Specific Agents

Hydralazine [orally effective]

MOA: Not completely understood. Seems to be partially dependent on the release of EDRF and perhaps partially due to K+-channel activation
- in clinical doses action is manifest primarily on vascular smooth muscle (non-vascular muscle is not much affected).
- Re: Metabolism & Excretion. In cases of renal failure the plasma half life may be substantially increased (4-5 fold). One mode of metabolism is
via N-Acetylation (problem of slow acetylators)

Side Effects

- those typical of vasodilation = headache, nasal congestion, tachycardia etc.
- chronic treatment with high doses > 200 mg/day may induce a rheumatoid-like state which may resemble lupus erythematosus.

Minoxidil (Loniten) [orally effective]

MOA: K+-channel agonist

-    very effective antihypertensive. Used primarily to treat life-threatening hypertension or hypertension resistant to other agents.

Side effects - growth of hair

Diazoxide (Hyperstat) [used only IV]

MOA: K+-channel agonist

- Administered by rapid IV injection; action appearing after 3-5 min; action may last from 4 to 12 hours.

Nitroprusside (Nipride) [used only IV]

MOA: increase in cGMP

- unlike the other vasodilators, venous tone is substantially reduced by nitroprusside.
- rapid onset of action (.30 sec); administered as an IV-infusion.
- particularly useful for hypertension associated with left ventricular failure.
 

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

Second Generation Cephalosporins

Prototype drug is CEFUROXIME (IV) and CEFUROXIME AXETIL (oral). CEFOXITIN has good activity vs. anaerobes.

1. Expanded activity against gram negative bacilli. Still have excellent activity against gram positive (Staph. and Strep.) bacteria.

Activity for Gram negative bacteria

Neisseria sp. (some gonococci resistant)
H. influenzae (including some ampicillin-resistant strains)
Moraxella catarrhalis (some resistance esp. to cefaclor)
E. coli
Proteus mirabilis
Indole + Proteus (some strains resistant)
Morganella morganii (some strains resistant)
Klebsiella pneumoniae
Serratia sp. (many strains resistant)

2. Anaerobic infections - CEFOXITIN & CEFOTETAN only

Moderate activity against Bacteroides fragilis group.

Good activity for other Bacteroides sp., Peptostreptococcus, Fusobacterium, Clostridium sp

Uses
1. Community-acquired pneumonia - Cefuroxime is widely used for empiric therapy. Has activity vs. many ampicillin-resistant H. influenzae strains.
2. Skin and soft tissue infection
3. Urinary tract infections
4. Upper respiratory tract infections (otitis media, sinusitis). Some resistance to H.influenzae to cefaclor (20-30%).
5. Mixed aerobic & anaerobic infections - Cefoxitin & Cefotetan. Resistance to B.fragilis is increasing.
6. Surgical prophylaxis - Cefoxitin or cefotetan are widely used in cases where mixed aerobic & anaerobic infections may occur, esp. intra-abdominal, colorectal, and gynecologic operations. For cardiovascular and orthopedic procedures, cefuroxime and others may be used, but cefazolin is cheaper and appears to work well.

Streptomycin

Streptomycin was the first of a class of drugs called aminoglycosides to be discovered, and was the first antibiotic remedy for tuberculosis. It is derived from the actinobacterium Streptomyces griseus.

Streptomycin cannot be given orally, but must be administered by regular intramuscular injection.

PSEUDOEPHEDRINE

Pseudoephedrine appears to have less pressor activity and weaker central nervous system effects than ephedrine. It has agonist activity at both β1  and β2 adrenoceptors, leading to increased cardiac output and relaxation of bronchial smooth muscle.

Pseudoephedrine is rapidly absorbed throughout the body. It is eliminated largely unchanged in urine by N-demethylation.

It is indicated in symptomatic relief from stuffed nose, respiratory tract congestion, bronchospasm associated with asthma, bronchitis and other similar disorders.

Antipsychotic Drugs

A.    Neuroleptics: antipsychotics; refers to ability of drugs to suppress motor activity and emotional expression (e.g., chlorpromazine shuffle)
Uses: primarily to treat symptoms of schizophrenia (thought disorder); also for psychoses (include drug-induced from amphetamine and cocaine), agitated states

Psychosis: variety of mental disorders (e.g., impaired perceptions, cognition, inappropriate or ↓ affect or mood)

Examples: dementias (Alzheimer’s), bipolar affective disorder (manic-depressive)

B.    Schizophrenia: 1% world-wide incidence (independent of time, culture, geography, politics); early onset (adolescence/young adulthood), life-long and progressive; treatment effective in ~ 50% (relieve symptoms but don’t cure)

