Toyoaki Hayama

Pyrimethamine Teratogenesis by Short Term Administration in Goettingen Miniature Pig

Pyrimethamine was mixed with mashed feed and given to pregnant sows of Goettingen miniature pig through a part of the period of organogenesis. A high incidence of the major malformations such as cleft palate, club foot and micrognathia was observed in 13 out of 24 newborns from 5 pregnants which a teratogenic dose (3.6 mg/kg of body weight/day) from day 11 to day 22 of gestation, the first half of the organogenetic period. Only one cleft palate was observed among the 23 newborns from 4 pregnants administered the same dose through the second half of the period. Among the 51 newborns from 10 pregnants which the same dose through the first or second quarter, only 4 newborns showed external major malformations. However, 19 out of 38 live newborns without external major malformations in these groups died within 2 days after birth. Clinical symptoms of these neonatally dead young were similar to splayleg, a naturally occurring functional anomaly in pigs. No internal malformation was revealed by the autopsy of these dead newborns.

Use of the goettingen miniature pig for studying pyrimethamine teratogenesis

Although pigs are suitable animals for experimental teratology, use of miniature pigs developed as a medicobiological experimental animal is essential for this purpose. Miniature pigs are established genetically so that the background data on the naturally occurring birth defects are reliable, whereas the commercial breeds are always improved genetically to seek higher productivity. In this review the authors summarized pyrimethamine teratogenesis in Goettingen miniature pigs. Pyrimethamine administration to a pregnant sow during the early stage of the organogenetic period caused cleft palate and other birth defects, and also hind leg paralysis, a functional defect in newborns.

Effects of Folic Acid and Folinic Acid on Pyrimethamine Teratogenesis in Rats

Abstract The effects of folic acid (FA) and folinic acid (FNA) on the teratogenicity of the antifolate drug pyrimethamine (PYR) were examined in rats. PYR and FA were orally administered with mashed feed. FNA was intraperitoneally injected. The drugs were administered for 5 days of day 11–15 of gestation. Six groups were made; G‐I PYR 1.6 (mg/kg/day), G‐II PYR 3.6, G‐HI PYR 1.6 + FA 50, G‐IV PYR 3.6 + FNA 12, G‐V FA 50, G‐VI control. No malformations were found in G‐I, IV, V and VI. All fetuses in G‐II and III had malformations. Main malformations in G‐II and III were cleft palate and brachygnathia. Accordingly it might be demonstrated that the teratogenicity of PYR was potentiated by concurrent FA in rats.

Effects of Pyrimethamine and Folic Acid on Plasma Level of 5-Methyltetrahydrofolic Acid in Rats

Abstract: The relationship between pyrimethamine (PYR) teratogenesis and the plasma level of 5‐methyltetrahydrofolic acid (5MF), known as an active form of folate in plasma, was studied in rats using an HPLC‐ECD method for 5MF determination. The rat received, for 5 days, in‐feed PYR with or without folic acid (FA), which was previously reported as a potentiator of PYR teratogenesis. PYR alone caused a dose‐dependent decrease in the plasma 5MF level after the 5 day dosings. A potentiated decrease in the 5MF level was observed after the concomitant dosing of PYR with FA. The concomitant dosing of PYR 1.6 mg/kgBW/day (subteratogenic dose of PYR alone) with FA 50 mg/kg/day, which was 100% teratogenic dose in our previous report, decreased the 5MF level more than that after the dosing of PYR 3.6 mg/kg/day alone (100% teratogenic dose of PYR alone).

Ameliorative Effect of Folic Acid on Pyrimethamine Teratogenesis in Pigs

Abstract The effects of oral dosing of folic acid (FA) on pyrimethamine (PYR) teratogenesis were examined in Goettingen minipigs. PYR (3.6 mg/kg/day) was orally administered in the feed to sows with or without FA (2.5, 10 or 50 mg/kg/day) for 12 days, (days 11 ‐ 22 of gestation). Major malformations, such as cleft palate, cleft lips, micrognathia and clubfoot, were observed in all treated groups. The incidence of malformed fetuses decreased dose‐dependently as the FA level was raised. This new finding suggests FA administration may prevent newborns from PYR induced malformations. This result contrasts in the observations in rats, in which PYR teratogenesis was potentiated by the concurrent oral dosing of FA. Neither PYR blood concentrations nor plasma protein binding was significantly affected by FA dosing in nonpregnant sows. These results suggest a mechanism other than pharmacokinetic modification was responsible for the protective effect of FA on PYR teratogenesis in minipigs.

