Intracellular accumulation and activity of ampicillin used as free drug and as its phthalimidomethyl or pivaloyloxymethyl ester (pivampicillin) against Listeria monocytogenes in J774 macrophages

AIMS

To determine the intracellular accumulation in a macrophage cell line of ampicillin and ampicillin esters, and to measure their activity against intracellular Listeria monocytogenes.

METHODS

Quantitative evaluation of the activity of ampicillin, phthalimidomethylampicillin (PIMA) or pivaloyloxymethylampicillin (PIVA) against intracellular L. monocytogenes, and direct measurement of cellular ampicillin concentration in J774 macrophages.

RESULTS

Ampicillin, PIMA and PIVA caused a 0.5 log decrease in cell-associated cfu within 5 h when used at an extracellular concentration of 3.6 microM [10 x MIC of ampicillin (1.25 mg/L); 1.83 mg/L for PIMA and 1.67 mg/L for PIVA]. Addition of beta-lactamase in the extracellular milieu abolished the activity of ampicillin and of PIMA but not that of PIVA. At low extracellular concentrations [0.5 x MIC ampicillin (62.5 microg/L); equimolar concentrations for PIMA (91.5 microg/L) and PIVA (83.5 microg/L)], ampicillin and PIMA lost all activity (compared with controls), but PIVA remained as active as at the higher concentration. Incubation of cells with PIVA at the low concentration (83.5 microg/L) for 20 h caused a 2 log reduction of cfu if the medium was changed every 5 h (to compensate for the degradation of extracellular PIVA). Incubation of cells with PIVA allowed for a marked (four- to 25-fold) cell accumulation of ampicillin, whereas no ampicillin accumulation was seen for cells incubated with ampicillin or with PIMA.

CONCLUSIONS

This is the first demonstration that PIVA (a prodrug of ampicillin) can be used to promote ampicillin cellular accumulation and, thereby to increase ampicillin intracellular activity. PIVA could be useful for control of the intracellular multiplication of L. monocytogenes.

Distribution of penicillins into subcutaneous tissue chambers in ponies

The distribution of penicillins into a tissue chamber implanted subcutaneously in ponies was studied. Ampicillin sodium (equivalent to 15 mg/kg ampicillin) was administered intravenously. Pivampicillin, a prodrug of ampicillin, was administered by nasogastric tube to fed ponies at a dose of 19.9 mg/kg (equivalent to 15 mg/kg ampicillin). Procaine penicillin G was administered intramuscularly at a dose of 12 mg/kg (equivalent to 12000 IU/kg). Six ponies were used for each medication. Antibiotic concentrations in plasma and tissue chamber fluid (TCF) were measured for 24 h after administration. Mean peak concentrations of ampicillin in TCF were 7.3 micrograms/mL, reached at 1.7 h, and 1.3 micrograms/mL, reached at 2.7 h, after administration of ampicillin sodium and pivampicillin respectively. The mean peak concentration of penicillin G of 0.3 microgram/mL was reached 12.3 h after administration of procaine penicillin G. Concentrations in TCF remained above the minimum inhibitory concentration of Streptococcus zooepidemicus for the proposed dosing intervals of 8, 12 and 24 h for ampicillin sodium, pivampicillin and procaine penicillin G respectively.

Formation of pivaloylcarnitine in isolated rat heart cells

Pivaloyl-containing antibiotics and pivalic acid in man or rat have been reported to cause increased urinary carnitine loss secondary to pivaloylcarnitine generation. Pivaloylcarnitine concentration was especially high in heart after administration of pivalic acid or pivampicillin in vivo. Formation of pivaloylcarnitine was therefore studied in isolated rat heart cells in the presence of sodium pivalate. Formation of pivaloylcarnitine in rat heart cells increased with incubation time, after a lag time from 0 to 2 h and linearly up to 6 h. The formation increased with increasing concentration of sodium pivalate, followed Michaelis-Menten kinetics with an apparent Km = 348 +/- 10 microM and Vmax = 116 +/- 20 pmol.mg protein-1.h-1. Bromoacetylcarnitine inhibited the pivaloylcarnitine formation to Ki = 116 +/- 43 microM and Vmax = 107 +/- 14 pmol.mg protein-1.h-1. The uptake of carnitine in heart cells was suppressed 62-74% by deoxycarnitine (40 microM) and D-carnitine (200 microM), and 95% by NaF (5 mM), NaN3 (500 microM) or at temperature 4 degrees C. Pivaloylcarnitine inhibited carnitine uptake to 33-35% of the controls, while sodium pivalate did not. More than 90% of intracellular pivaloylcarnitine was released from the heart cells after 18 h of incubation in the absence of sodium pivalate and L-carnitine. These data show that pivalate is readily converted to pivaloylcarnitine in heart cells, in contrast to the limited conversion in hepatocytes.

