Zinc phosphide toxicities among patients of the University of Benin Teaching Hospital, Benin city, Nigeria: A 10 year experience

Background: Due to the poor success rate associated with zinc phosphide ingestion, it became necessary to assess the incidence. Objective: To assess the incidence of zinc phosphide toxicities reported between June 2000 and June 2009 in the University of Benin Teaching Hospital, Benin City, Nigeria. Material and Method : Data were sourced from the archives of casualties of zinc phosphide poisoning. These were entered into a generated case data form after obtaining an ethical permission. Results: All the ages of the 23 casualties reported were within 37.74±13.20 years. The male-female ratio was 4.75:1. Nineteen [78.26%] died after reporting 13.52±11.34 hours following single ingestion. Twenty cases were due to suicidal tendencies; the most common reason given was because of frustration in life related to marital affairs. Among the three unintentional, two were accidental while the other was due to assassination. Postmortem was refused in all the patients that died. One attempted herbal medication. Oil and milk were the most frequent solvents used at home as first-aid care therapy. Three were unintentional. Nine came with empty sachets and containers brought by relatives. Sodium chloride intravenous infusion was the most frequently used. Duration of hospitalization was 13.38±15.60 hours. Intravenous ciprofloxacin and metronidazole were the most common antibiotics used. Oxygen was instituted in 78.26% of the victims during respiratory distress. One ate meal prepared from poisoned rodent and died after reporting. One had alcohol along with the Zinc Phosphide ingestion. Nine were reported at the drug and poison information centre. Conclusion: Attention is needed by all for proper regulation in the handling of poisons and related substances to reduce burden minimally.

Keywords: Approaches, casualties, toxicities, zinc phosphide

Metallic phosphides are commonly used as rodenticides. Metals available as different phosphides are: aluminum, calcium, magnesium, and zinc. Aluminum and zinc phosphides are highly effective insecticides and rodenticides and are used widely to protect grain in stores and during its transportation. ^[1] They can be harmful to humans when ingested. However, because of the duration of discomfort and pain before death it has been suggested that the use of rodenticides can be considered as inhumane. ^[2] Globally, intentional application has been classified into assassination, murder, suicide, and execution. ^[3] The primary aim is to get rid of rodents that are potential hazards to food and other materials of economic value to man. Other classes of rodenticides have also been identified. ^[4],[5] In Benin City and its environs, metallic phosphides are commonly sold and relatively cheap. Different preparations are sold in sachets or prepacked in cellophanes. They are commonly sold in the markets and road sides areas that are busy places where there are human and vehicular activities. Most times carcasses of rodents are displayed to buttress the effectiveness. The regulation guiding the purchase and sale of toxic substances is not totally enforced. There exist a Drug and Poison Information Centre [DPIC] of the University of Benin Teaching Hospital, Benin City, Nigeria, where poisons and other related substances are reported. Only few individuals are aware that such centre. The centre works in collaboration with the National Agency of Food and Drug Administration and Control [NAFDAC]. However, the mortality associated with zinc phosphide poisoning was assessed retrospectively among casualties that reported at the emergency centre of the hospital.

Toxicity resulting from the use of zinc phosphide was assessed after obtaining ethical approval from the authority of the establishment. The study was carried out by retrieving archives of patients that reported with the poison ingestion between June 2000 and June 2009 in the Accident and Emergency Centre of the University of Benin Teaching Hospital Benin City, Nigeria. The centre is located in the south-south of the city. Most medical and accident cases are reported at the centre. Data were classified as age, sex substance ingested, duration before report, Home therapy, duration of management, outcome of therapy, and drug utilized in clinic. Patients without proper confirmation of the poisoning even with the submission of the sachets or containers or other related proofs were excluded from the study. Others excluded were those brought in dead without proper clarification of the toxicant.

Statistical Analysis

Data collected were entered into Microsoft excel, SPSS version 11.0 (SPSS, Inc. Chicago, IL, USA). Where necessary, data were computed as numbers, percentages, and mean±standard deviation.