Effect of Folic Acid on Pharmacokinetics of Pyrimethamine in Rats

The effect on pyrimethamine (PYR) pharmacokinetics of folic acid (FA) which potentiated the PYR teratogenesis was studied in rats. Gavage administration of PYR 1.6 mg/kgBW/day from day 11 to day 15 of gestation did not cause any malformation, but with concomitant dosing of FA 50 mg/kg/day in feed caused malformations in 75% of fetuses. Neither the plasma concentration‐time profile nor the plasma protein binding of the gavaged PYR was affected by the concomitant dosing of FA in the non‐pregnant rats. The pregnant rats which received the gavaged PYR with or without FA in feed for 5 days (from day 11 to day 15 of gestation) were killed at 4 or 12 hrs after the last dosing of PYR, and their plasma and fetuses were subjected to determination of PYR. The PYR concentration in the maternal plasma was comparable in both groups. The PYR concentration in fetuses of the PYR alone group was significantly higher than that of the PYR with FA group 4 hr after but not 12 hr after the last dosing. These results indicated that the pharmacokinetics of PYR was not affected by the concomitant dosing of FA, suggesting that FA potentiated the PYR teratogenesis by other mechanisms than pharmacokinetic modifications.

Transdermal delivery and intramuscular injection of trimethoprim/sulphadiazine in sucking piglets

The pharmacokinetics of a combination of trimethoprim (TMP) and sulphadiazine (SDZ) after topical application to sucking piglets was compared with the pharmacokinetics after intramuscular injection. A long-lasting and fairly constant SDZ/TMP concentration ratio in plasma was obtained after topical application. The mean plasma concentration of TMP ranged from 0.091 to 0.17 micrograms/ml and that of SDZ from 0.72 to 1.1 micrograms/ml for at least 24 h. TMP and SDZ had different half-lives after intramuscular injection. Transdermal delivery of a combined preparation of TMP/SDZ may be usable for colibacillosis of sucking piglets, although the bioavailability of the drugs is poor.

Oral dosage regimen in the nonlinear pharmacokinetics of sulphadimethoxine in pigs.

An oral high dosage regimen of sulphadimethoxine (SDM) was examined in pigs. The dose (50 mg/kg) in the therapeutic range, showed nonlinear pharmacokinetics, and administered by drench once a day for 4 days. The unbound plasma concentration-time profile was compared with that of the dosage regimen based on nonlinear pharmacokinetics, where a pharmacokinetic model and parameters were used except for the first order absorption rate constant (ka) and bioavailability (F). F and ka were obtained from oral and intravenous administration of 20 and 10 mg/kg of SDM. The unbound plasma concentration was observed almost within the setting range by the dosage regimen through the experimental period. This result suggested that the dosage regimen, based on the nonlinear pharmacokinetic model, resulted in an appropriate effect in the clinical use.

Effect of albumin distribution

The effects of altered albumin distribution on the apparent volume of distribution (V) and the apparent elimination rate constant (k) of drugs were investigated by a simulation analysis. The Equations derived by Øieet al. were modified for this purpose. Within the range observed in normal healthy subjects and patients, the change in albumin distribution significantly affectedV of drugs but, in general, notk. For drugs with more than 90% plasma-protein binding,V changed by more than 100%. The change in plasma-protein binding caused by an altered albumin distribution produced a greater effect onV than that caused by an altered albumin amount. These results suggest that albumin distribution is an important factor in controlling the kinetics of drugs which are highly bound to plasma protein. This is illustrated using midazolam as an example.

Correlation of Active Folate Availability with Effects of Folic Acid on Pyrimethamine Teratogenesis in Rats

Oral administration of pyrimethamine (PYR) 3.6 mg/kgBW/day to the pregnant rats from day 11 to day 15 of gestation caused malformations in all the fetuses, but concomitant intraperitoneal administration of folic acid (ip FA) 50 mg/kg/day inhibited the incidence of malformations by 25%. On the other hand, the same dose of oral FA (in feed) had an opposite effect on PYR teratogenesis; the incidences of malformed fetuses were 0% in the PYR 1.6 group, but 100% in the PYR with oral FA group. The plasma levels of 5‐methyltetrahydrofolic acid (5MF), a principal transfer form of folate, were measured after single oral administration of PYR with or without FA (ip or oral) in non‐pregnant female rats. The area under the plasma concentration‐time curve (AUC) after the concomitant administration of PYR with ip FA was larger than that after PYR alone. This result indicated that the available 5MF for the peripheral tissues was increased by the concomitant administration of ip FA. The AUC after the concomitant administration of PYR with oral FA was smaller than that after PYR alone. These results suggested that ip FA increased the available 5MF to ameliorate, but oral FA decreased the availability to aggravate the PYR teratogenesis.