Prostaglandins & NSAIDS 2

Transcription

1 Prostaglandins & NSAIDS 2 รศ. พ.ญ. มาล ยา มโนรถ ภาคว ชาเภส ชว ทยา คณะแพทยศาสตร จ ดประสงค การศ กษา เม อส นส ดการเร ยนการสอน และการศ กษาด วยตนเองเพ มเต ม น กศ กษาสามารถ 1. ทราบถ งชน ดของ NSAIDs 2. ทราบถ งเภส ชจลนศาสตร เภส ชพลศาสตร และอาการข างเค ยงของ NSAIDs 3. ทราบถ งความแตกต างของ aspirin ก บ NSAIDs ชน ดต างๆ The Salicylates Salicylic acid, aspirin (acetylsalicylic acid ; ASA), sodium salicylate, methyl salicylate, diflunisal, salsalate, sulfasalazine Acetylsalicylic acid : ASA 1763 Reverend Edmund Stone ( powdered form of the bark of willow success in treating fever) 1853 : ASA was synthesized 1899 : use Pharmacokinetics The salicylates are rapidly absorbed from the stomach and upper small intestine, peak plasma salicylate level within 1-2 h is absorbed as such and is rapidly hydrolyzed (serum T1/2 15 min) to acetic acid and salicylate by esterase in blood and tissue salicylate is bound to albumin, but the binding is saturable Sodium salicylate and aspirin are equally effective anti-inflammatory drugs, though aspirin may be more effective as an analgesic metabolic pathways for salicylate disposition become saturated when the total body load of salicylate exceed 600 mg As dose of aspirin increase, salicylate elimination half-life increase from 3-5 h (600 mg/d) to h (> 3.6g/d) salicylate are excreted in the urine as free salicylate (10%), salicyluric acid (75%), salicylic phenol (10%), acyl glucuronides (5%), gentistic acid (<1%) alkalinization of the urine increases the rate of excretion of free salicylate and its watersoluble conjugates 1

2 2 Mechanism of action Anti-inflammatory effect is a nonselective inhibitor of both COX isoforms, but salicylate is much less effective in inhibiting either isoform irriversibly inhibits COX and inhibit platelet aggregation, while nonsalicylated salicylated do not also interferes with the chemical mediators of kallikrein system (inhibiting granulocyte adherence) Antipyretic effect aspirin reduces elevated temperature, whereas normal body temperature is only slightly affected (COX inhibition in the CNS and inhibition of IL-1) The fall in temperature is related to increased dissipation of heat caused by vasodilation of superficial blood vessels and may be accompanied by profuse sweating Analgesic effect aspirin is most effective in reducing pain of of mild to moderate intensity through its effect on inflammation and because it probable inhibits pain stimuli at a subcortical site Antiplatelet effect single low doses of aspirin (81 mg daily)produce a slightly prolonged bleeding time, which doubles if administration is continue for a week (irreversible inhibition of platelet COX, so that aspirin s antiplatelet effect lasts 8-10 days) Should be stopped 1 week prior to surgery to avoid bleeding complications Clinical Use antiplatelet action : mg/day analgesic or antipyretic less than g oral dose commonly use ant-inflammatory dose adult 45/kg/day in divided dose

3 3 Adverse effects 1. GI disturbances and increase risk of bleeding 2. Chronic aspirin overdosing : associated with reduced synthesis of prothrombin 3. hypersensitivity : may experience asthma ( synthesis of LT) 4. At higher doses (salicylism) : vomiting, tinnitus, decrease hearing, virtigo, 5. At very high doses : metabolic acidosis, dehydration, hyperthermia, collapse, coma, and death 6. Children with viral infections : risk of developing Reye s syndrome (hepatic fatty degeneration and encephalopathy) 7. : lower dose : serum uric acid dose > 4 gm : serum uric acid Nonacetylated salicylates COX-2 selective inhibitors celecoxib, etoricoxib, meloxicam, rofecoxib, valdecoxib fewer GI side effects recommended mainly for treatment of osteoarthritis and rheumatoid arthritis Celecoxib : about times more selective for COX-2 than for COX-1 it is a sulfonamide, may cause rashes dose not affect platelet aggregation causes no more edema or renal effects than other members of the NSAIDs Etoricoxib structural similars to diclofenac, monitor hepatic function Meloxicam an enocarboxamide related to piroxicam preferntial inhibit COX-2 over COX-1 Nonacetylated salicylates Nonselective COX inhibitors Diclofenac phenylacetic acid derivative at a dosage of 150 mg/d appears to impair renal blood flow and GFR elevation of serum aminotranferases may occur more commonly than other NSAIDs 0.1% ophthalmic preparation : prevention of postoperative ophthalmic inflammation

4 4 Etodolac a racemic acetic acid derivative slightly more COX-2 selective than most other NSAIDs (COX-2:COX-1 activity ratio of about 10) Ibuprofen anti-inflammatory effect, ibuprofen 2400 mg/d = 4 g aspirin analgesic effect : < 2400 mg/d GI irritation : less frequently than ASA Naproxen half-life 12 h : permit less frequent dosing Piroxicam dosage > 20 mg/d : increase incidence of PU and bleeding long half-life (57 h) permits once-daily dosing Sulindac sulfoxide product reversible metabolized to active sulfide metabolite enterohepatic cycling prolongs the duration of action to h because sulfide may be reoxidized to the inactive product in the kidney: may inhibit renal COX less than other NSAIDs elevation of serum aminotransferase Meclofenamate & mefenamic acid diarrhea and abdominal pain may be more common Meclofenamate : contraindicated in pregnancy Mefenamic acid : less effective than aspirin as an anti-inflammatory agent and is clearly more toxic should not be used for longer than 1 week and should not be given to children Indomethacin potent nonselective COX inhibitor and may also inhibit phosphlipase A and C use in rheumatoid conditions, gout ophthalmic preparation : conjunctival inflammation SE : GI, headache (15-25% of patients) should be avoid in patients with nasal polyps or angioedema (in whom asthma may be precipitate)

5 Clinical Pharmacology of The NSAIDs) all NSAIDs including aspirin are about equally efficacious with a few exception NSAIDs tend to be differentiated on the basis of toxicity and cost-effectiveness diclofenac and sulindac : associated with more liver function test abnormalities than other NSAIDs nonselective NSAIDs + omeprazole or misoprotol : patients at highest risk for GI bleeding 5