NEET MDS Lessons
Pharmacology
Clarithromycin Used to treat pharyngitis, tonsillitis, acute maxillary
sinusitis, acute bacterial exacerbation of chronic bronchitis, pneumonia (especially atypical pneumonias associated with Chlamydia pneumoniae or TWAR), skin and skin structure infections, and, in HIV and AIDS patients to prevent, and to treat, disseminated Mycobacterium avium complex or MAC.
Unlike erythromycin, clarithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes.
Clarithromycin has a fairly rapid first-pass hepatic metabolism, i.e it is metabolised by the liver. However, this metabolite, 14-hydroxy clarithromycin is almost twice as active as clarithromycin.
Contraindications Clarithromycin should be used with caution if the patient has liver or kidney disease, certain heart problems (e.g., QTc prolongation or bradycardia), or a mineral imbalance (e.g., low potassium or magnesium levels).
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.
Anesthesia agents
1. Inhalation anesthetics (volatile anesthetics)
- gases : N2O, xenon
- Fluids (vaporisers)
2. Intravenous anesthetics
- Barbiturans : thiopental
- Others : propofol, etomidat
3. Pain killers
- Opioids: fentanyl, sufentanil, alfentanil, remifentanil, morphine
- Non Steroid Anti Inflamatory Drugs: ketonal, paracetamol
4. Relaxants
- Depolarising : succinilcholine
- Non depolarising : atracurium, cisatracurium, vecuronium, rocuronium
5. adiuvants
-benzodiazepins: midasolam, diazepam
Neurophysiology
Nerve fibers exhibit wide range of sensitivity to nerve blockade-in order of increasing resistance to block are the sensations of pain, cold, warmth, touch, pressure, proprioception and motor function
Nerve Fibers:
|
Types |
Size |
Speed |
Occurrence |
|
A (α) |
20 µm |
80 - 120 |
Myelinated (Primarily for muscular activity). |
|
β |
8 - 15 µm |
|
Myelinated (Touch and pressure) |
|
γ |
4 - 8 µm |
|
Myelinated (Muscle spindle tone) |
|
δ |
3 - 4 µm |
10-15 |
Myelinated (Pain and temperature sensation) |
|
B |
4 µm |
10-15 |
Myelinated (Preganglionic autonomic) |
|
C |
1-2 µm |
1 - 2 |
Unmyelinated (Pain and temperature sensation) |
Myelinated = faster conducting
Unmyelinated = slower conducting
- Small non-myelinated fibers (C- pain fibers) and smaller myelinated pre-ganglionic B fibers are more readily blocked than are larger myelinated fibers responsible for muscle activity and touch [A-alpha and A-beta].
- Clinically, a person would notice complete lack of sensation to a pinprick, while at the same time still be able to move their fingers.
NSAIDs: Classification by Plasma Elimination Half Lives
Short Half Life (< 6 hours):
more rapid effect and clearance
• Aspirin (0.25-0.33 hrs),
• Diclofenac (1.1 ± 0.2 hrs)
• Ketoprofen (1.8± 0.4 hrs),
• Ibuprofen (2.1 ± 0.3 hrs)
• Indomethacin (4.6 ± 0.7 hrs)
Long Half Life (> 10 hours):
slower onset of effect and slower clearance
• Naproxen (14 ± 2 hrs)
• Sulindac (14 ± 8 hrs),
• Piroxicam (57 ± 22 hrs)
On the basis of Receptors, drugs can be divided into four groups,
a. agonists
b. antagonists
c. agonist-antagonists
d. partial agonists
a. Agonist
morphine fentanyl pethidine
Action : activation of all receptor subclasses, though, with different affinities
b. Antagonist
Naloxone , Naltrexone
Action : Devoid of activity at all receptor classes
c. Partial Agonist: (Mixed Narcotic Agonists/Antagonists)
Pentazocine, Nalbuphine, Butorphanol , Buprenorphine
Action: activity at one or more, but not all receptor types
With regard to partial agonists, receptor theory states that drugs have two independent properties at receptor sites,
a. affinity
The ability, or avidity to bind to the receptor
Proportional to the association rate constant, Ka
b. efficacy
or, intrinsic activity, and is the ability of the D-R complex to initiate a pharmacological effect
Drugs that produce a less than maximal response and, therefore, have a low intrinsic activity are called partial agonists.
These drugs display certain pharmacological features,
a. the slope of the dose-response curve is less than that of a full agonist
b. the dose response curve exhibits a ceiling with the maximal response below that obtainable by a full agonist
c. partial agonists are able to antagonise the effects of large doses of full agonists
Barbiturates
1. Long-acting. Phenobarbital is used to treat certain types of seizures (see section on antiepileptic drugs).
2. Intermediate-acting. Amobarbital, pentobarbital (occasionally used for sleep), secobarbital.
3. Short-acting. Hexobarbital, methohexital, thiopental—rarely used as IV anesthetics.