As in [Table 1], all their ages were within 37.74±13.20 years. Out of the 23, the male-female ratio was 4.75:1. Nineteen died after reporting 13.52±11.34 hours following single ingestion. They were all accompanied to the clinic by their relatives and friends. Most were due to suicidal tendencies. The most common reason given was because of frustration in life related to marital affairs. Among the three unintentional, two were accidental while the other was due to assassination. Postmortem was refused in all the patients. One attempted herbal medication. Oil and milk were the most frequent solvents used in home first-aid therapy. Three were unintentional. Nine came with empty sachets and containers brought by relatives. Few of the sachets brought to clinic were intact. Sodium chloride intravenous infusion was the most frequently used. Duration of hospitalization was 13.38±15.60 hours. Intravenous ciprofloxacin and metronidazole were the most common antibiotics used. Oxygen was instituted during respiratory distress in 78.26% of the victims. One ate meal prepared from rodent poisoning and died after reporting. Although he claimed to be a farmer and he only ate the muscle and bone after roasting off the hair. One had alcohol along with the zinc phosphide ingestion. Nine were reported at the drug and poison information centre.

The mortalities as seen in this study can be attributed lethal effects that have been considered inhuman. ^[2] The common utilization as suicidal agents can be related the common availability on the streets of Benin City Nigeria. However, such availability is a reflection policies not put in place. The sale may be purposely for rodent eradication. Buying and keeping at home can be risky. Accessibility could be due to the cheapness and negligence of the implementation of the policy guiding the regulation. Other agents such as vitamin D has been known to be toxic to rodents and can act synergistically with other anticoagulants, so far from the investigation, none of the patients were on anticoagulant like wafarin that could have potentiated the effect. The cascade of homeostasis may have been interfered most especially in some of the casualties that may be on one traditional medication that were not disclosed. It is common practice in the area when people self-medicate for one reason or the other, coupled with the use of substances during social activities. These were not disclosed in the report because of fear of being apprehended for drug abuse. Those that did not survive may have ingested up to 1 g that is regularly packaged in sachets by the manufacturers. Therefore, toxicities as seen in this study can be dose related as seen in the child of 7 years and other casualties.

The time of report to the clinic was a significant factor in affected the outcome of therapy. To have victims reporting after 10 hours of ingestion showed a gross delay in report. Delay in reporting has been identified to contribute to mortalities associated with poisons. ^[6],[7] For many persons to have delayed in reporting, factors such as heavy traffic and inaccessibility to vehicle could have contributed to poor prognosis as previously observed to be common among individuals seeking medical attention at the centre ^[8] and other centers. ^[9],[10] Impression that such a situation may not need medical attentions can also be a contributory factor.

The substance may have caused irritant effect due to the phosphine gas that is known to be released in the gastrointestinal tract followed by the interference with the homeostatic pathway. ^[1] Six cases were brought in dead with proof of the empty sachets or containers; these could be extensively due to delay in reports. Confirming this further, relatives and friends claimed they saw them ingesting the substance and during the cause of interaction before the incidence the casualties said that they were going to commit suicide due to their frustrating situation in life. Relatives and friends decided to bring the empty sachets and containers or other left over content to the emergency centre in order to help in prompt diagnosis. Facts could have been well established if postmortem investigations were requested by the relatives or friends. Factors that tend to influence the intentional use were marital relationship and frustration in life. Even unmarried persons were casualties due to casual relationship. These were more prominent in the report. Some casualties may have reported at private hospital where they had inadequate treatment and this may have caused the delay in reporting to the center where they would have been adequately managed. Initial intervention of items may have been initiated at home such as milk, oil, and local charcoal. All these substances may not have had a therapeutic effect, rather potential effects. Most milk preparation in the environment contains vitamin D which can potentiate anticoagulant activity. A similar effect by other anticoagulants has reported previously. ^[4],[5] The common approach by relatives and close associates like friends and relatives may have contributed adversely to the mortalities recorded in the first-aid care. The inaccessibility to equipped medical centers as the only tertiary health institution servicing a population of about 1.4 million in the year 2006 showed a gross inadequacy of medical facilities. Relation and friends refusing post mortem investigation that would have helped significantly in establishing the pathological damage is a great drawback.

