Thursday, November 15, 2007

Miscellaneous drug facts most people do not know

 Antiepileptic drug random facts
1. Phenytoin (more misc. on than we already new)- a.   increases HDL levels.
    b. Formula to adjust PTN dose.  In zero order kinetics, a fixed AMOUNT not percentage of phenytoin is metabolized.  Vd= .7 L/kg     Loading dose = (Vd) x (desired change in concentration)  so eg. raise the level from 5 to 18 in a 100 kg man would mean Vd=70L, loading dose = 70 x 13= 910 mg.  Phenytoin is saturably absorbed in duodenum and affected by food and by antacids

2.  Cerebyx has the same Tmax as Dilantin due to time required to cleave the "fos" of fos phenytoin. Cerebyx also has some cardiac toxicity despite the absent phenylene glycol adjuvant.  Infusion can be faster than Dilantin but not more than 150 mg/min. It prevents the purple glove but not time to treat SE.

3. PTN, CBZ and PB block efficacy of some chemotherapeutic agents (see post)

4. Depakote
a.  may be useful in brain tumor treatment irrespective of AED effect (see post)
b.  Depakote is highly bound but not to albumen; and free levels are difficult to measure.  Its level rises in cirrhosis.  Its path is 80 % direct glucuronidation, 17 % is in same oxidative path as free fatty acids and enters the carnitine shuffle, leading to 4, en VPA.  Many ICU patients are carnitine deficient which shunts VPA to toxic metabolism so give these patients carnitine 25 mg/kg png over six hours leads to less NH4+.

5. Vimpat can cause angioedema


1. Rivastigmine patches can be left on for more than 24 hours as they have a 24 hour half life (in effect, patients are throwing away active drug). Wearing multiple patches, duly labelled, is one way to dispense a higher dose, usually with limited adverse effects

 2. Memantine has histamine blocking properties and its use may limit GI adverse events of individuals taking rivastigmine or other drugs.

3. Cholinesterase inhibitors inhibit metabolism of suxamethonium, prolonging neuromuscular blockade

1. Prazosin is highly effective for post-traumatic stress disorder
2. Levodopa-carbidopa and gabapentin are two rare drugs that are gastric absorbed and in fact compete with each other. Better to stop the gabapentin in Parkinson patients.3. Protease inhibitors potentiate toxicity of GHB, so HIV patients attending circuit parties are at extra high risk of coma and death.
4. Drug rash to Sinemet is due to yellow dye not levodopa carbidopa (see post)
 5. Natalizumab also blocks trafficking of B cells into CNS
 6. . Atorvastatin, even brief exposure, causes a marked decrease in blood Co Q 10 concentration (shares the synthetic pathway of cholesterol). Primary CoQ10 deficiency causes mitochondrial encephalomyopathy with recurrent myoglobinuria; this may pertain to AE's of atorvastatin. Also, CoQ10 is an excellent free radical scavenger and the effects on degenerative disease are not known. Rundek et al,. Arch Neurol 2004; 61: 889-892.

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