NEET MDS Lessons
Pharmacology
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.
Osmotic diuretics
An osmotic diuretic is a type of diuretic that inhibits reabsorption of water and sodium. They are pharmacologically inert substances that are given intravenously. They increase the osmolarity of blood and renal filtrate.
Mechanism(s) of Action
1. Reduce tissue fluid (edema)
2. Reflex cardiovascular effect by osmotic retention of fluid within vascular space which increases blood volume (contraindicated with Congestive heart failure)
3. Diuretic effect
o Makes H2O reabsorption far more difficult for tubular segments insufficient Na & H2O capacity in distal segments
o Increased intramedullary blood flow (washout)
o Incomplete sodium recapture (asc. loop). this is indirect inhibition of Na reabsorption (Na stays in tubule because water stays)
o Net diuretic effect:
Tubular concentration of sodium decreases
Total amount of sodium lost amount increases
GFR unchanged or slightly increased
Toxicity
Circulatory overload, dilutional hyponatremia, Hyperkalemia, edema, skin necrosis
Agents
Mannitol
ISOPRENALINE
It is beta-receptor stimulant, which stimulates the heart and causes tachycardia.
It relaxes the smooth muscles particularly the bronchial and GIT. It is mainly used in bronchial asthma, in the treatment of shock and as a cardiac stimulant in heart block.
ORCIPRENALINE
Is a potent β-adrenergic agonist.
Receptor sites in the bronchi and bronchioles are more sensitive to the drug than those in the heart and blood vessels.
AMPHETAMINE
increases the systolic and diastolic blood pressure. Amphetamine is a potent CNS stimulant and causes alertness, insomnia, increased concentration, euphoria or dysphoria and increased work capacity.
Amphetamines are drugs of abuse and can produce behavioural abnormalities and can precipitate psychosis.
PHENYLEPHRINE
It is used as a nasal decongestant and mydriatic agent and also in the treatment of paroxysmal supraventricular tachycardia.
UTERINE RELAXANTS (TOCOLYTICS)
ISOXSUPRINE
Isoxsuprine has a potent inhibitory effect on vascular and uterine smooth muscle and has been used in the treatment of dysmenorrhoea, threatened abortion, premature labour and peripheral vascular diseases.
Dental implications of these drugs:
1. Adverse effects: gingival hyperplasia (phenytoin), osteomalacia (phenytoin, Phenobarbital), blood dyscrasias (all but rare)
2. Drug interactions: additive CNS depression (anesthetics, anxiolytics, opioid analgesics), induction of hepatic microsomal enzymes (phenytoin, Phenobarbital, carbamazepine), plasma protein binding (phenytoin and valproic acid)
3. Seizure susceptibility: stress can → seizures
Doxycycline
Commonly prescribed for infections and to treat acne. treat urinary tract infections, gum disease, and other bacterial infections such as gonorrhea and chlamydia., as a prophylactic treatment for infection by Bacillus anthracis (anthrax). It is also effective against Yersinia pestis and malaria.
Local anesthetic selection
Local anesthetics are typically divided into 3 main categories:
short, intermediate and long acting local anesthetics.
Based on duration of the procedure and the duration of the individual agents
|
|
Infiltration |
Nerve block |
||
|
|
Pulpal |
Soft tissue |
Pulpal |
Soft tissue |
|
Short |
30 min |
2-3 hrs |
45 min |
2-3 hrs |
|
Intermediate |
60 min |
2-3 hrs |
75-90 min |
3-4 hrs |
|
Long |
40 min |
5-6 hrs |
3-4 hrs |
6-8 hrs |
Short acting agents
1. Mepivacaine 3 %
2. Lidocaine 2%
Intermediate acting agents
1. Lidocaine 2% 1:100000 epi
2. Lidocaine 2% 1:50000 epi
3. Mepivacaine 2% 1:20000 neocobefrin
4. Prilocaine 4%
5. Articaine 4% 1:100000 epi
Long acting agents
1. Bupivacaine 0.5% 1:200000 epi
Dissociation constants
|
Local anesthetic |
pKa |
% of base(RN) at pH 7.4 |
onset of action(min) |
|
Lidocaine |
7.8 |
29 |
2-4 |
|
Bupivacaine |
8.1 |
17 |
5-8 |
|
Mepivacaine |
7.7 |
33 |
2-4 |
|
Prilocaine |
7.9 |
25 |
2-4 |
|
Articaine |
7.8 |
29 |
2-4 |
|
Procaine |
9.1 |
2 |
14-18 |
|
Benzocaine |
3.5 |
100 |
- |