Procaine benzylpenicillin

Dosage and Administration

Aqueous suspension of procaine penicillin for IM administration is available in disposable syringes, each containing 1.0 or 1.5 g of procaine penicillin. During the later stages of treatment of many infections such as pneumonia, procaine Pen G can be substituted for crystalline Pen G. This penicillin is useful because absorption of an IM injected dose continues for up to 24 hours, so that injections may be separated by this interval, but lower serum levels are obtained. These injections are less painful than injections of crystalline Pen G. A common adult dosage for procaine Pen G is 1.0 g i.m. once or twice a day. In milder infections procaine Pen G may be satisfactory for initial treatment. This compound must never be given intravenously.


Occasionally, severe reactions, and even death, occurring during or shortly after an IM injection of procaine Pen G may result from accidental i.v. injection. These reactions are partly caused by microembolization of procaine Pen G particles to the lungs and brain, which produces hyperventilation, dilation of pupils, convulsions, and coma. Toxicity due to the procaine component of the drug is contributory.

Early manifestations include marked anxiety, fever, hypertension, tachycardia, vomiting, and audiovisual hallucinations. In severe cases, there may be convulsions, abrupt hypotension, and cardiorespiratory arrest which may simulate anaphylaxis.

Three patients to whom aqueous procaine Pen G was administered inadvertently by i.v. infusion have been reported [1]. Within 15 minutes, one patient developed a generalized seizure and cardiorespiratory arrest with slow idioventricular rhythm, but recovered with resuscitation. The other two patients had acute anxiety, tachypnea, dizziness, and tinnitus.

Procaine Pen G may cause less severe side-effects. Some patients experience extreme anxiety and a sensation of impending death after an IM injection, but show no abnormal physical signs, such as shock or bronchospasm. Hallucinations, disorientation, or psychotic behavior may occur. Minor physical abnormalities, such as tachycardia, hypertension, or twitchings of extremities, are sometimes observed.

Attacks usually subside after 15–30 minutes, but some patients may exhibit mental lability for several months [2]. These side-effects may occur more commonly in patients with a past history of mental instability [3]. Minor reactions to procaine Pen G develop in about 0.1–0.3% of treated patients, and probably result from direct procaine toxicity. In vivo, procaine is quickly liberated from procaine Pen G; it can be detected in the serum immediately after an IM injection and measurable levels persist for about 30 minutes [4]. Accidental i.v. injection of part of the dose may sometimes be a factor. Patients exhibiting this side-effect may be regarded as hysterical by those who are unaware of this clinical entity.


After IM injection of an aqueous suspension of procaine Pen G, a peak serum level is reached in about 2–3 hours, and, in adults given 0.6 g or more, detectable levels are usually maintained for at least 24 hours. When IM procaine penicillin in a dose of 50 mg/kg is given to children, the peak serum level 3–6 hours later is 4–6 mg/ml and the serum level remains above 1 mg/ml for 26 hours [5].

In infants of less than 1 week, following IM procaine Pen G in a dose of 50 mg/kg body weight, the mean serum level 2–12 hours later is 7 mg/ml, and the level at 24 hours is 1.5 mg/ml. Pen G does not accumulate in the body if this dose is repeated every 24 hours. Lower serum levels (5–6 mg/ml) during the first 4 hrs and 0–0.4 mg/ml at 24 hours occur if this dose is given to infants older than 1 week [6-7].


1. Galpin J.E., Chow A.W., Yoshikawa T.T., Guze L.B. "Pseudoanaphylactic reactions from inadvertent infusion of procaine penicillin G". Ann. Intern. Med. 81: 358, (1974).

2. Silber T.J., D’Angelo L. "Psychosis and seizures following the injection of penicillin G procaine". Am. J. Dis. Child. 139: 335, (1985).

3. Menke H.E., Pepplinkhuizen L. "Acute non-allergic reaction to aqueous procaine penicillin". Lancet 2: 723, (1974).

4. Green R.L., Lewis J.E., Kraus S.J., Frederickson E.L. "Elevated plasma procaine concentrations after administration of procaine penicillin G". N. Engl. J. Med. 291: 223, (1974).

5. Shann F., Linnemann V., Gratten M. "Serum concentrations of penicillin after intramuscular administration of procaine, benzyl and benethamine penicillin in children with pneumonia". J. Pediatr. 110: 299, (1987).

6. McCracken Jr G.H. "Group B streptococci: the new challenge in neonatal infections". J. Pediatr. 82: 703, (1973).

7. McCracken Jr G.H., Nelson J.D. "Antimicrobial Therapy for Newborns", 2nd edn. p. 8. New York: Grune and Stratton, (1983).


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