NEET MDS Lessons
Pharmacology
Antidiarrheal
Antidiarrheal drugs may be given to relieve the symptom (non-specific therapy) or may be given to treat the underlying cause of the symptom (specific therapy).
Ι. Drugs used for the symptomatic (non-specific) treatment of diarrhoea include:
• Opiates and opiate derivatives are the most effective (such as morphine), but it is not used because of potentially serious adverse effects. Other agents, such as diphenoxylate and loperamide, are commonly used.
• Adsorbent – demulcent products such as kaolin – pectin preparation may be included in antidiarrheal preparations. Unfortunately, they may adsorb nutrients and other drugs, including the antidiarrheal agents if given concurrently.
• Anticholinergic agents e.g. atropine is occasionally used to decrease abdominal cramping and pain associated with diarrhoea.
ΙΙ. Specific therapy may include the use of antibacterial agents that are recommended for use in carefully selected cases of bacterial enteritis. For example, severe diarrhoea by salmonella, shigella, campylobacter and clostridia species can be treated by antibiotics (ampicillin, chloramphenicol, co-trimoxazole).
First Generation Cephalosporins
Prototype Drugs are CEFAZOLIN (for IV use) and CEPHALEXIN (oral use).
1. Staph. aureus - excellent activity against b-lactamase-producing strains
Not effective against methicillin-resistant Staph. aureus & epidermidis
2. Streptococci - excellent activity versus Streptococcus sp.
Not effective against penicillin-resistant Strep. pneumoniae
3. Other Gm + bacteria - excellent activity except for Enterococcus sp.
4. Moderate activity against gram negative bacteria.
Caution: resistance may occur in all cases.
Susceptible organisms include:
E. coli
Proteus mirabilis
Indole + Proteus sp. (many strains resistant)
Haemophilus influenzae (some strains resistant)
Neisseria sp. (some gonococci resistant)
Uses
1. Upper respiratory tract infections due to Staph. and Strep.
2. Lower respiratory tract infections due to susceptible bacteria e.g. Strep.pneumoniae in penicillin-allergic patient (previous rash)
3. Uncomplicated urinary tract infections (Cephalexin)
4. Surgical prophylaxis for orthopedic and cardiovascular operations (cefazolin preferred because of longer half-life)
5. Staphylococcal infections of skin and skin structure
Azithromycin
Azithromycin is the first macrolide antibiotic belonging to the azalide group. Azithromycin is derived from erythromycin by adding a nitrogen atom into the lactone ring of erythromycin A, thus making lactone ring 15-membered.
Azithromycin has similar antimicrobial spectrum as erythromycin, but is more effective against certain gram-negative bacteria, particularly Hemophilus influenzae.
azithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids.
Main elimination route is through excretion in to the biliary fluid, and some can also be eliminated through urinary excretion
Antimania Drugs
MANIC SYMPTOMSMANIC SYMPTOMS
Elevated or irritable mood
Increased activity or psychomotor agitation
Reduced need for sleep
Inflated self esteem or grandiosity
Increased or pressure of speech
Flight of ideas
These drugs are used to treat manic-depressive illness.
1. Lithium
2. Carbamazepine
3. Valproic acid
Mechanisms of action
1. Lithium works inside the cell to block conversion of inositol phosphate to inositol.
2. Carbamazepine blocks sodium channels
3. Valproic acid blocks sodium and calcium channels
PHARMACOKINETICS
Absorbed readily and almost completely from the GI tract; peak concentrations in 1-2 hrs
Lithium toxicity
1. Nausea, diarrhea, convulsions, coma, hyperreflexia, cardiac arrhythmias, hypotension.
2. Thyroid enlargement; increases thyroid stimulating hormone (TSH) secretion; may cause hypothyroidism.
3. Polydipsia, polyuria (lithium inhibits the effect of antidiuretic hormone on the kidney).
Clinical applications concerning lithium
- Patients must be warned against sodium-restricted diets because sodium restriction leads to greater retention of lithium by the kidney.
- Patients must have regular (e.g., monthly) blood checks because the margin of safety is narrow.
Endocrine Effects – Goitre and hypothyroidism commonly
Cardiac Effects:– ECG changes(common) - T-wave flattening/inversion and appearance of U wavesflattening/inversion and appearance of U waves
Li and Pregnancy -1st Trimester:Cardiovascular anomalies of the newborn, especially Ebstein's malformation
- 3rd Trimester: Neonatal goiter, CNS depression, hypotonia ("floppy baby" syndrome)
Drug–drug interactions of lithium
Diuretics and newer nonsteroidal anti-inflammatory drugs (NSAIDs) reduce lithium excretion and may cause lithium toxicity.
Carbamazepine (Tegretol): most common; for generalized tonic-clonic and all partial seizures; especially active in temporal lobe epilepsies
Mechanism: ↓ reactivation of Na channels (↑ refractory period, blocks high frequency cell firing, ↓ seizure spread)
Side effects: induces hepatic microsomal enzymes (can enhance metabolism of other drugs)
Itraconazole:
The drug may be given orally or intravenously.
Valdecoxib
used in the treatment of osteoarthritis, acute pain conditions, and dysmenorrhoea
Etoricoxib new COX-2 selective inhibitor