Differential excretion of xenobiotic acyl-esters of carnitine due to administration of pivampicillin and valproate

The fate of supplemental carnitine was studied in human subjects treated with drugs known to cause carnitine deficiency. Six children were treated with pivampicillin and equimolar L-carnitine for 7 days. On the last day of treatment, the plasma levels of total and free carnitine were decreased, but acylcarnitine levels were increased. A 12-fold increase in urinary excretion of acylcarnitines was found; it increased from 188.5 +/- 82.7 to 2218.4 +/- 484.1 mumole/day, and 84% was pivaloylcarnitine. Free carnitine excretion was reduced. Ten epileptic children on chronic valproate treatment received equimolar carnitine for a 2-week period. Plasma carnitine levels were elevated on the last day of treatment. A 3.4-fold increase in urinary acylcarnitines was found, but most of the excreted carnitines were free (64.5-fold increases). These data show that pivalate is readily converted to carnitine esters, in contrast to the limited conversion of valproate to acylcarnitines in humans.

Ampicillin in breast milk during puerperal infections

Low concentrations of ampicillin were found in colostrum/breast milk from 6 mothers treated with pivampicillin 1.05 to 2.1 g daily during the first to eighth day postpartum in the maternity ward. It was calculated that the breast-fed infant could theoretically receive 0.05-0.37% of the dose/kg given to the mother. It is concluded that direct exposure of the breast-fed infant suckling from a mother under treatment with ampicillin or pivampicillin seems to be minimal.

Kinetics and mechanism of enzymatic hydrolysis of pivampicillin monolayers

A study of the enzymatic hydrolysis of pivampicillin (an insoluble penicillin) extended as a monolayer on the aqueous interface at a constant surface pressure has been performed. Penicillinase promotes intensive hydrolysis of the pivampicillin monolayers, inducing their solubility. However, no action was observed with dog liver esterase. The hydrolytic process, which was dependent on the film surface pressure and on the quantity of the injected enzyme, is of the Michaelis-Menten type in two dimensions.

Serum concentrations and penetration into prostate of mecillinam and ampicillin

The absorption of the two antibiotic pro-drugs pivmecillinam and pivampicillin was investigated in 10 patients with normal or slightly impaired renal function. After a therapeutic dose of 200 mg pivmecillinam plus 250 mg pivampicillin, the mean peak concentration in serum was 2.3 micrograms mecillinam and 5.3 micrograms ampicillin per ml. The elimination half-life was approximately 2 hours for both antibiotics. Consequently, a ratio of 2:5 was maintained in serum during the excretion period and this ratio is within the range where optimal synergistic effect between the two antibiotics against many Gram-negative organisms is most likely to occur. Penetration of mecillinam and ampicillin into the prostate, determined in tissue homogenate obtained from 10 patients undergoing transurethral resection of the prostate showed that the antibiotics penetrated equally well with a serum tissue ratio of approximately 2:1.

The oral absorption of ampicillin, pivampicillin and amoxycillin in infants and children

The oral absorption of comparable doses of mixtures of ampicillin, amoxycillin and pivampicillin was studied in 38 children from 6 months to 6 years of age. Plasma concentrations following pivampicillin and amoxycillin were higher than those following the administration of ampicillin. No significant difference was found between amoxycillin and pivampicillin. The oral absorption of pivampicillin mixture was further studied in 12 infants, 0-1 month and 1-5 months of age. The absorption was faster in infants and children more than 6 months of age than in the 1-5 months group. The excretion, indicated by the slope of the plasma concentration curve, was delayed in infants less than one month of age. The oral absorption of amoxycillin and pivampicillin from tablets was also studied in 12 infants and children, 6 months-6 years of age, in the same doses as when mixtures were studied and was more complete with pivampicillin than with amoxycillin. The absorption of pivampicillin was more complete from tablets than from mixture. Also with amoxycillin there was a trend towards more efficient absorption from tablet than from mixture.

Study of ampicillin levels in maternal serum, umbilical cord serum and amniotic fluid following administration of pivampicillin

Premature rupture of the membrane is often followed by intrauterine infections. Antibiotic prophylaxis is recommended, but the effect has been debatable. Thirty pregnant women received pivampicillin 350 mg 4 times daily. The ampicillin levels in amniotic fluid and in the serum of the fetus and of the mother were determined and related to pivampicillin dose and time after administration. In the amniotic fluid the average concentration was 3.4 micrograms/ml, which is considered therapeutic. In maternal and fetal serum the ampicillin concentrations were low and took an almost parallel course. To obtain the same ratio between ampicillin serum levels and MIC (minimum inhibitory concentration) in the pregnant as in the non-pregnant subject, a double dosage should be used.

