 (patient genetic
variability- fast, intermediate, slow metabolisers) resulting in
variable clearance.
Genetic Polymorphism: approximately 10% of the population
are slow metabolisers of perhexiline and are at a higher risk of
toxicity, thus requiring decreased doses
Perhexiline and its metabolites undergo extensive hepatic
metabolism and are excreted in bile and urine (ratio 1:2
respectively)
It has a low therapeutic index; so therapeutic drug monitoring
is essential.
Therapeutic Drug Monitoring factors: Individualised dosage; Target range;
Concentration related effects (therapeutic and adverse); Narrow Therapeutic Index;
Desired therapeutic effect is difficult to monitor.
Perhexiline pharmacokinetics
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>80% of perhexiline maleate is absorbed from the GIT after
oral dosing
Large volume of distribution, that is probably related to the
tissue binding of perhexiline and its metabolites
It crosses the BBB (lipophilic)
Highly protein bound (>90%). Some binding to erythrocytes
Saturable rate of hepatic metabolism (genetic polymorphism
of CYP2D6)
Several metabolites with unknown pharmacological activity
Racemic mixture- 2 Enantiomers
Perhexiline toxicity
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long term- usually occurs > 3 months of continued therapy
Directly related to perhexiline blood concentrations
Hepatotoxicity- elevation in serum liver enzymes (AST
aspartate aminotransferase, ALT alanine aminotransferase,
alkaline phosphatase, LDH lactate dehydrogenase). Monitoring
is essential at least every month.
In Mr Pex: AST, ALT Alkaline Phosphatase, LDH: elevated. These
liver enzymes show that the liver is damaged. They increase with
liver dysfunction
 Aminotransferases- ALT, AST are sensitive indicators of hepatic
inflammation and necrosis. ALT is more specific as it is mainly
found in the liver.
 Alkaline Phosphatase: primarily made in liver, but also in bones.
Sensitive marker of damage.
 LDH: LDH4, LDH5 appear mainly in the liver and in skeletal
muscles
 Total Bilirubin (conjugated + unconjugated): low
Hepatotoxicity
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Hepatitis and Cirrhosis have been reported. (Higher AST vs.
ALT may be indicative of cirrhosis but chronic alcohol
consumption must be excluded)
Though, more specifically the non-alcoholic fatty liver
disease Non-alcoholic Steatohepatitis (NASH) is associated
with perhexiline maleate
NASH is usually asymptomatic and may progress to cirrhosis
within 7 years (inflammation and necrosis)
Abnormal liver function test results are present
 Markers: Serum aminotransferase activities usually <4
fold above the upper limit of normal; moderately
elevated serum ALT and AST
Insulin resistance may occur and may be unrelated to the
presence/absence of obesity
Non-alcoholic steatohepatitis
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No biological test to positively identify it
The following diagnostic approach can be used by health care
professionals, to show hepatotoxicity
Peripheral neuropathy
Occurs when nerves connecting spinal cord and brain to other
parts of the body become damaged
 3 different types: mono- (damage to a single nerve); multiple
mono- (two or more nerves) poly-neuropathy (many nerves
throughout the body)
 Most common causes: drugs eg. perhexiline, diabetes
Patient signs and Symptoms
 (begin in hands or feet; may spread throughout the limbs)
 Tingling, prickling, numbness
 Sharp pain
 Decreased or lack of sensation
 Muscle weakness
 Lack of muscle control
 Burning or freezing sensations
 Extreme sensitivity to touch
 Loss of balance or coordination
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Tests for signs and symptoms
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Signs of muscle cramping/twitching and muscle weakness
Skin sensitivity to temperature changes, touch, vibration,
pinpricks
Observation for clinical signs of hepatic involvement eg.