Another determinant factor is the toxico-kinetics\dynamics profile of the substance as documented. ^[1] Toxicity profile has not been fully elucidated in man. The pattern should have yielded interesting result, if the post-mortem investigations have been conducted. Refusal of postmortem could be associated with poverty, illiteracy, and spiritual beliefs in persons having scarification at birth have been identified. ^[7]

It interesting to note that therapy in most poisoning situations is mostly supportive since antidotes are available for few toxins. ^[11] The use of vitamin K, sodium bicarbonate, and other supportive techniques may be theoretical. ^[1] They have not survived as specific antidote practically. Pharmacodynamic profile of those agents seems to resolve the clinical symptoms rather than being direct antagonist to the poison. The study suggests specific antidote for therapy need to be recommended as defined. ^[6] Suicidal tendencies in the utilization of such agent can be due to poor socio-economics status within and outside the area. If the victim of middle age persons were gainfully employed and have reliable source livelihood, the perception about life will change positively. Even if there is little enforcement of the policies regulating the poisons, they will certainly have self-control when they are assured of hope of life. The only few cases of victim below 10 years can be said to be related to unintentional poisoning. That was why they all survived and with help of the parents and guardian. This is also related to the small dose ingest which may be insufficient to cause toxicity rather than suicidal. Parents or guardian may have used oil and milk as common local antidotes in the area. There would have been more vulnerability due to immaturity of their organs. The study showed that toxicity may not be dose related because the victim only took part of the rodent meat as source of food. Skin roasted intestine removed other parts used in preparing food. Muscles and other parts were eaten. The bioavailability may not have been sufficiently distributed in the entire rodent eaten. This was a case of unintentional poisoning.

The age range of 32±1.04 years can be attributed to the very active group where there is quest for achievement in life, most especially marital relationships. It is expected in the environment that individuals who fall within such age bracket individuals should be married and have means of livelihood any deviation from that is regarded as a failure. The factor may have influenced males becoming casualties. Marital relationship in terms of jilting, loss of loved one, and other disappointments are contributory factors to this.

The 7 year old case report used the container to drink water. This is related to low dose and added to that the parents practically reported on time. Management was instituted on time. Although oil was administered, there was no pharmacological proof that the substance has antidotal properties but it can be inferred that the substance being non polar may hinder the absorption of polar solvent. The container was brought to the clinic for easy identification.

The case study of a male in the midst of friends drinking alcohol was found to be secretly opening a strange sachet into his drink. Onlookers thought it was a powdered tobacco. After which the patient suddenly collapsed and was rushed to within 1 hour of the incidence to the emergency centre. Clue to initiating therapy was established when the empty sachet was picked along with him and unutilized the sachet in his pocket. Due to the illiteracy of the peer friends, they could not easily identify the substance. The substance was only identified after bringing the sachet to the center where therapy was instituted immediately. At the time report to the centre, the patient was vomiting. The vomiting may be due to the direct irritant effect of the phosphine gas. Most patients vomited even without inducing emesis. This could be as a result of the irritant effect of zinc phosphide on the intestine or its influence on the vomiting centre. Emesis may be helpful as seen in one of the victims, some author have suggested that it should be induced within four hours of ingestion. ^[6] It was observed that zinc phosphide was common in the area and cheap sold at 20 naira per sachet. There is improper regulation of poisons. Individuals tend to buy and keep them primarily for eradication of rodents.

When selling on the street, this substance is commonly called OTAPIAPIA or rat killer. Hawkers do repeat by saying “kill the rat.” “gbogbo the rat” as rhythm. The carcasses look attractive as they are attached to the bag for conveyance. The regulation guiding the purchase and sales of such toxic substances are not totally enforced due to lack of personnel willing to work in rural areas. Most casualties that reported with both intentional and unintentional poisoning should have been able to recognize the odor so that any form of encounter such can easily be recognized. All the pattern of report can be regarded as acute poisoning rather than chronic poisoning resulting from bioaccumulation as previously observed. ^[7] Adequate management of poison following some clinical feature can be referenced as suggested. ^[1],[12]

The mortality associated with the use of zinc phosphide ingestion calls for urgent attention. It is therefore recommended that public enlightenment should be regularly conducted through the media, such as newspapers, radio and television for individuals to desist from the compound that is primarily used as rodenticides. The sales of poisons and related substances should be strongly regulated to disallow individuals in having access to them.

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1755-6783.92874

[Table 1]