Heme/Onc Flashcards
Purine Degradation
-Purine -> Xanthine or hypoxanthine –> uric acid (xanthine oxidase)
Urate in the Kidney
- Urate is filter, secreted, and reabsorbed
- reabsorption predominates
- URAT-1 (OAT)
Causes of Hyperuricemia
- Under excretion due to renal impairment, HTN, low dose aspirin
- Urate overproduction from purine rich diet, tumor lysis syndrome
TX of asymptomatic Hyperuricemia
-Diet modification and weight loss
TX of symptomatic Hyperuricemia
- Diet modification
- Drug therapy to lower risks of recurrent attack, relieve symptoms of acute attack, and reduce serum urate levels
Drug Classes
- Uricostatic agents: reduce formation of uric acid
- Enzymes: metabolize uric acid
- Uricosuric Agents: Increase excretion of uric acid by the kidney
- Anti-inflammatory agents: relieve acute attacks of gout
Allopurinol
- Analog of hypoxanthine acts as competitive inhibitor of xanthine oxidase
- XO turns allopurinol into oxypurinol which is a non competitive XO inhibitor (longer half life)
- Dissolution of tophi by lowering serum levels of urate
- Decreases risk of nephropathy
- Increase risk of acute attacks due to tissue mobilization of urate (Colchicine given before therapy is started)
- Probenecid increases clearance of oxypurinol which requires incr. dose, but allopurinol increases the half life of probenecid requires lower dose
- Mercaptopurine and azathioprine require dose reduction due to inhibition of XO
- Hypersensitivity RXN (rash fever malaise and myalgias)
Feboxostat
- Non-purine, non-competitive inhibitor of oxidized and reduced form of XO
- Used as an alternative to allopurinol approved for hyperuricemia with gout attacks
- Abnormal liver functions, nausea, joint pain and rash
Pegloticase
- Urate oxidase that converts rate to inactive and soluble allantoin
- Peds tumor lysis syndrome in cases of leukemia, NOT CHRONIC GOUT
- pegylation increases half life and reduces antigenicity
- Blood samples for urate levels must be chilled to prevent enzymatic degradation
- Hemolytic anemia in G6P, anaphylaxis, metheglobinemia
Probenecid
- Decreases reabsorption of urate by inhibiting URAT-1
- Liberal H20 intake to prevent stones and keep urine pH above 6
- DONT USE: nephrolithiasis, over production of urate and patients with renal insufficiency
- Combine with Colchicine to prevent acute attacks
- GI irritation use caution with patients who have ulcers
- Salicylates reduce efficacy:
- Low dose blocks proximal tubule secretion of urate -> hyperuricemia
- High doses: block secretion and reabsorption w/ increase risk of stones
Losartan
-moderate uricosuric option for patients w/ HTN who are intolerant to probenecid
Anti-inflammatory Drugs
- NSAIDS: within 24 hrs of onset for 3-4 days and then taper for 7-10 (aspirin contraindicated)
- Glucocorticoids: Use if NSAIDs don’t work, intra articular administration effective if 1-2 joints affected
Colchicine
- Anti-inflammatory
- prevents activation, degranulation, and migration of neutrophils that mediate gout symptoms
- Enterohepatic recirc, dose reduction in liver and renal insufficiency
- Uses acute gout, and fixed dose combo with probenecid
- GI effects are frequent
- myelosuppression, leucopenia, granulocytopenia, thrombopenia, aplastic anemia
- Don’t use with 3A4 and P-glycoprotein inhibitors
- minimum of 3 days between treatments
Indomethacin
- nonselective COX-inhibitor
- 30-50% experience adverse effects
- GI effects can be fatal
- severe frontal headaches
- Seizures, depression, psychosis, hallucinations, and suicide
Amino Esters
Benzocaine cocaine Tetracain Procaine
Ester linkage between lipophilic and hydrophilic ends
Amino Amide
Lidocaine, Prilocaine, Meprivacine, Bupivacaine
-Amide linkage between lipophilic and hydrophilic ends
Mechanisms of action for local anesthetics
- Block Na channels along Axons when the channel is open in a voltage and time dependent manner.