Weakness, loss of appetite, weight loss
Nerve function tests eg. EMG (Electromyography- measures
muscle electrical activity)
Analysis of serum enzymes (AST, ALT, alkaline phosphatase,
LDH) and bilirubin- abnormalities or persistent elevations
Blood Glucose measurements- persistent/marked
hypoglycaemia
Weight- excessive weight loss (>10% initial weight)
Perhexiline plasma levels- therapeutic target range
Gliclazide
Symptoms of
hypoglycaemia:
 Comfusion
 Agitation
 Tachycardia
 Tremor
 Hypothermia
 May progress to
coma/convulsions
Risk Factors:
• Advanced age
• Poor nutrition
• Alcohol
• Renal disease
• Hepatic disease
• Concurrent
medications
Rarely associated with increases in ALP, AST and
bilirubin
Hypersensitivity can occur with accumulation
Fluoxetine (1)
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Metabolised by 2D6, as is perhexiline
Clinically significant drug interactions occur when:
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Therapeutic index of substrates is narrow (applies to
perhexiline)
Isozyme involved in competition is the primary metabolic
pathway (applies to perhexiline and fluoxetine; both
pathways are saturable at therapeutic concentrations)
Concentration of inhibiting substrate reaches sufficient
levels in vivo (demonstrated for both)
Fluoxetine (2)
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Liver enzyme elevations may occur (reported in about
0.5% of patients receiving SSRIs)
 >58,000 reports of hepatic ADRs with SSRIs ±
other medications
 493 suspected to be due to fluoxetine
 12 = acute hepatitis (6 were on concurrent
medications)
 5 = asymptomatic increase in serum
transaminases
 80 with paroxetine
 65 caused by sertraline
 54 attributed to fluvoxamine
Management of Mr. Pex
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Perhexiline?
 Discontinue
 Reassess angina (severity, frequency of attacks) and
initiate alternative treatment
Fluoxetine?
 Reassess the need for this treatment
 Phenotyping may be of some value if PM status is
suspected
 Alternative agent could be used (different class of
antidepressant, or try fluvoxamine/sertraline which are
less potent CYP2D6 inhibitors and less frequently
associated with hepatic ADRs
Gliclazide?
 Assess glycaemic control (ongoing)
 Determine hepatic and renal function
 Change of agent may be necessary
Bilirubin
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Outline the chemical basis for the spectrophotometric
analysis of bilirubin
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Look at the various techniques used to obtain values
for total and direct bilirubin
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Examine the problems and variations of different
approaches used to examine patient bilirubin profiles
Bilirubin
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bile pigment formed from the breakdown of Haemoglobin
found in serum as unconjugated, conjugated and delta
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Unconjugated bilirubin is insoluble in aqueous solution, bound to
serum albumin and represents bilirubin prior to hepatic processing
Conjugated bilirubin is formed subsequent to hepatic processing and
is yielded by unconjugated bilirubins esterification of its two
proprionic side groups with glucoronic acid.
Delta bilirubin represents bilirubin which is covalently bound to
albumin
Since the liver is involved in the enzymatic modification of
bilirubin, the serum plasma concentration is used as a test for
hepatic function
Elevation in unconjugated bilirubin can occur as a result of
excessive bilirubin production eg. haemolysis, or the inability
to conjugate or take up bilirubin from the circulation
Elevations in conjugated bilirubin are commonly seen in
hepatocellular or biliary dysfunction
Analysis of bilirubin in serum
The most widely used methods for the measurement of serum
bilirubin are based on the diazo reaction
Total bilirubin
Unconjugated bilirubin
+
Unconjugated bilirubin
Diazotized sulfanilic acid
+
+
Caffeine-benzoate
→
Azobilirubin A & B
(Isomers 1 & 2)
Analysis of bilirubin in serum
Jendrassik Grof Assay
 Uses caffeine-benzoate which acts as an accelerator
 Caffeine benzoate displaces unconjugated bilirubin from
albumin perhaps making it more water soluble by disruption
of the internal hydrogen bonds → making bilirubin more
readily available for reaction with the diazo reagent
 Performed at alkaline pH
Azobilirubins produced in these reactions are measured
spectrophotometry at 600nm
Evelyn Malloy Assay
 Uses methanol to dissociate albumin
 Performed at acidic pH
 Absorbances are measured at 560nm producing red or purple
colour
Direct bilirubin
Conjugated Bilirubin + Diazotized sulfanilic acid →
Azobilirubin B (Isomers 1 & 2)
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Measures the majority of conjugated and delta
bilirubin and a variable but small percentage of
unconjugated bilirubin
To prevent measurement of unconjugated bilirubin,
the serum should be diluted with HCl first
Total bilirubin
Total bilirubin
Unconjugated bilirubin
+
Unconjugated bilirubin
Diazotized sulfanilic acid
+
+
→
Azobilirubin A & B
(Isomers 1 & 2)
Caffeine-benzoate
DIRECT BILIRUBIN
Conjugated Bilirubin + Diazotized sulfanilic acid →
Azobilirubin B (Isomers 1 & 2)
INDIRECT BILIRUBIN
Total Bilirubin – Direct Bilirubin = Indirect Bilirubin
Other methods used to obtain
bilirubin fractions
High Performance Liquid Chromatography
Measures four bilirubin fractions in serum
Unconjugated bilirubin
Delta bilirubin
Bilirubin monocongugate
Bilirubin diconjugate
Other methods (cont.)
