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Pharma 2 > Adjuvant Analgesics. Drugs used to treat Gout. Centrally-Acting Muscle Relaxants > Flashcards

Adjuvant Analgesics. Drugs used to treat Gout. Centrally-Acting Muscle Relaxants Flashcards

1
Q

Adjuvant Analgesics

Background Information

A

Are drugs that lack analgesic effect but reduce neuropathic pain
Effective only in neuropathic pain

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2
Q

Neuropathic Pain

A

Caused by damage to peripheral or central pain pathw.:
Polyneuropathy
Traumatic nerve lesion
Spinal cord injury
Damage at level: middle brain/thalamus/cortex

Types
   Phantom Limb Pain
   Diabetic Neuropathy
   Postherpetic Neuralgia
   Trigeminal Neuralgia
   Pain post Stroke

Symptoms
Spontaneous pain (often paroxysmal)
Mechanical heat/cold hyperalgesia
Allodynia (pain caused by non noxious stimuli)

Even opioids have limited effect

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3
Q

Adjuvant Analgesics

Drug Groups

A

TCA
Anti-epileptics
Na Channel Blocking Agent
Capsaicin

Can also use
Glucocorticoids
Cannabis preps
Alpha 2 R agonist: clonidine

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4
Q

Adjuvant Analgesics

TCAs

A

Amitiyptyline, Nortriptyline, Imipramine, Clomipramine

First generation
NA and 5 HT reuptake inhibitors
Significant first pass metabolism (dose should be increasing), lipid soluble, large Vd
Metabolism: N demethylation–> active metabolite, hydroxylation–> glucuronide conjugation (inactive)

Side Effects:
Antagonism of M1 R: anticholinergic (dry mouth, urinary retention, blurred vision)

Antagonism of H1 R: sedation/ weight gain

Antagonism on alpha R: orthostatic Hypotension

Direct membrane effects: convulsion/ arrhythmias
Toxicity: the “3 Cs”: coma, convulsions, and cardiotoxicity

Drug interactions:
− Hypertensive crisis with MAO inhibitors
− Serotonin syndrome with SSRIs, MAO inhibitors, and meperidine
− Prevent antihypertensive action of α2 agonists

!!! TCAs potentiate the sedative effect of ethanol !!!

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5
Q

Adjuvant Analgesics

Na Channel Blocking Agent

A

Lidocaine

Non ionised from crosses axonal membrane
From within: ionised from blocks inactivated Na channel
Slows recovery and prevent AP propagation

Order of sensitivity
B and C > Adelta > Abeta > Agamma > Aalpha

Recovery follows reverse order

Coadminister with alpha 1 agonists to decrease absorption into systemic circulation; prolong effects; reduce toxicity

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6
Q

Adjuvant Analgesics

Capsaicin

A

Local as transdermal patch

Desensitised (irreversibly damages) nociceptive nerve endings

–> Herpes zoster; diabetes

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7
Q

Adjuvant Analgesics

Anti-epileptics: Phenytoin

A

Blocks axonal Na channels in their inactivated state
Prevents seizure propagation

Variable absorption
Nonlinear kinetics
Inducer of CYP450
Elimination: Zero order of kinetics

SE
   CNS depression
   Gingival hyperplasia
   Hirsutism
   Osteomalacia (decerase Vit D)
   Megaloblastic Anaemia (decrease folate)
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8
Q

Adjuvant Analgesics

Anti-epileptics: Carbamazepine

A

Blocks axonal Na channels in their inactivated state
Prevents seizure propagation

Inducer of CYP450

SE
Osteomalacia (decerase Vit D)
Megaloblastic Anaemia (decrease folate)
CNS Depression

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9
Q

Adjuvant Analgesics

Anti-epileptics: Valproic Acid

A

Blocks axonal Na channels in their inactivated state
Also inhibits GABA transaminase (degrades GABA)
Blocks T type Ca channels

Inhibits CYP450

SE
Hepatotoxicity
Thrombocytopenia
Pancreatitis

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10
Q

Adjuvant Analgesics

Anti-epileptics: Gabapentin

A

Affects calcium channels and NT release

GABA effects too

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11
Q

Adjuvant Analgesics

Anti-epileptics: Lamotrigine

A

Blocks Na and glutamate Rs

SE
Steven Johnsons

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12
Q

Gout

Breakdown of purines

A

GMP and AMP–>hypoxanthine–>xanthine–>uric acid

Enzyme: Xanthine Oxidase

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13
Q

Disorders of Uric Acid

Consequences

A

Hyperuricemia: disturbance of uric acid metab. and excretion

Primary (inherited)
Defect of uric acid sectretion (99%)
Overproduction of uric acid (1%)

Secondary
Malignant tumor, chemo, radio-> urate overproduction
Renal failure/drugs-> reduced urate excretion

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14
Q

Gout

Drug Categories

A

Prototype
Uricosuric Drugs
Acute Gouty Arthritis Drugs

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15
Q

Gout

Allopurinol

A

Orally used
Analogue of hypoxanthine-> alt substrate for xanthine oxidase

Allopurinol converted–> oxipurinol (first pass in gut wall and liver)–> inhibition of urate formation

