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

BETA-LACTAM ANTIBIOTICS
β-lactam antibiotics are a broad class of antibiotics including penicillin derivatives, cephalosporins, monobactams, carbapenems and β-lactamase inhibitors; basically any antibiotic agent which contains a β-lactam nucleus in its molecular structure. They are the most widely used group of antibiotics available.

Mode of action All β-lactam antibiotics are bactericidal, and act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls.β-lactam antibiotics were mainly active only against Gram-positive bacteria, the development of broad-spectrum β-lactam antibiotics active against various Gram-negative organisms has increased the usefulness of the β-lactam antibiotics.

Common β-lactam antibiotics

Penicillins

Narrow spectrum penicillins:  

benzathine penicillin
benzylpenicillin (penicillin G)
phenoxymethylpenicillin (penicillin V)
procaine penicillin

Narrow spectrum penicillinase-resistant penicillins

methicillin
dicloxacillin
flucloxacillin

Moderate spectrum penicillins : 

amoxicillin, ampicillin

Broad spectrum penicillins :      

co-amoxiclav (amoxycillin+clavulanic acid)

Extended Spectrum Penicillins:    

piperacillin
ticarcillin
azlocillin
carbenicillin
 

Distribution

Three major controlling factors:  

Blood Flow to Tissues:  rarely a limiting factor, except in cases of abscesses and tumors.
Exiting the Vascular System:  Occurs at capillary beds.
- Typical Capillary Beds - drugs pass between cells 
- The Blood-Brain Barrier-  Tight junctions here, so drugs must pass through cells.  Must then be lipid soluble, or have transport system.
- Placenta - Does not constitute an absolute barrier to passage of drugs.  Lipid soluble, nonionized compounds readily pass.  
- Protein Binding:  Albumin is most important plasma protein in this respect.  It always remains in the blood stream, so drugs that are highly protein bound are not free to leave the bloodstream.  Restricts the distribution of drugs, and can be source of drug interactions.

Entering Cells:  some drugs must enter cells to reach sites of action.

Neurotransmitters can be classified into:
1. Biogenic amines:
ACh, NA, DA, 5-HT, Histamine
2. Amino acids:
Excitatory (glutamate & asparate)
Inhibitory (GABA& glycine)
3. Others:
Adenosine, melatonin

Gastric acid neutralizers (antacids)

Antacids act primarily in the stomach and are used to prevent and treat peptic ulcer. They are also used in the treatment of Reflux esophagitis and Gastritis.

Mechanism of action: 

Antacids are alkaline substances (weak bases) that neutralize gastric acid (hydrochloric acid) they react with hydrochloric acid in the stomach to produce neutral or less acidic or poorly absorbed products and raise the pH of stomach secretion.

Antacids are divided into systemic and non-systemic.

• Systemic antacids (e.g. sodium bicarbonate) are highly absorbed into systemic circulation and enter body fluids. Therefore, they may alter acid–base balance. They can be used in the treatment of metabolic acidosis. 

Non-systemic: they do not alter acid–base balance significantly, because they are not well-absorbed into the systemic circulation. They are used as gastric antacids; and include:

• Magnesium compounds such as magnesium hydroxide and magnesium sulphate MgS2O3. They have relatively high neutralizing capacity, rapid onset of action, however, they may cause diarrhoea and hypermagnesemia.

• Aluminium compounds such as aluminium hydroxide. Generally, these have low neutralizing capacity, slow onset of action but long duration of action. They may cause constipation.

• Calcium compounds such as. These are highly effective and have a rapid onset of action but may cause hypersecretion of acid (acid - rebound) and milk-alkali syndrome (hence rarely used in peptic ulcer disease). 

Therefore, the most commonly used antacids are mixtures of aluminium hydroxide and magnesium hydroxide . 

Cephalosporins

Produced semisynthetically by chemical attachment of side chains to 7-aminocephalosporanic acid. Same mode of action , same resistance mech. 
But tend to be more resistant than penicillins to certain beta –lactamases .

GENERATION BASED ON :
-- BACTERIAL SUSCEPTIBILITY PATTERNS
-- RESISTANCE TO BETA –LACTAMASES
--NOT EFFECTIVE AGAINST -MRSA , L. MONOCYTOGENES , C. DIFFICLE , ENTEROCOCCI

First Generation 

Parentral

- CEPHALOTHIN
- CEFAZOLIN

Oral

- CEPHALEXIN
- CEPHRADINE
- CEFADROXIL

Second Generation

Parentral

CEFUROXIME
CEFOXITIN

Oral

CEFACLOR
CEFUROXIME AXETIL

Third Generation

Parentral

CEFOTAXIME 
CEFTIZOXIME
CEFTRIAXONE 
CEFTAZIDIME
CEFOPERAZONE

Oral 

CEFIXIME 
CEFPODOXIME
CEFDINIR 
CEFTIBUTEN

Fourth Generation

Parentral

CEFEPIME
CEFPIROME