NEET MDS Lessons
Pharmacology
Phenytoin (Dilantin): for tonic-clonic and all partial seizures (not effective against absence seizures)
Mechanism: ↓ reactivation of Na channels (↑ refractory period, blocks high frequency cell firing, ↓ spread of seizure activity from focus)
Side effects: ataxia, vertigo, hirsutism (abnormal hair growth), gingival hyperplasia, osteomalacia (altered vitamin D metabolism and ↓ Ca absorption), blood dyscrasias (rare; megaloblastic anemia, etc)
Drug interactions: induces hepatic microsomal enzymes (can ↓ effectiveness of other drugs); binds tightly to plasma proteins and can displace other drugs
Seizure classification:
based on degree of CNS involvement, involves simple ( Jacksonian; sensory or motor cortex) or complex symptoms (involves temporal lobe)
1. Generalized (whole brain involved):
a. Tonic-clonic:
Grand Mal; ~30% incidence; unconsiousness, tonic contractions (sustained contraction of muscle groups) followed by clonic contractions (alternating contraction/relaxation); happens for ~ 2-3 minutes and people don’t breathe during this time
Drugs: phenytoin, carbamazepine, Phenobarbital, lamotrigine, valproic acid
Status epilepticus: continuous seizures; use diazepam (short duration) or diazepam + phenytoin
b. Absence:
Petit Mal; common in children; frequent, brief lapses of consciousness with or without clonic motor activity; see spike and wave EEg at 3 Hz (probably relates to thalamocorticoreverburating circuit)
Drugs: ethosuximide, lamotrigine, valproic acid
c. Myoclonic: uncommon; isolated clinic jerks associated with bursts of EEG spikes;
Drugs: lamotrigine, valproic acid
d. Atonic/akinetic: drop seizures; uncommon; sudden, brief loss of postural muscle tone
Drugs: valproic acid and lamotrigine
2. Partial: focal
a. Simple: Jacksonian; remain conscious; involves motor or sensory seizures (hot, cold, tingling common)
Drugs: carbamazepine, phenytoin, Phenobarbital, lamotrigine, valproic acid, gabapentin
b. Complex: temporal lobe or psychomotor; produced by abnormal electrical activity in temporal lobe (involves emotional functions)
Symptoms: abnormal psychic, cognitive, and behavioral function; seizures consist of confused/altered behavior with impaired consciousness (may be confused with psychoses like schizophrenia or dementia)
Drugs: carbamazepine, phenytoin, laotrigine, valproic acid, gabapentin
Generalizations: most seizures can’t be cured but can be controlled by regular administration of anticonvulsants (many types require treatment for years to decades); drug treatment can effectively control seizures in ~ 80% of patients
Paracetamol
Paracetamol or acetaminophen is analgesic and antipyretic drug that is used for the relief of fever, headaches, and other minor aches and pains.
paracetamol acts by reducing production of prostaglandins, which are involved in the pain and fever processes, by inhibiting the cyclooxygenase (COX) enzyme.
Metabolism Paracetamol is metabolized primarily in the liver. At usual doses, it is quickly detoxified by combining irreversibly with the sulfhydryl group of glutathione to produce a non-toxic conjugate that is eventually excreted by the kidneys.
Heparin:
- Inhibits blood coagulation by forming complexes with an α2-globulin (Antithrombin III) and each of the activated proteases of the coagulation cascade (Kallikrein, XIIa, XIa, IXa, Xa, and Thrombin). After formation of the heparin-ATIII-coagulation factor, heparin is released and becomes available again to bind to free ATIII.
- Blocks conversion of Prothrombin to Thrombin and thus inhibits the synthesis of Fibrin from Fibrinogen.
- Inhibits platelet function and increases vascular permeability. May induce moderate to severe thrombocytopenia.
- Is prescribed on a “unit” basis.
- Heparin is not effective after oral administration and is generally administered by intravenous or subcutaneous injection. Intramuscular injections should be avoided.
- Heparin does not cross the placenta and does not pass into the maternal milk.
- is contraindicated in any situation where active bleeding must be avoided.
Ulcerative lesions, intracranial hemorrhage, etc.
Overdosage:
• Simple withdrawal.
• Protamine sulfate: Highly basic peptide that binds heparin and thus neutralizes its effects.
Classification Based on
a. Chemical structure
I. Sulphonamidcs.and others - c.g.. sulphadiazine. etc.
2. Beta-lactum ring - e.g.. penicillin
3. Tetracycline - e.g.. Oxytetracycline,.doxycycline.etc.
b. Mechanism of action
1. Inhibits cell-wall synthesis - penicillin. cephalosporin..cycloserine. etc.
2. Cause leakage from cell-membrane – polypeptides (polymyxin, Bacitracin), polyenes (Nystatin)
3. Inhibit protein synthesis - tetracyclines. chloramphenicols. erythromycin.
4. Cause mis-reading of mRNA code - aminoglycosides
5. Interfere with DNA function - refampicin.. metronidazole
6. Interfere with intermediary metabolism - sulphonamides. ethambutole
c. Type of organism against which it is primarily activate
I. Antibacterial - penicillin.
2. Antifungal - nystatin.
d. Spectrum of activity
1. Broad spectrum - tetracylines .
2. Narrow spectrum - penicillin G (penG). streptomycin.erythromycin
e. Type of action
I. Bacteriostatic - sulphonamides, erythromycin.tertracyclines
2. Bacteriocidal - penicillin. aminoglycoside
f. Source
I. Fungi - penicillin. cephalosporins
2. Bacteria - Polymyxin B
Distal (Potassium Sparing) Diuretics
Agents:
spironolactone
triamterene
Mechanism of action
Inhibition of Na/K exchange at aldosterone dependent distal tubular site
Spironolactone - competes with aldosterone for regulatory site
Triamterene - decreases activity of pump directly
• Either mechanism decreases potassium wasting
• Either mechanism produces poor diuresis (when used alone)
o relatively unimportant Na recovery site
Diurectic activity increased if:
• sodium load (body) is high
• aldosterone concentrations are high
• sodium load (tubule) is high - secondary to diuresis
Other electrolytes unaffected
Toxicity
• spironolactone may produce adrenal and sex hormone effects with LONG-TERM use
• Both drugs may produce electrolyte imbalance
Mucosal protective agents.
These are locally active agents that help heal gastric and duodenal ulcers by forming a protective barrier between the ulcers and gastric acid, pepsin, and bile salts. They do not alter the secretion of gastric acid. These drugs include sucralfate and colloid bismuth compounds. (e.g. tripotassium, dicitratobismuthate). Colloidal bismuth compounds additionally exert bactericidal action against H.pylori. Also, Prostaglandins have both antisecretory and mucosal protective effects.
Example: Misoprostol- used for prevention of NSAID – induced ulcer.
- Drugs that exert antimicrobial action against H.pylori such as amoxicillin, metronidazole, clarithromycin and tetracycline are included in the anti-ulcer treatment regimens.