Direct Spectrophotometric Method
 Measures conjugated and unconjugated bilirubin and
calculates delta bilirubin as the difference between the sum of
these and total bilirubin
 Based on the absorbance of unconjugated bilirubin at 454nm
and Hb at 540nm
Enzymatic Methods
BOX
Bilirubin + ½ 0² → Biliverdin + H2O
 Based on enzyme bilirubin oxidase
 Oxidation rates depend on the pH of the reaction mixture
Maximum oxidation
Conjugated
pH 4.5 & 10
Unconjugated
pH 6
Delta
pH 4
Problems with techniques
Despite the advances of these methods, in the clinical
laboratory they still have limitations. Some of these are
related to bilirubin's instability and insolubility in water,
but there are also problems of assay interference, lack of
pure conjugated bilirubin standards, and interpretation of
bilirubin fractions depending on the method on use
Malloy Evelyn
Jendrassik-Grof
not as accurate as the Jendrassik Groft
method
Has higher molar absorptivity and is more
sensitive and precise at low bilirubin
concentrations than the Malloy Evelyn
Is susceptible to significant hemoglobin Hemolysis causes negative error in
interference
bilirubin assay, although the error is less
than in the Malloy-Evelyn method
Diazo method
Limitations include:
The assumption that direct and indirect bilirubins represent
conjugated and unconjugated bilirubins, respectively although
in several assays this may be incorrect.
The lack of adequate standards for calibration of the direct
bilirubin assay. Direct bilirubin assays have used
unconjugated bilirubin for assay calibration, not a particularly
stable compound and is not ideal because assays should be
calibrated with the analyte that they are designed to measure.
Many manufacturers now use synthetic forms of bilirubin in
their calibration and control material, and it is hoped that use
of these synthetic variants will help improve the accuracy of
the direct bilirubin assay
Direct bilirubin assay is dependent on reaction conditions,
especially pH and often underestimates conjugated bilirubin ,
this leads to inaccuracies in indirect bilirubin
Direct spectrophotometry
The assay is only suitable for serum neaonates (usually
less than 2 - 3 weeks of age) because other pigments,
notably carotene, start to appear as infants get older
and cause interference at 454nm.
Studies have shown that such spectrophotmeteric
methods are not only rapid, easy to carry out,
requiring small samples but also are less influenced
by factors like hemoglobin concentration and
hemolysis
HPLC
Originally limited by inadequate fraction quantitation and the
large sample size requirement
Modifications allowed measurement of all four fractions using
small sample size. More recently developed procedures do not
precipitate albumin and lose delta bilirubin
Delta bilirubin represents bilirubin covalently bound to plasma
proteins, predominately albumin. This binding unlike that of
unconjugated bilirubin, is resistant to physical, chemical, and
enzymatic treatments
HPLC is considered the gold standard as it measures all four
fractions, however, it is extremely expensive, elaborate and
time consuming for routine clinical use. It is also labor
intensive and requires specialized equipment and therefore not
a method suited for a laboratory required to perform bilirubin
7 days per week, often on a 24-hour basis. It does however
remain a method to which the more commonly used
procedures can be compared
Specimen requirements
Because both conjugated and unconjugated forms of
bilirubin are photo-oxidised on exposure to UV light,
it is recommended that sample should be protected
from light. Bilirubin is unstable and light sensitive
and therefore the assay should be carried out within 2
hours of sample collection. If a longer delay is
unavoidable, refrigerate the sample. Bilrubin is stable
in the refrigerator (40C) for 3 days. Samples can be
frozen at -700C, to keep bilirubin stable for 3 months
Measurement in urine
Because conjugated but not unconjugated bilirubin is excreted in
urine, uniary examination may be used as a simple screen to
determine whether high levels of bilirubin is due to prehepatic
causes or to hepatic or post hepatic disorders.
The urine specimen to be investigated should be fresh. If delays
are anticipated, the urine container should be protected from
light and refrigerated.
Urine bilirubin measurements are often made using qualatative
methods such as dipsticks impregnated with diazo reagent,
which reacts with bilirubin to produce a colour change.
The conjugated forms of bilirubin can be isolated from bile
however, are not suitable for mass isolation and use in
calibrators and control material and therefore unstable
References
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