Symptoms: antipsychotics control positive symptoms better than negative

a.    Positive: exaggerated/distorted normal function; commonly have hallucinations (auditory) and delusions (grandeur; paranoid delusions particularly prevalent; the most prevalent delusion is that thoughts are broadcast to world or thoughts/feelings are imposed by an external force)

b.    Negative: loss of normal function; see social withdrawal, blunted affect (emotions), ↓ speech and thought, loss of energy, inability to experience pleasure

Etiology: pathogenesis unkown but see biochemical (↑ dopamine receptors), structural (enlarged cerebral ventricles, cortical atrophy, ↓ volume of basal ganglia), functional (↓ cerebral blood flow, ↓ glucose utilization in prefrontal cortex), and genetic abnormalities (genetic predisposition, may involve multiple genes; important)

 Dopamine hypothesis: schizo symptoms due to abnormal ↑ in dopamine receptor activity; evidenced by 

i.    Correlation between potency and dopamine receptor antagonist binding: high correlation between therapeutic potency and their affinity for binding to D2 receptor, low correlation between potency and binding to D1 receptor)

ii.    Drugs that ↑ dopamine transmission can enhance schizophrenia or produce schizophrenic symptoms:

A)    L-DOPA: ↑ dopamine synthesis
B)    Chronic amphetamine use: releases dopamine
C)    Apomorphine: dopamine agonist

iii.    Dopamine receptors ↑ in brains of schizophrenics: postmortem brains, positron emission tomography

Dopamine pathways: don’t need to know details below; know that overactivity of dopamine neurons in mesolimbic and mesolimbocortical pathways → schizo symptoms

i.    Dorsal mesostriatal (nigrostriatal): substantia nigra to striatum; controls motor function
ii.    Ventral mesostriatal (mesolimbic): ventral tegmentum to nucleus accumbens; controls behavior/emotion; abnormally active in schizophrenia
iii.    Mesolimbocortical: ventral tegmentum to cortex and limbic structures; controls behavior and emotion; activity may be ↑ in schizophrenia
iv.    Tuberohypophyseal: hypothalamus to pituitary; inhibits prolactin secretion; important pathway to understand side effects

 Antipsychotic drugs: non-compliance is major reason for therapeutic failure

1.    Goals: prevent symptoms, improve quality of life, minimize side effects
2.    Prototypical drugs: chlorpromazine (phenothiazine derivative) and haloperidol (butyrophenone derivative)
a.    Provide symptomatic relief in 70%; delayed onset of action (4-8 weeks) and don’t know why (maybe from ↓ firing of dopamine neurons that project to meso-limbic and cortical regions)
3.    Older drugs: equally efficacious in treating schizophrenia; no abuse potential, little physical dependence; dysphoria in normal individuals; high therapeutic indexes (20-1000)

Classification: 

i.    Phenothiazines: 1st effective antipsychotics; chlorpromazine and thioridazine
ii.    Thioxanthines: less potent; thithixene
iii.    Butyrophenones: most widely used; haloperidol

 Side effects: many (so known as dirty drugs); block several NT receptors (adrenergic, cholindergic, histamine, dopamine, serotonin)  and D2 receptors in other pathways

i.    Autonomic: block muscarinic receptor (dry mouth, urinary retention, memory impairment), α-adrenoceptor (postural hypotension, reflex tachycardia)
Neuroleptic malignant syndrome: collapse of ANS; fever, diaphoresis, CV instability; incidence 1-2% of patients (fatal in 10%); need immediate treatment (bromocriptine- dopamine agonist)

ii.    Central: block DA receptor (striatum; have parkinsonian effects like bradykinesia/tremor/muscle rigidity, dystonias like neck/facial spasms, and akathisia—subject to motor restlessness), dopamine receptor (pituitary; have ↑ prolactin release, breast enlargement, galactorrhea, amenorrhea), histamine receptor (sedation)

DA receptor upregulation (supersensitivity): occurs after several months/years; see tardive dyskinesias (involuntary orofacial movements)

Drug interactions: induces hepatic metabolizing enzymes (↑ drug metabolism), potentiate CNS depressant effects (analgesics, general anesthetics, CNS depressants), D2 antagonists block therapeutic effects of L-DOPA used to treat Parkinson’s

Toxicity: high therapeutic indexes; acute toxicity seen only at very high doses (hypotension, hyper/hypothermia, seizures, coma, ventricular tachycardia)

Mechanism of action: D2 receptor antagonists, efficacy ↑ with ↑ potency at D2 receptor

Newer drugs: include clozapine (dibenzodiazepine; has preferential affinity for D4 receptors, low affinity for D2 receptors), risperidone (benzisoxazole), olanzapine (thienobenzodiazepine)

Advantages over older drugs: low incidence of agranulocytosis (leucopenia; exception is clozapine), very low incidence of motor disturbances (extrapyramidal signs; may be due to low affinity for D2 receptors), no prolactin elevation

Side effects: DA receptor upregulation (supersensitivity) occurs after several months/years; may → tardive diskinesias