Adobe Systems
Department of Pharmacology
1
PHENOBARBITAL

Adobe Systems
CLINICAL APPLICATION OF UNDERSTANDING MECHANISMS OF ACTION (EXAMPLE)
ELIMINTION OF HYPNOTIC DRUG PHENOBARBITAL (AND OTHER ACID SUBSTANCES)
FROM ORGANISM (E.G. OVERDOSING)
PRESO EN MI PROPIO HOGAR - POR RAZONES X VIVO ENCERRADO EN MI CASA NO LO SOPORTO LO PEOR ES QUE ES
MI CULPA SIMPLEMENTE MI CULPA YO SOY CAUSANTO DE UN GRAN DOLOR Y DESILUCION HE HECHO COSAS FEAS HE
DICHO COSAS MALAS QUE TIPO DE BASURA SOY BUENO CREO QUE EL PEOR QUISAS ME LLEGEN POST DICIENDO LO
CONTRARIO PERO UT NO SABEN LAS ATROSIDADES QUE COMITE UNA MIERDA COMO YO SOLO TIENE UNA SALIDA
suicidio sin dolor compren un frasco de insulina ,se la inyecta y caen en inconciencia muriendo a
los pocos minutos,es irreversible. Si pueden ,morfina,es una muerte indolora rapida y segura,ademas
de higienica. Si van a conectar la manguera del auto para asfixiarce ,les recomiendo beber ua gran
cantidad de whisky u otro licor de alta graduacion,tambien es muy compatible el cloroformo.No
sentiran absolutamente nada amigos. Otra manera muy eficaz es fenobarbital,y si quieren morir
contentos tomen alcohol antes y luego una dosis abundante de este farmaco,les aseguro que no sabran
ni sentiran nada. Espero haberles sido de ayuda con mi humilde aporte y saludos desde Chile,pais
maravilloso. - Fotolog

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Diffusion of a drug across biological membrane – the substance must be non-ionised.
Level of ionisation affect: dissociation constant of the drug
                                              pH of environment
DISSOCIATION CONSTANT
-Constant for each drug
-
-It is not changed owing to factors of environment
-
-Indicated with symbol pK

Adobe Systems
Barbiturate hypnotic drug phenobarbital has pK value = 7,5
Hypnotic drug phenobarbital has pK = 7,5 this means that at pH = 7,5 we find 50 % of the
substance in the form of ions – ionised (I) and 50 % in the form of molecules – non-ionised (NI).

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Phenobarbital is a very weak acid.
The effect of different pH in organism on phenobarbital dissociation.
BLOOD (pH = 7,4)
48,7
51,3

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The effect of different pH in organism on phenobarbital dissociation.
Eliminated to acidic URINE (pH = 5,0)
Acidic substances are in acid solution mainly in non-ionised form.
0,7
99,3

Adobe Systems
The effect of different pH in organism on phenobarbital dissociation.
When eliminated to alcaline URINE – shift of urine pH by alcalising substances (pH = 8,5)
Acidic substances are in alkaline solution mainly in ionised form.
Ionised part of the drug does not cross biological membranes by diffusion, because it is
not soluble in lipids.

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pH 7,5
pH 7,4 (blood plasma)
pH 5,0 (acidic urine)
Phenobarbital is eliminated via urine
Usual pH of urine = 5,0
Phenobarbital is immediately converted to almost non-ionised form in urine (99,3 % non-ionised)

Adobe Systems
Normally phenobarbital crosses biological membranes of kidneys back to the blood stream
and to the brain
- its sedative effects continues.
Therapy: acidic substances arte in alkaline environment
present mainly  in ionised form – they cross the membranes only to very limited extent.

Adobe Systems
Use of alkalising substances suppresses reverse resorption in kidneys
Non-ionised part in urine = 9,1 %, ionised part = more than 90 %
- significantly decreased reverse diffusion of phenobarbital.
pH 7,4 (blood plasma)
E.g. NaHCO3
pH 8,5 (alkalised urine)
pH 5,0 (acidic urine)