Intra-cavernosal Injection
of Vasoactive Drugs --Practical Approach
One
of the most dramatic changes in urology has been the introduction of
intracavernous injection of vasoactive drugs for the diagnosis and treatment of
ED. At the 1983 annual meeting of the American Urological Association, Brindley
personally demonstrated erection after injection of phenoxybenzamine(with much
surprise and shock to the audience). Subsequently, Zorgniotti and Lefleur
(1985) reported their experience instructing patients in the technique of
autoinjection of a mixture of papaverine and phentolamine for home use.
Intracavernosal injections provide an effective
therapy for men with erectile dysfunction who can not take oral agents or for
whom oral agents are not effective.
Drugs
and Pathophysiology:
Papaverine.
Papaverine, an alkaloid isolated
from the opium poppy, exerts an inhibitory effect on PDE, leading to increased
cyclic AMP and cyclic GMP in penile erectile tissue. Papaverine also blocks
voltage-dependent calcium channels, thus impairing calcium influx, and it may
also impair calcium-activated potassium and chloride currents.All these actions
relax cavernous smooth muscle and penile vessels. Papaverine is metabolized in
the liver, and the plasma half-life is 1 to 2 hours.
Alprostadil
(Prostaglandin E1).
Alprostadil is the synthetic form of a naturally occurring
fatty acid (i.e., alprostadil refers to the exogenous form, PGE1 to
the endogenous compound). It causes smooth muscle relaxation, vasodilation, and
inhibition of platelet aggregation through elevation of intracellular cyclic
AMP. Alprostadil is metabolized by the enzyme
prostaglandin-15-hydroxydehydrogenase, which has been shown to be active in
human corpus cavernosum. After intracavernous injection, 96% of alprostadil is
locally metabolized within 60 minutes and no change in peripheral blood levels
has been observed.
How
to give Injection:
The injection may be given anywhere from the base
of the penis to two-thirds of the way down the penile shaft at the 10 o'clock
and 2 o'clock locations on the upper side of the penis away from the urethra
and the head of the penis. Injections are rotated within that area and the side
of the injection is alternated with each injection.
Pathophysiology:
Preparation:
Methodology:
:Start with 29-30 G Insulin syringe for the injection therapy.
Papavarine:It
can be started with 15 and given till 60 mg. Inject in any corpus.
Bimix:Add
chlorpromazine ( 4 ml papavarine to 0.1 ml chlorpromazine combination) start
with 0.1 to 0.2 ml and then gradually increased .Again the injection can be
given in any one of the corpus.
Trimix:add
PGE-1 50 mcg( conventional vial contains 500 mcG so we will have to tae 0.1 ml
).
Procedure:
1)start
in lying down position
2)Give
complete privacy
3)Ask
patient to fantasize and stroke his penis(patient allowed to read erotic
materials)
4)If
no response after 15 minutes ask him to stand erect and repeat the procedure.
5)Some
men are known to have late response so minimum wait till 30-45 minutes
advisable.
6)If
no benefit call the pateint at next sitting and increase the dose.
Home Administered
Injection:
If
the diagnostic testing helps then patient is started on home administerd
injection.Prefilled Bimi Insulin syringes can be given.This can be stored at room
temperature for 6 months.
Good
sexual counselling and involvement of female partner is essential
Some
times obese person cannot do it on his own so wife can give injection while
husband stretches the penis.( Four hand technique: husband stretches the penis while wife gives the injection. This technique is good when husband is obese and unable to give injection properly because of buried penis).
The
patient has to be warned about priapism .It is always good for patient to have
access to the andrologist for any complications.
As
priapism is rare the pateint needs reassurance and fisrt 2 -3 injections can be
started in Clinic to gain confidence and allay fears about the injection.
Patient Acceptance and
Dropout
In long-term studies, 13% to 60% of patients drop out for a
number of reasons. These include loss of interest, loss of partner, poor
erectile response, penile pain, concomitant illness(Many obese individuals are
relunctant for injection because abdominal fat apron prevents them good vision
of the penis.And the partner initially may help but later on gives up thinking
this as more of mechanical process than romantic emotional encounter) , recovery of spontaneous erection, and
ultimate choice of other therapy(Many people in the interim go for penile
implant without having to resort to injection everytime they have sexual act).
Serious Adverse Effects
Priapism and fibrosis are the two more serious side effects
associated with intracavernous injection therapy. Some people face pain on
injection and this can be a reason for abandoning the injection therapy.
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