- No loss of consciousness
- Reversible
- Ionized form has a higher affinity for the receptor
Local anesthetics crossing the membrane and blocking the receptor
-Non-ionized form diffuses across the nerve membranes while the ionized form (with H+ ion) blocks the receptor
Effects of Na+ blockage on nerve conduction
- Threshold for excitation increases
- Impulse conduction slows
- Action potential amplitude decreases
- Eventually ability to generate action potential is completely abolished
Fibers affected by Local anesthetics
- Local anesthetics are more efficacious on nerves that are rapidly firing or chronically depolarized
- C and B (pain)fibers are blocked first followed by A fibers
- A-alpha are blocked last (motor and proprioception)
- Recovery occurs in the reverse order
Potency and Duration of Local anesthetics
-Increases in lipophilicity –> increases in duration and potency.
Vasoconstrictors with Local Anesthetics
-Used to reduce rate of systemic absorption and prolong duration of action
Most potent and longest lasting amino ester
-Tetracaine (procaine shortest and weakest)
Most potent and longest lasting amino amide
-Bupivacaine (mepivacaine the worst)
Metabolism of Esters and amides
- Esters: Metabolized in plasma by plasma cholinesterases
- Amides: Metabolized in the liver by cytochrome P450 enzymes
Toxicity of local anesthetics
- Degradation: Hypersensitivity due to formation of benzoic acids and derivatives -> allergic rxns
- CNS: sedation, visual and auditory disturbances, tongue numbness and metallic taste, Nystagmus and muscular twitching –> tonic-clonic convulsions (depression of inhibitory pathways)
- Cardio: cardiac conduction and function effects (Bupivacaine)
Transient Nuerological Symptoms
-Syndrome of transient pain or dysethesia from spinal or epidural administration
General anesthesia
-Reversible CNS state loss of response to and perception of stimuli
Dissociative Sedation
-Trance like cataleptic state in which the patient experiences analgesia and amnesia but retains reflexes and CV stability
Inhalation
-Continuous inhalation of gas or volatile liquid which rate depth and duration of anesthesia are under control. Recovery occurs when gas is turned off and anesthetic is eliminated by exhalation
Intravenous
-Lipophilic and injected, rapid onset, but depth and duration are not well controlled, duration depends on rate of metabolism.
Stages of Anesthesia
- Conscious but drowsy with variable degrees of analgesia
- Excitement and delirum –> unconscious reflex response to pain (during recovery)
- Surgical anesthesia regular respiration
- medullary depression with loss of respiration and vasomotor control -> death
-Now defined as induction, maintenance and emergence
CV effects of general anesthesia
-Decrease mean arterial blood pressure by
vasodil, myo suppression, blunted baroreceptor reflex and decreased sympathetic tone
Respir effects of General anesthesia
- Reduced or eliminated vent. drive
- Lose gag and cough reflex
- reduced LES tone
Emergence
- Naseau and vomiting due to tim of CTZ (treat with 5HT3 agonist)
- Return of sympathetic tone –> Tachy and HTN
- Shivering treated with meperidine
Mechanism of Action
-Reversibly interact with hydrophobic sites of specific membrane receptors (enhance inhibit GABA)
Pharmacokinetics of Inhaled Anesthetics
-Achieve equilibrium between alveolar gas and brain tissue: exhaled gas = inhaled gas
which is affected by blood solubility, alveolar blood pressure and partial pressure
-Concentration is expressed as partial pressure (more H2O soluble = lower partial pressure)
-Blood solubility: Lower solubility = higher partial pressure = faster rate of induction
Nitrous Oxide
- Use in dental procedures or in combo to reduce dose of other inhalation agents
- Advantages: good analgesia and amnesia, minimal CV effects, Reduced side effects of other inhalation agents
- Disadvantages: Not complete anesthetic, rigidty, Diffusion hypoxia, Pneumothorax, inhibits b12 dependent enzymes so don’t use chronically