Pharmacokinetics of ampicillin and its prodrugs bacampicillin and pivampicillin in man

Five healthy fasting male subjects were each given single doses of intravenous ampicillin (471 mg), oral ampicillin tablets (495 mg), oral bacampicillin hydrochloride tablets (562 mg ampicillin equivalent), and oral pivampicillin hydrochloride capsules (491) mg ampicillin equivalent) in a crossover experiment. The resulting concentrations of ampicillin were determined in plasma and urine. The pharmacokinetic analysis was made according to a two-compartment open model. The total distribution volume of unbound ampicillin during the disposition phase was 0.247 +/- 0.045 (SD) liter/kg, which is only slightly more than the extracellular fluid, suggesting that tissue binding and intracellular distribution of ampicillin are limited. The bioavailability of the esters bacampicillin (86 +/- 11%) and pivampicillin (92 +/- 18%) was significantly greater than that of ampicillin (62 +/- 17%); however, the difference between the esters was not statistically significant. The adsorption for all drugs given orally proceeded at a constant rate, suggesting zero-order release rates from the products. The adsorption rate was highest for bacampicillin (0.89 +/- 0.39 of dose absorbed per minute), followed by pivampicillin (0.64 +/- 0.19) and ampicillin (0.58 +/- 0.16). Bacampicillin also had the shortest lag time for the start of absorption (7.0 +/- 0.9 min) under the present conditions. Thus, in comparison with ampicillin, the esters have a higher bioavailability, which, in fact, is close to the theoretically highest possible value by clearance concepts. The higher bioavailability in connection with higher absorption rates may be clinically important in ampicillin treatment by the oral route.

A gastroscopic and pharmacological study of the disintegration time and absorption of pivampicillin capsules and tablets

1 An in vitro investigation showed that pivampicillin tablets disintegrated more rapidly than pivampicillin capsules. This result was demonstrated and confirmed by gastroscopy in a cross-over study in healthy volunteers. 2 There were no differences in serum levels of ampicillin obtained with the two preparations, but compared with non-gastroscoped volunteers, there was delay of 0.5--1.5 h in the appearance of peak serum ampicillin concentrations after gastroscopy. 3 Half of the volunteers receiving pivampicillin capsules developed hyperaemia, interstitial bleeding or erosions of the gastric mucous membrane. No such reactions were seen after pivampicillin tablets. 4 In one volunteer, a pivampicillin capsule was trapped in a not previously noticed hiatus hernia and local changes and pain occurred.

Oral absorption of pivampicillin and ampicillin in young children: cross-over study using equimolar doses of a suspension

In a cross-over study, the oral absorption following equimolar doses of ampicillin corresponding to 16.7 mg/kg administrered as pivampicillin ('Pondocillin') suspension and ampicillin ('Doktacillin') suspension respectively, was investigated in 11 children aged from 8 months to 4.5 years. Pivampicillin produced a mean peak serum concentration of 10.7 microgram ampicillin/ml compared with 5.8 microgram/ml after ampicillin. The mean area under the serum concentration-time curves was 29.2 microgram/ml-h after pivampicillin and 16.7 microgram/ml-h after ampicillin, reflecting the superior bioavailability of the ester form. In 4 of the children aged between 8 and 12 months, the serum levels after pivampicillin were consistenly lower than those recorded in the remaining 7 children beyound the age of 1 year. The mechanism and therapeutic implications of this finding require further study.

Ampicillin and pivampicillin in the treatment of urinary tract infection in children

16 children, aged 1-10 years, suffering from urinary tract infection were randomly divided into two groups. Ten children were treated with ampicillin pediatric suspension in a dose of 100 mg ampicillin/kg/24 hours divided in 4 doses, and 6 children with pivampicillin base pediatric suspension in a dose of 64.8 mg/kg/24 hours divided in 4 doses (approximately 50 mg ampicillin/kg). The treatment period was 14 days with all infections being cured. Despite the fact that pivampicillin was administered in half of the dosage of ampicillin the resulting peak serum concentration was 65% higher and was achieved more rapidly. The bioavailability and urine concentration were also greater. A marked change in the rectal aerobic bacterial flora occurred during both treatment regimens. In 13 children (81%) a shift took place from ampicillin-sensitive E. coli to ampicillin-resistant Klebsiella strains as the predominating microbe, equally often in both groups of treatment. Ampicillin-resistant E. coli appeared in one child in each group.