Formed oxipuranol is non competitive inhibitor of xanthine oxidase

Allopurinol T1/2: 1 hr
Oxipurinol T1/2: 24 hrs

Decreases uric acid production = uricostatic

Accumulating hypoxanthine and xanthine have good water solubility

Also: Slight decreases de novo purine synth

SE
Increased risk of acute attacks during first 2 weeks–>
can combo with colchicines or NSAIDs
GIT disturbance
Rash/ allergic reaction
Dose should be reduced in renal failure

Interactions
   (slight) CYP inhibitor
   Decreased metab. of mercaptopurine 
   Via xanthine oxidase inhibitin: coumarin, theopyliine: 
       decreased metab.
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16
Q

Gout

Febuxostat

A

Also inhibits xanthine oxidase

17
Q

Gout

Rasburicase

A

Reduces uric acid levels
Is a recombinant urate oxidase–> converts urate to allantoin (water soluble)

Used to prevent tumor lysis syndrome

18
Q

Gout

Uricosuric Drugs

A

Probenecid, Benzbromarone

Inhibit urate reab in proximal tubule–> increase excretion

Given p.o.
Significant PPB

Site of action: luminal membrane of proximal tubule

Lower dose: urate retention due to. competitively inhibiting active secretion of urate in proximal tubules
(Benzbromarone doesn’t do this)

Th dose: net increase in renal excretion

SE
Increased risk of acute attacks during first 2 weeks–>
can combo with colchicines or NSAIDs
GIT disturbance
Rash/ allergic reaction
Dose should be reduced in renal failure

CI
Renal insufficienty

Interactions
Inhibit secretion of weak acids: penicillins, cephalosporins

Low dose of aspirin inhibit effect or uricosurics by reducing secretion of urate and drugs

19
Q

Drugs of Acute Gouty Arthritis

Colchicines

A

Bind to tubulin and inhibit polymerisation of these into microtubules

Also reduce chemotaxis and phagocytotic activity of neutrophils

Good oral absorption, can also be given IV

Metabolism
Partial via CYP
Partly unchanged into urine and bile

Undergoes enterohepatic circulation

Decrease dose in hepatic or renal failure

SE
   Hemorrhagic gastroenteritis
   Hematuria
   Myelosuppression 
   Diarrhoea, GIT pain
   Peripheral Neuropathy
20
Q

Drugs of Acute Gouty Arthritis

A

NSAIDs
Drugs of choice because have lower SE than
colchicines
Mainly those with lower GIT side effects; meloxicam,
Ibu, diclofenac

Intra-articular Steroids

21
Q

Centrally Acting Muscle Relaxants

General

A

Most drugs act on spinal cord

Reduce path increased tone of skeletal muscle without compromising voluntary contractions

Common side effects
Sedation
Muscle weakness

22
Q

Centrally Acting Muscle Relaxants

Groups according to clinical efficacy
Site of action

A

Effective in spasticity only
Effective in acute muscle spasm only
Effective in both conditions

Site of action: Spinal Cord
Presyn Inhibition
Inhibition of excitatory transmitter from presyn neuron

23
Q

Centrally Acting Muscle Relaxants

Indications

A

Spasticity
Chronic
Impairment of descending corticospinal inhib pathways
regulating stretch reflex
Spasm of antigravity muscles, enhanced stretch reflex,
pain and disability

Acute Muscle Spasms
Reversible, self improving
Trauma or inflammation–> reflex mech–> muscle tone
increase

24
Q

Centrally Acting Muscle Relaxants

Grouping of Drugs

A

Centrally acting Muscle Relaxants Effective in Spasticity
only

Centrally acting Muscle Relaxants Effective in Acute
Muscle Spasms only

Centrally acting Muscle Relaxants Effective in Spasticity
and Acute Muscle Spasms

Peripherally acting Agents used in Spasticity

25
Q

Centrally acting Muscle Relaxants Effective in Spasticity

only

A

Baclofen
Agonst of presyn GABA B R (Gi coupled)
Reduces glutamate release -> inhibits stretch reflex
Oral or intrathecal admin
Excreted unchanged renally
Withdrawals: convulsion/ hallucinations

THC
Gabapentin

26
Q

Centrally acting Muscle Relaxants Effective in Acute

Muscle Spasms only

A

Cyclobenzaprine
Unknown MoA; inhibits polysyn stretch reflex
May cause strong atropine like effects and hallucinat.

Mephenesin and Chlorfenesin
Unknown MoA; inhibits polysyn stretch reflex

27
Q

Centrally acting Muscle Relaxants Effective in Spasticity

and Acute Muscle Spasms

A

Benzos
Positive allosteric modulation of GABA a R–> increased
presyn inhibitory effect of spinal GABA ergic
interneurons
Reduced transmitter release

Tolperisone
Na channel block–> AP propagation inhibited
Reduced transmitter release
Enhances peripheral blood flow
IV or oral
SE: hypotension, headache; NO sedation

28
Q

Peripherally acting Agents used in Spasticity

A

Dantrolene
Reducation Ca release from SR via blockage of
Ryanodine R
Used in malignant hyperthermia; neuroleptic malignant
syndrome
SE
Liver damage

Botulinum Toxin
Irreversible inhibition of ACh release

Pharma 2 (19 decks)

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