Comparative effect of food on absorption of ampicillin and pivampicillin

The effect of food on the absorption of simultaneously ingested ampicillin or pivampicillin was compared in a crossover study in eight healthy volunteers. The absorption of both ampicillin and pivampicillin was delayed by simultaneous food intake as judged by serum concentration and urinary excretion of ampicillin. The total absorption of ampicillin, but not that of pivampicillin was decreased by simultaneous food intake as indicated by the are under the serum ampicillin concentration-time curves and by 24 hours urinary excretion of ampicillin. The excretion of ampicillin into urine was about 30% of the dose when ampicillin was ingested with water into an empty stomach and about 20% when ingested with food. The respective excretion of ampicillin following the ingestion of pivampicillin was about 60% of the dose taken either with or without food.

Pivampicillin and ampicillin in bile, portal and peripheral blood

In 7 patients with a catheter in the portal vein and a T tube in the common bile duct, the concentration of unhydrolyzed pivampicillin and of ampicillin was measured simultaneously in portal and peripheral blood and in bile after oral administration of 700 mg pivampicillin. In both portal and peripheral circulation of concentration of unhydrolyzed pivampicillin was always less than 1% of the levels of ampicillin, indicating the effectiveness of the intestinal mucosa in the hydrolysis of pivampicillin. Evidence for the ability of the liver to excrete ampicillin against a concentration gradient into the bile was established by direct measurements. Only about 1% of the dose given could be recovered in the bile. There was an unexplained reduction of about 70% in the absorption of the drug induced by the catheter itself.

Absorption of ampicillin derivatives from the bovine udder

The rates at which ampicillin, amoxycillin, metampicillin, hetacillin, and pivampicillin are absorbed from the bovine udder were compared, with the absorption rate of (14C)urea as reference. Straight-line semilogarithmic plots of the percentage of unabsorbed drug against time were obtained, suggesting first-order kinetics for the absorption process. Ampicillin, metampicillin and hetacillin were most slowly absorbed. Amoxycillin was absorbed twice as fast as ampicillin. Pivampicillin was absorbed most rapidly-at more than three times the rate of ampicillin.

Gastrointestinal absorption and metabolism of two 35S-labelled ampicillin esters

Two ampicillin esters, 35S-pivampicillin and 35S-carampicillin and polyethylene glycol (nonabsorbable marker) were given orally to healthy subjects with gastrointestinal tubes. The cumulative absorption of radioactivity in both compounds (60-90%) was higher than (25-67%) previously found after administration of 35S-ampicillin. The pek plasma levels of radioactivity were reached earlier and were about twice as high as in the latter study. The amount of radioactivity excreted in urine was about the same as that absorbed from the proximal part of the gastrointestinal tract. Both 35S-pivampicillin and 35S-carampicillin were partly hydrolyzed in the stomach and upper small intestine and labelled ampicillin was released. They were also decomposed after absorption since all the radioactivity recovered from blood and urine appeared to be attached to ampicillin and ampicillin metabolites. Studies in vitro indicated that ampicillin esters absorbed intact may be hydrolyzed not only in the blood but also in the intestinal wall and the liver.

Serum concentrations of ampicillin and probenecid and ampicillin excretion after repeated oral administration of a pivampicillin-probenecid salt (MK-356)

Twenty male volunteers received oral doses (2100, 1050, and 525 mg) of a pivampicillin-probenecid salt in a 1 to 1 molar ratio (MK-356) at 12 hour intervals. After each dose peak serum concentrations of probenecid were observed 2 hours later than peak concentrations of ampicillin. Following the first dose of MK-356 the apparent elimination rate of ampicillin was dose-dependent and did not follow first order kinetics, as it showed a longer apparent half life after a higher dose. An equal dose of MK-356 administered 12 hours later caused an increase in the peak serum ampicillin level greater than expected from the concentration of ampicillin after the preceding dose. In twelve male volunteers who received at random 525 mg of MK-356 or 350 mg of pivampicillin, each three times daily for 4 days, the areas under the ampicillin concentration curve were the same after the first or last dose of either drug. When 2100 or 1050 mg of MK-356 was taken as an initial dose, 30 to 40 per cent of the ampicillin was recovered from urine in the ensuing 12 hours. The results indicate that when at least 400 mg probenecid was coadministered twice daily with 700 mg pivampicillin (MK-356), the peak serum concentrations of ampicillin were increased and its elimination rate slowed following successive doses.

Concentrations of ampicillin in human urogenital tissue, serum and urine after intake of pivampicillin

The ampicillin concentrations in serum, urine, kidney, urinary bladder, prostate gland, testis, muscle and skin from 64 urological patients with normal renal function were determined with the agar diffusion method after oral doses of 700 mg of the pivaloyloxymethyl ester of ampicillin (pivampicillin, Pondocillin). The tissue samples were obtained at urological operations, prostatectomy, nephrectomy and orchiectomy. The serum concentration was highest between 2 and 4 h and the urine concentration between 4 and 6 h after intake. The serum concentration was considerably lower than reported in literature, which was shown to 0e due either to the effect of preoperative medication or anesthesia, or to both.